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HomeMy WebLinkAboutRevised plan request 10.29.2025 75 State Street, Suite 701 Boston, Massachusetts 02109 tel: 617 452-6000 October 29, 2025 Yarmouth Conservation Commission 1146 Route 28 South Yarmouth, MA 02664 Subject: Plan Revision Request Order of Conditions DEP Wetlands File No: 083-2442 Dear Commission Members: On behalf of the Town of Yarmouth, Department of Public Works, CDM Smith Inc. (CDM Smith) submits this Plan Revision request to existing Order of Conditions (OOC) (DEP File No. 083-2442) issued on September 24, 2024, and valid until September 24, 2027. The Plan Revision consists of relocation of proposed Pumping Station No. 2 (PS2) in Contract No. 6. A nonbinding measure was approved at special Town meeting in December 2024 to move PS2 from its original proposed location at 316 Route 28. The Town is now proposing to construct PS2 at 280 Route 28 (Map 38 Lot 4), on land owned by Bellew Realty. The parcel is previously developed and the portion proposed for the relocated PS2 consists of a gravel parking area (see attached photos) where the leaching field for the building on the parcel was constructed; that is, the area has been previously disturbed. The Town is in the process of securing a utility easement on this privately owned property for the purpose of building and maintaining the pumping station. Since the new sewer system is a gravity system, options for relocating PS2 are very limited since the pumping station has to be located within the lowest portion of the area to be sewered. Proposed Plan Revision The relocated PS2 will be the same type of pumping station as the previously proposed station - it will be submersible type with a wet well (i.e., deep below ground structure) that will house submersible pumps. Valving and a meter will be housed in separate below grade precast concrete structures adjacent to the wet well. Each area will be accessed by individual H-20 rated hatches or traditional manhole covers. An 11.5’ by 17’ precast building (control room) with concrete pad at the doorway will house all of the electrical and pump control equipment and alarms. A standby natural gas generator will be placed on a 5’ by 12’ concrete pad. Odor control is not included in this design but there is space allocated on site (5’ by 8’ concrete pad) for a future odor control system, if needed. All these components of the pumping station are the same as the originally proposed station; they are just located on a different site in a slightly different orientation. Yarmouth Conservation Commission October 29, 2025 Page 2 Wetland Resource Area Impacts The relocated PS2 results in a decrease in impacts to wetland resource areas compared to the original location at 316 Route 28. The eastern half of the new site for PS2 will encroach into Land Subject to Coastal Storm Flowage (LSCSF) which extends up to el. 11 ft (see Figure 2: FEMA Flood Map and Plan Sheets. Fill material will be brought in to build up the site to approximately elevation 13 feet in order to allow the first- floor elevation (FFE) of the control building and critical infrastructure to be placed at elevation 14. Engineering design standards require that critical infrastructure (i.e., electrical and control equipment, including natural gas standby generator) be elevated 3 feet above the effective 100-year floodplain (i.e., 11 feet). The PS2 site will be final graded with crushed stone and a portion of the existing the gravel parking area will be paved to provide access to the station for maintenance vehicles. The eastern slope will be restored to a 3:1 slope and seeded with a native wildflower seed mixture. Tree and shrub plantings are also proposed to screen the site from Route 28 as shown on Sheet CD-6 It is estimated that approximately 765 square feet (sf) of LSCSF would be permanently altered and an additional 765 square feet temporarily altered by bringing in approximately 120 cubic yards (CY) of fill material at a 3:1 slope as shown on attached Plan Sheet CD-6. This is a reduction from the permanent alteration of approximately 3,490 sf of LSCSF approved under the existing OOC for the original PS2 site. The relocated PS2 avoids all impacts to the 35-ft and 50-ft setbacks and reduces impacts to the 100-ft Buffer Zone (from 4,885 sf approved under the existing OOC to 2,630 sf at the new site). Table 1 provides a summary of wetland resource area and buffer zones impacts for the relocated vs. previously approved PS2 location. Table 1: Summary of Wetland Resource Areas and Buffer Zone Impact for PS 2 LSCSF (sf) 100-ft Buffer Zone (sf) 0-35 ft Setback (sf) (temp.) 35-50 ft Setback (sf) (temp.) PS2 – Permitted Location at 316 Route 28 3,490 (permanent) 4,885 656 755 Yarmouth Conservation Commission October 29, 2025 Page 3 PS 2 – Proposed