HomeMy WebLinkAboutCorrespondence - 1600 OSGOOD STREET 6/28/2005 Marchlonda m Mimp COPY
& Associates, L.P.
Engineering and
Planning Consultants RECEIVED
June 28, 2005 JUN 2 9 2005
Eggleston Environmental NORTH ANDOVER
55 Old Coach Road CONSERVATION COMMISSION
Sudbury, MA 01776
Attn: Lisa Eggleston, P.E.
RE: Stormwater Management Review:
1600 Osgood Commerce Center,Building 20 & 21 Parking Lot
Dear Ms. Eggleston,
Marchionda & Associates, L.P. is in receipt of your June 24, 2005 comment letter to the
North Andover Conservation Commission regarding the subject project. We offer the
following responses and attached supplemental information in response to the comments.
Our responses (italicized) follow each of the comments below:
Standard#1. Untreated Stormwater
Standard #1 prohibits any new discharges of untreated stormwater to wetland resource
areas of the Town of North Andover, whereby treated stormwater is defined to the
stormwater that meets the requirements in Standards 2 through 9. As currently proposed,
most of the runoff flows from the paved areas of the project site would be routed through
deep sump catchbasins, a Stormceptor unit and an extended detention pond prior to
discharge. The remaining paved areas would be routed through at least one of these
BMPs prior to discharge. The adequacy of the treatment provided by these BMPs is
addressed under Standard#4. No response required
Standard#2. Post-Development Peak Dischg&e_Rates
The North Andover regulations require that post-development peak discharge rates for
the 1, 10 and 100-year storm events do not exceed pre-development peak discharge rates.
The state standards require this of the 2 and 10-year 24-hour storm events, with
evaluation to determine that the 100-year event does not cause increased flooding impacts
offsite. The North Andover regulations also call for a sub-watershed delineation of the
site, including the peak flow rate, time of peak flow and the volume of runoff at each
discharge point, to be used as a basis for the hydrologic analyses.
The NOI package includes a hydrologic analysis based on modeling conducted using the
Hydraflow model for the 1, 2, 10 and 100-year design storms, which indicates that the
62 Montvale Avenue Tel: (781) 438-6121
Suite I Fax: (781) 438-9654 website: http://www.marchionda.com
Stoneham, MA 02180 Email: mail@marchionda.com
Lisa D. Eggleston, P.E.
Marchlonda June 28, 2005
& Associates, L.P. Page 3 of 10
Engineering and
Planning Consultants
approximately 15,000 cubic feet and 45,000 cubic feet, respectively, both of
which are also insignificant compared to the total volume. As such, we do not
feel that the proposed project will affect the hydrology or flooding potential of
either wetland.
2. It is not clear how the infiltration system is being modeled, as the maximum
elevation reached and the associated storage volumes listed in the model output
are not consistent with the design plans.
The recharge area has been designed to allow stormwater to fill the infiltration
chambers prior to discharging to the downstream detention basin. Our primary
goal in modeling the recharge area was to accurately model the storage volume,
discharge volume, and peak discharge from the chambers into the proposed
detention basin. For the purposes of modeling, we simplified the input
parameters for the recharge area by assuming it to be a small rectangular basin
with vertical side slopes having a volume equivalent to the volume of the
chambers plus the void space of the surrounding stone. In order to account for
the overflow into the proposed downstream detention basin, we assumed a large
broad-crested weir (just for purposes of modeling) in order to minimize head
build-rip above the overflow elevation (thus stabilizing the assumed storage
volume). Had we assumed a smaller overflow structure, the model would have
built-up too much head over the spillway elevation which would have
incorrectly increased the storage volume and resulted in an inaccurate model
run. The maximum elevation listed in the modeling output data for the
infiltration area is therefore irrelevant (the water level in the chambers will
actually peak out at the elevation of the top of stone above the chambers).
With regard to the volumes listed in the output data, they indicate the volume of
water discharged from the chambers to the downstream detention basin, not the
volume of the recharge system.
Standard#3. Recharge to Groundwater
Standard #3 requires that the annual groundwater recharge from the post-development
site should approximate the annual recharge from the pre-development site, based on pre-
development soil conditions.
The NOI submittal includes infiltration volume calculations based on 138,600 acres of
net impervious area being added to the site in areas of HSG A and C soils. The calculated
recharge volume required is 2,888 cubic feet.
Lisa D. Eggleston, P.E.
Marcnionda
June 28, 2005
& Associates, L.P. Page 5 of 10
Engineering and
_°-rte' Planning Consultants
the highly permeable soils in the vicinity of the proposed chambers, it is
anticipated that the actual "capacity" (i.e. including recharge that takes place
during the duration of the storm event) would likely far exceed the volume of
the chambers and void space of the stone and would more than overcome the
volume lost above the pipe invert(it should be noted that this volume will in fact
be utilized in cases where the depth of flow in the outlet pipe to the detention
pond is 4" or more). However, in order to eliminate any concern that the
capacity of the chambers is too small, we have lowered the elevation of the
recharge system by four inches so that the top of the stone layer is just below
the invert of the pipe into the detention pond.
