HomeMy WebLinkAbout20231101_HW_SWPeerReview_HSA Response - - HANCOCK
ASSOCIATES
,!Wurvoyors ScieirniW.
November 1, 2023
Ms.Jean Enright, Planning Director
North Andover Planning Board
120 Main Street
North Andover, MA 01845
Dear Ms. Enright and Board Members,
On behalf of Home Grown Lacrosse, LLC, Hancock Associates hereby submits this response to Horsley
Witten Group's initial stormwater peer review letter regarding 492 Sutton Street dated October 18, 2023.
Comments issued by the various departments are shown below with Hancock Associates' responses italicized
and in red.
Stormwater Management Design Peer Review
In accordance with the North Andover Zoning Bylaw§195-8.14. E. (8)A Stormwater management plan is
required for all site plan review applications. The stormwater management plan shall be prepared in accordance
with the latest version of the Massachusetts Stormwater Handbook(MSH) and demonstrate full compliance
with the Massachusetts Stormwater Standards and the North Andover Stormwater Management and Erosion
Control, Chapter 165 of the Town Bylaws. Chapter 165 further references Chapter 250. Stormwater
Management and Erosion Control.
HW offers the following comments concerning the stormwater management design. We have used the
Massachusetts Stormwater Standards as the basis for organizing our comments.
However, in instances where the additional criteria established in §250-27 of the North Andover Code requires
further recommendations; we have referenced these as well.
1. Standard 1:No new storm water conveyances (e.g., outfalls)may discharge untreated storm water
directly to or cause erosion in wetlands or waters of the Commonwealth.
a. The Applicant has evaluated two discharge points from the project site. Under existing conditions
stormwater from Subcatchment 1S flows northwest towards Terminal Road. Stormwater from
Subcatchment 2S flows southeast towards Old Clark Street.The existing site consists of grass and
woods.There are no existing stormwater practices.
HSA Response:Acknowledged.
b. The Applicant proposes to construct a porous pavement parking lot with a subsurface reservoir to
infiltrate runoff from the proposed building roof and parking lot.The reservoir overflows to the
municipal stormwater system on Sutton Street.The remainder of the site flows into the Terminal
Road and Sutton Street/Old Clark Road drainage system.The site is not discharging to wetlands or
waters of the Commonwealth.
HSA Response:Acknowledged.
2. Standard 2:Stormwater management systems shall be designed so that post-development peak
discharge rates do not exceed pre-development peak discharge rates.
a. In accordance with §250-22 B. (6) a summary of pre-and post-development peak rates and
volumes of stormwater demonstrating no adverse impacts should be provided as part of the
narrative.The Applicant has provided the peak flows and the peak volumes for the 2-year, 10-
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year, 25-year, and 100-year storm events under Documenting Compliance in the Stormwater
Management Report. HW recommends that the Applicant provide a revised table if needed
based on the comments below.
b. In accordance with §250-22 B. (5) (a) a summary of proposed land area to be disturbed and
existing and proposed impervious area should be provided as part of the narrative. HW
recommends that the Applicant include the proposed land area to be disturbed and the
existing and proposed impervious area in the narrative.
HSA Response: A land disturbance summary has been added to the starmwater report
(Background Information,part C').
Total Disturbance=88,000 S.F±
New Impervious=599,515 S,F
c. The Applicant has modeled the porous pavement with a 597-minute time of concentration
(Tc) and then routed it through a pond. HW does not agree with this methodology.The
stormwater should flow through the porous pavement quickly and then will be held in the
pond for an extended period as it infiltrates. Including the lengthy Tc and the pond is
doubling the affect that the porous pavement will have. HW recommends that the Applicant
revisit the model or justify its methodology.
HSA Response: The intent of modelling an extended Tc was to represent the impact of the
multiple courses of materials in providing treatment and attenuation to flow through the
system. The Tc value of the porous pavement subcatch ent has been reduced to a standard 5
minutes to reflect water quickly flowing through the porous layer of the pavement. In doing
this however, it eliminates the benefits of the porous pavement system in regards to
attenuation. In order to accurately model the effects of the overlaying courses of material to
the reservoir course a modified CN is used rather than a C'N=98 which would essentially model
the porous system as a parking lot free flowing to a conventional infiltration practice such as
underground chambers which is not an accurate representation.