Relocation to 280 Route 28 765 (permanent) 765 (temporary) 335 (new impervious) 2,295 (temporary) 0 0 Stormwater Management Design Stormwater for the relocated PS2 site will be collected in deep sump hooded catch basins and treated in a subsurface infiltration system, with all stormwater through the 50-yr storm retained on site. The stormwater design will meet the required Massachusetts Stormwater Standards for new development. Treated stormwater over the 100-year storm will be discharged to the existing stormwater system in Route 28. Please refer to the enclosed Pumping Station 2 Stormwater Report for a detailed discussion of existing stormwater conditions, drainage analysis, proposed stormwater management, and compliance with the Massachusetts Stormwater Standards. Mitigation Measures The following summary presents the mitigation measures that will be implemented by the Contractor to avoid and minimize wetland impacts during construction. There are no proposed changes to the mitigation measures from the original NOI. Please refer to the original project plans for typical details of measures to protect wetlands and waterways including coastal resources during and after construction. Construction Period ▪ Staked compost logs will be installed at the limit of work prior to commencement of construction to prevent the transport of sediment and debris to downgradient drainage ditch and to demarcate the limit of work. A stockpile of compost logs will be stored in an easily accessible location for routine maintenance and emergency repairs. The compost log barrier will be inspected weekly and after all storm events and repaired as needed. The barrier will be left in place until the area is permanently stabilized. ▪ Construction access will be from Route 28. The last crew to leave the site each day would be responsible for regularly sweeping the roadways, if and when sediment and/or rock have been tracked onto the street. ▪ Dewatering may be necessary during construction of the proposed PS2. Water will be pumped into a filter bag or dewatering basin consisting of a filter bag with straw bale or silt Yarmouth Conservation Commission October 29, 2025 Page 4 fence perimeter controls which will be located in approved areas outside wetland resource areas. The pump intake hose will not be allowed to set on the bottom of the excavation throughout dewatering. The basin and all accumulated sediment will be removed following dewatering operations, and the area will be seeded and mulched with straw. The bag will be surrounded with additional sediment filtration such as fiber rolls, straw bales, or other appropriate containment. Post Construction Measures ▪ If seeding occurs outside of the growing season, temporary stabilization measures (i.e., mulching or erosion control blankets) will be used to prevent erosion until the area can be seeded during the following growing season. ▪ All disturbed soils will be restored by installing native plantings and seeding with native seed mixture; and ▪ The compost log barrier will not be removed until a vegetative cover dense enough to prevent erosion is established. Summary The Town of Yarmouth is requesting that the Plan Revision as described above and on shown on enclosed the Plan Sheets be approved. We look forward to presenting the details of the Plan Revision at your next meeting scheduled for November 6, 2025. Feel free to call me at (617) 452-6597 or Michael Guidice, Project Manager, at (401) 457-0310 with any questions. We look forward to continuing working with the Yarmouth Conservation Commission on this very important project. Sincerely, Magdalena Lofstedt, PWS Environmental Scientist CDM Smith Inc. cc: Jeffrey Colby, P.E., Department of Public Works Director Michael Guidice, P.E., CDM Smith Project Manager Enclosures: Yarmouth Conservation Commission October 29, 2025 Page 5 Figure 1: Project Location Map Figure 2: FEMA Floodplain Map Photographs Plan Sheets CD-4: Existing Conditions, CD-5: Site Preparation, CD-6: Site Improvements, and CD-11: Misc. Details Pumping Station 2 Stormwater Report (bound separately) Figure 1: Project Location Map, PS 2 Proposed PS 2 Relocation Previously Reviewed PS 2 Location National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or Depth Zone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mile Zone X Future Conditions 1% Annual Chance Flood Hazard Zone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to Levee Zone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood Hazard Zone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 10/17/2025 at 9:27 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 70°15'25"W 41°39'26"N 70°14'48"W 41°38'59"N Basemap Imagery Source: USGS National Map 2023 Photo 1: Proposed PS 2 Site Location Photo 2: Proposed PS 2 Site Location (close-up)