3. Site specific soil testing data is needed to confirm infiltration rates, depth to
groundwater, depth to bedrock, and general suitability for infiltration at the
proposed recharge system location, and also to support the assumption of 50
percent HSG A and 50 percent HSG C soils used in the calculations. The drainage
report indicates that soil testing has been conducted, but the soil logs and test pit
u.
locations were not included in the materials I reviewed.
Soil test pit and percolation test information is attached.
4. The applicant needs to provide calculations demonstrating that recharge facilities
will be totally dewatered within 72 hours following a storm event.
The total depth of the recharge system (including stone layers) is 42 inches.
The minimum percolation rate in order to infiltrate the entire depth in 72 hours
would be approximately 0.6 inches/hour. Based on the actual percolation data
(attached) and the results of the test pits conducted in the vicinity of the
proposed recharge area (also attached), the actual percolation far exceeds the
required percolation. Thus, this condition will easily be met.
5. DEP design guidelines for subsurface infiltration systems call for a setback of 100
feet from slopes greater than 20 percent. The proposed recharge area is
immediately adjacent to the detention pond embankment with a slope of 33
percent, thus there is significant potential for breakout into the detention pond.
While this may not negatively impair the detention pond functioning (assuming
the slope is adequately stabilized), it does defeat the purpose of groundwater
recharge if the infiltrated flow is subsequently discharged as surface flow.
We were aware of the DEP guideline during the design of the recharge area.
However,from a maintenance and accessibility standpoint, we felt that it was
important to keep the recharge area outside the limit of pavement to the extent
possible. We feel this decision is justified since the underlying soils in the
Lisa D. Eggleston, P.E.
Marchmionala June 28, 2005
& Associates, L.P. Page 7 of 10
Engineering and
Planning Consultants
3. As proposed, the TSS removal in the drainage area discharging to the southern
wetland would only be 32.5 percent. While the DEP guidelines do allow for
averaging of removal rates among multiple treatment trains, it is only when the
discharges are within the same subbasin. Additional treatment needs to be
provided for the runoff discharged to this wetland.
In order to increase the treatment to the southern area to above 80 91c, we have
added a Stormceptor® unit downstream of DMH-IA (refer to revised Sheet 2
and revised TSS calculation worksheet). Please note that the revised TSS
calculation worksheet reflects only the impervious areas (thus the areas listed
on the bottom of the sheet have changed) based on Vanasse Hangen Brustlin,
Inc.'s (VHB's) review of the Site Plan, in which they indicated that TSS
removal calculations should not factor in unpaved areas of the project.
4. Calculations should be provided demonstrating that the Stormceptor unit is
designed to treat the entire tributary flow generated by 0.5-inches of runoff to the
level of treatment stated (71 percent) without bypassing.
Standard 4 of DEP's Stormwater Management Policy does not require 80%
TSS removal for every storm. Instead, the standard requires the removal of at
least 80% of the average annual load of TSS. The TSS removal credit used for
the Stormceptor® (7101c) is the average annual TSS removal provided by the
unit (not the TSS removal for every storm) and accounts for the bypass that will
inevitably take place during certain storm events (refer to Stormceptor®
modeling output).
5. Additional information is needed to demonstrate that the proposed extended
detention basin would provide adequate detention to achieve the stated pollutant
removals. Specifically, the basin should provide a minimum of 24 hours detention
for the range of storms that would occur over a year (not just the one year storm)
and should empty within a 48 to 72-hour period following a storm to provide
storage capacity for the next event. A low flow channel should be incorporated in
the basin design and the flow path through the basin should be maximized. As
currently proposed the 4-inch outlet, with its invert at grade, would provide no
detention for low flow conditions, and most of the basin would be short-circuited
by the flows discharged through FES-02.
The Massachusetts Stormwater Management Policy specifically recommends
the "design of the detention basin should target 24-hour average detention time
for the entire spectrum of storm events in each year." Marchionda &
Associates generated the one-year hydrograph for the proposed detention basin
to ensure that the design was consistent with this recommendation. The "tail"
Lisa D. Eggleston, P.E.
Marcnionda
® June 28, 2005
& Associates,
L P Page 9 of 10
Engineer ing and
ILI Planning Consultants
Standard#5. Higher Potential Pollutant Loads
The proposed project does not constitute a land use with higher potential pollutant loads.
No response required
Standard#6. Protection of Critical Areas
The project site is not located in a critical area as defined by the Stormwater Management
Policy.
