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HomeMy WebLinkAboutProposed Wasterwater Treatment & Disposal Facilities FRONTENAC DEVELOPMENT COMPANY COMMERCIAL DEVELOPMENT STATION AVENUE YARMOUTH, MASSACHUSETTES ENGINEERING REPORT ON PROPOSED WASTEWATER TREATMENT AND DISPOSAL FACILITIES SEPTEMBER 1986 PREPARED BY LAND ENGINEERING ASSOCIATES, INC. MONROE FAIRFIELD RIDGEFIELD TABLE OF CONTENTS PAGE I. Introduction 1 II. Water Quality Consideration 2 III. Wastewater Sources 4 IV. Wastewater Characteristics 5 V. Wastewater Flow Rates 6 A. Flow 6 B. Peaking Factors 7 VI. Denitrificatian Systems 8 VII. Design Criteria and Description of 13 Facility Components A. Conveyance Piping 14 B. Primary Treatment 14 C. Recirculating Sand Filter 16 D. Recirculating Tank 19 E. Leaching Facility Dosing Tank 19 F. Leaching Facility 20 VIII. Treatment System Monitoring 24 IX. Groundwater Monitoring 25 X. Operation and Maintenance 25 References Appendix A -- Design Calculations Appendix B -- Site Map Down Cape Engineering LIST OF TABLES TABLE NO. TITLE PAGE NO, 1 Septic Tank Effluent Characteristics 6 2 Wastewater Flow and Flow Peaking Factors 8 3 Recirculating Sand Filter(Design Criter 12 4 Septic Tank and Grease Trap Sizes 16 5 Recirculating Sand Filter Design Criteria 18 6 Hydraulic Conductivities and LTAR 23 7 Leaching Facility Sizing 24 8 Operation and Maintenance 27 LIST OF FIGURES FIGURE NO. TITLE FOLLOWS PAGE NO. 1 Site Location Map 1 2 General Floor Layout and Treatment 4 2A Proposed Treatment and Disposal System 13 2B Proposed Treatment and Disposal System 13 3 Flow Schematic 13 4 Recirculating Sand Filter Plan View 18 5 Recirculating Sand Filter Section View 18 6 Long Term Acceptance Rate 21 7 Soil Boring Location 22 FRONTENAC DEVELOPMENT COMPANY Wastewater Treatment and Disposal Facilities Commercial Development, Station Avenue, Yarmouth, MA I. INTRODUCTION Frontenac Development Company is proposing to construct a 63, 098 square foot commercial shopping center consisting of a supermarket and several other retail outlets located on Station Avenue in Yarmouth, Massachusettes. The final project location is shown in Figure 1. Previous work has been completed by Down Cape Engineering of Yarmouth, Ma. and Geotoxi Associates, Inc. of Glastonbury, Ct. , pretain- ing to site engineering and hydrogeologic considerations, respectively. This work has concluded that a denitrifica- t i on sewage treatment system is required for the proposed development in order to protect groundwater quality from nitrate contamination and to meet the goals of the Town of Yarmouth Board of Health and the Cape Cod Planning and Economic Development Commission. Land Engineering Associates, Inc. of Monroe, Ct. has been retained by Frontenac Development Company to design a denitrification sewage treatment system. It is not the intention of Land Engineering to duplicate the large body of information which has already been developed in the above 1 • r� •dun �� u r11,,t � J, • /f.�. lli•e ••'•, '~ .•'.: / • I, ,10 . "-isQ fp.: 44 Ill-illrrffifr/ • ••,--.-"b7 .414. Nrk \• 1)0 •..••••4••-• •Q.---------.11-'w .0 . -1) ) 7 i t e Aiel' al . "t 1" ‘`‘,41"' kl• .." ••i 1..., ___Alwiiik.,.- - • . ' •-. .4.4.".2.t4 •---- ; i_. .... , ltd. , • . tio6,-..„.±,,,,..ditiT b • V V ..." . • r L.1, 1•r/.•p • ,r,.• • it L '. -° Vv .�i 1••+•- �• �• ['../J� 1- ` \) �� t. 0- - . `. .•. ....J S.nO •1•. 11,0 • .�. f..�'�. • ., f t� r•1 .r�.�,t,!�. ` Pity` 4. 'IA \.•. • % i '....\ • • : , :' ‘ /•,.. U . i . • r oillin I. ,r of a �;'•.. G jilt ^•, . . )• r •RN ---•• d . . . N .,\~' • o 1 i r) : 1 A.,• • SITE LOCATION •.:1•r'-- ,.-n fa �: - ,r,__'` N.,, Ne pl, �� 47 ‘i\I ' .-N-IIA - -71.41461,..."*.J (... MIVit i . • ; 1 • • • »F :.cam , •: /' •v '_�— h .....', 1, ir,!st. ` — ;� r 'Flat • • � • •� • •L.1k R M \ •oil U� T H -• • Pond ‘..-- •• 1 t ..I. .0 O t• • Y•rt•••rta•D.t•M : • I.; •' 1.�i YI•i SibL1 • rl d • itir*/ . ,..� r I, • y r\\, ,1` • ��� , •./ Q,• •um•pi a t . - ✓t •✓T4• • r 1 1; 'N i .• , - .1‘..-t.-••.•:-.•• : otos .6.2...• '..7 • . • ACI j w is , . �;a ,c'zaAuer i.1 •3 . rewind and Grin, • FIGURE 1 •..• s.P „1 • • ••!' �;b-:,`-f' • •', : TOPOGRAGHIC and SUP.FICIAL • .� �� •'�,' " GEOLOGY MAP ' f 4Plc • L..%. / c:j • • . FROM , . *� � `^� '. GEOTOXI ASSOCIATES INC. 4 ,i c~' Os Qhl $a • SCALE ' j �k ��, • c' • ._ —. • 1 INCH — 2,000 FEET referenced work, but to supplement it on the issue of sewage treatment and disposal. The purpose of this report is to provide a sound techni- cal basis for the preparation of construction plans and specifications which will be submitted to the Town of Yar- mouth Board of Health and Health Director for review and approval. Site plan by: Down Cape Engineering 926 Main Street Yarmouth, Ma. 026640 dated 8/7/86 Hydrogeologic reports: Synopsis of Field and Laboratory Investigations Assessing the Hydrogeologic Setting of A Proposed Strip Shopping Center in Yarmouth, Ma. November 1985 Synopsis of Nitrogen Dilution Calculations for a Proposed Strip Shopping Center in Yarmouth, Ma. July 1986 by: Geotoxi Associates 2377 Main Street Glastonbury, Ct 06033 II. WATER QUALITY CONSIDERATIONS The primary water quality consideration given the deve- lopment proposal of Frontenac Development Company is the effect of wastewater discharges, on groundwater nitrate con- centrations. The level of concern over groundwater quality and nitrate consentratians by Town of Yarmouth Board of Health and the Cape Cod Planning and Economic Development Commission is emphasized by the Federal Environmental Pro- tection Agency designation of Cape Cod is a sole source aquifer. The development site under consideration is on the secondary recharge area to Yarmouth Water Department wells No. 15 and 16. Yarmouth is presently applying a nitrate-nitrogen concentration standard of 5 mg/1 for lar- ger development proposals, with technical evaluations made on a case by case basis. By requiring larger developments to keep nitrate-nitrogen concentrations within the 5 mg/1 limit through on-site dilution and advanced treatment as required, the municipal groundwater supply should not be in danger of exceeding the drinking water standard of 10 rng/1. The hydrageologic investigations by Geotoxi Associates have evaluated the impacts of the proposed wastewater dis- charges utilizing conventional subsurface sewage disposal systems. Their analysis shows the average daily mass of nitrate-nitrogen diluted with on-site precipitation will cause increases of nitrate-nitrogen in the groundwater to the range of 6. 1 to 6. 7 rng/i. This of course is dependent upon the volume of sewage discharged and the concentration of nitrogen in the wastewater. Geotoxi Associates has used existing commercial development flow monitoring data and wastewater sampling for nitrogen in arriving at the flow and nitrogen concentration data used in their analysis. The net result of this analysis points out . that in order to bring nitrate-nitrogen concentrations below the 5. 0 mg/1 standard, a reduction in nitrogen concentration of 21-29% will be required. A 40% removal effciency or higher should bring nitrate-nitrogen concentration to approximate- ly 4. 0 mg/1 or less. III. WASTEWATER SOURCES The proposed development consists of a supermarket, drugstore, and several retail outlets with a total floor space of 66, 098 square feet. Figure 2 details the general layout of floor space. Yarmouth regulations prohibit rest- urants or laundrornats for the existing zone designation. Sources of wastewater will include domestic and process uses. A11 retail space, except for the supermarket, will gen- erate sewage primarily through employee use of toilet and hand sink facilities. Each employee wil generate approxi- mately 15 gallons per day. In addition to wastewater of domestic origin, the supermarket will generate flows from daily cleaning operations in the meat department, produce, delicatessen and bakery, as well as daily miscellaneous water use for these activities. 4 IV. WASTEWATER CHARACTERISTICS The non-domestic wastewater fraction generated by the supermarket can conservatively be estimated to be equal in strength to resturant wastewater. The clean up of food processing areas, warm temperatures of wash down waters, and high oil and grease content of the meat department wash down all are contributing factors to this rational. Typi- cal resturant wastewater following primary treatment in septic tanks and grease traps should contain approximately 525 mg/1 of Biochemical Oxygen Demand (BODS) and 200 mg/1 of Total Suspended Solids (TSS) . This is compared to typical septic tank effluent of domestic nature with a combined BOD and TSS of approximately 250 mg/1. Combining the 5 supermarket process wastewater with domestic wastewater from other sources will result in an approximate septic tank effluent with 400 mg/1 combined ROD and TSS. 5 Total nitrogen content of septic tank effluent has been determined from samples taken by Geotoxi Associates of sim- ilar commercial facilities and analyzed at a certified test- ing laboratory. The total nitrogen concentration has been established at 61 mg/1. This concentration is noted to be in line with literature data for similar facilities. Wastewater characteristics anticipated to be generated in the septic tank effluent are listed in Table 1. 5 • TABLE 1 SEPTIC TANK EFFLUENT CHARACTERISTICS Typical Domestic Septic Tank Effluent Parameter Concentration BOD5 + TSS 250 mg/1 Nitrogen 30 - 40 mg/1 Commercial Wastewater Septic Tank Effluent Parameter Concentration BOD + TSS 400 mg/1 5 Nitrogen 61 mg/1 V. WASTEWATER FLOW RATES A. Flow Commercial wastewater flow rates can vary considerably depending upon the specific commercial activities. A laundrornat for example is a high rate water user and will average 400 gallons per day per machine, with a typical 15 machine facility generating 6, 000 gallons per day. Commercial uses at the other end of the spectrum would include warehousing where a very large floor space is occupied but a relatively small flow rate is generated at 6 15 gallons per employee per day. A large warehouse facil- ity may generate only 300 gallons per day of wastewater. For the Frontenac development proposal, Geotoxi Asso- ciates obtained water meter readings for similar commer- cial facilities, one specifically including a supermarket of the same relative size. Both of these facilities generated and average water use rate of 0. 05 gallons per square foot per day, based upon total floor space. This figure has been used to set the basis for design of waste- water conveyance, treatment, and disposal facilities in this report. B. Peak Factors In the design of any sewage system component peaking factors must be considered and applied for successful system operation. The average annual design flow of 0. 05 gallons per day per square foot will be exceeded on a maximum month, week, day, and hour basis. Various system components should be designed to accommodate certain peak flow frequencies, depending upon their specific function. Daily maximum flows will vary from average annual flow by a factor of 1. 3 to 1. 8. Design calculations have con- sidered a maximum daily flow of 1. 5 times the average annual daily flow for design of the recirculating sand filter and leaching facility. A peaking factor of 2. 0 has been used for design of septic tanks and grease traps. A 7 peak hourly factor of 3. 0 has been used for pump design. Table 2 summarizes flow and flow peaking factors. TABLE 2 WASTEWATER FLOW AND FLOW PEAKING FACTORS Flow Peaking Factor Design Flow Average Annual Daily Flows 1. 0 3305 gpd Maximum Daily Flow 1. 5 - 2. 0 4960 - 6610 gpd Maximum Hourly Flow 3. 0 9915 gpd VI. DENTRIFICATION SYSTEMS Design criteria currently exist for a variety of waste- water treatment systems designed to remove nitrogen. These systems, referred to as den i t r i f i cat i on treatment systems, range from highly complex and operational intensive to more passive systems. To a certain extent the degree of corn- plexity varies with the degree of nitrogen removal desired. A systems complexity should be targeted to those long term operational conditions you envision taking place in the field. If one expects to achieve a consistent, successful system operation and removal efficiencies, one would not design a highly complex and sensitive treatment system un- less it would receive full time attention by highly trained operators. Other system designs, however, require consider- ably less attention and their operation is more straight 8 forward. In view of these considerations it was decided to design a denitrification system that would remove the neces- sary percentage of nitrogen while at the same time being as passive and require as little operation and maintenance as possible. Most denitrification systems require a nitrification step and a denitrification step. During the nitrification pro- cess bacteria convert ammonia and organic nitrogen to nitrite and then to nitrate under the presence of aerobic conditions. This process can be acheived by sewage treat- ment through activated sludge processes, trickling filters, rotating biological contactors, or sand filters to name a few of the more common types. The sand filter has been selected in this instance for nitrification of the waste- water. The denitrification process which removes nitrogen from the wastewater takes place by bacterial reduction of nitrate to nitrogen gas, which is then released to the atmosphere. Denitrification requires anaerobic conditions to exist where bacteria utilized the oxygen present in the nitrate molecule as an oxygen source for respiration. The process also requires that a carbon source be present and certain temperature and pH conditions exist. One form of dentrification introduces nitrate rich wastewater into an an- aerobic tank where a carbon source such as methanol or gray water (sink, laundry, and shower wastewater) is introduced. 9 Given a 12-24 hour detention time, bacteria will remove a high percentage of nitrogen. Other systems introduce septic tank effluent as the carbon source, however here a trade off takes place to a certain degree because while adding a carbon source, nitrogen in the form of ammonia and organic nitrogen is also introduced. Research has also shown that rapid infiltration systems where sewage is applied for a period of time to a sand bed followed by a period of rest is successful in removing nitrogen. In this process ammonia and organic nitrogen are converted to nitrate during the rest period between doses and as the sewage travels downward through the sand under unsaturated conditions. A percentage of this high nitrate wastewater remains in the capillary pores of the sand, while the balance drains from the media. During the following dosing cycle short term anaerobic con- ditions are created in microscopic sites within the upper reaches of the sand, whereby a carbon source from the sewage is present and a certain amount of denitrification takes place. This also occurs in sand filters. In 1969, Michael Hines and R. E. Favreau, sanitary en- gineers with the Illinois Department of Public Health, in- vestigated the use of recirculating sand filters. Sand filters are nothing new and have in fact been widely used for sewage treatment since the 1800' s. The work of Hines and Favreau was directed to solve characteristic odor prob- 10 `./ lerns that occurred when septic tank effluent was applied to a surface sand filter. . Their concept was to install a recirculation tank which mixes the incoming septic tank effluent with aerated sand filter effluent to eliminate odors. This procedure has proven to be highly effective and has received widespread use in Illinois. More recently, attention has been focused on the denitrification capabili- ties of recirculating sand filters. Studies of existing facilities indicate 40 - 60% nitrogen removal efficienties for recirculating sand filters due to denitrification taking place within the sand filters itself and to a greater extent in the recirculation tank. The recirculation tank mixing septic tank effluent with sand filter effluent will contain sufficent low oxygen zones to allow this degree of denitri- fication to proceed while at the same time not having oxygen levels so low overall as to cause odor problems. Laboratory column studies indicate recirculating sand filter nitrogen removal efficiencies of 70%. Monitoring data obtained for a recirculating sand fil- ter at a restaurant in Chester, Ct. (the first such system to be installed in that State) over the period 1985 - 1986 substantiates other reported findings. The Chester facil- ity serves a resturant and is of similar size to the system proposed for Frontenac Development Company. Monitoring is performed as a requirement of the Connecticut Department of 11 Environmental Protection State Discharge Permit. Four samples taken between the Fall of 1985, following a summer startup, and spring of 1986 showed an average of 60% nitro- gen removal efficiency. This data is presented in Table 3. TABLE 3 RECIRCULATING SAND FILTER EFFLUENT QUALITY • CHESTER, CT 1985 _ 1986 Average Concentration Average Septic Tank Concentration Percent Parameter Effluent RSF Effluent Removal BODS 618 mg/1 9. 9 mg/1 98% TSS 262 mg/1 5. 3 mg/1 98% TN 44 mg/1 17. 0 mg/1 61% With a nitrogen removal requirement of 20 - 30% for the proposed development as discussed earlier, the use of a recirculating sand filter with a 40 - 60% removal effic- iency should prove to be entirely satisfactory. There are several reasons that a seperate anaeorbic denitrification tank is not being proposed. First and foremost, the higher degree of nitrogen removal that such a tank would provide is not warranted; the use of methanol as a carbon source would entail chemical handling, storage, and metering requirements with added complexity; the only source 12 of gray water for a "RUCK" type system is the supermarket food processing wastewaters that will contain a high amount of oil and grease that would jeopardize the leachfield system if introduced following the sand filter. It is felt the proposed system will meet the nitrogen requirements and should, for some unforeseen reason further treatment be required in the future, the added step of a denitrification tank with carbon source could be considered. VII. DESIGN CRITERIA AND DESCRIPTION OF FACILITY COMPONENTS Figures 2a and 2b details the general layout of the sewage collection, treatment and disposal system. Figure 3 depicts a flow schemeatic. Design calculations are con- tained in Appendix A. The general system will consist of primary treatment through a series of two compartment septic tanks and grease traps with gravity flow leading to a recir- culating sand filter treatment system. The treatment system will be enclosed in a chain link fence with barbed wire top to protect components from vandalism. Screening could be provided by brown plastic inserts in the fencing and/or perimeter plantings such as arborvitae or japanese black pine. Effluent from the recirculating sand filter will be pumped or flow by gravity to a leaching gallery or leaching pit disposal system with 100% reserve area. 13 _ 'yk it 40011* ti :'Y :t-.:;• r-; ' ..,g,fi .,,:d mo . _ - `c4-" - - _ ._"z • '1 :.