HomeMy WebLinkAboutPeer Review 2022-09-28
September 28, 2022
Ms. Brittany DiRienzo, Conservation Administrator
Town of Yarmouth
Yarmouth Town Hall
1146 Route 28
South Yarmouth, MA 02664
Re: JDB 212 Mid-Tech Drive, LLC
Technical Stormwater Peer Review
186 & 212 Mid-Tech Drive
West Yarmouth, MA 02673
TRC Project No. 510575
Dear Ms. DiRienzo,
TRC has completed a technical stormwater peer review of the Stormwater Management Permit Application
prepared by Baxter Nye Engineering and Surveying submitted to the Commission on August 31, 2022 and
provided to TRC on September 2, 2022. The goal of the review was to determine if the application is technically
complete and to evaluate general compliance with the Yarmouth Stormwater Management Regulations, effective
July 1, 2021.
The following PDF documents prepared by Baxter Nye Engineering and Surveying were reviewed:
1. Site plans titled “Proposed Site Redevelopment, Contractor Bays, 186 & 212 Mid-Tech Drive, West
Yarmouth, Massachusetts 02673” dated August 31, 2022.
2. Stormwater Management Report, dated August 31, 2021.
3. Town of Yarmouth Stormwater Management Permit Application, dated August 31, 2022.
TRC’s observations are provided below, following the applicable standard in italics. TRC has determined that the
application is neither complete nor in compliance with the Stormwater Management Regulations as summarized
below. Revised documents and a detailed response to the following comments should be provided for further
review.
Yarmouth Conservation Commission Stormwater Management Regulations
2.04(1) Stormwater Management Site Plan
(h) The existing site hydrology;
1. A description of the existing site hydrology has not been provided. The existing hydrology, design points,
and stormwater management system should be described.
(i) A description and delineation of existing stormwater conveyances, impoundments, and wetlands on or
adjacent to the site or into which stormwater presently flows, or is proposed to flow;
1. No pipes or inverts associated with the existing catch basins shown on Sheet C1.0, “Existing Conditions
Plan” are shown. If these are leaching catch basins, they should be labeled as such.
2. The narrative does not describe the existing stormwater management features and how they will be
addressed under the proposed design.
3. The existing conditions HydroCAD model uses an infiltration rate of 8.27 in/hr for the existing Cultec
Chambers. Supporting data from the original design should be provided to support this infiltration rate.
(k) Estimated seasonal high groundwater elevation using the Cape Cod Commission adjustment method (Cape
Cod Commission Technical Bulletin 92- 001, as amended) in areas to be used for stormwater retention, detention,
or infiltration;
1. An analysis of the estimated seasonal high groundwater table has not been provided. Test pits have not
been excavated in the vicinity of the proposed infiltration areas. Grading and Drainage Note 10 on Sheet
C4.0 of the plan set specifies that the contractor shall verify the assumed 8.27 in/hr infiltration rate and
groundwater elevation prior to construction. If the Commission chooses to waive test pits, it is
recommended that the Commission consider a condition of approval requiring documentation of the
infiltration rate and 4 foot separation to seasonal high groundwater and restrictive layer prior to installation.
(l) The existing and proposed vegetation and ground surfaces with runoff coefficient for each;
1. The ground covers and associated runoff coefficients should be shown on the Drainage Area Plans.
(m) A drainage area map showing pre- and post-construction watershed boundaries, drainage areas, and
stormwater flow paths;
1. Stormwater flow paths are not provided.
2. The pre-construction drainage area boundaries do not appear to be correctly delineated. The
southeastern DA-2/DA-4 boundary is not drawn perpendicular to the contours and no elevation data is
provided along the northern boundary. The boundary should be corrected or flow arrows and spot
elevations should be provided to support the current delineation.
(n) A description and drawings of all components of the proposed drainage system including:
i. locations, cross sections, and profiles of all brooks, streams, drainage swales and their method of stabilization;
ii. all measures for the detention, retention, and/or infiltration of stormwater;
iii. all measures for the protection of water quality;
iv. the structural details for all components of the proposed drainage systems and stormwater management
facilities;
v. notes on drawings specifying materials to be used, construction specifications, and typical details and cross-
sections; and,
vi. proposed hydrology with supporting calculations.
1. Details and cross sections of the proposed Cultec Chambers and “bioswales” should be provided,
including separation from seasonal high groundwater.
2. The horizontal separation distance between the proposed Cultec Chambers and the proposed septic tank
and leaching chambers should be shown.
