13-073 WPA form 1 NE Deaconess association* J0 ;
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Massachusetts Department of Environmental Protection
Bureau of Resource Protection - Wetlands
WPA Form 1- Request for Determination of Applicability
Massachusetts Wetlands Protection Act M.G.L. c. 131, §40
City of Northampton Wetlands Protection Ordinance, Chapter 24
A. General Information city/Town
Northampton
Applicant:
New England Deaconess Association
Name E -Mail Address (if applicable)
80 De aconess Road
Mailing Address
Concord MA 01742
City/Town State Zip Code
978 - 369 -5151 978 - 371 -8091
Phone Number Fax Number (if applicable)
2. Representative (if any):
Coler and Colantonio, Inc.
Firm
David Thompson dthompson(acol- col.com
Contact Name E -Mail Address (if applicable)
55 Bob ala Road
Mailing Address
Holyoke MA 01040
City/Town State Zip Code
413 - 331 -0121 431 - 313 -01
Phone Number Fax Number (if applicable)
B. Determinations
1. 1 request the Northampton Conservation Commission make the following determination(s). Check any
that apply:
❑ a. whether the area depicted on plan(s) and /or map(s) referenced below is an area subject to
jurisdiction of the Wetlands Protection Act.
❑ b. whether the boundaries of resource area(s) depicted on plan(s) and /or map(s) referenced
below are accurately delineated.
R c. whether the work depicted on plan(s) referenced below is subject to the Wetlands Protection Act.
R d. whether the area and /or work depicted on plan(s) referenced below is subject to the jurisdiction
of any municipal wetlands ordinance or bylaw of Northampton.
❑ e. whether the following scope of alternatives is adequate for work in the Riverfront Area as
depicted on referenced plan(s).
WPA Formt
Rev. 02/00
Note: The Northampton Conservation Commission requires a total of nine (9) collated copies of
this application when it is submitted, together with the $50.00 filing fee.
Page t of 4
Massachusetts Department of Environmental Protection
Bureau of Resource Protection - Wetlands
WPA Form 1- Request for Determination of Applicability
Massachusetts Wetlands Protection Act M.G.L. c. 131, §40
City of Northampton Wetlands Protection Ordinance, Chapter 24
C. Project Description
1. a. Project Location (use maps and plans to identify the location of the area subject to this request):
corner Coles Meadow Rd./N. King St. Northampton
Street Address City/Town
13 073
Assessors Map /Plat Number (REQUIRED) Parcel /Lot Number (REQUIRED)
b. Area Description (use additional paper, if necessary):
Subject property is 11.51 acres at the northwest corner of the intersection of North King
Street and Coles Meadow Road. The property belongs to the New England Deaconess
Association and is currently occupied by Rockridge Deaconess, a retirement and nursing
home facility.
c. Plan and/or Map Reference(s):
Site Plan, Rockridge at Laurel Park, North King Street, Northampton, MA June 25, 2003
Title
Date
2. a. Work Description (use additional paper and /or provide plan(s) of work, if necessary):
New England Deaconess Association received an Order of Conditions on April 16, 2003, to
undertake a number of site improvements associated with new building construction at this
property (ref. wetlands file no. 246 -521). During site plan/special permit review, the
Northampton Planning Board requested that a 4' -wide sidewalk be added to the plans along
the property's North King Street frontage. The enclosed plan shows the previously approved
work in an illustrative format with the proposed sidewalk added. This plan is currently under
review by the District 2 office of the Massachusetts Highway Department. They are satisfied
with the proposed layout of the walk, but would like to receive a copy of the Northampton
Conservation Commission's decision on the work before they issue their permit.
b. Identify provisions of the Wetlands Protection Act or regulations which may exempt the applicant
from having to file a Notice of Intent for all or part of the described work (use additional paper, if
necessary).
No work is proposed within any resource area. An erosion/sedimentation control barrier is shown on
the plan between the proposed sidewalk and the bordering wetland. Notes are included on the plans
requiring that the sidewalk work conform to all the construction standards specified for the rest of the
approved work on the property, and shall comply with the Order of Conditions issued for the rest of
the work.
WPA Formt Page 2 of 4
Rev. 02/00
Massachusetts Department of Environmental Protection
Bureau of Resource Protection - Wetlands
WPA Form 1- Request for Determination of Applicability
Massachusetts Wetlands Protection Act M.G.L. c. 131, §40
City of Northampton Wetlands Protection Ordinance, Chapter 24
C. Project Description (cont.)
3. a. If this application is a Request for Determination of Scope of Alternatives for work in the
Riverfront Area, indicate the one classification below that best describes the project.