• rs Y>;' ,�, .� ".v ' e j T' -'�' _- ,� Via..• > ^ _ _ ., _ _ :-.;-':., _ r w• t'F.. r, a '- "' =ro' �: if, .fro, x iT - 3' �v - .�.." �_ R'RtA ty-y , ,k-L� ,� u z't, .yy. ,4444- " ad t C . Wi ,, • • ,._ _ }• s `raf • '� ' '��^��' - - - '--_:hum �� z x'. 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"�:, �i,. � -� �G3 P"« :' to s _'r' Ys 1 :...,.�, "k ma's .`5`� ,r v:; .' - i+ a�� y,y.-. _ �rvsw sr.:{,± tit. .,g„ ^�'�- y'. - � -' .. - _ �'. - --':z,`:ilc;,'aT -e-4�,",:�,;��-h�i-��,-4:��%= �'�;.:: _-e�T 1':=' •,...x�:ic�n'aro.`' • • I ( . C • Every panel hinged for access �'I Insulated Roof Panels .em s^ ----•-- ,�— I t-. i 2"Rigid Insulation • Finished Grade PVC. Ball Valve Shutoff ''• Spray Deflector Plate 4 �� * •, 2.10 SCH 40 PVC. Distribution Lateral—f ►! Underdrain Vent with Insect Screen �� ''•' ���/ 40 SCH 40 PVC /// ':_ _ - - 1` ��/�`� Distribution Manifold \� 4, ••-•'-• •• '• ••• •• • • ' '+ •.• !, i/ / :.b .Filter Sand E.S. 0.8-1.5 U.C. <3..5 • • '•" • . • • • . • • •• .; '••• \//v% �� Graded Gravel Filter ,4"0 SCH 40 R V.0 6" Concrete Slab at 1% ��/% / 4 0 SCH 40 P.V.C. Underdrain Collector Perforated Underdroln to Recirculation Tank SECTION VIEW OF RECIRCULATING SAND FILTER . OF . FRONTENAC DEVELOPMENT COMPANY YARMOUTH, MASSACHUSETTS Scale:l":4' September 10, 1986 • 86-0752 Cleo Al" Ic D. Recirculation Tank With a recirculation ratio of 4: 1 and a design sewage flow of 5, 000 gallons per day the RSF will be loaded with 25, 000 gallons of sewage per day. Using 15 minute doses every 2 hours, total daily pumping time equals 180 minutes. The resultsant pumping rate will be 140 gallons per minute provided by dual alternating pumps. Total dose volume will equal 2, 100 gallons which is equivalent to an approxi- mate depth of 2 inches over the sand filter. The recircula- tion tank will be provided with storage volume to retain in coming sewage flow during pump down time between doses. Tank volume is 4, 000 gallons. The inlet to the recircula- tion tank from the final grease trap will be a tee fitting plugged at the top and having a baffle end extending below the water line to prevent septic odors from entering the recirculation tank. The tank will also be provided with a high level alarm and emergency overflow to the leaching system. E. Leaching Facility Dosing Tank A dosing tank has been designed to load the leaching facility with 1, 000 gallon doses 5 times per day at approxi- mately 67 gallons per minute. A 2, 000 gallon tank is pro- posed. Due to favorable grading and depth to groundwater gravity flow can be achieved from the recirculation tank to the leach- 1S ing facility while still keeping galleries or pits at a reasonably shallow depth. It is requested that the Town of Yarmouth consider the discharge rate of the RSF as suffi- cient to adequately dose the leaching facility. Discharge to the RSF will take place at 140 gpm over a 15 minute period. Based upon observations it will take the sand filter approximately 30 minutes to drain. This results in and underdrain dis- charge rate of 70 gallons per minute which is sufficient to load a leaching facility through a properly designed distribu- t ion device. Elimination of the dosing pump station will result in the entire treatment system depending on only the dual alternating pumps in the recirculation tank. F. Leaching Facility Final disposal of wastewater following the denitrifica- t ion treatment system will be through a subsurface sewage disposal system. Even though the wastewater will be treated to a high degree by the RSF it will be further treated through filtration, adsorption and bacterial action by 20 ft+ of unsaturated sand prior to reaching the water table. Through this zone of soil BOD and TSS will be reduced to J insignificant levels, pathogenic bacteria will die off due to travel time through the soil, virus will be adsorbed to soil particles and phosphorus will be adsorbed as well. In a typical leaching system treating domestic septic tank 20 effluent, a biological slime growth layer 1 to 2 inches thick will develop at the systems stone-soil interface. This growth layer controls the rate at which effluent can pass into the soil and in turn system size. The biological slime growth at the stone soil interface will develop into a thicker more resistant layer with strong (HODS + TSS) wastewater and conversely into a less restrictive layer with weaker strength wastewaters. In addition, a more perm-eable soil will develop a less restrictive layer than a slowly permeable soil. These relationships of growth layer long term acceptance rates (LTAR) vs soil permability for typical domestic strength septic tank effluent are depicted in Figure 6. It should be painted out that these rates apply to ponded depth of 1. 0 ft above the growth layer providing a portion of the head to push water through. A formula which can be used to modify system acceptance rate due to lower or higher strength wastewater has been developed by R. Laak and is as follows: HODS + TSS mg/1 Factor = 250 mg/1 • In this formula average domestic septic tank effluent has a strength of 250 mg/1 combined HOD + TSS. If for 5 example an effluent had a combined strength of 500 mg/1, the system size would be increased by a factor of 1. 26. The hydraulic capacity of a site to transmit water will 21 • 1.0 • 0.9 N . LL LL O8 d a.: t9 0.7, U } IY 0:6 W _ 0 Q 0.5 W LTA = 5k- I.2 toga,k 0 • 0.4 .. LTA R= G.PD./Ft.2 OC 0.3 k= Ft/Min. W I- Z 02 O 0.1 • 0.• 0 5.0 10.0 15.0 20.0 25.0 30.0 0.0035 0.0069 0.0104 0.0139 0.0174 0.2083 HYDRAULIC CONDUCTIVITY - Ft./Day n. LONG TERM ACCEPTANCE RATE FRONTENAC DEVELOPMENT COMPANY FROM HEALY AND LAAK LLAND •ENGINEERIN.G ASSOCIATES,INC. CONSULTANT ENGINEERS S PLANNERS .AN1IItllo.�MoNgos.NIOO[I4 O•COIWACTICYT •• A 86-0752 also govern leachfield design but with the subject site this is not the limiting constraint. Design of the leachfield system for the Frontenac devel- opment proposal was based upon the following criteria: -- System sizing to meet Title 5 requirements -- System sizing by LTAR -- Reduction factor applied for high quality effluent from the RSF A design flow of 5, 00C) gallons per day has to be selected as the design flow for leachfield systems sizing. Title 5 -- For a perc rate of < 2 minutes/inch, an appli- cation rate of 1. 0 gallons per day/square foot for bottom area and 2. 5 gpd/square foot is used for typical septic tank effluent. Using leaching pits with a 14 foot effec- • tive diameter and six feet deep results in a requirement for six pits. Using a leaching gallery with a depth of six feet and width of 12 feet results in a requirement for 119 feet of gallery. LTAR -- Selection of a soil permeability (hydraulic con- ductivity) value has been based upon soil auger borings performed by Geotoxi Associates. Figure 7 from Down Cape Engineering and Geotoxi Associates, depicts soil boring locations. Borings 014, 015, and 021 were selected due to their proximatly to the system location. Table 7 1 `, Y. d - v- 4 A 7 1 � z �N .. � , L.) m % 5 W • d :-I- U 8 `' J J aa? • 01 9 d4 - o p c . d A- T . / ' -<<. . aNpe../ 0 t? I 8 00 016 • �' '5' J • � � Q 015 (•3 t. .: . _j•K It 0• 1 : ,. 4 • o:t.3. 6 2 2 i ;i 414 N � iY o Q 0 FIGURE 7 SURVEY MAP WITH AUGER • BORING .LOCATIONS - FROM •• • • . . GEOTOXI ASSOCIATES, INC. summarizes data from Geotoxi Associates on hydraulic con- ductivities and LTAR for the medium to coarse sand soils encountered in borings 014, 015, and 021. TABLE 6 HYDRAULIC CONDUCTIVITIES AND LTAR Hydrulic Conductivity LTAR Test Boring No. Ft/minute Ft/day ggd/ft2 014 6. 09 x 10-2 88 1. 29 -2 015 5. 57 x 10 80 1. 24 -2 021 2. 49 x 10 36 0. 87 For typical system sizing using LTAR a maximum value of 1. 0 is ►_used due to the more erratic results obtained beyond this point. The resultant system sizes for this design methodology •are based ►_upon an average LTAR of 1. 13 gpd/ft , ►_sing 1. 0 gpd/ft for design. Total area re- quired is 5, 000 ft . This calls for 12 leaching pits or 208 feet of gallery of the same dimensions as described earlier. Reduction Factor With the high quality effluent produced by the RSF application of a system reduction factor is logical. POD 5 and TSS concentrations of 10 mg/1 each were used in calcu- 23 lating a factor of 0. 43. This factor results in a total 2 system surface area requirement of 2, 150 ft which results in five leaching pits or 90 feet of leaching gallery. Figure 2-A and 2-B show leaching systems for either op- tion. Table 7 summarizes proposed leaching facility sizing. TABLE 7 Leaching Facility Sizing Alternative Corn2onets Dimensions Number or Length Leaching Pits 14 ft diameter 5 6 ft depth Leaching Gallery 12 ft width 90 ft. 6 ft deep VIII. TREATMENT SYSTEM MONITORING Monitoring of incoming flow can be accomplished through building water meters required by the Municipal Water Department. Appropriate points through the treatment sys- tern for quarterly monitoring of treatment system ef- ficiency are as follows: a. Final grease trap effluent b. Liquid from the recirculation tank just prior to pump dosing of the sand filter c. Sand filter effluent 24 Parameters of significance include: Biochemical oxygen demand -- 5 days Total suspended solids Nitrogen series pH Alkalinity IX. GROUNDWATER MONITORING Geotoxi Associates will be proposing a groundwater monitoring program to include upgradient and downgradient monitor wells. Sampling frequency and parameters for analysis will also be specified. Final construction plans will detail well construction and precise locations. X. OPERATION AND MAINTENANCE Any treatment system requires routine operation and maintenance procedures for long term use. The proposed facilities will require periodic pumping of accumulated solids from the septic tanks and grease traps, regular inspection of pumps and the control panel of the recircu- lation tank, regular raking of the sand surface in the sand filter, and infrequent (1 year +) removal of the top 1 - 2 inches of sand as it may become clogged. At the point when only 24 inches of sand remains, six inches of new sand meeting the specifications would be added to the 05 filter. Optimal frequencies for operation and main- tenance will best be determined over time. Table 8 lists operation and maintenance items and frequencies recom- mended to be implemented initially. This table should be used as a working guide to be modified as experience is gained. Table 8 is listed an the following page. PS TABLE 8 OPERATION AND MAINTENANCE OF WASTEWATER Conveyance,. Treatments and Disposal Facilities Item Freguency Pumping of septic tanks Initially inspect every six months for solids accumulation and pump as needed, 1 year frequency minimum Pumping of 2, 000 gal. grease trap Quarterly Pumping of 3, 000 gal. final grease Inspect every six months trap for solids accumulated and pump as need. Clean sewer lines with high pre- Annual ssure water .jet between the building and septic tanks and grease traps and the sewer leading to the final grease trap Check pumps in recirculation 2 weeks tanks, record time reading meters, control panel, high level alarms Pumping of recirculation tank Annual and cleaning Rake sand surface level in 2 weeks sand filter, check for odors when dosed, check distribution line orifices for plugging and clean as needed. Replace six inches of sand in When only 24 inches re- filter main Measure depth of ponding in Annual leaching system Water meter reading Quarterly 47 REFERENCES • 1. Andreoli, A. et al. , "Nitrogen Removal in a Subsurface Disposal System", Journal of the Water Pollution Control Federation, Vol. 51, No. 4 1979. 2. Cedergren, H. R. , "Seepage, Drainage and Flow Nets", John Wiley & Sons, Inc. , New York, New York, 1967. 3. Eastburn, R. P. , "Denitrification in On-site Wastewater Treatment Systems - A Review", On-site Wastewater Treatment, Proceedings of the Fourth National Synoposium on Individual and Small Community Sewage Systems, American Society of Agricultural Engineers, New Orleans, LA. , 1984. 4. Harris, S. E. et al. , " Intermittent Sand Filtration for Upgrading Waste Stabliiztion Pond Effluents", Journal of the Water Pollution Control Federation, p 83 - 102, January 1977. 5. Hathaway, R. J. and Mitchell, D. T. , "Sand Filtration of Septic Tank Effluent for All Seasons Disposal by Irrigation", On-Site Wastewater Treatment, Procceeding of the Fourth National Synoposium on Individual and Small Community Sewage Systems, American Society of Agricultural Engineers, New Orleans, LA 1984. 6. Healy, K. A. Laak, R. , "Site Evaluations and Design of Seepage Fields", Journal of the Environmental Engineering Division, ASCE. Vol. 100, No. 10, 1974. 7. Healy, K. A. and May, R. , "Seepage and Pollutant Renovation Analysis for Land Treatment Sewage Disposal Systems", Connecticut Department of Environmental Protection, Water Compliance Unit, Hartford, CT, 1982. 8. Hines, M. et al. , "Alternate Systems for Effluent Treatment and Disposal", Third National Synoposium, American Society of Agricultural Engineers, Chicago, Illinois, 1978. 9. Hines, M. and Favreau, P. E. , "Recirculating Sand Filter: An Alternative to Traditional Sewage Absorption System", Proceedings of the National Horne Sewage Disposal Synoposium, American Society of Agricultural Engineers, Chicago, Illinois, 1974. 10. Laak, R. , "Wastewater Engineering Design for Unserved Areas", Ann Arbor Science, Ann Arbor, Michigan, 1980. 11. Laak, R. , "A Passive Denitrification System for On-Site Systems", Proceedings of the Third National Synoposium on Individual and Small Community Sewage Treatment, American Society of Agricultrual Engineers, Chicago, Illinois, 1981. 28 12. Lance, J. C. , "Nitrogen Removal By Soil Mechanisms", Journal of the Water Pollution Control Federation, Vol. 44, Nco. 7, 1972. 13. Lance, J. C. et al. , "Maximizing Denitrification During Soil Filtration of Sewage Water", Journal of Environmental Quality, Vol- 5, No. 1, 1976. 14. Leach, L. E. and Enfield, C. G. , "Nitrogen Control in Domestic Wastewater Rapid Infiltration Systems", Journal of the Water Pollution Control Federation, Vol. 55, Nov. 9, 1983. 15. Loudon, T. L. et al. , "Cold Climate Performance of Recirculating Sand Filters", On-site Wastewater Treatment, Proceedings of the Fourth National Synoposium on Individual and Small Community Sewage Systems, American Society of Agricultural Engineers, New Orleans, LA. 1984. 16. Metcalf & Eddy, Inc. , "Wastewater Engineering : Treatment, Disposal, Reuse", 2nd ed. , McGraw Hill Book Company, New York, 1979. 17. New England Interstate Water Polution Control Commission, "Guides for the Design of Wastewater Treatment Works", 1980. 18. Otis, R. J. and Z iebel 1, W. A, "A Report of an Investigation of a Subsurface Sand Filter Leaded With Septic Tank Effluent at the Cleveland Heights Elementary School, New Berlin, Wisconsin", Small Scale waste Management Project, University of Wisconsin, Madison, Wisconsin, 1973. 19. Salvato, J. A. , Jr. , "Environmental Engineering and Sant itat icm", John Wiley & Sons, Inc. , New York, 1972. 20. Siegrist, R. L. et al. , "Commercial Wastewater On-site Treatment and Disposal ", Proceedings of the National Synoposiurn, on Individual and Small Community Sewage Systems, American Society, of Agricultural Engineers, New Orleans, LA. , 1984. 21. Sikora, L. s. et al, "Field Evaluation of a Denitrification System", Proceedings of the Third National Home Sewage Treatment Symposium, American Society of Agricultural Engineers, Chicago, Illinois, 1981 22. Sikora, L. J. and Keeney, D. R. , "Denitrification of Nitrified Septic Tank Effluent", Journal of the Water Pollution Control Federation, Vo 1. 48, No. 8, 1976. 23. State of Connecticut Department of Environmental Protection, Water Compliance Unit, State Permit Monitoring Files. 24. State of Massachusettes, "The State Environmental Code, Title 5: Minimum requirements for the Subsurface Disposal of Sanitary Sewage, 310 CMR 15. 00", January 1978. 29 25. Taske, M. G. , "Recirculation--An Old Established Concept Solves Some Old Established Problems", Presented at the 51st. Annual Conference of the Water Pollution Control Federation, Washington, D. C. 1978. 26. U. S. Environmental Protection Agency, EPA 625/1-81-013, "Pro- cess Design Manual, Land Treatment of Municipal Wastewater, " 1981. 27. U. S. Environmental Protection Agency, EPA 625/1-81-013a, "Process Design Manual, Land Treatment of Municipal Waste- water, Supplirnent an Rapid Infiltration and Overland Flow", 1984. 28. U. S. Environmental Protection Agency, EPA 625/1-77-009, "Process Design Manual, Wastewater Treatment Facilities for Small Sewered Communities", 1977. 29. U. S. Environmental Protection Agency, "Process Design Manual for Nitrogen Cottrol ", 1975. 30. U. S. Environmental Protection Agency, EPA 625/1-80-012, "Design Manual, On-site Wastewater Treatment and Disposal Syt ems", 1980. 31. Warnock, R. G. and Biwas N. , "Study of Columnar Dentrification For Application in an On-site System", Proceedings of the Third National Symposium on Individual and Small Community Sewage Treatment, American Society of Agricultural Engineers, Chicago, Illinois, 1981. 30 APPEND I X A DESIGN CALCULATIONS JOB R�0 ! c2 �rC.Y' 1Pr1Gc /.9✓ LAND ENGINEERING ASSOCIATES, INC. SHEET NO. / OF /418 Main Street CALCULATED BY 7G DATE //7[�/UQ MONROE, CONNECTICUT 06468 (203) 268-7943 CHECKED BY DATE SCALE - L D yyt v',i cfa f !'e a-S �.... . L. a w:N. e ,....L1. /n eEr K ,;p s old _ Z960• .. . . _... . bld• 5 6c0 5k.b' fiat../ z Ll -90 0Q- PAOLJCT 2041(iv /Inc.Won,Man mnl. cos �-g( 7-r--'c j/�' `-1-: ' c_ roc,/ <G LAND ENGINEERING ASSOCIATES, INC. 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Gt114 rau ciar&- '4.f .I- i 4ep%.... aIidd fU 1/r'._al '. . 7- ti ).-erer ea /r. f/e . . d'f c!_. a. �.. 07 S _ 6'. CU 1 ✓ �Ga 1c S �0er. f c/ 5-�c41cc � GnG �Q GG� c/ � 91 � ' ` , ✓�� anS r � d sart ±. ,vcc. =er G�r� �_ nd ' ........ f _ : f4I�e vo Cr . Qte .� avti. a(f,rep A.�r.cv u1/ , _.. Dlt'!{✓e r1-e/i 1��',r/L p cc .'F-. cp&-t C-J.-A.... c[�7�. .... (e _ ...l eo c L'_'^„.5 s/sfecA , , 4L(te4t .. l2 ,e0"pc -ie t 3 ore_ _. /C<u7&( 4-t e evQ 'n,_ 90- 0 . .c rt 'ur: Q fiery e' -z , . t '_..Y-X-k arm' - .. of __/5- -ac? . ..11.....(,vcc-4/ C .•%.Sf . t _ -- i t 1 r... i 1 t f . I- . j j ' F t t t # t E ._._..�-._.. . t i : 1 t t t _ s t i rnocua OH/NIa//I...smut wit ram - .