To determine a CN for special conditions the SC'S equation for potential maximum retention
can be utilized. Porous Cross Section Void Ratio Depth S=VR x D
4"porous pavement n/a n/a n/a
4"crush stone 0.4 4 1.6
1000 10 12"BR gravel 0.3 12 3.6
CN 3"peastone 0.4 3 1.2
where S is in inches
7S=6.4
Rearranged: 1000
1000 CN =6.4+10
CN =
S + 10
CN= 60.98
= 61
The main issue with attempting to model porous pavement is that programs such as
HydroC'AD can effectively model volume reduction or peak reduction but not bath. To
estimate bath the volume and peak reductions the modified CN is used since there is currently
no way to simultaneously model lag time through the system AND have a 6 minute Tc
through the permeable pavement layer. Modifying the CN as shown above►Weill estimate the
weak flow reduction but will not estimate the outflow volume since volume is being last by
modeling the subcatchment with a louver CN value.
The previously submitted report accurately represented volume going into the system due to
the 98 CN but relied on are extended lag time to reflect the impacts of the system on freak
outflow. The revised HydroCAD worksheets provide peak reduction calculations using the
modified CN=61 for the porous pavement subcatchment.
d. The Applicant has provided a detail for the porous pavement. HW has thefollowing
comments:
i. Note#10 in the General Construction Sequence—Porous Pavement calls for 6
inches of 3/4"to 1" diameter stone. However, the figure and schedule of
elevations show the depth to be 8 inches. HW recommends that the Applicant
revise the depth listed in the note.
HSA Responses!vote#10 updated to reflect 8"reservoir depth.
ii. HW recommends that the Applicant add the installation of the underdrains,
cleanouts, and OCS to the General Construction Sequence—Porous Pavement.
HSA Response:installation instructions have been added to the construction
sequence of the porous pavement for underdrains, cleanouts, and OCS.
iii. The figure calls out 4" SCH40 4" Perf. Pipe for the underdrain. However,the
Porous Pavement Area Connections and Grading & Drainage Plan call for 6"
Perforated ADS Pipe. HW recommends that the Applicant revise the detail
accordingly.
HSA Response:Detail updated to show 6"perforated ALAS pipe.
iv. HW recommends that the Applicant confirm if inspection ports are proposed for
the porous pavement area and show their locations on the Grading& Drainage
Plan.
HSA Response: inspection ports are shown at the each underdrain intersection
on the GDU sheet and ore noted in the C?&M plan for the porous pavement.
V. It appears that the reservoir layer for the porous pavement extends beyond the
surface porous pavement area. HW recommends that the Applicant explain the
installation process for this section of the stormwater practice and confirm if
additional instructions or details are necessary on the plans.
HSA Response:(Vote added to GDU sheet
e. The porous pavement reservoir is proposed to overflow into the proposed OCS and be piped
to a proposed offsite drain manhole.The connecting pipe is located very close to an existing
catch basin (RIM = 153.88) on Old Clark Street. It is unclear how the existing catch basin ties
into the street drainage system. HW recommends that the Applicant verify that the proposed
pipe has adequate separation from the existing catch basin and that it does not conflict with
the existing street drainage system. HW further recommends that the Applicant confirm that
the North Andover Department of Public Works has reviewed the proposed drain manhole
and the connection to the municipal system.
HSA Response.- The edge of the proposed pipe is located 6 feet away from the center of the
existing catch basin, assuming a standard 4 foot inner diameter structure, this leaves adequate
room to install the proposed pipe. Plans have also been submitted to the North Andover DPW
for review and comment.
f. The Applicant has provided existing and proposed subcatchment plans. HW recommends
that the Applicant include the Tc Flow Paths for the existing subcatchment plan.
HSA Response: Tc flow paths have been added to fare and Rost development subcatchment
plans.
g. HW recommends that the Applicant provide a typical pavement detail for the proposed driveway.
HSA Response:Bituminous concrete crass-section detail added to Detail sheet 2 of 2
h. The Applicant has provided a grass swale detail. HW recommends that theApplicant label
the proposed grass swale on the north side of the site.