❑ Single family house on a lot recorded on or before 8/1/96
❑ Single family house on a lot recorded after 8/1/96
❑ Expansion of an existing structure on a lot recorded after 8/1/96
❑ Project, other than a single family house or public project, where the applicant owned the lot
before 8/7/96
❑ New agriculture or aquaculture project
❑ Public project where funds were appropriated prior to 8/7/96
❑ Project on a lot shown on an approved, definitive subdivision plan where there is a recorded deed
restriction limiting total alteration of the Riverfront Area for the entire subdivision
❑ Residential subdivision; institutional, industrial, or commercial project
❑ Municipal project
❑ District, county, state, or federal government project
❑ Project required to evaluate off -site alternatives in more than one municipality in an
Environmental Impact Report under MEPA or in an alternatives analysis pursuant to an
application for a 404 permit from the U.S. Army Corps of Engineers or 401 Water Quality
Certification from the Department of Environmental Protection.
b. Provide evidence (e.g., record of date subdivision lot was recorded) supporting the classification
above (use additional paper and/or attach appropriate documents, if necessary.)
WPA Fortni Page 3 of 4
Rev. 02/00
Massachusetts Department of Environmental Protection
Bureau of Resource Protection — Wetlands
WPA Form 1- Request for Determination of Applicability
Massachusetts Wetlands Protection Act M.G.L. c. 131, §40
City of Northampton Wetlands Protection Ordinance, c. 24
D. Signatures and Submittal Requirements
I hereby certify under the penalties of perjury that the foregoing Request for Determination of Applicability
and accompanying plans, documents, and supporting data are true and complete to the best of my
knowledge.
I further certify that the property owner, if different from the applicant, and the appropriate DEP Regional
Office (see Appendix A) were sent a complete copy of this Request (including all appropriate
documentation) simultaneously with the submittal of this Request to the Conservation Commission.
Failure by the applicant to send copies in a timely manner may result in dismissal of the Request for
Determination of Applicability.
Name and address of the property owner:
New England Deaconess Association
Name
80 Deaconess Road
Mailing Address
Concord
City/Town
— MA 01742
State Zip Code
Signatures:
I also understand that notification of this Request will be placed in a local newspaper in accordance with
Section 10.05(3)(b)(1) of the Wetlands Protection Act regulations and that the $50.00 filing fee includes
this cost.
1/23 p3
Of
zs -e
Affidavit of Service
Under the Northampton Wetlands Protection Ordinance when filing a Request for Determination of
Applicability the following action is required:
I, 4v�A .'GMQe 6 * �J. - _________, hereby certify under the pains and penalties
(name of person making the Affidavit)
of perjury, that ------- I posted a sign on the property (facing the
(insert date)
public- right -of -way) at least 5 days prior to the public hearing stating that Request for Determination
is pending with the Northampton Conservation Commission and indicating where additional information
can be obtained.
WPA Formt Page 4 d 4
Rev. 02100
STORM DRAINAGE ANALYSIS AND D
for the
proposed improvements to
"Rockrdge at Laurel Park"
on
25 Coles Meadow Road
Northampton, Massachusetts 01060
Prepared For.
New England Deaconess Association
80 Deaconess Road
Concord, Massachusetts 01742
Project No. 60- 155.00
NARRATIVE / O &M PLAN ONLY
Prepared by.
Cofer & Colantonio, Inc.
1 Sugarloaf Street
South Deerfield, MA 01373
Tel: (413) 665 -5300
Fax: (413) 665 -5390
March 5, 2003
New England Deaconess 'ciation
80 Deaconess Road
Concord, Massachusetts 01742
STORM DRAINAGE ANALYSIS AND DESIGN
for the proposed improvements to
"Rockridge at Laurel Park"
25 Coles Meadow Road
in Northampton, Massachusetts
1.0 INTRODUCTION
Coler & Colantonio, Inc. has prepared this drainage analysis and design for the
proposed improvements to the `Rockridge at Laurel Park" assisted living facility in
Northampton, Massachusetts. The property is shown on Assessor's Map 13, Lot 073 and is
owned and operated by New England Deaconess Association of Concord, Massachusetts.
The existing 11.09 acre site is located at the intersection of Coles Meadow Road and
North King Street, adjacent to the Massachusetts State Police barracks. The property is
bounded on the North and West by land of the Laurel Park Association, on the East by
North King Street, and on the South by Coles Meadow Road (refer to project locus in
Appendix 1).