-. . APPENDIX B SITE MAP AND DOWN CAPE ENGINEEING 1 � . • t', T t "4 RECIRCULATION TANK• This unit provides for storage of the septic tank discharge and the re- cycled sand filter effluent between pumping cycles. The recirculation tank should have a capacity equal to at least one days retention time based on volume of raw sewage produced. In installations utilizing standard precast RECIRCULATING SAND FILTER: AN ALTERNATIVE septic tanks, an identical septic TO TRADITIONAL SEWAGE ABSORPTION SYSTEMS tank can be utilized for the recirculation unit. As an example, a system which has provided a 1,500 gallon septic tank to serve a three bedroom home would also incorporate • second 1,500 gallon GENERAL: con- Michael Hines R.E. Favreau septic tank for use as the recirculation unit. Recirculation tanks con- structe°d on site should contain same baffling arrangement to provide adequate The soil conditions in many areas are such that seepage field systems n8 f the septic tank effluent and the recirculated sand filter effluent. do not function properly resulting in discharge of inadequately treateequid sewage to the ground surface. Serious health hazards and very objectionable The filter discharge Tine passing through the recirculation tank may nuisance conditions are thus created. Most authorities agree that with ppd with a sanitary cross (as shown in Figure 1) or with a down-turned percolation rates in excess of 60 minutes per inch, seepage field systemssanitary "T' where regulatory agencies do not permit an emergency overflow. ted in which will not function properly. With percolation rates between 30 and 60 minutes Below the down-turned leg, a wire basket arran !s housed a common rubber ball of •lightly larger diametert is nthan,the diameter per inch, they may function properly if sized adequately; however, the re- of the . quired absorption area becomes considerably larger than the private home Pipe. As the filter effluent enters the recirculation tank the water owner in many cases is willing to install. As a result of these conditions, level rises in the tank until it forces the rubber ball tight private developers and experts in the field of waste treatment have for years i bottom of the down-turned en against the attempted to develop a system that would replace the septic tank-seepage leg. The remaining filter effluent then discharges on out the effluent line to a surface drain. field installation. Until recently, all such efforts have resulted in fail- ere. RECIRCULATION PUMP: In 1968 inelrecirculating sand filter wastes treatment syste Mlchaem eveloped in city In systems serving ing single family residences only, a pump with a cape- llinois Y Y 8 per minute !s reconmvended. With suitable timed con- They observed that open sand filters have been used for many years in con- I raw lsewhise cvolume. provide a recirculation rate of approximately 4 to 1 based on tionsisuchon las cath mps, sch000ld and tanks in the tsometceommercialnt of sfacilte itiesm..11Asnthelse tic be sized andactuatedntoa installations, the recirculation pump should tank effluentpassed throughthe sand filter, essentiallyall of the rticu- i ls- in 24 hours. The pumps pump4 or 5 times the amount of raw sewage produced junct papumping rate in gallons per minute is determined b late matter was removed as well as a considerable amount of biochemical number of minutes that the pump would operate in a 24 hourby the oxygen dmand. Effluents from these sand filter units were found to be I suns has shown that an optimum pumping period. Expert_ clear and essentially odor free and did not create nuisance conditions inff p P ng cycle is 10 minutes on and 20 minutes the receivingstreams. The majorproblem with this typeof system was the larger,installations, as total pumping time of 48ed minutes per day. Ia some j Y minutes off for a total pumping cycle is utilized withr5day. son and 25 fact that each time the septic tank effluent was dosed onto the sand filter pumping time of 240 minutes surface, considerable odor problem developed. Y• It !s advisable to provide duplicate pumping facilities which would The recirculating sand filter treatment system ,instate of a septic alternate in operation particularly 1n larger installation:. This provides ge tank, a recirculation tank and an open sand filter, as shown in Figure #1. i for continued operation of the facility should failure occur with one of the A pumping system consisting of a small pump (such as a submersible sump Pump unite. A small hole or spigot should be provided on the pump) and a time clock control mechanism provides a desired recirculation I line inside the recirculation tank to allow the discharge line tomdr•in badischack rate which results in a fresh liquid being dosed onto the surface of the into the tank during periods of freezing weather. sand filter, thus eliminating any odor conditions. The system which is dis- cussed in further detail below has proven to be very economical; yet it pro- The PUMP ODNTROL: vides an effluent quality such that, with disinfection, the effluent would meet the quality criteria of regulatory agencies. The mechanism for control of the pumping cycle is provided by • time clock switch unit. A variety of .these units are available on the market.SEPTIC TANK: The important criteria to consider in selection of a unit is the requirement All waste water generated by the facility to be served by this system designhofuthissystem.fOMoreesophiaticatedotime clock,unitarareisug !n the for larger pumping is discharged to a septic tank which is designed in accordance with standard 8 installations as this will allow the alteration of the pumping septic tank design procedures. United States Public Health'Service publi- cycle as necessary to fit varying flow conditions. cation #526, entitled "Manual of Septic Tank Practice" is the reference most commonly used by the public health professionals in sizing and design- ('FILTER: ing septic tank installations. A 750 gallon septic tank should be the mini- mum size tank used on any installation and a single family residence with The sand filter le very similar in covet sand filter.' The filter bed consists of a ruction to any open surface more than two bedrooms ct�ould use proportionately larger tanks, filter sand with a desired effective size ofr0 6 toe1.0 3mile terearse (pre- ferably the latter) and a uniformity.coefficient of less than 2.'5. Inrmany The authors ere: MICHAEL HINES and R. E. FAVREAU, Regional Sanitary Eng!- Y veers, Illinois Department of Public Health, Champaign and Marion, Illinois. areas, torpedo sand" has been found to serve quite satisfactorily as filter media. However, any sand proposed for use in such • unit should be checked 130 131 /I . by knowledgeable authorities before use since sand size is particularly criti- i.. 1 cal. Approximately 12 inches of graded gravel should be provided beneath the sand to support the sand and to surround the underdrain system. In residen- tial installations a single underdrain is adequate. For larger installations, j underdrains should be provided on 10 foot centers. Distribution troughs or pipes should be provided above the sand surface on 3 or 4 foot centers. The z material and type of construction of the distribution troughs or pipes can I vary with the imagination, but should be designed to prevent sag and to re- I ' , z i cult in even distribution of the applied sewage to the filter surface. t"�:q r` o 1F ' 1 i The sand filter should be designed on the.basis of 3 gallons per day IC r "^"-* 4!` , per square foot of surface area based on the raw sewage flow and not the re- y . 'l W I circulated flow. When the raw sewage flow expected is less than 300 gallons F per day, such as in single family residences, then the minimum sand filter J .. - area that should be provided is 100 square feet (10' X 10'). With filters ,! } serving systems including discharge from automatic washers and dishwashers, a m ' • . 1 ,e, . �, , minimum size of 144 square feet (12' X 12') is recommended. o `I ' rri: . 5.--; i' c $- . Q 1 INSTALLATION: z . d 4: F. ` ., ' . o • I The location and type of installation of the recirculating sand filter ;.,) ! :,. system will vary depending upon the topigraphical conditions present. The ,,, k+ i. tr, 0- filter should be located away from trees wherever possible to avoid problems N .-' - 0 I with leaves, but may be protected by small mash wire. An ideal installation a .. j would result in the septic tank and recirculating tank being buried just be- :� t/1 ! low ground surface with the sand filter installed so that the surface of the I sand is at or just slightly below the surrounding ground level. This ideal installation is possible on terrain that is rolling or hilly. On level Q A ground, it may be necessary to install the sand filter above ground surface -- -_-a% or provide for pumping of the effluent or both. I • cJ `s W � e 'The septic tank bury depth generally is determined by the depth of the - cC s b ?, I ti= I building sewer. Excessive depths should be avoided where possible since - V \6^ 1 N effluent from the septic tank flows into the recirculation tank by gravity. ua o ►y "' 'S The recirculation tank must be installed so that the effluent line from the CC o� : a w a o 1 • septic tank to the recirculation tank has the necessary slope. To minimize t.Z s ., a cost and to minimize the depth at which the recirculation tank is installed, q o - �. s a this unit would normally be located as close to the septic tank as possible. �� s\ L 2 i '" , The sand filter unit must be located so that the underdrain discharge Z line which passes through the top of the recirculation tank is provided with N W_ t\ V. 1' F sufficient slope to allow gravity discharge from the filter. The underdrain _� . 1 line will be approximately 4 feet below the level of the surface of the sand. \ 1j If the system is located on level ground, then the sand filter should be con- , ) Z I etructed above ground level to prevent the top of the recirculation tank from o; / 0. being located 5 to 6 feet below ground surface. When constructed above W ( ground level, it is necessaryto utilize reinforced concrete or other sub- - �' ., m-4 Q j stantial construction for the side walls on the filter. Concrete block walls 4 <'; a have proven to be unsatisfactory. When constructed below ground level, as Ir a Is. 3 would be the case on a hillside,_ then no particular side wall support is m`< V required. Where the filter is located below ground surface, surface water 0 � t o - should be diverted away from the filter by the use of earthen dikes or red- / f- `e/ W wood or concrete block diversion walls extending 8 inches to a foot above. 4 . ccsurrounding ground level. III W c t y N WINTER OPERATION: i11 \u Each time the recirculation tank effluent passes through the sand filter m ;; o ' , - improved quality is obtained. During freezing weather, however, a tempera- .. .W f ti tura drop would occur. With sufficient recirculation during periods of ex- .a� - tremely cold weather, freezing of the filter system can occur. Several possi- bla solutions exist to prevent the freezing of the system. Reduction of 133 132 r 4 recirculation would be one poasiblity. If the recirculation is terminated Figure 2 during such freezing periods, then the septic tank effluent remains at a i ILE1:Y gESL9ENCE temperature warm enough that freezing of the sand filter would not occur. To prevent the recirculation, the rubber ball valve may be tied to the bottom of RECIRCULATING SAND FILTER the down-turned leg in the recirculation tank during such periodsof fso inal tlall of the filter effluent passes through the line and out to a point EFFLUENT QUALITY disposal without entering the recirculation tank. Another mechanism would be the installation of a bypass line around ofefreezinglation weatherank thend filtered as shown in Figure 1 so that during periodsDATE BOD T.S.S. FECAL COLIF0R$ PH effluent may be bypassed around the tank directly to the point of final d!e- milligrams per liter per 100 ml posal. 10/15/69 1 1 4�500 7,0 DESIGN ERAMFLES• 1. Assume a system is to be designed to serve a three bedroom home 10/29/69 2 3 1,600 7,4 with garbage disposal and automatic clothes washer facilities.Based on sewage treatment design guidelines in use in the State 11/7/69 2 7 6.9 42.000 of Illinois, a 1,575 gallon septic tank would be required. A 11/14/69 5 4 42.000 6.8 second 1,575 gallon septic tank would be installed to serve as the recirculation tank. A pump with a capacity of 5 to 10 11/20/69 3 4 2.900 j,3 gallons per minute would be provided and set to operate with a _ 5 mute pumping cycle during ea30minut y depending s would pro- 12/3/69 2 4 1�100 6.9 vide a total of 1,200 to 2,400 gallonsper the pumping rate. The sand filter would be provided measuring 12/11/69 4_ 3 1.100 67.9 144 square feet in surface area. 2 2. Assume a system is to be designed to serve a trailer park which I - 12/17/69 5 18 6.600 ),3 will generate 3,000 gallons per day of raw nsewage. Based upon recognized design standards, a 3,500 gar Pge tB would1/14/70 4 3 19.441/ 6.8 be constructed. A second 3,500 gallon capacity tank should be i 1/21/70 7 4 36,000 7.5 constructed to serve as the recirculation tank. • • With a design pumping cycle of 10 minutes on and 20 minutes off each i 1/28/70 5 4 1�700 6.8 half hour, in order to provide the desired 4 to 1 recirculation rate, the 2/11/70 7 10 1.200 6.8 pump would be sized to provide 12,000 gallons of sewage in 480 minutes or approximately 25 gallons per minute of pumping capacity needed. An alter- 1 with the controls set 2/18/70 3 5 1.300 6.6 native would be to provide La 50 cyclegal eachhalfon per nhourute p� to provide a 5 minute pumping 2/25/70 3 1 • 800 6,9 The sand filter surface area required is determined by dividing the 3,000 gallons per day raw sewage flow by the design loading rate of 3 gallons surface of the sand must be raked and leveled as necessary. After extended ' period of operation, a crust maydevelopon the surface of the sand !a sons per day per square foot of sand surface. This indicates that for this n- stallation,bea sand filter measuring 1,000 square feet in surface area (32' X areas. In these areas, the upper to 1 inch of sand should be raoovad and 32') would necessary. discarded by use of a flat shovel. Sand may then be raked and leveled. 1t►L• # process of skimming off encrusted sand can continue until the upper 12 inches SYSTEM MAINTENANCE: of sand have been removed. At that time, new coarse sand may be placed into the filter to make up for the 12 inches of sand removed. However, it i• ant The recirculating sand filter system does require routine maintenance. necessary to replace Band each time the upper surface of the sand i• skimmed The amount of maintenance required, however, should be minimal. The septic and discarded. tank should be checked for sludge solids and scum build up each year and pumped out as necessary, but at least every other year. The recirculation EFFLUENT DATA: tank would require no particular routine maintenance. The recirculation pump will require periodic checking and cannot be expected to last indefinitely i everal hundred recirculating sand filter systems have been without replacement. It is recommended that in smell installations a dupli- ?:IiillirchilrInglio7ILTiltii: r:ledgcleF.Iiii.hrfecjei71: iil:a e private residences. Approximately fifty units have been be provided in storage for use should the system fail for any rea- son. omesticewage. Theseuitshavecosistently pravidsduents of such quality that with disinfection, local and state regulatory Most of the routine maintenance associated with this system involves agencyeffluent standards are satisfied. Figure 2 lists the effluent quality the sand filter unit. The distribution trough must be maintainedddso that ts must bthee parameters for one of the first recirculating Band filter systems installed. . sewage is distributed evenly over the surface of as theyilter.in short order The average SOD and Total Suspended Solids for the sampling period wars 4 eg/1 ' removed from the filter as soon as they appearand 5 mg/1 respectively. completely cover the surface of the filter rendering it unuseable. The 135 134 r 'r Due to severe shortages of staff and funds, the Illinois Department of Public Health has not been able to conduct an extensive laboratory evaluation of the effluent quality from recirculating sand filter units installed since 1970. Data has been collected by other state agencies, however. A review of these more recent effluent results indicates that ammonia is being con- verted to nitrites and nitrates by bacterial action within the sand filter. This biological metabolism results in considerable HOD reduction as well. REMOVAL OF VIRUS FROM SEPTIC TANK EFFLUENT SUMMARY: The recirculating sand filter system provides a waste treatment system BY SAND COLUMNS for use in areas where absorption field systems cannot function properly or where space is limited. The recirculating sand filter systemis designed on K.M. Green D.O. Cliver sound, sanitary engineering principles, deviation from which would result in failure of the waste treatment system. It is, therefore, important that any Mounds constructed of 60 cm of sandy fill between a soil-covered system proposed be designed and installed in accordance with the information seepage bed and the original topsoil have been designed to provide on-site presented herein. treatment and disposal of septic tank effluent 1 STE; Although minimal in amount, routine maintenance of the system is re- ( )• As a means of quired. Systems designed and installed in accordance with this information evaluating the efficiency of these mounds in removal of human intestinal can be expected to provide an effluent of superior quality eliminating the viruses from STE, a variety of sand-filled columns have been employed ae offensive odors and other nuisance conditions so common to_existing systems. models of the field system. Previous studies have shown varying degrees Imaginative landscaping can add a great deal to acceptance from an aesthetic standpoint. Direct health hazards are minimal and effluent disinfection of retention of viruses by sand filters, depending upon conditions (4,6-8); would control all pathogens. but little attention has been paid to the effect that long-term application of wastewater may have on the system.• METHODS The columns-have been of two types: 60 cm of medium sand (1) in 14.6 or 7.7 cm ID PVC cubing, corresponding to the path length of the field • system; and 2-4 cm (10-20 g) of sand in 1.9 cm ID tubing. The 60 cm columns have fritted glass bulbs inserted at intervals for fluid sampling, • and removable rubber stoppers for access to fill material. The columns were dosed with poliovirus type 1 (strain CHAT) grown in tissue culture (either primary monkey kidney or HeLa cells) and suspended in STE. The STE is delivered weekly to the laboratory and stored at 8 C until used. In some instances the virus was tagged with 32P before use (5); test samples were dried on aluminum planchets and assayed with a gas-flow GM counter. Viral infectivity assays were perforped by passing samples through 0.2 µm Gelman cellulose triacecate membrane filters to remove bacterial contamination (2), making serial dilutions, and testing in tissue cultures by the plaque technique (3). Virus was eluted from fill material by adding 1 ml of fetal or agamma calf serum per gram of fill and stirring for 1 minute. Particulate matter in suspension was removed by filtration through a Millipore AP 04 prefilter. • The authors are: K.M. Green, Research Specialist, and D.O. Cliver, Associate Professor, Food Research. Institute and Department of Bacteriolo- gy, University of Wisconsin, Madison, Wisconsin 53706. 