No response required
Standard#7. Redevelopment
The proposed project is not a redevelopment project as defined in the Stormwater
Management Standards since it represents a net increase in impervious surface.
No response required
Standard#8. Erosion and Sediment Control
Erosion and sediment control measures to be undertaken during project construction are
addressed in Section 8.0 of the NOI narrative and depicted on the project plans.
1. The plan should also include provisions to prevent heavy equipment from
compacting soils in the planned infiltration area during construction.
A note has been added to the plans accordingly.
2. The proposed project will be subject to NPDES permit compliance and will
require preparation of a construction Stormwater Pollution Prevention Plan
(SWPPP). The Commission should be provided the opportunity to review and
approve the SWPPP as it is developed. Provision for construction monitoring of
the site should also be established.
No response required
Marchlonda
& Associates, L.P.
Engineering and
Planning Consultants
RECEIVED
June 30, 2005 JUL 5 ® 2005
NORTH ANDOVER
Vanasse Hangen Brustlin, Inc. PLANNING DEPARTMENT
101 Walnut Street
P.O. Box 9151
Watertown, MA 02471-9151
Attn: Timothy B. McIntosh, P.E.
RE: Engineering Review: Response to Follow-Up Drainage Comments
1600 Osgood Commerce Center, Building 20 & 21 Parking Lot
Dear Mr. McIntosh,
Marchionda & Associates, L.P. is in receipt of your June 30, 2005 comment letter to the
North Andover Planning Board regarding the subject project. We offer the following
responses and attached supplemental information in response to the comments. Our
responses (italicized) follow each of the comments below:
1. The Applicant's Engineer should verify that there is adequate capacity in the
existing drainage piping system and that there is adequate outfall for the wetland
system. Addressed, however VHB recommends verification with the town,
owner and abutters that there is no history of flooding problems in this area.
Marchionda & Associates has received no indication that the existing southerly
drainage system is prone to flooding. If a flooding problem were to exist, the
proposed design would in fact help as the peak flow and volume to the existing
system are reduced in the proposed condition.
2. The generally accepted surface runoff coefficients for the rational method for
pavement and average grass surface are 0.9 and 0.3 respectively. The coefficients
used in the report were low. The rational method calculations should be
recomputed with these coefficients. The rational method run off coefficients
in the Mass Highway Design Manual Chapter 10 for pavement are 0.7-0.95,
which similar to Lindeberg, but for new pavement the number should be on
the high side of the range (smooth surface and no cracks). The number used
for the lawn area looks good given the description of the area as "Manicured
Lawn" on the soils testing logs.
62 Montvale Avenue Tel: (781) 438-6121
Suite I Fax: (781) 438-9654 website: http://www.marchionda.com
Stoneham, MA 02180 Email: inail@niarchionda.com
Timothy B. McIntosh, P.E.
Marchlonda June 30, 2005
& Associates, L.P. Page 2 of 4
t Engineering and
Planning Consultants
The modeling has been revised to reflect a C value of 0.9 as requested (see
attached modeling output).
3. The rational method calculations assume a free discharge at pipe ends. The
Applicant's Engineer should verify that this condition exists at the existing
drainage system connection (CB-85), the proposed detention pond and the
existing wetland and adjust the calculations if required. This analysis is
especially important because the proposed pipe system design allows stormwater
to surcharge and develop a higher hydraulic grade line. Additional information
was provided and is acceptable, but there is another main drain line
connection to the detention pond that has not been re-calculated with the
Hydraulic Grade Line (HGL). This entire drain line should be re-calculated
with the HGL.
As shown on the previously submitted plans, the main drain line referenced in
this comment discharges at an invert above the 100 year flood elevation.
Therefore, we assumed free discharge in the pipe sizing calculations, and no
revisions are required for this network.
4. The Applicant's Engineer should provide the test pit soils information, test pit
locations and percolation testing results that are discussed in the drainage report.
The soils information was provided. The Applicant's Engineer should verify
if and to what extents unsuitable soils in the detention pond area will need to
be removed. If required, add information to the plans detailing the extent of
removal and replacing with clean sand. Details should include elevations and
elevation of groundwater.
Test pits conducted by Marchionda & Associates indicated suitable soils in the
vicinity of the proposed basin, and we do not anticipate encountering unsuitable
materials in this area.
5. The Massachusetts Stormwater Management Policy allows averaging TSS
treatment trains when they are part of the same sub-basin. The proposed drainage
design consists of two separate sub-basins and two separate discharge points. The
Applicant's Engineer should recalculate the TSS removals for each sub-basin.
Treatment Trains #4 and 5 are almost completely grass or pond areas and TSS
pollutants should not be generated. New calculations were provided. See Note
#6 below.
No response required
Timothy B. McIntosh,P.E.
