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June 8, 2016
North Andover Planning Board
1600 Osgood Street
North Andover, MA 01845
Attn: Rebecca Oldham, Staff Planner
RE: Stormwater Review
North Andover DPW Building Improvements, 384 Osgood Street
Dear Ms. Oldham and Board Members:
Per your request, I have reviewed the following materials submitted in support of a Site
Plan— Special Permit Application for the above-referenced project:
■ Site Plans (Sheets SP-1, LP-1.1, A 1.1-A 1.3, & El), Improvements to the Public
Works Building,prepared by CSS Architects Inc. and Linden Engineering, dated
6 May 2016.
■ Civil Site Plans (Sheets C-1 through C-61)), Improvements to the Public Works
Building, prepared by CSS Architects Inc. and Linden Engineering, dated 27 May
2016 (electronic pdf version).
■ Plan of Land in North Andover, prepared by Christiansen& Sergi, Inc. and dated
5/22/16 (electronic pdf version).
■ Site Plan (Sheet C.01), prepared by Woodard& Curran, dated February 2016 and
revised 4/25/16 (electronic pdf version).
■ Stormwater Report, Town of North Andover Department of Public Works,
Improvements to the Public Works Building, 384 Osgood St, dated May 27, 2016
(electronic pdf version, preparer unknown).
I also conducted a brief site visit on June 2, 2016 to observe existing drainage patterns.
My primary focus in this technical review is on the overall stormwater management
approach and design concepts used in the project, as well as its compliance with the
Town of North Andover's Site Plan Review regulations, the Massachusetts Department
of Environmental Protection (DEP) Stormwater Management Standards and Regulations,
and the North Andover Wetlands Bylaw. It is my understanding that a Notice of Intent
(NOI) application for the project has been filed concurrently with the Conservation
Commission. My review is aimed at assisting both boards in their respective reviews of
the project.
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The project site is an approximately 3.58-acre parcel at the intersection of Osgood Street
and Wayne Street. It is currently occupied by the North Andover Department of Public
Works and includes a large storage/office building with associated parking, salt storage
building, vehicle fueling depot and exterior materials and equipment storage. There are
presently only a few drainage structures along the western (Wayne Street) edge of the
site, which discharge via a 36-inch drain across the site toward Cochichewick Brook to
the north. The site is relatively flat and much of the drainage is overland directly to the
adjacent wetlands to the north and west.
The proposed Base Bid plan calls for a two-story addition to the existing building and
reconfiguration of the existing parking area. As proposed, runoff from the new parking
area would be collected in a closed drainage system with deep sump catchbasins and
drain through a Stormceptor treatment unit prior to discharge via a new outall to the
wetlands associated with Cochichewick Brook. Roof runoff from the building addition
would also be drained through the Stormceptor unit and discharged through the new
outfall.
The work proposed under the Alternate Bid includes removal of the existing storage
building and construction of a new salt shed as well as regrading and repaving of the
areas surrounding the new shed. As proposed, the runoff from a portion of the pavement
area would be collected in a closed drainage system with deep sump catchbasins and
drain through a Stormceptor treatment unit prior to discharge via a new outall to the
wetlands associated with Cochichewick Brook.
My comments on the propsed design are outlined below. Please note that these comments
should be considered preliminary at this time, as I have not yet had the opportunity to
review the full Conservation Commission submittal packet:
1. The proposed project qualifies as a redevelopment project under MA Stormwater
Standard 7, hence it is required to comply with Standards 2 and 3 and the
pretreatment and structural best management practice requirements of Standards
4, 5 and 6 only to the maximum extent practicable. However, as set forth in the
DEP Stormwater Handbook, "to the maximum extent practicable" means that the
proponent has made all reasonable efforts to fully meet all of the Standards, and
that the highest practicable level of stormwater management for the project is
being implemented. In addition, all redevelopment projects are required to
improve existing conditions. Based on the plan submitted, the proposed project
would likely not increase the rate of runoff from the site and would provide some
improvement in the water quality of the runoff discharged through the two new
outfalls. I also concur that the recharge of stormwater is neither feasible nor
appropriate for this site. As is described further in my comments below however,
the proposed plan would not provide full compliance with the Stormwater
Standards and I do not believe that the Applicant has satisfactorily demonstrated
that full or at least better compliance is not practicable.
2. The proposed drainage design includes inline Stormceptor proprietary separators
as the sole BMP to treat the runoff discharged through the two new outfalls, and
the TSS calculations assume a removal rate in the of 80% TSS in the units. Based
on data presented by Tom Maguire of MassDEP and Jerry Schoen of MaSTEP in
their 2013 workshop on evaluating proprietary separators
(http://www.mastep.net/documents/MassDEP—Evaluating Nonrated—Stormwaterrmwater
_Treatment.pdf), a more realistic TSS removl rate for proprietary separators in
general is somewhere in the vicinity of 25-50 percent, but even this does not take
into account the presence of upgradient catchbasins, which would already have
removed some of the same coarse sediments that are most effectively treated in
the Stormceptor units. The Stormwater Handbook (Volume 2, Chapter 2, pg 10)
states that proprietary separators must be used for pretreatment and be placed first
in the treatment train to receive TSS removal credit. Proprietary separators may
be used as treatment BMPs in redevelopment projects where it has been
demonstrated that suitable alternatives do not exist, however no documentation of
alternatives considered was included in the materials I reviewed. With the
proposed addition of the two new outfalls I also don't believe that the proposed
stormwater management for the site would comply with Stormwater Standard 1,
since it specifically states that "no new stormwater conveyances (e.g. outfalls)
may discharge untreated stormwater directly to or cause erosion in wetlands or
waters of the Commonwealth."