HSA Response: Grass swale label added to GDU sheet.
i. The Applicant has provided a typical plan view detail for the outlet control structure (OCS).
HW recommends that the Applicant provide the cross-section detail for the OCS as well.
HSA Response: Cross section detail has been added to CICS detail.
j. The proposed HydroCAD model for the porous pavement uses a 4-foot sharp crested
rectangular weir for the OCS. HW recommends that the Applicant add this dimension to the
OCS detail.
HSA Response:4-foot weir labeled in OCS detail.
k. The Applicant has provided a Cape Cod berm detail. HW recommends that the Applicant
clarify where Cape Cod berm is proposed on the site and call it out in the plans.
HSA Response: Curbing has been added to the driveway entrance and shown on all sheets of
the plan set.
I. The Applicant has used precipitation values equal to or greater than the values provided by
National Oceanic and Atmospheric Administration (NOAA) Atlas 14 for the 24-hour storm
events, as outlined in §250-23 E. (19). No further action required.
HSA Responses Acknowledged
3. Standard 3 requires that the annual recharge from post-development shall approximate
annual recharge from pre-development conditions.
a. The Applicant has provided recharge volume and drawdown calculations. HW recommends
that the Applicant provided the stage storage data for the porous pavement system to
confirm the volume provided below the lowest outlet(elevation 159.52).
HSA Responses Stage storage table has been added to the stormwater report showing storage
volume equal to 4,933 CF at elevation 159.52.
b. The separation from the bottom of the porous pavement system to the Estimated Seasonal
High Groundwater(ESHGW) is 2 feet.The Applicant has provided a mounding analysis. It
appears that mounding will not affect the recharge and drawdown provided by the proposed
porous pavement system. HW has no further comment.
HSA Response:Acknowledged
4. Standard 4 requires that the storm water system be designed to remove 80% Total Suspended
Solids(TSS)and to treat 1-inch of volume from the impervious area for water quality.
a. The Applicant has provided a TSS worksheet that lists the porous pavement to provide the
90%TSS removal per the Town's requirements.According to MA MS4 General Permit
2.3.6a.ii.3.a3.2, the TSS removal efficiency of porous pavement is 90% if the storage bed is
sized to retain 1" water quality volume drained within 72 hours. HW recommends that the
Applicant address the comments under Standard 3 to satisfy this requirement.
HSA Response:Acknowledged
b. Per§250-23 B. (1)the Applicant is required to remove 60%of the average annual load of
Total Phosphorus.The Applicant has noted that it removes 62%of the Phosphorus load via
the 12-inch filter course in the porous pavement according to the MA MS4 General Permit
Table 3-22 of Appendix F, Attachment 3.The Applicant has provided sufficient phosphorus
removal. No further action required.
HSA Response:Acknowledged
c. The Applicant has noted in its narrative that the proposed stormwater system has been
designed to treat one inch of water quality volume. Per§250-23 B. (1)(b) new developments
are required to retain the volume of runoff equivalent to one inch multiplied by the total
post-construction impervious surface or meet a combination of retention and treatment
that achieves the above standards listed under§250-23 B. (1). It appears that the criteria
have been met. No further action required.
HSA Response:Acknowledged
5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads
(LUHPPL).
a. The project is not considered a LUHPPL. Standard 5 is not applicable.
HSA Response:Acknowledged
6. Standard 6 is related to projects with storm water discharging into a critical area, a Zone ll, or an
Interim Wellhead Protection Area of a public water supply.
a. A portion of the project site closest to Old Clark Street is within the North Andover
Watershed Protection District. In accordance with §195-4.19. B. (4)All construction in the
Watershed Protection District shall comply with best management practices for erosion,
siltation, and stormwater control in order to preserve the purity of the groundwater and the
lake, to maintain the groundwater table,and to maintain the filtration and purification
functions of the land. HW has listed comments under Standard 8 regarding erosion control
practices for the project site.
b. The existing conditions plan indicates that the boundary of the Watershed Protection District
is through the middle of the project area.The proposed site layout illustrates the Non-
Discharge Zone Watershed protection District only minimal crossing the project area. HW
recommends that the Applicant clarify where the boundary is on the siteplans.
