HomeMy WebLinkAboutResponse to CommentsBAXTER NYE ENGINEERING & SURVEYING
Registered Professional Engineers and Land Surveyors
78 North Street, 3rd Floor, Hyannis, MA 02601 Tel: (508) 771-7502 Fax: (508) 771-7622
Land Surveys · Site Design · Subdivisions · Septic Design · Wetland Filings · Planning
October 6, 2022
Ms. Brittany DiRienzo, Conservation Administrator
Yarmouth Conservation Commission
1146 Route 28
South Yarmouth, MA 02664
RE: Stormwater Management Permit – Engineer Review
212 Mid-Tech Drive, West Yarmouth, MA
Dear Brittany:
We have reviewed the comment letter from TRC Companies of September 28, 2022 concerning
our Stormwater Management Permit application to the Yarmouth Conservation Commission. We
have updated the plans and drainage calculations and are resubmitting them to you for approval.
Included in this resubmittal are:
· Updated Site Plans Sheets C0.0 to C6.2 (11 sheets), revision dated 10/6/2022.
· Updated SWM Report revision date 10/6/2022.
Following are responses to comments in the above noted letter. The Item number designations
correspond to item numbers within the comment letter:
2.04(1) Stormwater Management Site Plan
(h)
1. A description of the existing stormwater management systems has been added to the Site
Redevelopment Project Narrative.
(i)
1. The existing drainage systems is a series of leaching catch basins with 12” drainage pipes
connecting them. They are shown per Site Plan of Land by Weller & Associates, dated
November 4, 1998.
2: The narrative has been updated with a discussion of the existing drainage systems. These
existing leach pit drainage systems are not used in the proposed design and will be removed.
Limits of stone 4’ radially from the leaching basins has been added to the Grading Plan, sheet
C4.0.
3. Test pits for the proposed septic leaching facility performed on November 10, 2021 identify
sand soils. The US SCS mapping shows Carvers sand soils for this site. As allowed by DEP
SWM Policy, the Rawls rate for Sand type soils in Hydrologic Soil Group A is 8.27 inches per
hour. Confirmatory test pits will be performed at time of installation to verify consistency with
soils found at test pits performed on November 10, 2021. Additionally, Baxter Nye designed and
October 6, 2022
Ms. Brittany DiRienzo
Stormwater Management Permit – 212 Mid-Tech Drive, West Yarmouth, MA
Page
BAXTER NYE ENGINEERING & SURVEYING
78 North Street, 3rd Floor, Hyannis, MA 02601 Tel: (508) 771-7502 Fax: (508) 771-7622
2
inspected the bottom area for the existing Cultec system (which is to remain) during installation
on July 11, 2016. The soils found were medium to coarse sand underlying the entire bottom area
with no groundwater observed.
With the test pit information for the septic design performed for this project, prior inspection on
this site during the 2016 construction, and not wanting to excessively disturb the existing
developed site, we believe and would request that this is sufficient soil data for this project. At
the time of installation of the new swm facilities, bottom of hole inspection will be performed to
verify the soils are consistent with the design.
(k)
1. The November 10, 2021 soil testing at the site identified no groundwater down to 11.0 feet
below the surface. (Elevation 36.75). High groundwater adjustment calculations have been
provided which shows an adjustment of 4.4 ft. Historically in this area groundwater is below
15 ft +. The bottom of drainage infiltration systems is at elevation 41.94, or 5.19 feet.
Conservatively the bottom of the swm facilities will have over 5 ft separation from groundwater.
At time of construction, the contractor will dig down to four feet below the bottom of the drainage
systems to verify that no groundwater is encountered.
(i)
1. Groundcover types, curve numbers, and areas have been added to the pre and post-
development drainage area plans.
(m)
1. Times of concentration used are the assumed minimum time allowed, 5 minutes, which is the
most conservative and minimum time allowed in TR20TR55 calculations. No specific flow path
is required as we are using the min time allowed.
2. The drainage area boundaries in the area of DA-2 and DA-4 were modified on both pre and
post development drainage area plans. Some spot elevations and drainage flow arrows were also
added for clarity, and areas were updated in HydroCAD calculations.