136 137 / (week 14) for Waukegan silt loam, whereas Lester clay loam concentrations maintained relatively constant levels after septage application until the fall of the third year. COLD CLIMATE PERFORMANCE OF RECIRCULATING SAND FILTERS Phosphorus and Salts in the Soil Profile T.L. Loudon D.B. Thompson, L. Fay Analysis of variance indicates that application rates significantly Assoc. Mem. ASAE Assoc. Mem. ASAE affected only phosphorus and sodium concentrations in the soil profile taken from soil samples upon completion of the three-year study at an alpha L.E. Reese level of 0.01. Student Mem. ASAE Phosphorus applied in septage remained in the upper 15 cm of the soil profile (Fig. 5).- The largest increase of phosphorus occurred in Lester The recirculating sand filter (RSF) is a simple, compact method of providing clay loam where 1120 and 1500 kg/ha application rates increased phosphorus improved treatment with a low level of maintenance. Recirculating sand fii- concentrations by 2.6- and 1.7-fold (29 and 19 mg/kg), respectively. ters were developed in Illinois (Hines & Favreau, 1974) as a method of providing secondary treatment beyond a septic tank prior to surface dis- Sodium concentrations were greater in Lester clay loam and Waukegan silt charge. For individual homes the system consists of a recirulation tank, loam, possibly due to the increased cation exchange capacity of these two approximately the same size as the septic tank, which contains a mix of sep- soils. On the average, 1120 and 1500 kg/ha application rates increased tic tank effluent and effluent which has been through the sand filter. The sodium concentration 5.4-fold (143 mg/kg) over the top 40 cm of the sand filter itself consists og a sand 4ed approximately 1.2 a (4 ft) deep profile. For Hubbard loamy sand, the relatively small increase due to the providing approximately 0.03 m (1/3 ft') of surface area for each 3.8 L/d septage application could indicate that by the end of this three-year (lgpd) of design effluent loading. The RSF for a three-bedroom home is study, most of the sodium had leached below the sampling depth. - therefore about 3.7 a (12 ft) ,equare. The effluent mix from the recircul- ation tank is applied on the surface of the sand filter in frequent, small doses. Drainage from the sandfilter is collected and either returned to the CONCLUSIONS recirculation tank or discharged. Even though 225 kg/ha nitrogen applied in septage to a loamy sand soil Recirculating sand filter effluent has been discharged to surface waters increased nitrate concentrations in the upper 60 cm of the soil profile, following on-site chlorination (Hines & Favreau, 1974). The experimentation the nitrate concentrations below this point were similar to background with recirculating sand filters discussed in this paper was prompted by the concentrations. This indicates that for this soil type, the 225 kg/ha need to improve sewage treatment on small lots around lakes in resort areas. application rate may be considered acceptable. The goal was to provide improved treatment prior to discharge through a soil absorption system to achieve improved protection of lake water quality. The nitrogen application rate of 1120 kg/ha would exceed the nitrogen Bernhart (1973) presented evidence that effluent absorption in slowly perme- storage capabilities of silt loam and clay loam soils because nitrate able soils is greater for highly oxidized effluent such as achieved with a concentrations increased below the 105-cm depth, where crop nutrient uptake RSF than for septic tank effluent. The sand filter will also protect the is reduced. Since nitrate concentrations from the 225 kg/ha application soil absorption system against solids discharge from a septic tank which rate were less than or similar to background levels, the acceptable needs cleaning or is otherwise overloaded. application would be between these two rates. • Recirculating sand filters are not currently accepted by regulatory agencies Application of septage did not affect concentrations of fecal streptococcus in Michigan. Therefore, the devices described In this paper are considered and fecal coliforms in soil water. experimental in nature. Septage application resulted in a statistically significant increase in the concentration of soil water potassium, sodium, calcium and magnesium. SYSTEM DESCRIPTIONS Application of septage produced an increase in the phosphorus and sodium concentrations in the soil profile at the completion of this project. The recirculating sand filters studied are largely based upon design recommendations from Hines & Favreau (1974). Two RSFs have been built and REFERENCES monitored in Michigan. The first was built at Kirtland Community College American Public Health Association. 1975. Standard methods of the examination of waste and wastewater. 14th Ed. Washington, D.C. The authors are:- T.L. LOUDON, Associate Professor and Extension Ag. Engr., 1193p. Ag. Engr. Dept., Mich. State Univ., E. Lansing, MI; D.B. THOMPSON, Hydrol- ogist, Groundwater Division, Minn. Pollution Control Agency, Minneapolis, MN; Linden, D. R. 1977. Design, installation, and use of porous ceramic L. FAY. Assistant Sanitarian, Park County, Fairplay, CO., L.E. REESE, Grad. samplers for monitoring soil-water quality. ARS-USDA. Tech. Bull. Asst., Ag. Engr. Dept., Mich. State Univ., E. Lansing, MI. 1562. 16p. Soil Survey Staff. 1951. Soil survey manual. USDA Handbook No. 18. Soil Survey Staff. 1975. Soil taxonomy. USDA Handbook No. 436. 743 p. near Higgins Lake in the northern part of Michigan's lower peninsula in S•,,.hackr,,, 1976. The second was built-near E. Lansing in 1982. Both systems involve . ►l•.tI.Sheet« Woodee•• ' Free* W,w,.r r PVC subsurface discharge of effluent to soil absorption fields following sand Oh it,,onMean filter treatment. At both sites, the RSF was added on to an existing septic -a• i .j�.•=ve .0 1'" . system. In both cases, the soil absorption field was redone at the time of L! ,4.,°"rs.,,,ee ,.•,b,o sand filter installation. In the first case, the system was being upgraded to F j ori•rK Pipe provide a larger system as part of a routine improvement process ongoing in s•"'Filler n•n«3tr,Fe or r PVC Sent end the neighborhood. In the second case, a new field was constructed to increase _ 30Io.ot Welded the effluent loading on a slowly permeable soil to test the acceptance of sand filter effluent at rates much higher than the normal design values for Corr. Plastic Praia Tubing 7 �.° . this soil. �t`V /friC, 4+,A o%0 The sand filter design used in both systems is basically the same. It con- ,•' �,. �'A' :. 0.5 sists of a square sand bed 3.7 ■ (12 ft) square and 1.2 m (4 ft) deep, filled '� 2 C a 6 with a calcareous sand having an effective size (D 0) of 0.3 mm and uniform- r.o.Septic*•"`, 1 . _ ity coefficient of about 4.0 (Michigan Construction Grade 2NS). The sand �• r r— U beds are lined on the sides and the bottom with a complete envelope of two fleet Valve 111 To Soli AMorvt,on sr.t.s layers of 0.15 rm (6 mil) black polyethylene sheet folded to form a seamless easr.ar uee, ,.PVC leak free liner. This material provides a low cost, easily constructed liner ;__ adequate for a short life exprimental system. The bottom of the bed was Durable Robber shaped slightly to slope to the center where a single corrugated polyethylene Ball 1'2'Nee.ef across Mottoes drain tile is installed to pick up the percolating effluent. A sump just heracros To now.N„ outside the filter is provided for sampling purposes. The surface of the x«,rco,etIon Teo, filter is approximately at grade. The top edge of the filter is formed by a treated wooden frame and the plastic sheet material is wrapped over and fas- tened to the outside of the frame. • ,V The 3780 L (1000 gal) recirculation tank contains a pump which is operated by . Fig. 1 Schematic Diagram of Recirculating Sand Filter a' timer. Typical operation time is four to six minutes each hour except ')r during nighttime hours when no water use is expected in the home. At nightThe The E. Lansing system is in a soil with a perk rate of 18-24 min/cm (45-60- (V A the pump runs only twice to minimize operation on cold winter nights. min/inch). Since it Is necessary to pump the effluent to get it back to. the pump flow rate and total time of operation are balanced to provide a daily soil absorption system after it has passed through the sand filter, a small filter application amount equivalent to five times the daily effluent gener- diameter pressure distribution system was utilized. The field consists of ation rate. This means that the mixture of water going onto the filter is 73.2 m (240 ft) of 0.3 m (1 ft) wide trench with 15 cm (6 in) of stone under �+7 approximately one part septic tank effluent and four parts filter drainage. the pressure distribution pipe and approximately 5 cm (2 in) over the pipe. A gate valve is included between the pump and filter to provide for The system is set shallow with soil cover over the stone ranging from 13-33 adjustment of pressure in the application system so that the spray height and cm (5-13 in). Average daily water use for the three bedroom home served by droplet characteristics of sprinklers can be adjusted to prevent wind drift. this system is approximately 490 L/day (130 gpd). The water from the filter drains back into the recirculation tank where a float valve is provided in the return line. If the tank level is down, water PERFORMANCE draining back from the filter returns to the tank. When the recirculating tank is nearly full the float valve closes and flow is diverted for final Odor disposal through the soil treatment system. See Fig. 1. An alarm switch is — placed a few inches above the valve-closed level to warn of pump or float- Since a mixture of septic tank effluent and water which has been through the valve malfunction. filter is applied to the surface, a major concern was whether odor during The sprinklers utilized to distribute the effluent on the surface of the sand operation would be a problem. Both of these experimental systems were placed filtere were designed toprovides relativelylarge dropletse that are not sub-d over 30.5 • (100 ft) from the residence and neighboring houses. Very little g godor has been noticeable from either system. Occasionally, if one is stand- ject to wind drift but yet provide a high degree of aeration in the ing near the sand filter when effluent is being applied, a slight whiff of application process. The sprinklers consist of 3 mm (1/8 in) orifices in PVC septic odor can be detected; however, this is not a regular occurrence. pipe- which provide a water jet which impacts a section of standard window Neighbors indicate that they have never noticed any odor. When the system is screen placed approximately 50 mm (2 in) above the holes to provide the not running, odor from the system has never been detectable. stream break-up. The screen holder shown in Fig. 1 for the sprinklers was fabricated on site with sections of PVC pipe. Holes were drilled perfectly Freezing Temperatures vertical in the pipe using a portable drill guide. The use of recirculating sand filters with surface application has been The final disposal for the northern Michigan system is gravity flow to a confined primarily to less severe climates than in Michigan. Even though standard gravity septic system in a sandy soil. This particular site did not rather massive amounts of ice have formed on both filters during winter present any problem for a conventional septic system. However, it was lo- months in most years, both systems have functioned without requiring any cated in an area where there was interest in identifying and demonstrating . systems that might provide improved treatment for use around lakes. 1 • maintenance. The pipe network which contains the distribution sprinklers and Table 1. Weekly RSF System .Filter and Tank Temperature and Mean Air the pipe which delivers effluent from the pump to the surface distribution Temperatures for the Previous Week (°C). system both drain back through the pump into the recirculation tank immedi- ately when the pump shuts off. Date Mean Air Under Sprinkler Between Sprinklers Septic Recirc Filter Temp Prey. 2" 6" 18" 36" 2" 6" 18" 36" Tank Tank Drain The sprinklers used are relatively immune to icing and failure due to Week freezing. The characteristics of operation in freezing weather are that ice cones build up around each sprinkler but remain hollow (Fig. 2). In time, 1983 the ice provides a degree of protection around each sprinkler. The sand is 1/18 -1.5 -1.0 -0.5 1.5 1.5 -2.0 -1.0 2.0 1.5 - 4.0 2.0 course enough that water infiltrates before ice can freeze and coat the sur- 1/22 -9.0 0.0 -0.5 0.5 3.0 -0.5 -0.5 3.0 0.0 9.0 3.5 1.5 face under the sprinkler. The most difficult time of operation during the 1/29 -4.0 2.0 2.0 1.0 1.0 0.0 0.0 1.0 0.5 9.0 3.5 2.0 winter is when the ice cones are just beginning to form. If a severely cold 2/5 - -1.5 2.0 2.0 2.0 2.0 0.0 0.0 1.5 0.5 9.0 3.5 3.0 period is encountered prior to formation of the ice cones, the bed may ice 2/12 -6.0 1.0 1.0 1.0 1.0 -0.6 0.0 1.0 0.5 10.5 3.5 2.0 over quite completely, but our experience has been that the sprinklers con- 2/19 0.0 4.5 4.0 2.0 2.0 1.5 1.5 2.0 2.0 11.0 3.5 3.0 tinue to operate and melt a zone immediately around each sprinkler. These 3/12 6.0 8.0 9.5 4.5 4.5 11.0 3.5 4.5 3.5 12.0 6.5 5.0 melted zones continue to enlarge as the ice cones then form around each of 3/22 5.0 3.0 2.0 1.5 3.5 0.5 1.0 3.5 1.0 12.0 6.5 4.5 these zones. Table 1 'gives weekly environmental temperatures and sand bed 5/22 12.0 19.0 14.5 14.0 14.0 21.5 16.0 14.0 13.0 16.0 12.0 13.0 temperatures throughout the icing period of two winters for the E. Lansing RSF. lemperatures were determined both below a sprinkler under the area 1984 which is generally free of ice and between sprinklers under the ice pack 1/2 -15.0 -1.0 -1.0 0.5 4.0 -0.5 -1.0 1.0 4.0 - 4.5 2.0 which forms around each sprinkler. 1/7 - 5.0 -0.5 0.0 0.0 1.5 -0.5 0.0 0.0 1.0 11.5 4.5 2.0 1/14 -11.5 0.0 0.0 1.0 3.0 -0.5 0.0 0.5 2.0 11.0- 4.5 2.0 4 - 1/22 -16.5 -1.0 -1.0 0.0 2.0 -2.0 -1.0 0.5 2.0 11.5 4.5 2.0 Z 1/29 - 6.5 0.0 0.0 0.0 1.5 0.0 0.0 0.0 1.5 10.5 4.0 2.0 2/11 - 5.0 2.0 1.0 1.0 1.0 0.0 0.0 0.5 1.0 9.0 3.5 2.0 2/22 4.5 6.5 8.5 5.5 3.0 5.5 6.0 6.0 4.0 13.0 5.5 4.5 3/10 7.5. 0.0 0.5 0.5 2.0 - 0.0 0.5 2.0 9.0 3.5 1.5 - � 4/14 1.0 16.0 12.0 10.5 9.5 16.5 13.0 11.0 10.0 12.0 7.0 8.0 � 7- �� IFS mow,\ Early Stages of >� Ice Formation around each of these openings. Within a few days all but one of the sprin- klers was essentially free of ice and working normally. Though temperatures _, moderated, the ice cones remained and continued to build until mid-February. Probing of the sand underneath the sprinklers inside the ice cones indicated -' � that generally the sand was at least partially free of ice.under each sprin- :II kler. Occasionally, under the coldest weather conditions, some sprinklers had 1 1: �"�t�, an ice lens in the sand at 2.5-7.5 cm (1-3 in) below the sand surface. How- I T' " 4 - ever, when the sprinklers were running, water would infiltrate; and, when the r R"` u4Sillom sprinklers shut off, all ponded water under the sprinklers would disappear ... 4. within a few seconds. 4.4i ^,� a Mature Ice The winter of 1983-84 was severely cold. December 1983 is the second coldest Cones Around ;r ' ' !!!k. December on record at the Lansing Weather Station. Mean monthly tempera- Each Sprinkler - tures for December, January and February were 5.6°C (10°F) below, 3.9°C (7°F) wiallwiiiiititr _�.' ,,,A below, and 4.4 C (8°F) above normal respectively. During the first half of December 1983, ice came and went on the filter but Fig. 2 Winter ice formation on recirculating sand filter surface. about December 16 it turned bitterly cold•. Ice built rapidly on the surface of the filter. All sprinklers remained operational even though the small The winter of 1982-83 was considerably warmer than normal. Mean monthly air sand zones underneath them seemed to be frozen near the surface when probed. temperature for December 1982 - March 1983 was 3.9°C (7"•9°F) above normal, Water would pond some around the sprinklers during each pump run but would be 2.4 C (4.4°F) above normal, 3.5°C (6.3 F) above normal, and 1.9°C (3.4a F) all infiltrated within seconds after the pump shut off. Temperatures moder- above normal respectively. However, on January 16 the temperature dropped ated the week of January 1-7. By the end of that week, the sand around the suddenly and stayed below freezing for a period of six days with nighttime sprinklers was not frozen to the probe, and water was infiltrating readily temperatures ranging between -18°C (0°F) and -12°C (10°F) every night. At during each pump run. For the winter, the timer was adjusted so that between this time, there was very little ice on the sand filter. With no protective 8 pm. and 6 a.m. the pump ran only twice: once at 10 p.m. and once at mid- ice cones around the sprinklers, a solid sheet of ice formed with only small night. Ice cones continued to grow. By January 14, average ice cone depth openings around each sprinkler. Each time the pump ran, most of the applied was approximately 51 cm (20 in). During a severely cold period between Janu- water was deposited on the surface of the ice freezing another layer. About ary 15 A 21, the top of the cones began closing and several of them com- the fourth day it looked like the filter would fail, but the open space pletely closed. The more open cones exhibited freezing In the sand under- around each sprinkler began to enlarge. and a cone of ice began to build neath the sprinklers, but those that were nearly closed did not. n' Once the weather moderated, the ice melted.off the surface over a period of BON and Suspended Solids: The RSF system has been proven effective at re- 1-2 weeks both years. Ice reforms when periods of cold weather recur, but it moving organic matter as measured by low levels of suspended solids.and B0D5 has been quite transient except during January and early February on the E. in the filter drain effluent. Hines et al., (1977) reported that both sus- Lansing RSF. The ice covered period on the northern Michigan RSF has been pended solids and BODS are generally below 10 mg/L.in the final effluent with longer, but detailed records of dates formed and temperatures have not been many units achieving levels around 5 mg/L for these two parameters. Our data kept. on the E. Lansing filter has shown BONS to be consistently below 10 mg/L and total suspended solids to be always less than 5 mg/L. The data from the Table 1 shows that at times temperatures are near freezing down to the 46 cm northern system has shown slightly higher HOD levels in the final effluent (18 in) depth in the sand, but both probing and the rate of water infiltra- than the E. Lansing filter or than reported 6y others. Lab tests for the lion indicate that there are sufficiently open zones for the filters to con- northern system were done in a community college lab while the tests for the tinue to function. Having successfully operated through the