HomeMy WebLinkAbout2000-12-07 Stormwater Review f /2,j/2000 16: 23 FAX 781 982 5490 COLER&COLANTONIO C�j006/008
I
COLER &
COLANTONlO
EN0JNaFRS ANL]GCICNT15T 5
September 28, 2000
Heidi Griffin
Town Planner
C/o VHB
101 Walnut Street
Watertown, MA 02471
RE: Engineering Review
Endicott Plaza
Site Plan Review—Drainage Issues
Dear Ms. Griffin:
In respn)ase to your request, Coler & Colantonio, .Inc. has reviewed the submittal package
for the above referenced site, Our efforts included a comparison of informatioin
submitted with respect to the drainage requirements of the Zoning Bylaw. We also
compared the design assumptions and calealations with the DEP Stormwater
Management Policy and standard engineering practice. In addition, we visited the site on
September 22, 2000 to observe existing conditions. The submittal package included the
following information:
Plans Entitled
• "Site Plan for Endicott Plaza", located in North Andover, Mass."consisting of
six sheets dated 9/l/00, Prepared by Marchionda and Associates Inc.
Received 9/11/00.
• "Proposed Sewer Extension Osgood and Sutton Streets, North Andover,
Massachusetts" consisting of six sheets dated 8/30/00, Prepared by
Marchionda and Associates Inc, Received 9111/00.
Reports Entitled:
« "Notice of Intent Endicott Plaza" dated September 8, 2000, prepared by
Epsilon Associates, :received 9/11/00.
• Hydrologic Analysis", dated 8/17/00,Prepared by Marchimida and.Associates.
Received 9/11/00.
The site is located on the west side of Osgood Street near the intersection with Barker
Street. Presently the site is an active farm. The land slopes in a westerly direction to
wetlands either on or adjacent to the site.
We offer the following comments.,
101 Accord Park Drive 761-982-5400
Norwell,MA 02061-1685 Fax: 781-982-5490
I
09/28,2000 16:24 FAX 781 982 5490 COLER&COLANTONIO a047/40$
Section 8.3 5.E) vii
1. The existing conditions hydrology model indicates one discharge point. Our site
observations indicate that the site drains to two or more of the abutting wetlands.
Although the flow ultimately combines offsite, one of the areas appears to be a
pond and the other is a BVW. The design should not cut off a water souxce to a
wetland, which may be a result of this design. The design should meet flow
conditions at the existing discharge points.
2. The existing conditions cover type for approximately 30% of the site is indicated
as fallow bare soil with a CN of 91. Our observation of the site indicated that the
layout of crops would likely infiltrate more runoff than is accounted for by
Fallow/Bare soil conditions.
3. It is unclear- if there is a downstream restriction off-site. The submittal should
describe the impact of the increase in total runoff'volume. This increase could
raise the flood elevation in the wetland and potentially impact off-site property,
4. The design reflects recharge of the proposed roofs for a 100 yr. Storm. The
capacity of the recharge system is not clear. Permeability can not be directly
converted from percolation rates. For'a system of this size and sensitivity, we
would recommend that actual penneability tests be performed for the infiltration
system. Soils tests indicate variable percolation test results. Soils based on the
NRCS inaps would not be suitable for recharge based on DEP criteria. If the
system does not function as proposed an increase in runoff would result.
5. The subsurface infiltration system has no suitable'means of access to maintain it
without extensive excavation. Note that the top of the system is approximately
nine feet below grade. Area drains in addition to the roofs feed the subsurface
infiltration system themselves. A more detailed description of how this system
will be maintained should be provided. In addition, monitoring wells should be in
stalled in the system and measured on a specified basis to identify potential
deterioration of the system over time.
6. A, cross section, drawn to scale, through the retaining wall and recharge system
indicating the various features including length of geosynthetic reinforcement and
the proximity of proposed drainage for the wail to the recharge should be
provided. In addition, the plan view does not represent the wall hatter as indicated
on the detail. The batter may result in greater horizontal footprint as the height
increases, which may not be accommodated in some areas.