The project proposes the expansion and redevelopment of the Rockridge assisted
living facility with improvements to the access drive, parking, sidewalks, utilities,
landscaping, and a closed- conveyance drainage system with underground stormwater
detention system. The proposed expansion includes construction of a three -story building
and twelve one -story cottages with carports. The improvments will add 19 congregate
assited living units and 12 attached elderly housing cottages to the existing site for a grand
total of approximately 88 units. The existing main access drive has been lengthened and
terminates in a cul -de -sac near the new entrance. A new driveway across from the existing
parking area has been proposed to access the one - bedroom cottages and terminates in an
emergency hammer -head style turnaround. New parking areas have been added for
visitors and staff near the main entrance and service entrances. Independent water and
sewer connections have been proposed from Coles Meadow Road to serve the new
facility.
The property is located in the suburban residential district (SR) within the planned
village overlay. The surrounding areas along North King Street support a variety of mixed
residential and commercial uses. The proposed site is previously developed and consists
of an existing three - story/one -story combination building with gross floor area of
approximately 38,800 sf (14,500 sf + in plan area) and a parking lot for 44 vehicles. There
are two existing access points to the site; one on North King Street used for deliveries and
staff, the other off of Coles Meadow Road is the main entrance and includes visitor - parking
areas. A gravel access drive extends from the main entrance to Laurel Park and serves
primarily as a secondary access to that facility.
Topographic relief across the existing site is on the order of 32 feet. The site is
nearly level near North King Street and climbs moderately from the main entrance to the
western property line near Coles Meadow Road. The northeastern portion of the site
contains two separate narrow bands of bordering vegetated wetlands separated by small
New England Deaconess / ciation
80 Deaconess Road u
Concord, Massachusetts 01742
ridge. The tributary drainage area is approximately 14.91 acres and encompasses the land
between the property line and Coles Meadow Road to the West.
The purpose of this report is to compare the existing drainage conditions with the
proposed conditions relative to the down gradient runoff generated by proposed
improvements. Stormwater management will be provided according to policy established
by the Massachusetts Department of Environmental Protection "Stormwater Management"
Volumes 1 and 2 issued March 1997 and the current City of Northampton Site Plan
approval regulations. The proposed facility provides a conservative approach to the
development of the site through a careful design that will match or provide less impact as
compared to the pre - development conditions. The project has been designed to mitigate for
impacts to the 2 -year, 10 -year, and 25 -year storm events. The 100 -year storm event has
been evaluated against adverse impact to downstream properties and will not substantially
increase off -site flooding impacts.
The closed- conveyance drainage system has been designed with deep sump catch
basins, water quality inlets, smooth - walled HDPE, and Corrugates Steel Pipe (CSP) to
collect and direct the surface water from the newly developed and existing impervious
areas to a series of corrugated steel pipe underground storage tanks. Existing stormwater
controls have been retrofitted and upgraded to the extent practicable and feature a
Stormceptor® water quality inlet to treat the runoff from the service parking area. The
existing 44 car parking area has been rerouted into the new conveyance system for
treatment of suspended solids and detention prior to controlled release. The stormwater
management system has been designed to minimize the volume, rate of discharge, control
erosion and sedimentation, provide for recharge of groundwater, and reduce the runoff
characteristics for the 2 -year, 10 -year, and 25 -year storm events.
The proposed improvements are shown on the plans entitled "Proposed Site
Improvements, Rockridge at Laurel Park, Coles Meadow Road and North King Street,
Northampton, Massachusetts'; dated March 6, 2003 as prepared by Coler & Colantonio,
Inc., 1 Sugarloaf Street, South Deerfield, MA 01373.
1.1 METHODOLOGY
HydroCAD Stormwater Modeling System computer program by Applied
Microcomputer Systems was used to develop stormwater runoff rates and volumes for the
existing and proposed conditions at the project site. The software uses Soil Conservation
Service (SCS) methodology. The SCS method is based on rainfall observations that were
used to develop the Intensity- Duration - Frequency relationship or IDF curve. By studying
the Weather Bureau's Rainfall Frequency Atlases, the SCS determined that four "mass
curves" could be used to represent the characteristics of the rainfall distribution throughout
the country. The mass curve is a dimensionless distribution of rainfall over time, which
indicates the fraction of the rainfall event that occurs at a given time within a 24 -hour
precipitation event. This synthetic distribution develops peak rates for storms of varying
durations and intensities. The SCS distribution provides a cumulative rainfall at any point in
time and allows volume dependent routing runoff calculations to occur.