(r) Calculations supporting the design of the stormwater management system and its compliance with the
performance standards established in these regulations;
1. The proposed and existing “bio-swales” and associated Cultec Chambers are modeled as a single unit.
This approach does not demonstrate the inlet capacity of the beehive grate or 12 inch Cultec inlet pipe.
Nor does it demonstrate that sufficient head is provided between the grate invert and overflow weir to
prevent the “bio-swales” from over toping before the chambers fill. Additional documentation and
supplemental calculations should be provided to support this approach or the model should be revised.
2. Groundwater recharge and Water Quality Volume calculations provided are based on utilizing the
“bioswales” as infiltration practices. However, the “bioswales” function as sediment forebays and provide
pre-treatment for the Cultec chambers. Therefore, the Cultec chambers are the infiltration practice. The
recharge and water quality volume calculations should be revised accordingly.
3. Since the “bioswales” function as sediment forebays, sediment forebay design calculations should be
provided. It is recommended that the “bioswales” be relabeled “sediment forebays” in the plans and
documentation for clarity and consistency with the Mass Stormwater Handbook.
4. The required and provided water quality volumes are calculated on a site-wide basis. The calculations
should be broken out to demonstrate that the required water quality volume for each design point is
provided.
(s) Documents must be stamped and certified by a qualified Professional Engineer (PE) registered in
Massachusetts; and
1. The report should be stamped and certified by a professional engineer.
2.05 Stormwater Management Performance Standards
(2) Good housekeeping procedures shall be used to reduce sources of sediment, phosphorus, nitrogen and other
contaminants in stormwater runoff. These shall be documented in the Operation and Maintenance Plan and must
include…
v. Fertilizer containing phosphorus shall not be applied unless a soil test taken not more than three years before
the proposed fertilizer application indicates that additional phosphorus is needed for growth of that turf, or unless
establishing new turf or reestablishing or repairing turf after substantial damage or land disturbance;
1. The apparent typographical error in Good Housekeeping procedure v in the Stormwater Operations,
Maintenance, and Inspections Plan included in appendix 10 should be corrected for consistency with the
performance standard.
(3)(b) Structural pretreatment is required for all proposed infiltration devices to remove 44% TSS from runoff
before it enters the infiltration device. Runoff from non-metal roofs may be infiltrated without pretreatment. Runoff
from metal roofs may be infiltrated without pretreatment only if the roof is located outside the Zone II or Interim
Wellhead Protection Area of a public water supply and outside an industrial site, otherwise, pretreatment is
required as specified in the Stormwater Management Handbook.
1. 44% TSS removal is provided through the sediment forebay and deep sump catch basins. Street
sweeping is a non-structural treatment and should not be included in the pretreatment result described in
the Proposed Work section of the report.
2.06(4) Erosion and Sediment Control Plan
(4) Erosion and Sediment Control Plan Content…
1. An Erosion and Sediment Control Plan is not included in the plan set.
2. A copy of the NPDES Construction General Permit Stormwater Pollution Prevention Plan (SWPPP) has
not been provided.
2.07(1) Operation and Maintenance Plan (post-construction)
(a) The name(s) of the owner(s) for all components of the system.
1. This information is not included in the operation and maintenance plan.
(b) The names and addresses of the person(s) responsible for operation and maintenance;
1. This information is not included in the operation and maintenance plan.
(c) The person(s) responsible for financing maintenance and emergency repairs;
1. This information is not included in the operation and maintenance plan.
(f) A list of easements with the purpose and location of each;
1. This information is not included in the operation and maintenance plan.
(g) The signature(s) of the owner(s);
1. The copy provided has not been signed.
General Technical Review
The following general technical review comments should be addressed in addition to the technical regulatory review
comments provided above.
1. The existing drain lines should be shown on Sheet C1.0 and the catch basins should be labeled as leaching
catch basins for consistency with Sheet C4.0 and the HydroCAD calculations. The details of the existing
leaching basins including the size, type, and surrounding stone, should also be provided to support the
HydroCAD calculations.
2. The Limits of Disturbance should be shown on all proposed conditions sheets.
3. The section of the narrative titled “Stormwater Management Performance Standards” states that “Project is
a redevelopment project that reduces the amount of impervious coverage on the site from existing
conditions.” However, the existing and proposed impervious areas are not described.
Findings
Based on these observations, TRC concludes that the application is not in compliance with the Stormwater
Management Regulations. Additional calculations, drawings, and documentation should be provided to demonstrate
compliance as described above. A detailed response to the review comments should be provided along with a
reference to the associated revision or supporting material.
Sincerely,
TRC
Jason M. Gold, P.E.
Manager, Civil/Site Engineering Services