7. The hydraulics of the inlet pipe connections to the drywells should be described.
It appears that the pipes connect to a four-foot manhole section located over a 20-
inch +1- opening cast in the drywcll. Invert data and elevations of these inlets
should be provided together with velocity of flow in the structures. We
recommend an alternative connection detail be considered.
8. The plans should indicate the location of the overflow spillway for the detention
basin. The spillways for the detention basin should be constructed with riprap on
39/26/2000 16: 14 FAX 781 881 5499 COLER&COLANT'ONIO [�j008/008
both sides to avoid erosion and siltation. Spillway width and riprap sizes should
be specified based on calculated flow velocities.
9. The design of the detention basin includes a sump of unspecified depth (less than
two feet), Given the soils reported in tivs area it is likely that this will hold water
most of the time. We recommend the basin be designed with a gentle slope
between the inlet and outlet pipes pitch to drain dry between storm events.
10. The Existing Conditions plan sheet El was not included in the submittal package.
11, Flow and velocity of the culvert on the south of the site, which discharges runoff
froin Osgood Street has not included. It is unclear if the proposed roadway
improvements would result in an increase in flow to this culvert.
13. There are two drains without any flow or invert data, which could be potential
sources of erosion. One is identified as an overflow to the recharge system, the
other is labeled FD.
13. No calculations .for the storm sewer system were provided. The calculations
should include both pipe and inlet capacity, together with appropriate support data
and area plans. This data should be provided to demonstrate that the storm sewer
and roof drain systems could collect and convey the flow to the stormwater
management structures without bypass. Of particular concern is by-pass of th?
roof drainage system during the 100-yr storm.
14. We note that minimal separation is provided between drains and sewers in several
locations,
15. It is not recommended that drain lines be constructed beneath the building for
maintenance and accessibility reasons,
We appreciate the opportunity to assist the Planning Board on this project and hope that
this information is sufficient for your needs. We would be, pleased to mcet with the
Board or the design engineer to discuss this project at your convenience. If you have any
gaestions please do not hesitate to contact us.
Very truly yours,
COLER&COLANTONIO, INC.
Ci��I
ohn C. Chessia,F.E.
j as/JCC
11/07/2000 16:24 FAX 781 982 5490 COLER&COLANTONTO 0002
i
I
COLER &
ENMINEERS AND SGICNTIETG
November 7,2000
Heidi Griffin
Town Planner
C/o V10
101 Walnut Street
Watertown,MA 02471
RE: Supplemental Engineering view
Endicott Plaza
Site Plan Review—Drainage Issues
Dear Ms_ Griffin:
In response to your request, COIeT & Colantonio, Inc. has reviewed the supplemental
submittal package for the above referenced site. Our efforts included a comparison of
information submitted with respect to the drainage requirements of the Zoning Bylaw.
We also compared the design assumptions and calculations with the DEP Stormwater
Management Policy and standard a gineering practice. The submittal package included
the following information:
Plans Entitled
• "Site Plan for Endicott P aza", located in North,Andover,Mass." consisting of
Six sheets dated 9/1/0 , revised ,10/23/00_ Prepared by Marchionda and
Associates Inc. Deceive 10/26/00.
"Proposed Sewer Exte lion Osgood and Sutton Streets, North Andover,
Massachusetts" consisti g of six sheets dated 8/30100, revised 10/23/00.
Prepared by Marchionda Lnd Associates Inc. Received IOf26100.
Reports Entitled:
• "Notice of Intent Endic t Plaza" dated September $, 2000, revised 10/25/00
prepared by Epsilon Assc ciates,received 10/26/00.
e Hydrologic Analysis", dated 8117100, revised 10/25/00. Prepared by
Marchionda and Associates. Received 10/26/00.
Our latest comments are in italics:
Section 8.3 S.E)vii
1. The existing conditions by +logy model indicates one discharge point_ Our site
observations indicate that th6 site drains to two or more of the abutting wetlands.
