HomeMy WebLinkAboutConsultant Review - 102 PETERS STREET 1/23/2012 Eggleston Env,rowneri-tal
January 23, 20l2
North Andover Planning Board
l60O Osgood Street
North Andover, MA 0l845
Attn: JodyIymon, Town Planner
North Andover Conservation Commission
l6O0 Osgood Street
North Andover, M& 01845
Attn: Jennifer Hughes, Conservation Coordinator
IIB: Storo/v'utor Management Review
lU2 Peters Street
Dear Ms. Tvmou and Ms. Hughes:
Per your request, I have conducted no initial technical review of the Site y|ou Special
Permit application for the proposed commercial dovclopousrd at 102 Peters 8bcct,
Included in the roa1cdala I received and reviewed were the following:
• S1ozozv/u1or Report, 102 Psie[m Street, prepared for I}uodcu Properties, [LC by
Andover Consultants, Inc. and dated December l4' 20ll.
• Proposed Site Plan, 102 Peters Street, 3 sheets, prepared for Dundee Properties. �
LLCby Andover Consultants Inc. and dated December l3, 2011. �
�
It is my understanding that oNotice of Intent (NOI) application for the project is being �
- �
has been filed uon000eut|v with the Conservation Commission, and that my review is
intended to assist both the Planning Board and the Conservation Commission in their
respective reviews of the project. My primary focus in this review is therefore on the
overall atornnpn1ur nuanngonuco1 approach and design concepts used in the project, as
well as its compliance with the Town uf North Andover's zoning roguircnuouto for Site
P|oo Review, the &1axnnuhoaotts Wetlands Protection Act (WyA), the North Andover
Wetlands Bylaw, and the Massachusetts Department of Environmental Protection ([)EP)
3tonnp/u1or Management Standards and Regulations.
The project site is an approximately 0.3-acre poroo| on the south eb]o of Peters 8hoot,
oJioocnt to the Andover town lino. The property is currently occupied by u single Rzooi|y
house. Dude{ present conditions upp,osbnmtc|v one-third of the existing site dcohn»
overland toward Peters Street, and the remainder drains tnthe south and vvum{, toward an
existing wetland tothe south ofthe mbo. There are un drainage structures ou the property.
The proposed plan calls for dernolition of the existing house and construction of a single-
story 2"745 s[ con000cruioi building, with o new cnira000 driveway and associated
parking. As proposed, roof runoff fi-om the building would be infiltrated directly through
m aobmur[buo infiltration system comprised of eight precast dryv/el|sto the rear /socdh\ of
32 Old FramiD8hmrnRd Unit 29 Sudbury M4 01776 tei5O8.259.1137 fax 866.820.7840
107 Peters Street, Technical Review 2
January 23, 2012
the building. Runoff from the paved parking lot in front of the building would be
collected in a slotted vane drain across the entrance driveway and a single deep sump
catchbasin and discharged through a subsurface detention/infiltration system beneath the
parking lot. Excess flow from the detention/infiltration system would drain at a controlled
rate to a single 500-gallon drywell/infiltration pit at the northwest corner of the property,
adjacent to Peters St. When the capacity of the drywell/infiltration pit is exceeded,
overflow would be discharged through the surface grate and drain onto Peters St.
My comments are outlined below:
1. The proposed project would increase the impervious cover on the site from
approximately 11 percent to about 43 percent; however it does not appear that any
serious consideration was given to the use of Low Impact Development (LID)
techniques as is required by the DEP Stormwater Standards. In particular, the use
of bioretention and/or pervious pavement would be appropriate and potentially
more effective alternatives to the best management practices(BMPs) proposed.
2. The submittal packet includes HydroCAD 8.0 analyses and a tabular summary of
the peak flow rates under pre- and post-development conditions for the 1, 2, 10 and
100-yr design storms, indicating that the rate of runoff from the site would not be
increased as a result of the project. As outlined below, I do have a number of
concerns about the hydrologic model on which this is based. In addition though,
the applicant has not addressed changes in the volume of runoff that would result
from the project, as is required by both the DEP Stormwater Standards and the
Wetlands Bylaw. Based on the calculations submitted, the proposed
drywell/infiltration pit located in the existing driveway would overflow in all of
the design storm conditions, with the excess flow draining directly onto Peters
Street. The total volume of flow discharged to Peters Street in each storm would be
approximately double what it is under existing conditions, while the volume of
runoff toward the wetland area would be about half of the present volume.