Marchlonda June 30, 2005
& Associates, L.P. Page 3 of 4
Engineering and
u= Planning Consultants
6. The detention pond does not appear to meet the criteria for an extended detention
basin, as defined by the Massachusetts Stormwater Management Policy. The
requirements include providing 24 hour detention time for the stormwater and
incorporating a sediment forebay. Additional information on the proposed
detention time and a revision to the plan to include a sediment forebay is required
to meet the criteria. If the requirements can not be met, the TSS calculations will
need to be adjusted accordingly. A hydrograph was provided as confirmation
that the detention pond will provide an average detention time of 24 hours.
It is true that the 1-year hydrograph extends out past 24 hours but hours 0 to
12 there is no outflow. The average detention time can be calculated with a
plug flow calculation (time = volume/flow rate). This detention time is very
difficult to achieve without providing the water quality volume below the
outlet invert. Recommend evaluating as an Infiltration Pond (will need to
add a sediment forebay sized according to the Stormwater Management
Policy) or evaluate as a detention pond with a TSS removal rate generated
with the P-8 program. The TSS removal Calculations would need to be re-
done, but should still be above the 80% TSS Removal Requirement (for New
Development).
Based on nay conversation with Mr. Richard Mathews, P.E. of your office, I
have reclassified the basin as an infiltration basin. In order to justify this
change, I have attached calculations showing that the upstream recharge
chambers infiltrate the DEP Water Quality Volume, and I have also attached
the TSS calculations as revised accordingly.
7. The new pipe connection to the headwall appears to be in conflict with an existing
pipe that is shown on the existing conditions survey. The piping and the scope of
the proposed construction needs to be clarified in this area. Addressed.
No response required
Timothy B. McIntosh,P.E.
Marchlonda June 30, 2005
& Associates, L.P. Page 4 of 4
Y
Engineering and
Planning Consultants
8. The HDPE flared end sections should incorporate tie down anchors to prevent any
possibility of floating. Addressed.
No response required
9. The Applicant should consider including a 4-foot high chain link fence around the
perimeter of the detention pond for safety. It is unclear if a fence would be
required under State Building Code because the anticipated depth of stormwater
in the detention pond is less than 4 feet in the 100-year storm event and the
emergency overflow is set at 4.5 feet deep. The Applicant is not proposing a
fence. No further engineering review is required at this time.
No response required
Based on my conversation with Mr. Richard Matthews, P.E. of your office, I trust that the
information provided will adequately address all of VHB's final comments. If our
responses do not completely address your concerns please contact me at (781) 438-6121
as soon as possible so that we can provide any additional information that you may need
before the next Planning Board hearing (scheduled for July 5, 2005).
Very truly yours,
Marchionda &Associates, L.P.
Matthew A. Leidner,P.E.
Project Manager
Cc: Mr. Lincoln Daley (Town Planner)
Christian Huntress (Huntress Associates, Inc.)
File
H:\PROJECTS\670-09\Coaespondence\VHB Response\Response_063005.doc
1600 Osgood Commerce Center
Building 20&21 Parking Lot Design
North Andover, Massachusetts
TS REMOVAL BY TREATMENT AREA-NORTH
TREATMENT AREA 1 N (SWEEPING TO CB TO STORMCEPTOR TO DETENTION):
BMP DESIGN TSS REMOVAL CUMULATIVE TSS REMOVAL
Street Sweeping 10% 10.00%
Deep Sump/Hooded CB 25% 32.50%
Stormceptor 71% 80.43%
Infiltration Basin 80% 96.09%
TREATMENT AREA 2N (SWEEPING TO CB TO DETENTION):
BMP DESIGN TSS REMOVAL CUMULATIVE TSS REMOVAL
Street Sweeping 10% 10.00%
Deep Sump/Hooded CB 25% 32.50%
Infiltration Basin 80% 86.50%
TREATMENT AREA 3N (SWEEPING ONLY):
BMP DESIGN TSS REMOVAL CUMULATIVE TSS REMOVAL
Street Sweeping 10% 10.00%
COMPOSITE TSS REMOVAL-NORTH
TREATMENT AREA AREA FT2 CUMULATIVE TSS REMOVAL
1 N 130,590 96.09%
2N 23,097 86.50%
3N 1,064 10.00%
Composite TSS Removal*= 94.06%
'Composite TSS removal calculated as weighted average of cumulative TSS removal rates for individual
treatment areas
May 20,2005
Marchionda&Associates, L.P. Page 1 of 3 Revised June 30,2005
JOB U00 0 76000
MARCHIONDA & ASSOCIATES, L.P. '..' J
Land Planning, Surveying and Civil Engineering SHEETNO.— / — OF
62 Montvale Ave. — DATE
Stoneham, MA 02180 CALCULATED BY
781-438.6121, Fax 781-438-9654 CHECKED BY DATE,
www.marchionda.com
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