Although the Mow ultimately combines ofFsite, one of the areas appears to be a
101 Accord Park Drive 781-9132•6400
Norwell, MA 02061-1885 FaX:781-982-5490
11/07/2000 15:24 FAX 761 942 5490 COLER&COLANTONIO 10003
pond and the other is a BVW. The design should not cut off a water source to a
r wetland, which may be a result of this design. The design should meet flow
conditions at the existing discharge points,
Spot grades were added to the plans which indicate the existing stormwater flow
from the northwest corner of the site directed around the existing pond. No
further comment.
2. The existing conditions cover type for approximately 30% of the site is indicated
as fallow bare soil with a CN of 91. Our observation of the site indicated that the
layout of crops would likely infiltrate more runoff than is accounted for by
Fallow/Bare soil conditions.
The existing conditions model has been revised to indicate the cover type for the
field as Straight Row Crops-Good Condition CN=8S. No further comment:
3. It is unclear if there is a downstream restriction off-site. The submittal should
describe the impact of the increase in total runoff volume. This increase could
raise the flood elevation in the wetland and potentially impact,off-site property.
Reportedly, the downstream werland has free discharge to an existing stream and
is not restricted by topography or drainage structures. No further comment.
4. The design reflects recharge of the proposed roofs for a 100 yr. Storm- The
capacity of the recharge system is not clear. Permeability can not.be directly
converted from percolation rates. for a system of this size and sensitivity, we
would recommend that actual permeability tests be performed for the infiltration
system. Soils tests indicate variable percolation test results. Soils based on the
MRCS maps would not be suitable for recharge based on DEP criteria. If the
system does not function as proposed an 'increase in runoff would result.
Permeabiliry has been performed which indicated marginal soils for infiltration.
The infiltration system has been mod fled ro a sub-surface detention basin
including a sump to retain the required recharge volume. Satisfactorily
addressed.
S. The subsurface infiltration system has no suitable means of access to maintain it
without extensive excavation. Note that the top of the system is approximately
trine feet below grade. Area drains in addition to the roofs feed the subsurface
infiltration system themselves. A more detailed description of how this system
will be maintained should be provided. In addition,monitoring wells should be in
stalled in the system and measured on a specified basis to identify potential
deterioration of the system over time.
The sub-surface basin design has been modified to capture only roof nun-off and
redesigned to allow better access for maintenance. A cross-section of the
proposed basin has been provided. No further comment
6. A cross section, drawn to scale, through the retaining wall and recharge system
indicating the various features including length of geosynthetic reinforcement and
11/U7/LUUU M25 kAX 781 952 5480 COLER&COLANTONIO 4004
the proximity of proposed drainage for the wall to the recharge should be
provided. In addition,the plan view does not represent the wall batter as indicated
on the detail. The batter may result in greater horizontal footprint as the height
increases,which may not be accommodated in some areas.
A detail has been submitted for the proposed retaining wall which indicates that
the construction of the wall requires approximately 3 feet. We recommend
monitoring the construction of this wall to verify no impact within the non-
disturbance zone.
7. The hydraulics of the inlet pipe connections to the drywells should be described.
It appears that the pipes connect to a four-font manhole section located over a 2- 0-
inch +1- opening cast in the drywell. Invert data and elevations of these inlets
should be provided together with velocity of flow in the structures. We
recommend an alternative connection detail be considered.
The proposed drain manholes have been modified to standard size and
connections. Velocities have been provided and do not exceed 10 FPS anywhere
on the site_ No further continent.
S. The plans should indicate the location of the overflow spillway for the detention
basin. The spillways for the detention basin should be constructed with riprap on
both sides to Avoid erosion and siltation. Spillway width and riprap sizes should
be specified based on calculated flow velocities.
.A, rip rap spillway has been added to the plans for the detention basin. No further
comment.
9. The design of the detention basin includes a sump of unspecified depth (less,than
two feet). Given the soils reported in this area it is likely that this will hold water
most of the time. We recommend the basin be designed with a gentle slope
between the inlet and outlet pipes pitch to drain dry between storm events.