The HydroCAD software is a hydrograph generation and routing program similar to
TR -20. Both programs utilize the SCS methodology. The HydroCAD software has the
New England Deaconess / ciation
80 Deaconess Road \__11
Concord, Massachusetts 01742
additional capability to describe shallow concentrated flow. The "NEH -4 Upland Method"
included in the HydroCAD software is applicable for conditions which occur in the
headwaters of a watershed up to 2000 acres. The NEH -4 Upland Method allows the Time
of Concentration (T,) to reflect ground conditions such as overland flow, grassed
waterways, paved areas and upland gullies. The T, is the time required for water to flow
from the most distant point on a runoff area to the measurement or collection point. This
results in a model that more accurately reflects the ground surface for shallow concentrated
flow conditions, than TR -20 which is limited to distinguishing only paved and unpaved
surfaces. In instances where the watersheds are small and impervious, Tc has been
directly entered as a 5- minute minimum. This is consistent with the Rational Method, TR -55
Urban Hydrology for Small Watersheds, and standard engineering practice. The lower
boundary of 5 minutes will yield a conservative, yet practical measure of stormwater runoff
flow.
1.2 SOIL MORPHOLOGY
Soils are grouped according to their potential runoff characteristics. Soils are
assigned to four groups, A through D. Group A contains soils with high infiltration rates
when thoroughly wet and have low runoff potential. This group includes mainly sands and
gravels consisting of deep, well to excessively drained media (sand, loamy sand or sandy
loam). Group D, at the other end of the spectrum, has slow infiltration rates and high runoff
potential. High water table, clay layers, and nearly impervious material are all
characteristics associated with this group.
A USDA Soil Conservation Service map can be found in the appendix indicating
soils present on the project site according to the Soil Survey of Hampshire County
Massachusetts, Central Part, December 1981. Soils throughout the site were classified into
the following soil groups:
Soil Group / Symbol
Hydrologic Group
Hinckley loamy sands (HgA) A
Charlton sandy loams -Rock Outcrop Hollis complex (CrC) B
The Soil Conservation Service (SCS) defines Hinckley loamy sands as deep and
excessively drained. The soils are formed in glacial outwash deposits and are commonly
found on outwash plains, kames, and terraces. Typical profiles of these soils indicate a
very dark grayish brown loamy sand about 8 inches thick, and a 21 -inch subsoil consisting
of brown loamy and gravelly sand. The substratum extends to a depth of 60 inches or
more and is classified as a loose brownish yellow stratified sand, coarse sand, gravelly
sand, and gravel. Permeability of these soils is rapid in the subsoil and very rapid in the
substratum. These soils are well suited to cultivated crops, hay, pasture, and on -site
absorption systems. Hinckley soils are commonly found on level to gently sloping areas on
the sides of hills, ridges, and small drainage ways. Approximately 40% of the total tributary
drainage area or 5.96 acres± consists of the Hinckley series.
The Charlton series consists of deep, well- drained soils on uplands formed in
glacial till. This soil is commonly found on hills and the side slopes of small drainage ways.
3
New England Deaconess, ciation
80 Deaconess Road
Concord, Massachusetts 01742
A typical profile of Charlton soil is contained beneath wooded areas with a surface layer of
about 7 inches containing dark fine sandy loam, a 15 inch thick subsoil of yellowish- brown,
fine sandy loam and /or light -olive brown gravelly fine sandy loam, and an olive colored
substratum that extends from a depth of 60 inches or more containing a massive, firm,
gravelly sandy loam. Permeability of Charlton soil is moderately rapid in the subsoil and
substratum. These soils are well- suited to trees and most areas are wooded. Slope is the
main limitation of these soils for small commercial buildings and absorption fields. The
remaining 60% of the tributary drainage area or approximately 8.95 acres± is Charlton
soils.
1.3 DESIGN CRITERIA
This drainage analysis was developed utilizing a Type III, 24 -hour storm as
developed by the Soil Conservation Service. Two distinct design points were chosen at
down gradient points in the drainage area to compare development conditions for each of
the following storm frequencies. The design storm frequencies and corresponding rainfall
depths were compiled from the "Atlas of Precipitation Extremes for the Northeastern United
States and Southeastern Canada" and Technical Paper No. 40, Rainfall Frequency Atlas of
the United States for Durations from 30 Minutes to 24 Hours and 1 to 100 Years" and have
been estimated as follows:
Storm Frequency (Years)
100
25
10
2
Rainfall D epth (Inches
7.3
5.4
4.4
3.0
1.4 EXISTING CONDITIONS
The project site consists of an existing three -story building with one -story addition
and parking facilities for approximately 44 vehicles. All of the existing developments are
confined to the southern end of the site along Coles Meadow Road and North King Street.
The grounds around the facility consist of light woods and grassed areas. The remaining
land to the North and East of the existing buildings is wooded uplands. The site is bisected
by a bordering vegetated wetland and depression to the North of the existing facility. It was
determined through site visits, aerial photography, and soil surveys that the majority of the
site is woods, lawn, and woods /lawn mix in good condition. The tributary drainage area has
a weighted average CN value of 57.
The attached Existing Drainage Plan in Appendix C delineates the watersheds for
the project and has been divided into two distinct design points for runoff comparison.