winter of 1983- E. Lansing system were done in an EPA certified wastewater treatment plant 84, we expect sand filters to function throughout any winter we are likely to lab. The filter drain effluent has been consistently clear and odor free. experience in mid-Michigan. Fecal Coliform: Fecal colifor■ counts have been performed periodically on Septic tank, recirculation tank, and filter drainage water temperatures seem both RSFs. The tests for the E. Lansing RSF have been performed by a waste- to stay fairly uniform during the coldest period of the year as shown in water treatment plant lab which does this test regularly. Other tests were Table 1. Filter drain water temperatures are indicative of temperatures in done according to standard methods but by less experienced personnel. The E. the lowest portion of the filter. Recirculation tank temperatures are influ- Lansing system has been consistently very low in conform' organisms in the enced by septic tank temperatures, temperature of returning drain water, and final effluent, ranging from 5-30 organisms per 100 ml. soil temperature between 0.6 and 1.8 m (2 and 6 ft) below the surface. Nitrogen - Column Study: Little data on nutrient removal in recirculating Water Quality Parameters sand filters is available from the literature. Fay (1982) conducted a labo- Water samples were taken from the septic tank, the recirculation tank, and ratory column study simulating a RSF system with a 4:1 recirculation rate the water draining-out of the filter for laboratory analysis. :Tests which having a saturated zone in the bottom 30 cm of a 1.5 m deep column. He com- have been run include GODS, suspended solids, total phosphorous, fecal cola- pared nitrogen loss from columns having an organic layer (50 g of cracked form, and forms of nitrogen including ammoniam, nitrate, and total Kjeldhal corn in a 15.2 cm diameter column) in the saturated zone with control columns nitrogen. Table 2 shows average values for three parameters over three time having no organic matter. Columns ran for about 140 days with samples taken periods, two for the northern system and one for the E. Lansing system. Each for 70 days during the midperiod of the run. Table 3 shows average concen- value is the average of 6-7 samples taken during the period. Insufficient trations of forms of nitrogen at various locations in three treated and three samples have been analyzed to detect. any seasonal differences which may nontreated columns. Both systems we're effective in removing nitrogen from exist. the wastewater. Total'nitrogen In the column drain mai approximately 71% and 80% lower than in the septic tank effluent for the control and treated sys- Septic tanks, discharging to both sand filters were emptyied when the systems teams respectively. The major_ mechanism for nitrogen reduction was .probably were put into use. Therefore, a period of four to six months was allowed to the combination of nitrification of ammonia and organic nitrogen in the un- elapse prior to initiation of sampling. saturated zone of the columns followed by denitrification in the recircula- tion tank. An analysis of variance showed that the nitrogen reduction of the Table 2. Water Quality Parameter Values from the Septic Tank (ST), the Recirculation Tank (RT) and the Sand Filter Drain (FD) for Two Recirculating Table 3. Column Study Nitrogen Concentrations, mg/L (Fay, 1982) Sand Filters. SAMPLE MEANS OF 30-36 SAMPLES (95% CONFIDENCE INT.) LOCATION TKN AMMONIA-H NITRATE-N TOTAL N LOC PH SODS TSS FECAL TKN NH3-N NO3-N TOTAL TOTAL COLIFORH N P Septic Tank 37.2 30.5 0.8 38.0 mg/L mg/L NO./100m1 mg/L mg/L mg/L mg/L mg/L (26.9-47.5) (22.8-38.2) (0.3-1.3) (27.2-48.8) Northern Michigan 1/10/77 - 9/26/77 Control Columns ST 6.7 250 - - 130 57 2.9 133 28 Recirc. Tank 11.3 6.4 1.6 12.9 RT 7.2 120 - - 52 20 4.0 56 15 (5.6-17.0) (4.7-8.1) (0.7-2.5) (6.3-19.5) FD 7.2 38 - - 9 7 27 36 7.2 Suction Lys. 1.0 0.7 7.3 8.3 (0.4-1.6) (0.6-0.8) (6.1-8.5) (6.5-10.1) Northern Michigan 3/9/78-11/1/78 Drain 0.9 0.5 10.0 10.9 ST 7.2 230 - 1200+ 44 - 7.3 51 11 (0.7-1.2) (0.3-0.7) (8.0-11.4) (9.3-12.5) RT 7.2 82 - 400 19 - 10 29 10 FD 6.9 12 - 210 3.4 - 28 31 10 Treated Columns Recirc. Tank 8.8 5.7 1.2 10.0 E. Lansing 4/83-6/84 (4.1-13.5) (3.2-8.2) (0.5-1.9) (4.6-15.4) ST 7.4 150 42 3400 55 47 0 55 16 Suction Lys. 1.1 0.5 6.1 7.2 RT 7.0 26 12 1700 1.8 2.1 12 14 10 (0.8-1.4) (0.3-0.7) (5.1-7.1) (5.4-8.5) FD 7.0 6 2 14 2.3 2.1 24 26 7 Drain 0.8 0.2 6.8 7.6 (0.5-1.1) (0.1-0.3) (6.0-7.6) (6.5-8.7) 1.1M years later. Nothing other than r xi.^.g and .eed :-e-:oval has been :e to the treated columns was significantly greater at the 95% level of confidence than E. Lansing RSF. the nitrogen reduction from the control columns. Some of the 3 mm (1/8 in) holes in the distribution pipe have plugged occa- The fact that the data in Table 3 show higher total nitrogen concentrations sionally. These can usually be restarted by inserting a wire, but about once in the column drain than in the suction lysimeters which were placed just a year it seems desireable to flush out the pipe network on the surface. of above the saturated zone may have resulted from the method of taking samples. the system. Flushing seems to minimize orifice plugging for several months The lysimeter samples were a 24-hour composite, while the drain samples were following. taken as grab samples. Overall, this column study showed that a highly ni- trified effluent was produced by both sets of columns. Both systems were No pump; timer, or electrical system maintenance has been required on either effective in removing nitrogen from the wastewater, and the treated column system. No maintenance has been done on the surface of either system during produced an effluent which was generally below the 10 mg/L drinking water the winter so that we can learn how the systems function on their own during standard for nitrate nitrogen concentration. cold weather. Nitrogen-Field Systems: Average concentrations for forms of nitrogen in the septic tank effluent, recirculation tank and filter drain of field systems SUMMARY AND CONCLUSIONS are shown in Table 2. The total Kjeldahl nitrogen values for the 1977 sam- ples from the northern Michigan system were consistently high, but the total nitrogen in the final effluent from the filter are comparable with other The recirculating sand filter (RSF) system appears to be a viable alternative data. Except for those early northern Michigan samples, nitrogen removal for improved on-site wastewater treatment in cold climates as well as warmer rates have generally been 40-60%. These rates are lower than Fay (1982) ones. The systems studied involved application of a 4:1 mix of filter drain- reported for the column studies; but no saturated zone exists in the bottom age and septic tank effluent to the surface of a 3.7 m (12 ft) square sand of either field RSF, and temperatures are usually lower than in the labora- filter. The sprinkler devices utilized for surface application proved resia- tory columns. It is anticipated that the majority of the nitrogen removal tant to freezing while resulting in ice accumulation around the sprinkler being achieved is through nitrification in the soil filter and devices. The sand under the sprinklers remained adequately open to provide denitrification in the recirculation tank where septic tank effluent provides continued operation even under weather conditions unusually cold for mid- the carbon source needed for denitrification. Michigan. Almost all the nitrogen in the filter drain effluent, the final effluent from Filter drain effluent temperatures have dipped as low as 2°C(36°F) and recir- the system, is in the nitrate form. The nitrate levels have consistently been culation tank temperature as low as 3.5°C (38°F) but' seem to bottom out. at above 20 mg/L in the final effluent even though about half of the nitrogen ' about these values. BOD5 and suspended solids concentration in the final originally present in the septic tank effluent has been removed. effluent have generally been below 10 mg/L, and fecal coliform organism level has been mostly less than 200 per 100 ml. Phosphorous: Both systems.showed an initial reduction in phosphorous content of the filter drain effluent compared to septic effluent. Initially, phos- A laboratory column study simulating an RSF system showed nitrogen losses oT phorous concentrations were reduced to the range of 3-7 mg/L, but this reduc- 71-80% through the system, probably largely due to denitrification of nitri- tion gradually decreased. In both cases, after approximately two years of fled effluent in the recirculation tank. Nitrogen removal through two RSFs, operation (1.5 years of sampling) phosphorous removal had essentially ceased each serving a three-bedroom home, has averaged between 40 and 60%. Phospho- with concentrations in the filter drainage effluent being nearly equal to rous removal occurred initially for a calcareous sand filter but within two those in the septic effluent. The initial choice -of a calcareous sand years had dropped to near zero. probably provided the reduction early in the life of the system. The RSF represents a mechanically simple, low maintenance method of improving Ellis (1973) shows that for wastewaters with pH around 7.0, the concentration on-site treatment beyond the septic tank. It can provide a highly oxidized of phosphorous in water percolating through a soil with calcium present will effluent for subsurface disposal and an acceptable effluent for surface depend on the type of calcium phosphate being formed but will be bounded by a disposal where nutrients are not a major concern. Improved removal of lower limit between 2.7 and 8.0 mg/L. Thus this is the range of minimum nitrogen and phosphorous with recirculating sand filters needs further study phosphorous concentration which can be expected from our calcareous sand. and development. While the initial test values were in agreement with the minimum levels suggested by Ellis, the phosphorous reduction life of the system was short. If phosphorous reduction is to be reliably achieved, it must be done by some method other than simply selecting a calcareous sand. MAINTENANCE Maintenance requirements of the RSFs being studied have been minimal. The biggest task has been removal of weed growth from the surface of the filter about four times each summer. Usually weeds are hand pulled and the surface raked to discourage those were too small to pull and to relevel the surface. A shallow layer of sand (2-4 cm) has been removed from the northern system two times - first after about three years of operation and again about three 7. Rao, V.C.", et al., "A Simple Method for Concentrating and Detecting Viruses in Groundwater," Water Research, Vol. 6, pp. 1565-1576, 1972. DENITRIFICATION IN ON-SITE WASTEWATER 8. "Rules and Regulations Pertaining to Outdoor Bathing Places," Arkansas State Board of Health, Little Rock, TREATMENT SYSTEMS - A REVIEW Arkansas, July 1964. 9. Scalf, M. R., et al., "Environmental Effects of Septic Tank R. P. Eastburn W. F. Ritter Systems." EPA - 600/3-77-096. U.S. Environmental Protection Assoc. Member ASAE Member ASAE Agency, Ada, Oklahoma, 1977. Nitro en can exist at various oxidation states in nature. Nitrate is trans- 10. Scherer, B.P. and D.T. Mitchell, "Individual Household Surface _g Disposal of Treated Wastewater Without Chlorination," ass milarybl pathwayaexists forford by oraniss conversion ofalon twoths nitrateinhe anditrogen nitritecycle into ammonium On-Site Sewage Treatment Proceedings at the Third which is then used by the organism for growth. A dissimilatory pathway, the National Symposium on Individual and Small Community pathway of the denitrification process, follows the following sequence. Sewage Treatment, American Society of Agricultural Engineers, 1982. NO3 ---> NO2 ---> NO ---> N20 ---> N2 11. Sobsey, M.D., et al., "Modifications of the Tentative There are environmental limits to denitrification. Firestone (1982) lists Standard Method for Improved Virus Recovery Efficiency," the following four general requirements imposed by the microorganism on de- Journal American Water Works Association, June 1980. nitrification: 12. Sobsey, M.D., et al., Survival and Wastewater, Water Enteric Viruses s Research 1. Presence of suitable bacteria which are capable of producing the re- Soil Treatment Systems for astevatrt, quired enzymes. Institute of the University of North Carolina, Report No. 168, June 1981. 2. Suitable energy sources to fuel the anabolism. / 13. "Standard Methods for the Examination of Water and Wastewater," 3, Release of oxygen repression of these enzymatic systems. 15th Ed., American Public Health Association, Washington, D.C., 1980. 4. Suitable nitrogen compounds to serve as terminal electron sources in. place of oxygen. 14. Stone, B.G., "Suppression of Water Use by Physical Methods," Journal American Water Works Association, September 1978 The bacterium Propionibacterium_ is the only obligate denitrifier; all other pp. 483-486. denitrifiers are facultative (Firestone, 1982). In a practical sense, this means that these bacteria will preferentially use oxygen for respiration. 15. The Incidence Monitoring and Treatment of Viruses in Water Supply_ Thus, arises the obligate requirement of anaerobic conditions for denitrifi- Systems, American Society of Civil Engineers, Environmental cation. Two enzymes, dissimilatory nitrate reductase and dissimilatory Engineering Division, 1983. nitrite reductase, are the catalysts which permit the process to occur. They are inhibited by the presence of oxygen. Denitrification is influenced by temperature, pH, Eh, and high concentrations of heavy metals and pesticides. Bremner and Shaw (1958) reported denitrifi- cation rates increased with temperature over a 2-25°C temperature range. Crites et al. (1981) reported the minimum temperature for denitrification in land treatment systems is 2-5°C. Heavy metal and pesticides levels commonly found in soils will not affect denitrification. The C:N ratio of an average septic tank effluent is given in a review by Sikora and Corey (1974) as 10. They state that there 1s little nitrogen im- mobilization in the septa€ tank or in the ponded bed effluent. Under saturated conditions, NH4 -N would eventually be leached to the groundwater. The authors are: R. P. Eastburn, Soil Science Consultant, Middletown, DE and W. F. Ritter, Professor, Agricultural Engineering Department, University of Delaware, Newark, DE. P Denitrification is, they confirm, the only mechanism for effluent nitrogen reduction. The NH4+-N must be converted to NO3 by the aerobic process ni- MOUND SYSTEMS trification before denitrification can take place. The nitrogen must be in Magdoff et al. (1974a) described the operation of laboratory the NO3- tom to enter the sequence, dissimilatory nitrate reductase, is used to study mound typesoil columns substrate specific. disposal systems. The soil used was the Ap hori- zon of Batavia silt loam (Mollie Hapludalf). The sand fill used was the C horizon of Plainfield loamy sand (Typic Udipsamment). The silt loam soil CONVENTIONAL SYSTEMS was placed so as to represent the topsoil in the constructed mound. In Reneau (1977) reported on an investigation concerning the impact of a 15 year nature the fill portion of the mound is aerobic and the underlying soil is anaerobic due to saturation. To mimic these conditions, the model columns old septic system in a moderately well drained Varina sandy loam (Plinthic were perforated so that lateral movement of ox Paleudult) on the groundwater nitrogen content. The system had a loading nature. Ygen was the same as it I. in rate of 40.7 L/day/m2 and disposed of approximately 2,650 L/day. Large fluc- Results of experiments in which these columns were dosed with 2 cm of septic tuations of the NO3 -N:C1 ratio in the plinthic horizon indicated occurrence of nitrification followed by denitrification In the upper profile. Zones of tank effluent everysix hours for a total 8 cm/day,were created by fluctuations of the water table. Nitrate and et al. (l914b). The influent was a r were reported) by anic-Nf nitrite in the plinthic horizon did not undergo denitrification because of a bi ocondit o 75i NHG Nand ing organic-N. probable deficiency in organic carbon in and below this horizon. Although The importance en maintaining aerobic conditions in the overlying fill was denitrification is demonstrable in this system from changes in the N ion:Cl demonstrated when, after continuous ponding in the columns, NH4+-N rose in ratio, quantification from datapresentedyis notpossible. the column effluent to influent levels. An initial lag in th10 rise occur- red due to sorption of the NH4-N on the soil exchange complex. While low Eh values indicated conditions in the silt loam soil were anae- In another study, Reneau (1979) studied the interaction between the septic tank absorption fields of ten houses and a subsurface agricultural tile robic, lack of energy , drainage system with regard to chemical pollution of the groundwater. The 32 to supply the dKeeneyfier s metabolism limited nitrate concentration of the soil solution was found to decrease as a loga- rithmic denitrification [0 32X. and sef and Keeney luent reported that the columns were then allowed to dry and septic tank effluent was then applied at [he function of distance from the absorption beds. Nitrification in the rate of 8 cm/day in a single dose. Denitrification removal decreased to aerobic zone and denitrification in a subsequent anaerobic zone was shown only 7X of the influent nitrogen due to soil available carbon de lesion. to occur, but, system removal values could not be deduced from data presented. p Nitrate movement was considered to be by both mass flow and diffusion along Harkin et al. (1979) found that the value of 32% denitrification reported a concentration gradient created by denitrification. - by Magdoff et al. (1974b)was exceeded by operating mound systems. In a Reneau (1979) hypothesized that groundwater quality would beimproved with field study of thirty-three mound systems in Wiscnsin, they found that de- scone a more uniform effluent distribution in the seepage beds. A low pressure nitrification removed, on the average, about 44% of the nitrate formed in the mound system and for dosed systems which maintained an aerobic/anaerobic distribution system was recommended to provide the increased effluent dis- zone sequence, higher values were frequent. tribution uniformity. He considered that cultural practices such as garden- mound Was found to retard organic matter decomposition pfilliun and lowerdrloer nof i the ing and lawn care had more influence on the nitrate levels in the tile drain- tion in mounds with high dosing rates and hi eficient- h age water than the septic effluent disposal. Mounds with a high dosing rate and a low fill uniformity°coefficientlhadnta. An evaluation of groundwater quality adjacent to a septic system installed denitrification rates of 48 to 86X. Mounds with a low dosing rate and a in a soil association of Piedmont sandy loam and Pontiac