The basin has been redesigned to drain completely after all stormy . Satisfactorily
addressed.
10. The Existing Conditions plan sheet B1 was not included in the submittal package.
Pie existing conditions plan was submitted. Satisfactorily addressed.
11. Flow and velocity of the culvert on the south of the site, which discharges runoff
from Osgood Street has not included. It is unclear if the proposed roadway
improvements would result in an increase in flow to this culvert.
Reportedly, the proposed conditions will only discharge 0.2 acres of additional
nin-off to the existing culvert. The design engineer will reportedly install a rip rap
apron if requested by the Conservation Commission.
12. There are two drains without any flow or invert data, which could be potential
sources of erosion,. One is identified as an overflow to the recharge system, the
other is labeled FD.
11/07/2000 16:25 FAX 781 982 5490 COLER&COLANTONIO 10005
The recharge overflow and the footing drain have beery. labeled Elevations are
r approximately feet above grade for the outlets northwest of the subsurface
detention basin these outlets should be lowered.
13, No calculations for the storm sewer system were provided. The calculations
should include both pipe and inlet capacity, together with appropriate support data
and area plans. This data should be provided to demonstrate that the storm sewer
and roof drain systems could collect and convey the flow to the stormwater
management structures without bypass. Of particular concern is by-pass of the
roof drainage system during the 100-yr storm.
An inlet and pipe analysis has been submitted, which indicates capacity for the
.100-year storm. Manhole 3 overflows in a 100-year storm,
14. We note that minimal separation is provided between drains and sewers in several
locations.
Comment remains.
15, It is not recommended that drain lines be constructed beneath the building for
maintenance and accessibility reasons_
The drain line is indicated as within a vehicular passageway with I4 feet of
clearance.No further commenr.
We appreciate the opportunity to assist the Planning Board on this project and hope that
this information is sufficient for your needs. We would be pleased to meet with the
Board or the design engineer to discuss tivs project at your convenience, If you have any
questions please do not hesitate to contact us.
Very truly yours,
COLER&CO;LANI`ONIO,INC.
J n C. Chessia,P.E..
xc Marchionda and Associates
Michael Howard,Epsilon Associates
Jim Rand
jas/JCC
11/28/2000 11:57 FAX 781 982 5490 _ COLER & COLANTON10 0002/012
R `" '� U
CL� 9
Fr-jGiNEFH!;.AND S;DICIns I IST5
November 20, 2000
Heidi Griffin
oven Planner
C/o VHB
101 Walnut Street
Watertown, MA 02471
RE: Supplemental P;tigineering Review
Endicott Plaza
Site Plan Review--Drainage Issues
Dear Ms. Griffin:
In response to your request, Coler & Colantonio, Inc. has reviewed the supplemental
submittal package for the above referenced site. Our efforts included a comparison of
informations submitted with respect to the drainage requirements of the Zoning Bylaw.
We also compared the design assumptions and calculations with the DEP Storrnwater
Management Policy and standard engineering practice. The submittal package included
the following information:
flans Entitled
• "Site Plan for Endicott Plaza", located in North Andover,Mass" consisting of
six sheets dated 9/1/00, revised 11/14/00. Prepared by Marchionda and
Associates Inc. Received 11/17/00.
Reports Entitled:
Hydrologic Analysis", dated 11/14/00. Prepared by Marchionda and
Associates. Received 11/17100.
Our latest comments are in italics:
Section 8.3 5. E) vi i
1. The existing conditions hydrology model indicates one discharge point. Our site
observations indicate that the site drains to two or more of the abutting wetlands.
Although the flow ultimately combines offsite, one of the areas appears to be a
pond and the other is a BVW. The design shotild not cut off a water source to a
wetland, which may be a result of this design, The design should meet flow
conditions at the existing discharge points.
101 Accord Park Drive 781-982-5400
Norwell, MA 02061-1685 Fax:781-982-5490
11/28/2000 11:58 FAX 781 882 5490 COLER & COLANTONIO 10003/012
Section IV.)$.) North Andover and State Storrowater Standards:
2. Standard 1
The project appears to meet this standard, however, there: are two drains without
any flow or invert data which could be potential sources of erosion_ One is
identified as an overflow to the recharge system,the other is labeled FD.