Design Point 1 is the area tributary to the 24" Box Culvert that passes under Route 5 &10
(North King Street) and eventually travels into the Interstate 91 drainage system. Design
Point 2 is the area tributary to the 30" twin culverts to the extreme North of the site. This
design point remains unchanged in the post drain condition as no improvements are
proposed within this watershed. A limited stormwater conveyance system is contained
4
New England Deaconess, ciation
80 Deaconess Road
Concord, Massachusetts 01742
onsite and routes two catch basins from the main parking area under the building to the
northeast side where roof drains from the existing facility and a catch basin in the service
parking area terminate into an 12" RCP outfall. The outfall travels to an area upstream of
Design Point#1. There appears to be no existing infiltration or water quality BMP's utilized
in the current layout. The 100 -year storm was routed through the existing facility for
illustrative purposes only. The *HydroCAD model confirms that this limited system cannot
handle the expected flows from this storm event. * (see summary Section 1.7)
1.5 PROPOSED CONDITIONS
The Applicant proposes to construct a three -story addition to the existing facility
including twelve one - bedroom cottages with a new building footprint area of approximately
0.67 acres. The associated site improvements include driveways, parking facilites, site
utilities, ADA compliant walkways, landscaping, and a state -of- the -art underground
stormwater management facility utilizing innovative treatment technologies. The existing
entrance drive will be enlarged and extended to provide access to the new addition. A new
internal driveway will stem from the existing access drive to provide vehicular entry to the
cottages. Additional parking, including private parking areas and carports for the cottages
will be incorporated into the site design to provide parking areas for approximately 90 total
vehicles. Pedestrian access will be achieved through a system of lighted asphalt walks and
features a wooded park and formal garden area. The service area entrance will be
reconfigured and enlarged to provide parking spaces for staff including relocation of a
storage building from the south side of the facility. A boardwalk and footpath will be
constructed to provide access across the bordering wetland, making the existing
community garden site accessible to the residents of the assisted - living facility. Impervious
pavement areas will increase by approximately 1.1 acres have reduced calculated open
space from 89% to 71 %. The attached Proposed Drainage Plan contains the
subcatchments for each tributary watershed. The weighted average CN value for the
tributary watershed has increased to 63.
The closed- conveyance stormwater management system consists of smooth - walled
high - density polyethylene (HDPE) and corrugated steel drain pipe (CSP) connected
between a series of precast manholes and deep sump hooded catch basins. The proposed
underground detention facility is fabricated from perforated 60" diameter aluminized type 2
corrugated steel pipe (CSP) with 3 "x1" corrugations (12 ga.) to provide the required
detention volume. The underground stormwater management facility is backfilled with W
angular crushed stone and wrapped with an engineered non -woven filter fabric to provide
additional storage area and to facilitate infiltration into the surrounding soils. 36" diameter
CSP connects the facility to a 30" diameter riser outlet structure contained within a 72"
diameter manhole to control release rates of various design storms. The proposed
stormwater management detention structure outlets to a level spreader to dissapate energy
and control erosion. The existing 12" metal pipe /RCP drainage system and outlet will
continue to convey roof runoff from the existing three -story building.
To guard against possible impacts from the proposed, erosion and sedimentation
control measures will be incorporated into the sequence of construction. This will include
both modified construction procedures and temporary construction installations to control
the movement of sediment into protected areas. Upon completion of all work, restoration
and stabilization of disturbed areas will commence. Erosion /sedimentation control
New England Deaconess As , ion
80 Deaconess Road
Concord, Massachusetts 01742
installations include placement of hay bales and filter- fabric fencing around disturbed areas
and at storm drainage inlet points. On -going stabilization of disturbed areas will be
completed as the work progresses. Restoration/stabilization measures include seeding,
mulching, and placement of stabilization fabric where required. These controls will be
removed once a good vegetative cover is established and is accepted by the Northampton
Conservation Commission.
The proposed drainage improvements have been designed to meet the City of
Northampton site plan approval requirements as well as the Massachusetts Department of
Environmental Protection's Stormwater Management Policy. The stormwater conveyance
and detention system has been designed to mitigate the increases in the peak rates of
runoff from the site for the 2 -year, 10 -year, and 25 -year 24 -hour design storm events. The
100 -year design storm has been evaluated for the site and exceeds the flow of the pre -
development condition *, but does not appear to affect downstream properties.
1.6 SUMMARY OF RESULTS AND CALCULATIONS
The stormwater management for the proposed project includes: stormwater
collection, treatment, and infiltration systems. These proposed mitigation measures were
designed in accordance with the Massachusetts Department of Environmental Protection
" Stormwater Management Volume 1 & 2, the Vortech® stormwater system, and the
Stormceptor® system. In accordance with these regulations and standard engineering
practice, the potential impacts of this project on downstream properties are mitigated and
summarized in the tables below.