3. Per DEP criteria, the separators would need to be placed in an offline
configuration to maximize treatment effectiveness and prevent carryover of
accumulated sediments.
4. As proposed, roof drainage from the building addition would be discharged
through the Stormceptor unit located in the front parking area. Since roof drainage
is considered clean it does not need to be treated, hence the addition of this flow
would merely reduce the Stormceptor's effectiveness in treating the pavement
runoff.
5. The Alternate Bid portion of the project site constitutes a Land Use with Higher
Potential Pollutant Loading (LUHPPL) therefore the Stormceptor treating runoff
from that area needs to be sized for a one-inch water quality volume on an
equivalent flow basis.
6. It is not clear from the plan where the roof runoff from the new salt shed would be
discharged.
7. As proposed, only a portion of the runoff from the Alternate Bid portion of the
site would undergo any stormwater treatment; the majority of the runoff would
continue to drain untreated to adjacent wetland areas. Again, no documentation of
alternatives considered or demonstration that the proposed plan constitutes
compliance to the "maximum extent practicable" has been provided in the
materials I reviewed. As these areas contain some of the dirtiest operations of the
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site in terms of stormwater quality I believe that significantly more can be done to
improve existing conditions both through the addition of stormwater BMPs and
operational improvements aimed at minimizing pollutant sources.
8. In addition to structural BMPs, Stormwater Standard 4 requires a Long Term
Pollution Prevention Plan identifying suitable practices for source control and
pollution prevention, and Stormwater Standard 5 requires the implementation of
source controls and pollution prevention measures on the LUHPPL to eliminate or
minimize pollutant exposure to stormwater. Redevelopment projects are not
exempted from complying with these requirements fully. If the Town already has
a Pollution Prevention Plan for Municipal Operations as is required by EPA's
NPDES Phase 2 Permit for Small MS4s that should fulfill the requirements of
Standards 4 and 5, however there was no reference to such a plan in the materials
I reviewed and it does not appear that one is currently being implemented on the
site. The "Good Housekeeping BMPs" included with the O&M Plan are generic
and not specific to the operations on the site.
9. It is unclear why the plan calls for a portion of the pavement to the north of the
new salt shed to be removed and replaced with a gravel surface. If these areas of
the site are to continue to be used for materials and equipment storage an
impervious surface is more easily swept to remove excess sediments etc. and
provides more opportunity for spill control and containment.
10. The catchbasin outlet hood should be specified on the plan; I recommend the
LeBaron Snout or Eliminator brands.
11. If the Alternate Bid is included, the proposed project would entail the disturbance
of more than one acre of land and be subject to EPA's NPDES Construction
General Permit (CGP). Prior to the initiation of work the selected contractor will
need to file a Notice of Intent for coverage under the CGP, and prepare a
Stormwater Pollution Prevention Plan (SWPPP) to be implemented during
construction. This requirement should be clearly noted on the plans. The
Conservation Commission may also want to require proof of filing of the NOI and
the opportunity to review the SWPPP prior to the start of work.
12. I have the following comments on the Operation and Maintenance (O&M) Plan
included in the Stormwater Report:
■ Short-term, construction related measures should be removed from the O&M
Plan and included in a separate construction SWPPP. The long-term plan
should be structured as a standalone document to be maintained on site.
■ Catchbasins on the site should be inspected at least 4 times per year and
cleaned a minimum of once per year, not just when sediment thresholds are
reached.
■ Stormceptor units should also be cleaned a minimum of once per year, with a
vacuum truck.
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■ The plan should include a maintenance checklist and a simple figure showing
the locations of all stormwater BMPs to be maintained.
■ Designated snow storage locations should also be shown on the plan/figure.
To the extent possible, snow storage should be located upgradient of the
stormwater BMPs.
13. Stormwater Standard 10 prohibits all illicit discharges to the stormwater
management system and requires proponents to submit an Illicit Discharge
Statement demonstrating that no illicit connections exist on the project site.
Redevelopment projects must fully comply with this requirement, and must also
document all actions taken to identify and remove illicit discharges, including,
without limitation, visual screening, dye or smoke testing, and the removal of any
sources of illicit discharges to the stormwater management system. This
requirement has not yet been met for this project. Since the proposed plan calls
for portions of the existing drainage infrastructure and some of the buildings to
remain on the site they will need to be thoroughly investigated before such a
statement can be made.
I appreciate the opportunity to assist the North Andover Planning Board and
Conservation Commission with the review of this project, and hope that this information
is suitable for your needs. Please feel free to contact me if you or the applicants have any
questions regarding the issues addressed herein.
Sincerely,
EGGLESTON ENVIRONMENTAL
Lisa D. Eggleston, P.E.
C: Jennifer Hughes, Conservation Coordinator