The recharge ore;yloiv curd the.j6oring drums have bewi kcbeled. Elewai.ons are
ul�l�roxi»tear��ly 4 J&.-t above grade fear rile ourfels northwest of the subsaufiu'e
detenrion basin lh.cse outlets should be low-erod.
The outlet invert has been lowered to the proposed grade and the structure has
been modified to a drop manhole to maintain the slope. Satisfactorily addressed.
3. Standard 2
The existing conditions hydrology model indicates one discharge point, Our site
observations indicate that the site drains to two or more of the abutting wetlands.
.Although the flow ultimately combines offsite, one of the areas appears to be a
pond and the other is a$VW. The design should not cut off a water source to a
wetland,which may be a result of this design.
Spot grades were added to the plans which indicate the existing stannwater flows
from the northwest corner of the site are directed around the existing pored. No
further comment.
The discharge paint under pre and post development conditions is indicated as a
confined wetland. The total increase in runoff volume could raise the flood
elevation in the wetland. This impact should be assessed,
,Reportedly, the downvtream wetland has free discharge to an existing streams and
is not restricted by topography or drainage structures. Runoff does not discharge
to the pond as rioted above.No further comment.
The existing conditions cover type for approximately 30%v of the site is indicated
as fallow base soil with a CN of 91, Our observation of the site indicated that the
Iayout of crops would likely infiltrate more runoff than is accounted for by
Fallow/Bare Soil conditions.
The existing conditions model has been revised to indicate the cover type for the
field as,Straight Row Craps-Good Condition CN=85. No farther comment.
No calculations for pipe or inlet capacity were included in the submittal. This
data should be provided to demonstrate that the storm sewer and roof drain
SysiomS cau collect and convey the flow to the stonnwater management structuroS.
An inlet and Pipe analysis has been submitted, which indicates capacity for the.
100-year stonn. Manhole 3 overflows in a 100-year storm. Satisfactorily
addressed.
11/2VZUUU 11:50 FAX 7$1 962 5490 COLER & COLANTONIO 10004/012
Of particular concern is bypass of the root drainage system during the 100-yr
storm.
Koed djroin colt'trlrrtivns use ct 10 717ilatle lime ol, Concentration, hoer(wer a �
illinult< lirlrr� trf"c.r1111'r?irlrttliU►P,lk"M d J.ief r/g7rese is 1he proposed conditions- This
%]Et7nl�t? Ind ! )r]LIel will incre:tig e the pe(j.ik- lows (7/fd may impa r RDM11 s 4, > & 9,
The roof drain calculations were modified to include a S-minutes time of
concentration. These revised calculations indicate that the proposed system is
adequately sized to handle the modeled 100-year storm. No further comment.
An overflow spillway for the detention basin should be included on the plans.
Emergency overflow ,spillways have bee12 added to the plants. S'atisfactority
addressed_
4. Standard 3
It is likely that the required recharge volume would be met by the proposed
design. The design reflects recharge of the proposed roofs for a 100 yr. Storm.
The capacity of the recharge system is not clear. P-mveability can not be directly
converted from percolation rates. For a system of this size and sensitivity, we
would recommend that actual permeability test be perforated for the infiltration
system, Soils tests indicate variable percolation test results. Soils based on the
MRCS maps would not be suitable based on MP cute3ria.
Permeability has been performed which indicated marginal soils for infiltration.
The infiltration system has been modified to a sub-surface detention basin
including a sump to retain the required recharge volume. Satisfactorily
addressed.
The application should address the procedures to be used if this system requires
maintenance or replacement. A cross section, drawn to scale, through the
retaining mall and recharge system indicating the various feature including length
of geosynthetic reinforcement and the proximity of proposed drainage for the wall
to the recharge should be provided,
Th.e sub-surface basin design has been modified to capture only roof tiro-off and
redesigned to allow better access for taintenance. A cross-section of the
proposed basin has been provided.No fi<rther comment.