The following is a summary of the calculation results for runoff encompassing the
areas tributary to the Rockridge at Laurel Park improvements for the 2 -year, 10 -year, 25-
year, and 100 -year design storm events. Detailed routing and volume calculations can be
found in various sections appended to this narrative.
Existing Conditions Summary
N.
Design Point 1 - 24" Box Culvert *Design Point 2/20 - Twin 30" Culverts
New England Deaconess Asl&_Ation
80 Deaconess Road
Concord, Massachusetts 01742
Pr000sed Conditions Summary
Design Point 10 - 24" Box Culvert
UNMITIGATED uNMiTinaTEn •• urrit2%Aren .. MS
ry Y}4 %
F_ r
+k �5• ", .tt'
N
}' Y s{ e} @
� �S
s
2- r
3.0
6.94
0.724
1.90
0.403
10- r
4.4
14.57
1.477
7.00
1.082
25- r
5.4
21.47
2.116
11.97
1.688
1 00- r
7.3
36.70
3.486
34.09
3.005
Notes:
Design Point #2 is identical to Design Point #20. No improvements are proposed in
the area tributary to this point, therefore no comparison between existing and
proposed is warranted.
Mitigated runoff rates and volumes as shown include the benefit of BMP's,
Detention, and Infiltration Measures.
# The 100 year storm values as shown are for illustrative purposes only. The
HydroCAD model for the existing storm drainage condition indicates that the current
system cannot handle this storm event.
The tables above indicate that peak rates have remained consistent or decreased
between post- drainage and pre- drainage conditions when summed at the design points
down gradient of the site. The new stormwater system conveyances will not discharge
untreated runoff into any resource or buffer areas and have been designed to infiltrate into
the surrounding soils through partial exfiltration in the underground stormwater
management system. A presumed increase in runoff is shown for the 100 -year post
condition at Design Point 10. The 100 -year storm is conveyed through a 30" horizontal
orifice emergency outfall emptying into the wetland upstream of the 24" square box culvert.
The existing 12" RCP outfall has been retained to convey clean roof runoff from the existing
three -story building to the wetland.
The groundwater recharge volume for this site has been calculated based upon
type A and type B hydrologic soils. The overall tributary drainage area consists of a 60 -40
split for group B and A soils respectively. Only 5% of the proposed impervious area covers
Type A soil. The recharge calculations have been adjusted to reflect a decrease in
required volume to compensate for existing impervious areas. The adjusted recharge
volume is calculated by reducing the total required recharge volume by the existing
required volume to total 0.037 acre -feet or 1,600 cf. Groundwater recharge is achieved
through partial exfiltration in the underground stormwater management system below the
outlet structure and in the stone and perforated pipe infiltration trench near the main
7
New England Deaconess >,_�ciation
80 Deaconess Road
Concord, Massachusetts 01742
entrance. The 2ft x aft x145 ft long infiltration trench has been incorporated into the design
to help convey snowmelt and runoff from Subcatchment 26. This area was removed from
Subcatchment 3 to help reduce the burden of the existing drainage system and to increase
the "dead storage" available for recharge. A total of approximately 1,600 cf of "dead
storage" is available for infiltration in these BMP's prior to any release. It is important to
note that these BMP's will continue recharge to groundwater as flow rates increase above
outlet inverts. The post- drainage conditions will not reduce groundwater recharge as
compared to the existing site and should improve as much of the existing impervious areas
have been directed towards the detention facility for partial infiltration.
A long -term infiltration rate of 2.2 inches per hour or 0.003 feet per minute was
estimated using the USDA soil classification of gravelly sandy loam and loamy sands
presumed in the detention area. This infiltration rate is consistent with the rapid
permeability in the substratum as listed in the USDA Soil Survey Engineering Properties
and concurs with published permeability rates for Charlton (CrC) and Hinckley (HgA) soils
ranging from 0.6 to 20 inches /hour. The depth to groundwater and long -term infiltration rate
will be confirmed through exploratory borings scheduled in for building and foundation
design.