HSA Response:Existing conditions plan and site plan have been revised to show both general
Watershed Protection District and lion-Discharge Zane Watershed Protection District.
7. Standard 7 is related to projects considered Redevelopment.
a. The project is considered new development. Standard 7 is not applicable.
HSA Response:Acknowledged
8. Standard 8 requires a plan to control construction related impacts including erosion,
sedimentation, or other pollutant sources.
a. The Applicant has included an erosion control barrier along the lease limit of the site and
catch basin inlet protection to the Grading and Drainage Plan. HW recommends that the
Applicant create an Erosion &Sediment Control Plan on a separate sheet in the plan set.The
Erosion &Sediment Control Plan should also include a stabilized construction entrance and
temporary stockpile locations.
HSA Response: Temporary stabilized construction entrance has been added to the Erosion and
Sedimentation Control Plan.
b. HW recommends that the Applicant include the Limit of Work (LOW) on alldrawings
within the plan set.
HSA Response:Limit of Work has been labeled can all sheets of the plan set.
c. The Applicant has provided a straw wattle detail that also shows a silt fence. HW
recommends that the Applicant add more information about silt fence installation to the
detail.
HSA Response:Additional detail for silt fence installation has been added to the Erosion and
Sedimentation Control Plan.
d. According to the HydroCAD models,the Applicant proposes to decrease the woods on site by
approximately 6,000 sf. HW recommends that the Applicant demonstrate which trees are
proposed to be removed and which trees will be protected on the plans.
HSA Responses Proposed tree line has been added to the GDU sheet. Proposed limit of work
shall serve as the limit of clearing.All trees outside of the limit shall be protected.
e. HW recommends that the Applicant add a note stating, prior to any land disturbance
activities commencing on the site,the developer shall physically mark limits of no land
disturbance with tape, signs, or orange construction fence, so that workers can seethe
areas to be protected.The physical markers shall be inspected daily.
HSA Response:Note stating that physical markers shall be installed prior to any construction
activity has been added to the Erosion and Sedimentation Control Plan.
f. The Applicant is proposing to disturb more than one acre of land. In accordance withthe EPA
Construction General Permit, the Applicant is required to file a Notice of Intent with the EPA and
prepare a Stormwater Pollution Prevention Plan (SWPPP). HW recommends that the Applicant
provide the Town of North Andover with a copy of the SWPPP a minimum of 14 days prior to land
disturbance.The Planning Board may choose to require receipt of the final SWPPP signed by the
contractor as a condition of approval.
HSA Response: Note stating that the contractor shall be responsible for filing a CPG with the EPA no
less than 30 days prior to the anticipated land disturbance over one(1) acre.
9. Standard 9 requires a Long-Term Operation and Maintenance(O& M)Plan to be provided.
a. The Applicant has provided an Operation and Maintenance Plan in the Stormwater
Report. HW recommends that the O&M Plan become a standalone document to be
signed by the owner.
HSA Response; O&M plan has been removed from the stormwoater report and shall be
submitted as a standalone document.
b. The Applicant has included the pervious pavement as a maintenance item in theO&M Plan.
HW recommends that the Applicant clarify if inspection ports are proposed and mention
them in the O&M Plan.
HSA Response; The monitoring and inspecting of proposed inspection ports has been noted
in the O&M Plan under the Porous Pavement item: "Inspect surface and inspection ports
after storm events to insure proper drainage"
c. HW recommends that the Applicant include the maintenance of the OCS and roof drains in
the O&M Plan.
HSA Response; Outlet control structure and roof drain leader operation and maintenance
plans and lags have been added to the O&M Flan.
d. HW recommends that the Applicant include a budget in the O&M Plan.
e. HW recommends that the Applicant provide a simple plan, drawn to scale clearly noting all
stormwater practices requiring long term maintenance.
10. Standard 10 requires on Illicit Discharge Compliance Statement be provided.
a. The Applicant has provided an Illicit Discharge Compliance Statement in the Stormwater
Report. HW recommends that the Town require the submission of the Illicit Discharge
Statement signed by the property owner prior to discharge of stormwater to post-
construction best management practices as a condition of approval.
HSA Response:Acknowledged