(n)
1. Details for Cultec Recharger 330 systems were added on additional detail plan sheet, C6.2.
2. Distances from septic leaching facility (and reserve area) to forebays were added to the Utility
Plan, sheet C5.0.
(r)
1. Inlet capacities for the three beehive grates were calculated in the HydroCAD model. These
calculations are relabeled as OC for orifice check. These calculations are included in the
HydroCad calculations for the 2, 10, 25, and 100 year events. The beehive grates were modeled
with sixteen 1.5” x 2” openings at the bottom of the grate, ten 1.5” x 1.5” openings three inches
above the grate bottom, and six 1.5” x 1.5” opening five inches above the bottom of the grate per
the grate detail.
October 6, 2022
Ms. Brittany DiRienzo
Stormwater Management Permit – 212 Mid-Tech Drive, West Yarmouth, MA
Page
BAXTER NYE ENGINEERING & SURVEYING
78 North Street, 3rd Floor, Hyannis, MA 02601 Tel: (508) 771-7502 Fax: (508) 771-7622
3
2. Groundwater recharge volume shown are now based on volume provided in the Cultec
chambers. Water Quality Volumes are based on volumes provided in the forebays below the
beehive rim outlet elevation.
3. The bioswales are now shown as sediment forebays.
4. The recharge calculations and water quality volume calculations have been broken out for each
design point. Sediment forebay 2 was enlarged slightly to provide additional volume required by
the revised calculation.
(s)
1. The revised drainage report has been stamped by a Professional Engineer.
2.05 Stormwater Management Performance Standards
(2) (v)
1. The good housekeeping procedures language has been updated for consistency with the
performance standards.
(3) (b)
1. Street sweeping has been removed from the TSS train. 44% pre-treatment TSS removal will
still be provided.
2.06 (4) Erosion Control Plan
1. Erosion control plan and notes were shown on sheet C4.0. The sheet title has been revised to
be “Grading, Drainage and Erosion Control Plan”. Additional notes concerning erosion control
have been added to sheet C4.0 under Operation and Maintenance Plan notes, numbered 10
through 14. Note that there is no phasing proposed for this project.
2. The SWPPP information provided meets the NPDES General Permit requirements and all
information is provided within the Grading, Drainage, and Erosion Control Plan and within the
Stormwater Operations, Maintenance, and Inspections Plan.
2.07 (1) Erosion and Maintenance Plan
(a)
1. The name of owner for all components of the system has been added to the plan
(b)
1. The name and address of the person responsible for maintenance has been added to the plan.
(c)
1. The person responsible for financing maintenance and emergency repairs has been added to
plan.
October 6, 2022
Ms. Brittany DiRienzo
Stormwater Management Permit – 212 Mid-Tech Drive, West Yarmouth, MA
Page
BAXTER NYE ENGINEERING & SURVEYING
78 North Street, 3rd Floor, Hyannis, MA 02601 Tel: (508) 771-7502 Fax: (508) 771-7622
4
(f)
1. An existing 10 foot wide electric easement across the entire parcel frontage is shown on the
existing conditions plan. There are no other easements proposed.
(g)
1. The owners agent has signed the Stormwater Operations, Maintenance, and Inspections Plan.
General Technical Review
1. The existing leaching catch basins have been labeled as LCB (Leaching Catch Basin). The
drain lines in between the basins are 12” pipes and shown per Site Plan of Land by Weller and
Associates. These basins and piping will be removed during the construction phase.
2. The limit of work has been added to each relevant sheet of the site plans.
3. The existing and proposed impervious coverage has been added to the narrative. Proposed
impervious coverage is approximately 37,100 sf. Existing impervious coverage is approximately
38, 700 sf.
Thank you for your consideration of our responses. I would appreciate an opportunity to discuss
any additional comments, if necessary, with the reviewer to assist in approval of this submittal.
Please contact me with any questions or additional information you may need once you have
completed your review.
Very truly yours,
Baxter Nye Engineering & Surveying
Matthew Eddy, P.E.
President
Cc: Jeff Bilezikian, Rick Fenuccio
Enclosures: Revised Site Plans, Drainage Report, and Stormwater Operation Maintenance, and
Inspections Plan