Treatment of stormwater runoff volume equal to 0.5" of rainfall over the proposed
impervious areas tributary to the drainage area has been provided by the stormwater
management system for the purpose of meeting water quality standards. An increase of
1.76 acres ± of impervious area is proposed in the current layout (3.24a total - 1.48a
existing = 1.76a). The total impervious area of 1.76 acres produces the required total
volume of 0.073 acre -feet. A separate storm drainage conveyance system has been
designed to covey approximately 0.67 acres (29,000 sf ±) of new clean roof runoff to the
detention system for partial exfiltration. The actual volume to be treated has been reduced
to 0.045 acre -feet or 1,960 cubic feet by factoring in the reduction of roof top runoff volume
(1.76a - 0.67a =1.09a x 0.5" depth or 1,960 cf) because it is separated and conveyed
separately to the stormwater management facility. The required water quality volume has
been met through innovative technology by incorporating Stormceptor ® and VortechsTM
treatment systems. These water quality inlets incorporate baffles, weirs, and hydrodynamic
forces to enhance gravitational separation of floating and settling materials from stormwater
flows without conventional sediment traps. The Stormceptor® has been sized based upon
proprietary software which calculates sediment removal efficiency based upon particle size
distribution. The VortechsTM system has been specified as an off -line system that diverts
low flows to the unit for treatment. Each system has a high flow by -pass to safely convey
large, low probability storm events.
The proposed stormwater management system has been designed to provide in
excess of the required "calculated" 80% removal of Total Suspended Solids (TSS) tributary
to the conveyance system on the proposed site per the Massachusetts D.E.P. Stormwater
Management Policy. Discretionary street sweeping, deep sump catch basins, inlet
Stormceptor® and off -line Vortechs® systems have been utilized in the design to remove
an average of 87% of the Total Suspended Solids (TSS) from the tributary site runoff. The
performance of the Vortech® and Stormceptor® systems have been verified by the
Massachusetts Envirotechnology Partnership (STEP) and are approved for wide spread
use. The effect of the underground detention facility was not factored into the calculations
because the removal of accumulated sediment is more difficult than a conventional at-
grade system.
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New England Deaconess A,,_ ociation
80 Deaconess Road
Concord, Massachusetts 01742
The existing asphalt parking and service areas were retrofitted and routed through
water quality inlets and detention facilities to further reduce impact from the site. A chart
illustrating each proposed conveyance to the detention facility is provided in the
supplemental calculations. The supporting calculations indicate that the proposed facilities
are more than sufficient to mitigate the effects of the development on stormwater runoff
quality entering the resource areas.
1.7 STORMWATER MANAGEMENT STANDARDS
The following is an explanation on how the proposed project meets the Stormwater
Management Standards as prepared by the MA Department of Environmental Protection
and the MA Office of Coastal Zone Management. Please refer to the Stormwater
Management Form in Appendix B.
Untreated Stormwater (Standard 1) - No new stormwater system conveyances will
discharge untreated runoff into the resource or buffer areas or cause erosion in the onsite
wetlands. A closed- conveyance drainage system has been designed to direct stormwater
runoff from the newly developed areas to Stormceptor® and VortechsTM water quality inlets
for pre- treatment prior to partial exfiltration of first flush runoff through the underground
stormwater management system. A riprap outlet spreader will dissipate runoff energy from
significant storm events before release into a wetland resource area. The wetland will
transmit the clean runoff to the 24" Box Culvert eventually traveling into the Interstate 91
drainage system.
Post - Development Peak Discharge Rates (Standard 2) — The peak discharge rates
were calculated with the aid of a hydrograph routing program using TR -20 methodology. A
multi -stage outlet structure has been sized to meet the run -off rates for the 2 -yr, 10 -yr and
25 -yr storm events and reduce the volume of runoff over unmitigated levels. The
stormwater detention system will partially detain the 100 -year storm event to provide a
buffer against off -site flooding impacts. A 30" diameter emergency overflow orifice has
been incorporated into the outlet structure to convey the 100 -yr storm event. Exfiltration
will occur in the underground stormwater management system after pre- treatment through
deep sump catch basins and water quality inlets.
Recharge to Groundwater (Standard 3) - The majority (95 %) of the impervious areas for
the tributary drainage area are contained within Hydrologic Grouping B as shown on the
drainage area maps. Recharge to groundwater will be provided through partial exfiltration
in the underground stormwater management system and through a 145 -foot long infiltration
trench. An exfiltration rate of 2.2 inch /hour (0.003 feet/minute) is utilized in the calculations
and is consistent with sandy loam /loamy sand soils mapped onsite. The proposed
development and expansion will not reduce groundwater recharge as compared to the
existing site and will approximate current conditions to the extent feasible. Supplemental
drainage calculations found in the appendix.
Removal of 80% TSS (Standard 4) - The proposed stormwater management system has
been designed to provide the required "calculated" removal of the Total Suspended Solids
(TSS) for the conveyance system on the proposed site per the Massachusetts D.E.P.