The hydraulics of the inlet pipe connections to the drywells should be described.
It appears that the pipes connect to a four-foot manhole section located over a 20-
incb +\- opening cast in the drywell. Invert data and elevations of those inlets
should be provided together with velocity of flow in the structures.
The proposed drain manholes have been modified to standard size and
connections. Velocities have been provided and do not exceed 10 FPS. No further
c on,un a t
11/26/20OU 11:59 FAX 761 eSZ 5490 COLER & COLANTONIO 10005/012
5 Standard 4
It is unclear that the site wi)) be swept frequently enough to receive credit,
however the TSS removal will be achieved with or without street sweeping.
No further comment.
G Standard 5
'rhe water quality volume should be calculated and treated in accordance with the
Stormwater Management policy.
The water quality volume has been calculated and will be treated to 80°lo TSS
removal by the stormwater management gpstem as designed. Satisfactorily
addressed.
7 Standard 6
Not Applicable.
8 Standard 7
Not applicablo.
9 Standards 8 &9
The subsurface infiltration system has not suitable means of access to maintain it
without excavation. Note that the top of the system is approximately nine feet;
below grade. .Area drains in addition to the goofs .feed the subsurface infiltration
system themselves. A more detailed description of how this system will be
maintained should be provided. In addition, mon.itoriug wells should be in stalled
in the system and measured on a specified basis to identify potential deterioration
of the system over time.
The sub-surface basin has been modified to a detention basin, which captures
only roof top ninoff. The cover has been reduced and a proposed monitoring well
within the system has been added to the plans. No further comment.
10 Section IV L B. Minimum Submittal Requirements. It is unclear if an agent of
the Town witnessed the test pits.
Coler & Colarntonio stuff witnessed soil borings and permeability testings
Reportedly, the .Corrunission was igonned of the perfonnance of test pits,
however were not able to attend. No further comment.
11 Section 1V, C. 6. c_ The plans should indicate the location of the overflow
spillway for the detontion basins. The spillways for both detention basins should
be constructed with riprap on both sides to avoid erosion and siltation. Riprap
sizes should be specified based on calculated flow velocities,
A rip rap spillway has been added to the plaits for the detention basin. No further
comment.
11/28/2000 11:59 FAY 781 882 5480 COLER & COLANTONIO UOOO/012
12 Section TV. C. 6. d, The design of the detention basin includes a sump of
uulspecified depth (less than two fectj. Given the soils reported in this area it is
likely that this will hold water most of the time.
De basin has been redesigned to drain completely in all stonns•. Satisfactorily
addressed.
13 Section VI B. 4. The Existing Conditions plan sheet El was not included in the
submittal package.
Tho existing conditions plan was submitted. Satisfactorily addressed.
14 Section V1 B. 4. J Flow and velocity of the culvert on the south of the site, which
discharges runoff from Osgood Street has not included.
It is required b1-[his stundar'd to 7nodet all on lira.tire.
Reportedly, the proposed development will have little impact on the existing
culvert, however it has been indicated that this outlet will be upgraded and
protected if necessary.No firdter cormnent.
General Comments:
15 A structural design for the proposed retaining walls should be indicated. It does
not appear feasible to Construct these walls without impacting the 25-PO
disturbance zone.
See response to comment 1.
16 It is pot recommended that drain lines be constructed beneath the building for
maintenance and accessibility reasons_
The drain line is indicated as within a vehicular passageway with 14 feet of
vertical clearance.No further comment.
We appreciate the opportunity to assist the Conservation Commission on this project and
hope that this information is sufficient for your needs. We would be pleased to meet with
the Board or the design engineer to discuss tiffs project at your convenience. If you have
any questions please do not hesitate to contact us.
Very truly yours,
COLER& COLAN T•O1VIO,.INC.
XCChe5sia,P.E.
xc Marchionda and Associates
Michael Howard,Epsilon Associates
Jim Rand