silt loam/silt low fill uniformity coefficient also had an 86X removal rate. clay loam, is reported by Viraraghavan and Warnock (1976). The system was loaded once daily at a loading rate of 50 L/m2/day. Nitrification was shown to occur within the first three meters of percolation from the system ALTERNATIVE UN-SITE SYSTEMS AND ENERGY SOURCES by increasing nitrate (0.01 to 0.45 mg/L) and decreasing ammonium (40 to Without a sufficient energy source, denitrification will not take lace. tank ngsor 1 mg/L) levels. A shallow water table, which varied between 0 and 3 m below Sikoro and Keeney (1974) stated that in a septicP the soil surface, and cold temperatures were reasons denitrification did not energy source is the most difficult problem inption field, the occur in this system. They used continuous flow columns with aerated contain- ingseptici tank eeffluent aFifteen conventional and alternative systems were evaluated for a period of 40 to 50.mg/L NO3-N in their study. Denitrification occurred in less than two hours with methanol added at twice the stoichromecrlc ratio. In 18 months by Cogger and Carlile (1984) to determine the effect of high water tables on their functioning. Systems which were continuously saturated had some systems an energy source is used to promote denitrification. groundwater which was higher in NH4+-N and lower in NO3--N than other Stewart et al. (1979), in a column studyevaluated the applicability of a systems in the study as would be expected from the need for an aerobic en- histic epipedon-sand mixture to supply energy if Y nitri- vironment for nitrification. ' Dilution not denitrification was the prime fled septic tank effluent. The histic epipedon fromdenitrification o of C factor in nitrogen level reduction. From Information presented in the Fear seriesAt P seaon 93% r the Ap of the Cape paper, it appears that denitrification did not occur in these systems due (Typic Udaysgoflop tin, days a v reductionfe cino um -N was achieved. After 95 days of operation, the removal from the colum� leachate to either lack of a suitable energy source and/or failure of effluent had dropped to only 222. They concluded that soil organic matter is probably nitrogen to be converted to nitrate. Some denitrification was considered g . to have occurred during the first year of the study, but, was reduced the an unsatisfactory denitrification energy source for treating septic tank effluent. second year. Several of the systems were reported to be loaded beyond their - design requirements as well. Sand filtration of septic tank effluent was studied by Sauer and Boyle (1977). Loading was at the rate of 0.2 m3/day with system regeneration whenever wastewater ponded more than 30.4 cm above the sand surface. While the unit 306 307 was found to be efficient for nitrification of the septic tank effluent, no satisfactory for system operation. . change iu nitrogen concentration was found to occur. Problems identified during field testing of the RUCK system centered on the The same conclusion was reached by Kristiausen (1981a, 1981h), who reported sand filter. Liner deterioration and overloading were principal problems on the operation of sand filter trenches; units used in Norway in areas nut which had to be corrected in the field system. It was concluded that the available for conventional septic seepage beds. The system is loaded by RUCK system reduced the rate of septage accumulation and would provide an gravity distribution with progressive clogging iron the influent end. effluent which had received treatment above that of a conventional system. Aerobic conditions are maintained by air vents. Due to aerobic conditions and lack of an available energy source, denitrilication was not found. Warnock and Biswas (1981) also studied the problem of using kitchen waste- Kristiansen recommended dosing to provide uniform distribution and intermit- water as an energy source for denitrification. The kitchen wastewater used tent operation as methods to favor denitrification. Collecting and recycling in their column study was effluent from a kitchen garbage grinder. The nitrified titter effluent by mixing it-with incoming influent was another columns were filled with coarse sand and an influent of 25 mg/L NOg -N as a method suggested fur achieving denitrification. KNO7 solution was used. In their study a C:N ratio of 4:1 was found to be optimal to produce satisfactory denitrification. A system which will function for.denitrifi.catton following a sand filter system if an energy source is provided was described by Sikora et al. (1977). It should be noted that these two studies did not provide the same conditions A mixing tank was followed by a stone filled denitritication tank. Methanol for denitrification. They both concluded, however, that household wastes was added at a stoichiometric ratio of 2:1 in the mixing tank as an energy could be used as an energy source for denitrification. The availability of source. After conditioning, a 12 hr. residence time resulted in an average an energy source produced on-site, and which the system could be designed to removal rate of 90% (range 81 to 99%). They felt that the 12 hr. residence add passively, is valuable. time might not he sufficient for influent concentrations greater than 30 mg/L N. By combining a suitable energy source, anaerobic conditions and a CRUSTING AND DOSING nitrified effluent, this system supplies the prerequisites necessary for denitrification. Sikora et al. (1977), recommended that the unit be buried in climates such as Wisconsin's as the unit did not operate properly with Crusting ambient temperatures of approximately 6°C. They also recommended that the system is most suitable for multidwelling waste treatment systems in con- The importance of crust formation and the application of septic tank effluent is shown by results of a study performed by Walker et al. (1973a, 1973b). _ junction with a sand filter. They examined the nitrogen transformations of septic tank effluent in five Reynolds et al. (1979), reported on a modified septic tank disposal system subsurface seepage beds located in sandy soils of Wisconsin. Crust formation in which methanol was also used as the energy source for denitrification. was found to have occurred in all seepage beds, reducing the effective in- Atl impermeable shield was located below the leaching field with an imperme- filtration rate from 500 to 8 cm/day. Nitrogen in and immediately under the able pan located below it. The shield was for flow control and the pan was septic bed was predominantly NH4 -N. Nitrification commenced under the CO provide anaerobic conditions for denitrification. The methanol was added saturated zone and was complete within 6 cm. Concluding that denitrification . to the soil percolate above the impermeable pan. Septic tank effluent was was the only reaction which would reduce the nitrogen content after nitrift- added to the system.and steady state conditions developed six months after cation of the percolate, they considered that such reduction was unlikely start-up. Nitrification of the percolate was found to occur within 1.2 m,. for seepage beds built in deep sandy soils. It is interesting to note that Denitrification in the pan one month after:beginning the methanol additions Harkin et al. (1979) reported that the sites used in Walker's studies were reduced NO3-N concentrations in soil solution from the pan to as low as 0.1 the worst functioning cases of previous studies conducted by the Wisconsin mg/L. System removal levels were not pertinent due to much of the percolate investigators. missing the pan because the soil vertical hydraulic conductivity was not greater than the horizontal conductivity as assumed. Percolate which missed A major factor in the functioning of septic system seepage beds in deep sandy the pan was not denitrified because of the lack of an energy source. soils is the rate and conditions of crust formation. Jones and Taylor (1965) observed that crust formation was most rapid at the gravel/sand interface ' Laak ac al. (1981) and Laak (1981) reported on "a different modification of a and that soil clogging was three to ten times faster under anaerobic than conventional septic tank system. In their.RUCK system, domestic wastewater under aerobic conditions. Their observations were made on laboratory columns is split into graywater containing the flow from the kitchen and laundry and with a septic tank effluent percolate. blackwater containing flow from the bathroom. The kitchen in the house where the system was tested did not have a garbage grinder. The blackwater is Dosing treated in a septic tank and the septic tank effluent is nitrified in an aerobic sand bed. Flow from the sand bed and from a septic tank treating the Dosing is important to the amount of denitrification in an on-site septic graywater are mixed in an anaerobic up-flow rock tank where denitrification system due CO the cf.angss it induces in the soil water status below the takes place. The effluent from the rock tank is disposed of by a seepage bed. seepage bed. One investigation of dosing and resting time to improve the Evaluating the two flow streams, they reported that the blackwater contained functioning of soil absorption beds was conducted by Rouse et al. (1974). over 807 of the nitrogen load and represented 40".! of the total flow. Organic Field observations were made utilizing a trench built in the Silty clay loam carbon in the graywater flow was found to be as efficient as methanol in • B22t horizon on a Batavia silt loam (Mollie Hapludalf) with a percolation supporting denitrification. They found that with a graywater organic carbon: rate of 12 min/cm. The 0.9 m x 25.2 m bed was loaded once daily with 756 L blackwater NO3 N ratio of 0.7 or greater and a three- CO five-day detention of septic tank effluent via a 3_1 cm-diameter pipe to provide more even time in the rock tank, denitrification was satisfactory. They concluded that distribution. The trench continued to perform satisfactorily after ten an overall nitrogen removal level of 702 could be achieved using the passive months of operation with a loading rate 331 greater than that recommended by RUCK system. Denitrification levels ranged during field testing .from 0 to the Wisconsin health code and demonstrated the importance of retaining the 97X removal with an average level of 91% removal being found for the test large soil pores to maintain infiltration. system. The ratio of the graywater: blackwater waste streams was 308 309 in a companion paper to the above study, Converse (1974) reported on the 3. Crusting in the seepage bed of a domestic waste disposal system has evaluation of various pressurized pipe configurations and gravity flow for uniformity of effluent distribution in a dosing system. With gravity flow, been shown to provide those conditions which should improve denitri- fication. distribution was found to be very poor with progressive clogging of the bed. Daily pressure dosing provided more even distribution, improving the func- 4. Alternatives exist for on-site wastewater treatment which will reduce tinning of the absorption bed and probably increasing denitrification. nitrogen discharge from the system by 70 to 802 if a supplemental energy source is used. Moderately permeable, 12 to 24 min/cm, fine silty soils were studied by Bouma et al. (1975), regarding the absorption of septic tank effluent. 5. Denitrification rates under conventional septic systems may vary from They stated that system failure is usually associated with a reduction in 0 to 35%. Systems installed in areas with an extremely high water absorption capacity associated with construction induced or biological soil table may have insignificant denitrification because of the lack of clogging. Biological clogging results from bacterial growth with associated nitrification of the septic tank effluent. Absolute values of denitri- deposition of polysaccarides and polyurinides and suspended solids deposi- fication for conventional septic systems cannot be P Y predicted based on tion. Dosing was found to result in the following: the available literature. 1. increased formation of macropores by soil biota; 6. Dosing provides a more uniform effluent distribution and will increase the denitrification potential of an on-site wastewater disposal system. 2. reduced hypothetical probability of clogging; Denitrification rates as high as 40 to 45% of the influent nitrogen may be achieved on some soils with dosing. 3. achievement of 'optimal" purification. Another study evaluating the application of pressure dosing to soil absorp- REFERENCES tion systems was conducted by Converse et al. (1974). They found that clogging was more significant in weakly structured sandy loam and loam 1. Bouma, J., J. C. Converse, J. Carlson, and F. G. Butler. 1975. Soil soils than in well structured silt loam and clay soils. Column studies and absorption of septic tank effluent in moderately permeable fine silty field evaluations resulted in the following conclusions. soils. Trans. of the ASAE. 18:1094-1099. 1. Once or twice a day dosing should be practiced as more frequent dosing 2. Bouma, J., J. C. Converse and F. R. Magdoff. 1974. Dosing and resting results in poorer distribution and purification. to improve soil absorption beds. Trans. of the ASAE. 17:295-298. 2. Uniform distribution is necessary to provide adequate purification with 3. Bremner, J. H. and K. Shaw. 1958. Denitrification in soil. II. seepage beds in sandy soils. - Factors affecting denitrification. J. Agr. Sci. 51:40-52. 3. After clogging results in sandy systems, unsaturated flow occurs with 4. Cogger, C. G. and B. L. Carlile. 1984. Field performance of conven- resulting increased purification. tlonal and alternative septic systems in wet soils. J. Environ. Qual. 13:137-142. An evaluation of.operating mound systems in Wisconsin conducted by Harkin et al. (1979), also concluded the frequent small doses of septic tank 5. Converse, J. C. 1974. Distribution of domestic waste effluent in soil effluent would result in better nitrogen removal than less frequent larger absorption beds. Trans. of the ASAE. 17:299-304, 309. doses. Intermittent dosing in the Wisconsin design is by pressure distri- bution. They concluded that the nitrogen transformations are governed in 6. Converse, J. C., J. L. Anderson, W. A. Ziebell, and J. Bouma. 1974. the mound by soil moisture and organic matter availability due to the Pressure distribution to improve soil absorption-systems. Proc. of absence of a clogging mat achieved by dosing. They cited research of National Home Sewage Symposium, Dec. 9-10, 1974, Chicago, IL. ASAE Patrick and Reddy who found that maximal nitrogen loss via nitrification/ Pub. PROC-175. pp 104-115. denitrification occurred with temporal cycling between aerobic/anaerobic conditions on a 6 to 12 hr. frequency. Harkin et al. (1979) therefore 7. Crites, R. W., E. L. Meyer and R. G. Smith. 1981. Process Design recommend two to four daily dosing cycles. Manual for Land Treatment of Municipal Wastewater. EPA 625/1/81/013. 8. Firestone, M. K. 1982. Biological denitrification. In; Nitrogen in CONCLUSIONS Agricultural Soils, J. Stevenson, ed. Monograph No. 22. American Society of Agronomy, Madison, WI. pp 289-326. The following conclusions can be drawn from this literature review. 9. Harkin, J. M., C. P. Duffy and D. G. Kroll. 1979. Evaluation of 1. Denitrification, a mandatory anaerobic process, is the result of the mound systems for purification of septic tank effluent. University of dissimilatory nitrate reduction pathway of anaerobic respiration Wisconsin Water Resources Center, Madison, WI. Technical Report engaged in by-chemoheterotrophic facultative anaerobic bacteria. WIS-WR G79-05. 2.- A metabolizable energy source is required for denitrification. Soil 10. Jones, J. H. and G. S. Taylor. 1965. Septic tank effluent percolation organic matter and wastewater available metabolizable carbon levels through sands under laboratory conditions. Soil Sci. 99:301-308. • may be inadequate to support sufficient denitrification to reduce - pollution by nitrogen. With the addition of a sufficient energy source, denitrification can practically remove 902 of the influent nitrate and theoretically remove 100%. 310 311 11. Kristiansen, R. 1981a. Sand-filter trenches for purification of 25. Stewart, L. W., B. L. Carlile and D. K. Cassel. 1979. An evaluation septic tank effluent: I. The clogging mechanism and soil physical of alternative simulated treatments of septic tank effluent. J. environment. J. Environ. Qual. 10:353-357. Environ. Qual. 8:397-402. 12. Kristiansen, R. 1981b. Sand-filter trenches for purification of 26. Viraraghavan, T. and R. G. Warnock. 1976. Groundwater quality adja- septic tank effluent: II. The fate of nitrogen. J. Environ. Qual. cent to a septic tank system. J. Amer. Water Works Assoc. 68:611-614. 10:358-360. 27. Walker, W. G., J. Bouma, D. R. Keeney and F. R. Magdoff. 1973a. 13. Laak, R. 1981. A passive denitrification system for on-site systems. Nitrogen transformations during subsurface disposal of septic tank Proceedings of Third National Symposium on Individual and Small effluent in sands: I. Soil transformations. J. Environ. Qual. Community Sewage Treatment, Dec. 14-15, 1981, Chicago, IL. ASAE 2:475-479. Pub. 1-82. pp 108-115. 28. Walker, W. C., J. Bouma, D. R. Keeney and P. C. 0lcott. 1973b. 14. Laak, R., M. A. Parsee and R. Costello. 1981. Denitrification of Nitrogen transformations during subsurface disposal of septic tank blackwater with graywater. Amer. Soc. Civil Engr., J. Environ. Engr. effluent in sands: II. Groundwater quality. J. Environ. Qual. Div. 107:581-590. 2:521-525. 15. Magdoff, F. R. and D. R. Keeney. 1976. Nutrient mass balance in 29. Warnock, R. G. and N. Biswas. 1981. Study of columnar denitrification columns representing fill systems for disposal of septic tank effluent. for application in an on-site system. Proceedings of the Third Environ. Letters 10.385-294. National Symposium on Individual and Small Community Sewage Treatment, Dec. 14-15, 1981, Chicago, IL. ASAE Pub. 1-82. 16. Magdoff, F. R., J. Bouma and D. R. Keeney. 1974a. Columns represent- ing mount-type disposal systems for septic tank effluent. I. Soil- water and gas relations. J. Environ. Qual. 3:223-228. 17. Magdoff, F. R., D. R. Keeney, J. Bouma, and W. A. 'Liebell." 1974b. - Columns representing mound-type disposal systems for septic tank effluent. II. Nutrient transformations and bacterial populations. J. Environ. Qual. 3:228-233. 18. Reneau, R. E, Jr. 1979. Changes in concentrations of selected chem- ical pol-utants in wet, tile drained soil systems"as influenced by disposal of septic tank effluents. J. Environ. Qual. 8:189-196. 19. Reneau, R. B., Jr. 1977. Changes in inorganic nitrogenous compounds from septic tank effluent in a soil with fluctuating water table. J. Environ. Qual. 6:173-178. . 20. Reynolds, R. R., A. Andreoli, N. Bartilucci, and R. Forgione. 1978. Nitrogen removal in a subsurface disposal field. Amer. Soc. Ag. Engr. St. Joseph, Ml. ASAE Paper No. NAR-79-204. 