3. No credit should be taken for infiltration or storage volume within groundwater.
While the HSG B soils at the site are suitable for infiltration, it appears fi•om the
limited soils data provided that all three proposed subsurface infiltration structures
would be in or near the groundwater table during high groundwater conditions.
The DEP Handbook calls for a minimum of two feet of separation fi•om infiltration
structures to the estimated seasonal high groundwater elevation (ESHGW). This is
particularly important where the infiltration system is also being used to meet the
80 percent TSS removal requirement, as is the case for the detention/infiltration
system beneath the proposed parking area. Based on the data from Test Pit #2, the
ESHGW would be approximately commensurate with the invert of the
detention/infiltration system, providing no separation or dead storage during high
groundwater conditions.
4. Neither of the two test pits conducted on the site were within the locations
proposed for infiltration and, in the case of the overflow drywell/infiltration pit, the
107 Peters Street, Technical Review 3
January 23, 2012
closest test pit is 75 ft away and four feet higher in elevation. Site specific testing
within each proposed infiltration location will be needed prior to system
installation to verify soil suitability and ensure adequate depth to groundwater
and/or bedrock.
5. The proposed project calls for the infiltration BMPs to attenuate large storm flows
(10-yr and larger), therefore the DEP standards require that a mounding analysis be
performed since the separation to seasonal high groundwater is less than 4 feet. In
the event that a calculated mound reaches the infiltration structure, additional
storage volume would be lost.
6. It is not clear why the overflow drywell/infiltration pit is modeled with an
exfiltration rate of 0.17 inches/hr, rather than the 0.52 inches/hr used elsewhere.
Are the soils different in that location, or is the reduced infiltration rate based on
the fact that the drywell is located beneath the existing driveway, therefore the
soils may be compacted?
7. The rate of flow fi-om the proposed detention/infiltration system in the HydroCAD
analysis appears to be driven more by the modeled tailwater conditions in the
downstream drywell (with its limited exfiltration capacity) than by the outlet
orifice. I recommend running the analysis without the tailwater conditions to better
assess the effectiveness of the detention system.
8. In accordance with the DEP handbook, exfiltration from the three infiltration
structures should be modeled over bottom area only, not the wetted area.
9. It appears that post-development subcatchment "Developed 2" in the HydroCAD
model should be routed to Pond P1 (the catchbasin), rather than directly to the
subsurface detention system.
10. The pavement area in post-development subcatchment "Developed 2" should have
a CN of 98, not 95.
11. The stone depth in the proposed detention/infiltration system is modeled as being
192.25 ft high, it should be 4.25 ft.
12. Consideration should be given to raising the outlet invert from the subsurface
detention system to increase the dead storage volume in the system and enhance
infiltration.
13. The overflow drywell/infiltration pit closest to Peters St is modeled as having a rim
elevation of 188.8, but the plan shows a rim elevation of 189.9 and the detail gives
a rim elevation of 188.9.
14.As indicated above, the proposed treatment train (deep sump catchbasin followed
by infiltration) does not meet the 80 percent TSS removal requirement because
107 Peters Street, Technical Review 4
January 23, 2012
there is not adequate separation to groundwater. In addition, however, there is a
high rate of failure of subsurface infiltration structures where there is only minimal
pretreatment such as is proposed for this project. Consideration should be given to
either augmenting the solids removal provided before infiltration, or implementing
a more aggressive sweeping program to reduce the solids loading to the drainage
system.
15.The drywell details shown on Sheets 2 and 3 should be labeled as to which system
they correspond to.
16. The ESHGW elevation should be shown on each infiltration system detail.
17. The depth of stone under the detention/infiltration system should be shown on the
design details.
18.The outlet pipe from the proposed drain manhole is shown as being 8 inches on the
DMH detail, and 10 inches on the drywell detail.