21. Sauer, D. K. and W. C. Boyle. 1977. Intermittent sand filtration and disinfection of small waste water flow. Proceedings of Second National Home Sewage Treatment Symposium, Dec. 12-13, 1977, Chicago, IL. ASAE Pub. 5-77. pp 164-174. 22. Sikora, L. J. and R. B. Corey. 1976. Fate of nitrogen and phosphorus in soils under septic tank disposal fields. Trans. of the ASAE. 19: 866-870, 875. 23. Sikora, L. J. and D. R. Keeney. 1974. Laboratory studies on simula- tion of biological denitrification. Proceedings of the National Home ' Sewage Disposal Symposium, Dec. 9-10, 1974, Chicago, IL. ASAE Pub. PROC-175. pp 64-73. 24. Sikora, L. J., J. C. Converse, D. R. Keeney and R. C. Chen. 1977. Field evaluation of a denitrification system. Proceedings of the Second National Home Sewage Treatment Symposium, Dec. 12-13, 1974, Chicago, IL. ASAE Pub. 5-77 pp 202-207. 312 313 1 / 10882 OCTOBER 1974 ` teltri$ EE5 JOURNAL OF THE ENVIRONMENTAL ENGINEERING DIVISION SITE EVALUATION AND DESIGN OF SEEPAGE FIELDS By Kent A. Healy r and Rein Lack,2 Members,ASCE IrernooucnoN The percolation test has been widely used to evaluate sites for subsurface disposal systems for septic tank effluent. However, research carried out by Healy.and Laak (6) and Hill (7) has shown that the-percolation rate can be very misleading and does not directly measure-any soil characteristic that can be used in the rational design of a seepage field. A seepage field is considered herein to be a subsurface disposal system of any configuration., Before any new site evaluation methods could be developed,it was necessary to understand the operation of a seepage field. Studies supervised by the writers • (2,8) indicated that seepage.field problems, aside from those,due to.poor construction or lack of maintenance, could be separated into two categories, those fields that failed because of the greatly reduced permeability of the soil interface due to biologic. growth and.clogging by,solids,and those fields that failed because the ground surrounding the field:could not absorb the liquid. Consequently, this study was carried out in two parts, one part devoted to - determining the soil acceptance rate of septic tank effluent and what it depends on,and one part devoted to determining the hydraulic conductivity of the ground surrounding the seepage field. By combining the results of these two investigations it was possible to develop 10882 SITE EVALUATION AND DESIGN OF SEEPAGE FIELDS ; improved site evaluation techniques and improved methods of designing seepage fields. KEY WORDS: Absorption; Effluents; Environmental engineering; Groundwater flow;Ground water recharge; Seepage;Seepage control; Septic tanks LoNn-Tawt Accersaca RATE of SOW Taws EFR.ue r ABSTRACT: A reevaluation of previous work by others indicated that soil can absorb Many engineers and health officers feel that all seepage fields have a finite septic tank effluent indefinitely if the application rate is kept below a certain level, life and will eventually is a function of soil permeability. This lor.g-term acceptance rate is independent fail due to the gross reduction of the soil permeability of whether the soil is continuously or intermittently flooded, and varies from approx at the trench walls and bottom by solids and biological growth. The writers 0.3 gpd/sq ft(0.01 m/day)for clay loam and silt to approx 0.8 gpd/sq ft(0.03 m/day) for sand. A study of the ground-water flow pattern below a seepage field showed that Note.—Discussion open until March 1, 1975. To extend the closing date one month, it is, in many cases, the hydraulic conductivity of the ground surrounding the field, as a written request must be filed with the Editor of Technical Publications, ASCE. This determined by the external water table, soil permeability, and impervious strata, that paper is part of the copyrighted Journal of the Environmental Engineering Division, controls the size of the.field required. Reliable techniques for site evaluation of soil Proceedings of the American Society of Civil Engineers, Vol. 100, No. EE5, October, permeability, depth to water table, and depth to any impervious strata are presented, 1974.Manuscript'was submitted for review for possible publication on October 12, 1973. and a chart is given for designing a seepage field based on this information. Design 'Assoc.Prof.,Dept.of Civ. Engrg.,Univ.of Connecticut,Storrs,Conn. examples are included. • 2Assoc.Prof.,Dept.of Civ.Engrg.,Univ.of Connecticut,Storrs,Conn. REFERENCE: Healy, Kent A., and Leak, Rein, "Site Evaluation and Design of - Seepage Fields," Journal of the Environmental Engineering Division, ASCE, Vol. 100, 1133 No. EE5,Proc.Paper 10882,October, 1974,pp. 1133-1146 1 1134 OCTOBER 1974 EE5 EE5 SEEPAGE FIELDS 1135 theorized, however, that at some loading rates, decomposition would match TABLE 1.-Long-Term Acceptance Rates accumlation and growth, and absorbtion could continue indefinitely under this long-term loading rate. Long-Term Work done by other investigators (1,4,9,10,11,12,14,15) was reviewed to Acceptance determine their findings concerning the acceptance rate of septic tank effluent Initial Head Rate, in by soil. These previous investigators were concerned primarily with determining perme- across gallons per how long it would take to clog soil and their studies consisted primarily of ability, top day per applying effluent to soil lysimeters under varying loading patterns and hydraulic in 2 in. square foot loading conditions, and measuring the change of the rate with time at which feet (50 mm), per Type in As H= the effluent was accepted by the soils. In all the investigations, it was observed Source Soil minute loading feet° run 1.0 ft that the reduction in permeability of the soils due to biological growth and (1) (2) (31 (4) (5) (6) (7) clogging occurred in the top 2 in. (50 mm)or so of the soil sample. The results Thomas, Ottawa 3.0 x 10-1 Flooded 0.5 5 10 of these previous investigations were reevaluated by the writers and it was Sch- sand (approx) observed that 100 days to 200 days after loading began a low but relatively wartz, constant rate of acceptance occurred. These previous results were studied Bendixen carefully and the following data were considered to be most important for this (14) study: (1) The initial permeability of the soil as measured by the acceptance Jones and Uniform 14.4 x 10-2 Flooded 7.5 5.5 2.75 rate of clear water, in feet per minute (meters per second), under hydraulic Taylor medium gradient of unity; (2)-the hydraulic head lost over the upper 2 in. (50 mm) (9) sand of soil; (3) the loading pattern used, i.e., continuous or intermittent flooding; Fine sand 1.4 x 10-2 Flooded 25 1.4 0.70 and(4) the long-term acceptance rate of effluent. Leak(11) Ottawa 1.0 x 10-' Flooded 0.7 4 6 A summary of these data from previous investigations is given in Table 1. sand Different hydraulic heads had been used in the case reviewed and the results Kropf(10) Fine sand 2.0 x 10-2 Intermit- 0.5 0.35 0.70 of tests by Healy (5) and Jones and Taylor (9) had shown that the long-term tently and acceptance rate was deendent to a certain extent on the hydraulic head. These . , flooded • tests indicated that going from a hydraulic head of a few inches to. several Silty sand 3.2 x 10-' Intermit- 0.5 0.25 0.50 feet could double the long-term acceptance rate. The rates in Table I were concen- tently therefore adjusted to approximate the rate that would have occurred if the • crated and _ head had been I ft(0.3 m). sand flooded The conclusions,drawnfrom this survey of previous work are: 5.0 x 10-2 Intermit- • 0.5 0.7 1.40 tently 1. There is little difference in the final or long-term acceptance rate between and a soil that is flooded continuously leading to anaerobic decomposition and the 2 flooded same soil that is flooded intermittently, allowing aerobic decomposition. Orlob and Oakley 2 x 10 Flooded 4.0 0.75 0.37 But2. The fact that a relatively stable long-term acceptance rate develops indicates (12) sand Yolo loam 1.0 x 10-2 Flooded 4.0 1.9 0.95 that a balance is achieved between bacterial growth and decomposition of clogging Hanford • matter within the active interface zone. Material is accepted only at the rate loam 2 x 10-3 Flooded 4.0 1.5 0.75 at which it can be consumed. The accumulation of inorganics at the soil interface Hesperia forms a new soil layer. loam 1.6 x 10-' Flooded 3.9 1.1 0.55 3. In general, the more permeable the soil, the further the suspended and Columbia dissolved materials can move into it. This results in a thicker active zone, loam 6 x 10-4 Flooded 3.9 .75 0.37 allowing a higher long-term acceptance rate. The depth of the active zone is Winne- Oakley 5.2 x 10-2 Flooded 1.1 2.0 2.00 also dependent on the hydraulic head available to push the material or the Berger,et sand (15) nutrients, or both, into the soil. Bouwal. er(1) Fine sand 2.8 x 10 ' Flooded 2.0 0.75 0.37 4. A hydraulic head of approx 1 ft (0.3 m) of water to push the nutrients Healy(5) Medium 4.6 x I0-2 Intermit- 0.7 1.5 2.2 and fluid into the soil leads to efficient operation of a seepage field. sand tently 5. Effluent containing smaller amounts of material allows a higher long-term 'Based on flow and original permeability. acceptance rate. Note: 1 ft/min = 0.305 m/min; 1 ft = 0.305 m; 1 gpd/sq ft = 0.041 m/day. 6. The results of the previous investigations are remarkably consistent if the 1136 OCTOBER 1974 EE5 EE5 SEEPAGE FIELDS 1137 permeability of the soil used and the hydraulic head maintained are considered, ranged from 0.33 gpd/sq ft (0.01 m/day) for a clay loam to 0.83 gpd/sq ft (0.03 mm/day) for a fine to medium sand. These long-term acceptance rates....--- A plot of long-term acceptance rates reported by the various investigators —may be somewhat low as the effect of a high water tabl‘(`on some of the and adjusted for a hydraulic head of 1 ft (0.3 m) versus soil permeability is fields was not considered. This study also cited seepage fields that had operated given in Fig. 1. successfully for several years when flooded continuously. An approximation of the permeabilities of soils encountered in the FHA study was made and 7 l t these data are shown as solid dots in Fig. 1. * Leak All of the data surveyed indicated that there is a long-term acceptance rate ❑ Jones and Taylor 6 A Kropf * at which a seepage field will operate almost indefinitely if a sufficient hydraulic o Orlob and Butler head is available to push the liquid through the zone of reduced permeability 0 5 + winneberger et al. at the soil interface. "easy u These data are consistent enough to provide design criteria for seepage fields x Bouwer et al.° 4 . FHA° and these criteria are represented in Fig. 1 by the dashed line, which was aFull scale tests drawn as the best fit through the data points. 1 m3 HvDnAUUC Cofuoucnvtry 5. 0 Assumed criteria The hydraulic conductivity of a seepage -field is defined as the number of 2 •+ for design of _ gallons of clear water per day that can be absorbed by the field. The conductivity I seepage field of a field is dependent on: (1) The permeability of the soil in which the field ii 1 is constructed;(2) the geometry of the field;(3) the position of any impermeable o ° o boundaries that may be present, e.g., bedrock or layers of clay; (4) the gravity ` 1 0 x 8 flow potential which is determined by the position of the water table; and (5) 0.0002 0.0004 0.001 0.002 0.004 , 0.01 0.02 0.04 0.1 0.2 0.4 evapo-transpiration from the ground surface which is determined by the weather, j soiiVpermeability,in feet per minute I soil type, vegetation, and degree of saturation. 5 t ' ;{ , - 1 = Evapo-transpiration can remove a substantial proportion of the liquid from FIG. 1.—Long-Term Acceptance Rete of Effluent by Soil(1 gpd/sq ft = 0.41 m/day; the area of a seepage field during dry months; however, the winter and spring 1 fpm = 0.305 m/min) months, when the ground is wet and there is no transpiration, are usually the - most critical months and most failures occur during this period. For this reason Distribution pipe Loam Crushed stone or gravel seepage in temperate zones should be designed to function under I ii / I / i // i / ram% // / fieldsP gn gravity Effluent ponded flow potential only, if they are to perform satisfactorily gear round. 1 ft in trench '.1,‘- Flow in capillary zone The hydraulic conductivity of a seepage field can be calculated using flow / t; nets if it is assumed that the field is flooded long enough for a steady-state 71/ii :; •y� flow pattern to develop. Most seepage fields are flooded intermittently, but as long as the total number of gallons per day is less than the calculated steady-state Original height hydraulic conductivity the field will not fail due to lack of hydraulic conductivity. of water table Knowing the boundary conditions and the permeability of the soil,and assuming t no evaporation and steady-state flow due to gravity potential, it is possible to calculate the hydraulic conductivity of a seepage field that can be used for design.The thin zone of reduced permeability at the soil interface can be ignored if it is assumed that a head of 1 ft (0.3 m) due to flooding in the trench will be available to push the liquid through this zone. If the soil surrounding the • _t field can carry the liquid away faster than 1 ft (0.3 m) of head supplies it, there will be, in addition, capillary head available to pull the liquid through FIG. 2.—Assumed Pattern of Flow from Seepage Trench(1 ft = 0.305 m) this thin zone. With this capillary head; I ft (0.3 m) of flooding will not occur. The assumed pattern of flow is shown in Fig. 2. These. conclusions are substantiated by the results of the study done for Flow nets for a variety of positions of the ground-water.table and bedrock the Federal Housing Administration(FHA)by the Robert Taft Sanitary Engineer- were drawn, using an electrical, analog, showing the pattern and amount of ing Center (4). From that study the average loading rates for seepage fields ground-water flow from a three-trench and a one-trench seepage field. The that had operated successfully for at least 4 yr were determined. These rates lateral boundary conditions are indeterminate and it was assumed that flow r 7 1138 OCTOBER 1974 EE5 EE5 SEEPAGE FIELDS 1139 from the seepage field would have no effect on the initial water table, 30 ft The flow calculated from these flow nets neglects the flow out of the ends (9 m) from the field. The actual extent of the influence will vary with the of the fields. This is relatively small for long narrow fields, and for fields size of the field and the depth to the impermeable strata. The position of the that are more nearly square, corrections can be made based On the perimeter. initial water table is also dependent on the lateral boundary conditions. A typical A summary of the results of these flow nets is shown in Fig. 4. flow net is shown in Fig. 3. These flow nets are two dimensional and represent Several important relationships are shown by these plots: (1) The hydraulic a cross-sectional flow pattern,The flow per running foot of field can be calculated conductivity of a seepage field is directly dependent on the depth of the water table in the area surrounding the field (note that the water table is mounded up in the vicinity of the field);and(2)the hydraulic conductivity is very dependent on the position of any impermeable.strata underlying the field. Hty2 ft Ill Using these plots it is possible to design a seepage field having adequate 1..,. hydraulic conductivity if the permeability of the soil, the highest position of ■ 111111 the water table, and position of any impermeable strata are known. 1111111 _ ■■ _ III o M Z SITE EVALUATION The evaluation of a site for a seepage bed involves the determination of _'�` 'k• - -- '— ' the highest seasonal elevation of the water table, the depth to any impermeable NDN =123;Q per ft of field=2 XKx2=j2K cu ft per min per ft of field strata, and the permeability of the soil in which the field is to be constructed. The first two factors can best be determined by a deep test pit dug in early FIG. 3.—Typical Flow Net(1 ft = 0.305 m; 1 fpm = 0.305 m/min) spring and left open several days to allow the water level to come to equilibrium with the surrounding ground-water table. If the site evaluation must be made 50000 some other time than the wettest time of year, an estimate can be made of Three-trench field the highest position of the water table by examining the records of wells dug E - H�=18 ft . in similar soil in the area or identification of mottling in the soil profile. If Q.▪ 40000 20000 there is any doubt,however,the evaluation must be made in the spring.Evaluation s I of the permeability is generally more difficult. c Htp92 ft Permeability is defined by the equation, K = Q/iA, in which K = the z- - permeability,in feet per minute; Q = the rate of flow, in cubic feet per minute; 15 30000 15000 i = the hydraulic gradient, in feet of head, lost per foot of soil; and A = Three-trench yield the total cross-sectional area through which the water is flowing.The permeability r of a soil deposit is affected by the following: a u 20000 10000 1. The type of soil or grain size distribution. The permeability can vary from • Hr=loft 10-10 ft/min (5 x 10-13 m/s) for a fat clay to 1.0 ft/min (5 x 10-3 m/s) N F. for a coarse sand. • loom • 5000-- 2. The relative compaction of the soil. The permeability can vary by a factor ©' -Single-trench field of five between loose and dense soil. • H,=S ft 3. Discontinuities in the soil deposit. Clay seams, sand seams, root"holes, • o I 0 i I etc., may increase or decrease the overall permeability of a soil deposit by 0 2 4 6 0 5 10 15 20 a factor of 1,000. Value of Hw,in feet Value of Hi,in feet" 4. Degree of saturation. Air trapped in the soil can decrease the permeability FIG. 4.—Results of Flow Nets (1 ft = 0.305 m; 1 fpm = 0.305 m/min; 1 gpd/sq by a factor of two or three. ft = 0.41 m/day) Consideration must be given to the preceding factors when evaluating the by the following equation: Q/per foot = (Nf/Nd) x H x K; in which Q permeability of a soil deposit. Tests on disturbed samples of homogeneous sand is given in cubic feet per minute; H = difference in elevation between the and gravel deposits give reasonable results•as these soils are not sensitive to disturbance.The less permeable soils, however,must be tested in an undisturbed bottom of the trench and the external water table, in feet; Nf = number of flow tubes; Nd = number of head drops; and K = permeability of the soil condition, either as small tube samples or larger in situ samples. surrounding the field, in feet per minute. There are two relatively simple tests that are not affected by capillarity and 7 1140 OCTOBER 1974 EE5 EE5 SEEPAGE FIELDS 1141 can be used to measure the permeability of the soil in the area planned for underway to determine if the rate of water level rise in a test pit can be used a seepage field. directly in the design of a seepage field, eliminating the need for defining the TUBE SAMPLE Petrt TESTS boundary conditions and evaluating the permeability. Several further comments concerning site evaluation in temperate zones should Undistributed samples of 1-1/2-in. (38-mm) diam to 2-in. (50-mm) diam are be made. A water table that rises to less than 3. ft (0.9 m) from the ground taken from the sides or bottom of test pits using a 6-in. (150-mm) long piece surface in the spring indicates that rain or surface water is entering the area of thin wall tubing greased on the inside. The permeability test is run using the sample tube as the permeameter. This technique is described by Healy I TABLE 2.-Bailing Test Data and Laak (6). Several samples should be tested from each test pit for reliable l evaluation of the deposit. The disadvantage of this type of test is that important ( Assumed discontinuities of the soil deposit, e.g., sand or clay seams, may not be tested. I depth This test is rapid and simple and in homogeneous deposits provides a reliable Depth to measurement of the permeability. Depth to imperme- K-tube PrrPetfenenmTFsrs • of water able K-bailing, sampling, pit, table, strata, in feet in feet In order to overcome the disadvantages of the tube permeameter tests, a in in in per per pit permeability test was developed and tried in the field. This test makes use Site feet feet feet minute minute of the test pit that is dug to determine the depth to the water table and the (1) (2) (3) (4)- (5) (6) position of any impermeable strata. The water table must be within 8 ft-10 Ashford feet (2.4 m-3 m) of the ground surface in order to run the test. The test itself 3-A 6.0 2.66 6.0 1.8 x 10-3 9 x 10-3 is identical to the auger hole bailing test described by Sutton (13), but it is 5-A 6.0 2.75 6.0 2.9 x 10-3 8 x 10-3 applied to a different shaped hole. Conventional well theory, as described by Hanks Hill a Cedergren(3),was applied to this case as shown in Fig.5.The radius of drawdown 1 5.5 2.8 5.5 9.8 x 10_3 9 x 10_ 2 5.5 2.0 5.5 7.9 x 10 2 x 10 3 was assumed equal to four times the effective radius of the test pit. The 3 5.0 2.9 5.0 6.2 x 10-3 3 x 10-3 approximate depth to any impermeable strata should be known or estimated. Eastford 7.75 3.0 • 7.75 6.5 x 10-0 1 x 10-' The calculated permeability is not sensitive to the radius of drawdown or the Wormwood - depth to the impermeable strata. In sites where the depth to any impermeable Hill 7 1.3 7.0 2.4 x 10-2 2 x 10-3 strata is not well defined, it can be assumed equal to the depth of the pit Note: 1 ft = 0.305 m; 1 ft/min=0.305 m/min. without much loss of accuracy. There are two ways to carry out this test. The first entails measuring the rate of water level rise in the test pit when it is first dug and returning a day or two later to establish the equilibrium water level. The second entails digging the test pit, waiting several days for the water level to stabilize, lowering the water level by bailing and measuring the rate at which it rises. The water level should be lowered at least 1 ft (0.3 m) for reliable measurements. Most test pits are dug in a roughly trapezoidal shape and in order to measure the inflow rate, the area of the water surface must be measured every time the water level is measured. A series of pit permeability tests were carried out in the Mansfield, Conn. area and tube permeameter tests were run also. The results of these tests are given in Table 2, and show fairly good agreement between the tube tests and the pit tests. It must be remembered that the test i , >o� pits allow the measurement of the permeability of a relatively large volume y K rEK of soil and will reflect the overall permeability of a deposit more accurately than a small tube sample. Careful inspection of the. test pit•is necessary to Q-n KfH'-n;, _on __n xfH2-no) ;h Ph A determine if layers of clay are present that would not be penetrated during 2.31og;; Q p, xA _ 2.3�og4 ' e`nt xAs2.27 KfH -h,); Ksor X 2.27 lH, ., , the installation of the seepage field; and would impede the downward flow assumed=4,.K-permeability of soil;A-area of water surface. of liquid from the field. . '-h=rate of water level rise;and H-equilibrium position of water table. I Sometimes the permeability of a soil deposit-gradually decreases with depth �` and the boundary conditions are difficult to define. Investigations are presently FIG. 5.-Pit Permeability Test r 1142 OCTOBER 1974 EE5 EE5 SEEPAGE FIELDS 1143 • • faster than it can leave. This may be due to impermeable underlying strata adequate hydraulic conductivity to carry the liquid away; and (2) sufficient or soil of low permeability,either of which would make extensive site alterations soil interface area be available to filter the effluent as it is applied. necessary for the installation of a seepage field. A typical seepage field applies To simplify the design procedures, a seepage field consisting of three parallel water at a rate of approx 5 ft/yr (1.5 m/yr) over the field area, which is trenches, 2 ft (0.6 m) wide, 2-1/2 ft (0.75 m) deep, and 8 ft (2.4 m) on centers, only slightly more than the average rainfall in the Northeast. If the area cannot was chosen as a reasonable and efficient system.Variation in capacity is obtained absorb the rainfall, it certainly will not be able to absorb additional liquid from by varying the length of the field. This system is a total of 18 ft (5.4 m) wide a conventional seepage field. On the other hand, if the water table in an area • and, if the effluent is assumed to flood the trench to a depth of 12 in. (300 remains 7 ft (2.1 m) or more below ground surface all year, the ground will mm), it has a soil interface area of 12 sq ft/running ft (3.6 m2/m) of field. be able to absorb the additional liquid with no difficulty from a seepage field The hydraulic conductivity of such a field was derived from the results of of adequate size: It is those sites which lie between the preceding limits that the flow nets as given in Fig. 4. It was found that if the relative hydraulic require conscientious evaluation for proper design of seepage fields. conductivity, Q/K, per foot of field was plotted versus the distance from the bottom of the trench to an impermeable strata, H1, plus five times the distance SEEPAGE BED DESIGN from the bottom of the trench to the original external-water table, Hw, a fairly continuous curve resulted, as is shown in Fig. 6. This curve allows the effect The factors that must be considered in the design of a seepage field are of an impermeable strata and the effect of the water table to be considered the amount and quality of effluent, the permeability of the soil, the highest together in the design. elevation of the water table, and the depth to any impermeable strata. The The required soil interface area of such a field was based on the laboratory following design method assumes average quality effluent from a private home lysimeter tests, as shown in Fig. 1, which gives the long-term acceptance rates, septic tank. It is also assumed that the seepage field is constructed of parallel in gallons per day per square foot versus permeability of the soil. stone-filled trenches, three trench widths apart, 2 ft-3 ft (0.6 m-0.9 m) deep These two factors, hydraulic conductivity and soil interface area,are combined with 4-in. (100-mm) diam perforated pipe for distribution. The two major - in Fig. 7 for calculating the required length of a three-trench field for a given considerations are that: (1) The ground surrounding the seepage field have number.of gallons of effluent per day (cubic meters per day). The hydraulic conductivity versus soil permeability is drawn as a series of curves for different 50000 V v U? o HI-10 ft o T i3 E A Hy-18 ft n 40 000 0 i a , v Ti 20 13 30000 Hydraulic conductivity criteria o • I — 1.5 0 d Value of HI+5Hty o. 15 — e) rho N ti� —. `9_ a m,. A 1..,ea ve, -o t w ..z• .• 20000 a e — 1.0 `o 0 o — m o m • 5 0 E -o 5 / N W .5 O / 00 Q 10000 d Z. 2 ��� — 0.5 fiF: t yn 5 — — Ar Ca Interface > — — loaning criteria j I 0 0 0 0 10 20 30 40 •50 0.0001 0.0002 0.0005 0.001 0.002 0.005 0.01 . Permeability of sod,in feet per minute Value of HI+5Hw,in feet FIG. 6.—Hydraulic Conductivity of Three-Trench Field(1 ft = 0.305 m) FIG. 7.—Capacity of Three-Trench Field (1 fpm = 0.305 m/min; 1 gpd/sq ft = 0.41 m/day) 1144 OCTOBER 1974 EE5 EE5 SEEPAGE FIELDS 1145 positions of the water table and impermeable strata. The allowable soil interface bed, the trenches are 2.5 ft deep; the bedrock is 9.5 ft below ground surface; loading rate versus soil permeability is drawn in also. A field must be sufficiently Highest water table is 5.5 ft below ground surface; Permeability of soil is 2 large that the rate of loading is lower than the maximum allowable soil interface x 10' ft/min; Hi = 9.5 ft - 2.5 ft = 7 ft; Hw = 5.5 ft - 2.5 ft = 3 ft; loading rate and also is lower than the maximum rate for hydraulic conductivity, and Hl + 5 Hw= 22. as determined by the particular conditions of impermeable strata and water The Q allowable for hydraulic conductivity is more than 20 gpd/ft of field, table and the Q allowable for soil interface area is 5 gpd/ft of field. Therefore the Note, in Fig. 7, that in soils of low permeability it is generally the hydraulic Q allowable is 5 gpd/ft of field. conductivity of the field that controls the design, whereas in soils of higher A three-bedroom house using 300 gpd needs a field that is 300/5 = 60 ft permeability, it is the soil interface area that controls the design. long. No adjustment is required for end effects because the soil interface area These particular design charts should be used only where the conditions are controls. the same and they are presented to show the design principles.The flow pattern Design Example 2.-The following information (1 ft = 0.305 m; 1 ft/min for other conditions could be determined and used as a basis for design. = 0.305 m/min; and 1 gpd/sq ft = 0.041 m/day) is given: For a three-trench bed, the trenches are 2.5 ft deep; the bedrock is 7.5 ft below ground surface; Suwvwty highest water table is 4.5 ft below ground surface; permeability of soil is 5 x 10' ft/min; HI = 7.5 ft - 2.5 ft = 5 ft; Hw = 4.5 ft - 2.5 ft = 2 ft; A literature survey indicated that there is a long-term acceptance rate, which and Hi + 5 Hw= 15. is a function of the soil permeability, at which septic tank effluent can be From Fig. 7, the allowable for hydraulic conductivityis 2.5 Q y gpd/ft of absorbed indefinitely. This rate was determined by numerous investigators and field and the Q allowable for soil interface area is 3.5 gpd/ft of field. Therefore, their results are very consistent. This acceptance rate is independent of whether Q allowable is 2.5 gpd/ft of field. the soil is continuously or intermittently flooded, and varies from approx 0.3 A four-bedroom house uing 400 gpd needs a field that is 400/2.5 = 160 gpd/sq ft for a soil with a permeability of 0.0002 ft/min (6 x 10' m/min) ft long field. Hydraulic conductivity controls size so that field length can be to approx 3.0 gpd/sq ft (12 cm/day) for a soil with a permeability of 0.1 reduced because of end effects. The field is 18 ft wide so it can be reduced ft/min(0.03 m/min). to 160 - 2 x 18 = 124 ft. The loading rate is now 400 gpd/124 = 3.23 gpd/ft A study of the groutti-water flow pattern below a seepage field showed that and is still less than the 3.5 gpd/ft allowed for soil interface area. it is, in many cases, the hydraulic conductivity of the ground surrounding the' Note that this field would normally be considered too long for proper distribution field,as determined by the external water table;soil permeability,and impervious and site alterations might be necessary. strata, that controls the size of the field required. " Reliable techniques for site evaluation of soil permeability, depth to water APPENDIX tl.-REFERENCES table, and depth to any impervious strata are presented, and a chart is given for designing seepage field based on this information. Design examples are 1. Bouwer, H.,et al., "Renovating Secondary Sewage by Ground Water Recharge with presented. Infiltration Basins," Office of Research and Monitoring, Environmental Protection Agency,Washington,D.C., 1972. CONCLUSIONS 2. Bradshaw,D.L., "An Investigation of Seepage Field Failure," C.E.320,Department of Civil Engineering, University of Connecticut,Storrs,Conn.,Jan., 1972. Seepage fields that will operate successfully for very long periods can be 3. Cedergren, H. R., Seepage Drainage and Flow Nets, John Wiley and Sons, Inc., New York,N.Y., 1967.- designed and constructed if: (1) Accurate measurements are made of soil 4. Coulter,B.,Bendixen,T.W.,and Edwards,A.B.,"Study of Seepage Beds,"Federal permeability, position of the water table, and position of any impervious strata; Housing Administration,Robert A.Taft Sanitary Engineering Center, Dec., 1960. and (2) the loading rate, in gallons of effluent per day per square foot of soil 5. Healy,K.A.,"Wastewater Disposal Systems in Unsewered Areas,"State of Connecti- surface, is kept below a certain value that is a function of the soil permeability. cut, Hartford,Conn.,June, 1973,Appendix IV. 6. Healy,K. A.,and Laak,R., "Factors Affecting the Percolation Test," Journal Water Pollution Control Federation,Vol. 45,No. 7,July, 1973. ACKNOWLEDGMENT 7. Hill,D.E.,"Percolation Testing for Septic Tank Drainage,"Bulletin of the Connecticut Agricultural Experiment Station,No.678, New Haven,Conn., 1966. This work was carried out in the Civil Engineering Department of the University 8. Johnston, R. E. L., "A Survey of Subsurface Sewage Disposal.Failures," Civil of Connecticut, Storrs, Conn., under a grant by the Connecticut Research Engineering Department,University of Connecticut,Storrs,Conn., May, 1971. Commission. 9. Jones, J. H., and Taylor, G. S., "Septic Tank Effluent Percolation Through Sands Under Laboratory Conditions," Soil Science,Vol.99, No. 5, 1965. 10. Kropf, F., "Effect of Frequency and Duration of Septic Tank Effluent Submergence APPENDIX 1.-DESIGN EXAMPLES on Soil Clogging,"thesis presented to the University of Connecticut at Storrs, Conn., in 1972, in partial fulfillment of the requirements for the degree of Master of Science. Design Example 1.-The following information is given (1 ft = 0.305 m; 1 II. Laak,R.,"Influence of Domestic Wastewater Pretreatment on Soil Clogging,"Journal ft/min = 0.305 m/min; and 1 gpd/sq ft = 0.041 m/day): For a three-trench Water Pollution Control Federation,Aug., 1970. fr, 1146 OCTOBER 1974 EE5 12, Orlob, G. T., and Butler, R. G., "An Investigation of Sewage Spreading on Five California Soils,"Sanitary Engineering Research Laboratory,University of California, Berkeley,Calif., 1955. 13. Sutton, J. G., "Installation of Drain Tile for Subsurface Drainage," Journal of the Irrigation and Drainage Division, ASCE, Vol. 83, No. IR3, Proc. Paper 2591, Sept., 1960,pp. 27-49. 14, Thomas, R. E., Schwartz, W. A., and Bendixen, T. W., "Soil Chemical Changes and Infiltration Rate Reduction Under Sewage Spreading," Proceedings,Soil Science Society of America,Vol. 30, 1966. 15. Winneberger,J. H., et al., "Biological Aspects of Failure of Septic Tank Percolation Systems,"Sanitary Engineering Research Laboratory,University of California,Berke- ley,Calif.,Aug., 1960. APPENDIX III.—NOTATION The following symbols are used in this paper: A = area; H = head; • HE = depth from bottom of trench to impermeable strata; Hw = depth from bottom of trench to water table; • K = permeability; Nd = number of head drops; Nt = number of flow tubes; Q = rate of flow; R = radius of drawdown;and • • ro = radius of pit. • .--,,k . _ _ _ . n � nerhopes .. .. • ne , ... w system , iswater say.... . er .. - By. MAN TARCY SP. . `WRITER r4 r The system, its FALMOUTH — Michael'McGrath b • smiles at the suggestion that a'state- distributor say s, of-the-art septic waste disposal sys- could reduce`b y 75 tern he is installing in East Falmouth 7\ could save Cape Cod's ground water. -percent the amount �` \ McGrath, president of the engi-. of nitrates entering neering firm Holmes and McGrath ` Is not naive enough to think he and ground water, his new company, Southeast Ruck compared with a Systems Inc.,is on the verge of being conventional septic canonized by the church of conservationism. system. Every little bit helps,however,and if McGrath's system works, it could mean a brighter future for water crease the amount of oxygen in the bodies. baby's blood system,she said. 0 The system,designed by civil engi "The babies don't usually die, but neering professor Rein Laak of,the the result is mental retardation," University of Connecticut, could re- Ms.Nickerson said. duce by 75 percent the amount of ni- The black water is pumped into a trates entering ground water, com- tank where it filters through layers of pared with- a conventional septic ;rock, sand and air, and the nitrogen system,McGratbsaid ,-and ammonia are transformed into Mc.G has 'entered wnto an nitrates,Dudley said. a gire �t with Leak to be the sole After it has gone through this sys- supplier,ef the in Southeast- 'tem, the black water containing the ern Masita , nitrates are then mixed with the gray The system is based on pumping' water in another chambe ,,set low in "black wat r"from toilets and bath- the ground with no oxyg ., rooms to adifferent place than"gray "this allows'for the,deitryfying water?'fromhitche�ns�iaundry. bacteria to grow. The gray ovate is :{. 4 The gray watery pumped to a stor- acting as a carbon source,which the age tank, McGrath said. The black bacteria need. By mixing the gray water is pumped to another storage water with the nitrate-loaded water, tank that"takes advantage of the na- the bacteria converts the nitrates tural cycling of nitrogen,"said Brian into nitrogen gas, which is not clan- Dudley,a junior environmental engi- gerous,"Dudley said. neer for Southeast Ruck Systems Inc. From there, the water, which has "What happens naturally in the 75 percent less nitrates than water ground, Dudley explains, "is or- coming from a conventional system, genic nitrogen and ammonia are is pumped to leaching beds,McGrath broken down into nitrates." said. Ground water levels of nitrate,or nitrate nitrogen, of more than 10 The state Department of Environ- parts per million could cause,gas- mental Quality Engineering has giv- trointestinal cancer, Susan Nicker- en McGrath permission to install the son, water rescources coordinator system on land owned by Loren for the Cape Cod Planning and Eco- nomic Development Commission, in a two-year test. said earlier this year. Wentworth at Bournes Pond for use Another danger of nitrate nitrogen If the system works as expected,he is the "blue-baby syndrome," in said, McGrath will be allowed to in- which the toxic substance can de- stall other systems elsewhere. "l'tt'$6 ?%• - ‘Alp 5,....4.* T oiAAS J. McLELL4n, be W., CAPE EuG . 3-6 7- 5t dtiA g-p a/,A Yf,P /e4 yF4°,..rv4 r/ Svc/ice BOG-3S3-3/0 Rol 14 E t.3TJRL.eIt r� f:e 14 Y c - c-f So f Z?3 - (0 3 bJ .[ --1 any - e;i 1 - E Pt \gin, .w-- LE 41s.0�(Z-cJ3) z6 8 -7943 1 7?l4 S" 4 o M &s ,Ty-,1i6 -ss7 /(1k(t -ram r - � 4� 4" -Cot`7- 771 _ 2214) i,, P� cpro -e. mu,fekty ti cif c`r\--\ 44-cj-9(417 ' { il, I is i it I,j III