19. Inspection ports are needed on the detention/infiltration system, and inspection of
that system included in the O&M Plan.
20. The O&M Plan should include an O&M schedule and log form (for long-term
maintenance tasks) as required per the DEP regulations. I generally find it useful to
include a simple sketch plan showing the locations of the BMPs to be maintained.
21.The Long Term Pollution Prevention Plan calls for snow to be stored just off the
edge of pavement; hence most of the snowmelt will bypass the stormwater
treatment train.
22. The proposed project will not entail disturbance of more than one acre, thus it is
not subject to coverage under the EPA Construction General Permit. The
Construction Period Pollution Prevention and Erosion and Sediment Control Plan
should identify proposed stockpile locations and identify measures to protect the
proposed detention/infiltration area during construction.
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
f
r
Lisa D. Eggleston, P.E.
������������ �K���^�����������K
_ ' - _ . - .
February 24 2012
North Andover Planning Board
]d00 Osgood Street
North Andover, MA 0l045
A1 o: JndyTyoonn, Town Planner
North Andover Conservation Commission
1600 Osgood S1zuct
North Andover, M/\ 0l845
Attn: Jennifer Hughes, Conservation Coordinator
|0I: Stnnuvvutcx Management Review
102 Peters Street
Dear Ms. 7vroou and Ms. Hughes:
In follow up to my previous comments of January 23 m and February 7"', l have received
and reviewed the ±ol|ovvhog revised plans and documentation prepared by Andover
Consultants oo the above-referenced project:
N Suyp\cnoccd to Storoufo1er Report, 102 Peters 81,cot' prepared for [)uudoo
Properties, I.LCby Andover Consultants, Ioo,, dated January 25. 20l2.
m Proposed Site Plan, 702 Peters Skruct, 3 sheets, prepared for Dundee Properties,
l.I.0 by Andover Consultants Inc. revised through February 22, 2012. [LsUoo1
version received o\sctrouico|k).
I have also had acvoro} telephone conversations with Jim Fokn/oo1bcr of Andover
Consultants regarding the project.
My comments are outlined below:
l. The design revisions on|| for moving the overflow dryweU approximately 35 feet �
back on the site (away from Peters 81retA and incorporating an overflow mwa|o �
with a stone trench to further enhance infiltration and direct the overflow onto the |
shoulder of Peters Street. This should mitigate any increases in runoff Volume �
generated by the development and prevent the direct discharge of flow onto Peters �
Street. It will also provide some degree of treatment for snop/nmck off of the west �
side of the proposed parking area.
2. The Qtoroovvaio|'Report should be revised to reflect the rnodifloutb»oa to the outlet
design. Cu|ou|utod storage in the outlet dryn/uU and overflow trench should be
Unndud to that which in above the |BSllGW level in that location, so that the
modeled discharges are representative of"worst case" conditions. Based on the
existing gcudom on the site and the ESf{(3VY elevation in the two teat pits, it
appears that this would bo somewhere around elevation |88.O.
3Z Old F[a0inghannRd Wit l9 Sudbu[yMA 01776 tet5O8.259.11]y fax 866.820.7840
107 Peters Strect, Technical Review 2
February 24, 2012
3. During periods of seasonal high groundwater there will be no dead storage in the
detention system beneath the parking lot, hence no water quality treatment via
infiltration. It is my understanding that the overflow trench has been designed to
capture and infiltrate the water quality volume, however calculations are needed
to demonstrate this.
4. The plans should show the perimeter drain proposed for the collection and
conveyance of roof runoff.
5. A design detail of the overflow swale/trench is needed. The side slopes of the
swale should be vegetated or otherwise stabilized. I have not seen the landscaping
plan, but presume that it may also need to be revised to show the swale.
6. I suggest rewording item #3 in the O&M Plan to say that the catchbasins should
be cleaned when the sediment level is within two feet of the outlet pipe; this is
easier to measure than the depth of sediment accumulated. The O&M Plan should
also include maintenance of the overflow swale/trench.
Once again, 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: Jim Fairweather, Andover Consultants