Stormwater Management Policy. Discretionary street sweeping, deep sump hooded catch
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New England Deaconess A, . ciation
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basins, innovative water quality inlets, and a partial exfiltration detention facility has been
utilized in the design to remove an average of at least 80% of the Total Suspended Solids
(TSS) from the total site storm runoff. Large portions of the existing impervious parking and
service areas have been captured and treated by the proposed system to provide an
increase in treatment for the redeveloped portions of the site. A chart illustrating each
proposed conveyance outfall is provided in the supplemental calculations.
Land Uses with Higher Pollutant Loads (Standard 5) — The property is zoned suburban
residential (SR) district within the planned village overlay. The proposed use as an assisted
living facility is not considered a land use with high pollutant loads.
Critical Areas (Standard 6) — The project is not located within a critical area as defined
the Stormwater Management Policy. For the purposes of this design, an equivalent Water
Quality Volume of 0.5" x new impervious area was maintained and treated through
innovative technologies to preserve and protect the Bordering Vegetated Wetland resource
areas and buffer zones.
Redevelopment (Standard 7) — The project proposes a combination of redevelopment
and new development on the site. The associated improvements have been designed with
BMP's to the extent practicable to meet the performance standards in the Stormwater
Management Policy including retrofitting and expanding the existing system to meet TSS
removal, water quality, and mitigation of peak discharge rates.
Erosion and Sediment Controls (Standard 8) — Staked hay bales and filter- fabric fencing
will be used during construction as outlined in the Operation & Maintenance Pan and
shown on the plan set. Direction of silt -laden runoff shall be directed towards vegetated l
areas, temporary sedimentation basins, and diversion swales.
Operation and Maintenance Plan (Standard 9) — An Operation and Maintenance plan
has been customized to fit the design of the proposed Rockridge site improvements.
Provisions to maintain runoff control devices have been assured through structural, non-
structural, and construction management approaches. Please see the attached O &M Plan.
1.8 CONCLUSION
In conclusion, the results of this report indicate that the proposed stormwater
management plan appears to meet all requirements of the City of Northampton and the
Massachusetts Department of Environmental Protection's " Stormwater Management
Policy" within the scope and parameters of the proposed project.
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New England Deaconess A,-.cciation
80 Deaconess Road
Concord, Massachusetts 01742
STORMWATER OPERATION AND MAINTENANCE PLAN
OWNER AND RESPONSIBLE PARTY:
Construction Phase Activities:
New England Deaconess Association
80 Deaconess Road
Concord, Massachusetts 01742
Contact: Mr. Walter Bartkus, Director of Engineering Services
Phone: (978) 369 -5151
Day -to -day Operation and Maintenance:
Rockridge at Laurel Park
25 Coles Meadow Road
Northampton, Massachusetts 01060
Contact: Mr. Walter Jones
Phone: (413) 586 -2902
PROJECT OVERVIEW
The proposed project includes construction of a three -story addition (37,500 sf
gross floor area) to the existing facility plus 12 one - bedroom cottages and
associated site improvements including parking facilites, paved access drives,
utilities, landscaping, ADA compliant walkways, and a closed- conveyance
stormwater managememt system.
CONSTRUCTION MANAGEMENT
A construction manager with adequate knowledge and experience on projects of
similar size and scope shall be employed to oversee all sitework related
construction.
During construction, silt -laden runoff or discharge from dewatering operations (if
necessary) will be prevented from entering wetlands and resource areas untreated.
Siltation barriers consisting of a filter fabric silt fence, hay bales will be erected in
advance of construction along the downstream edge of all disturbed areas and
maintained throughout the construction period. Check dams will be used in
temporary constructed drainage ways as necessary to reduce erosion.
If dewatering is required during the construction, discharges may be directed toward
vegetated areas for settlement of suspended solids. Outflow of silt -laden runoff shall
not be permitted to flow directly into the wetlands or resource areas. Upon
completion of site stabilization, the catch basins and existing conveyance system
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New England Deaconess 1' ,, ,,ciation
80 Deaconess Road
Concord, Massachusetts 01742
shall be thoroughly cleaned of silt and sediment and made ready for the proposed
operation.
Siltation barriers, temporary settling basins, and diversion berms shall be
constructed and inspected by the resident project Engineer on a monthly basis or
as necessary, after any significant (0.5" or more) storm event and daily while
dewatering operations are proceeding.
Care should be taken when constructing stormwater control structures. Light earth -
moving equipment shall be used to excavate in the vicinity of the infiltration areas.
Use of heavy- equipment causes excessive compaction of the soils beneath the
basin resulting in reduced infiltration capacity. At no time shall temporary infiltration
areas or settling basins be constructed in the vicinity of the proposed infiltration
system in order to prevent the soils from becoming clogged with sediment.
NON - STRUCTURAL APPROACHES
PARKING LOT /DRIVEWAY SWEEPING
The property owner shall maintain a program of parking lot/driveway sweeping to
reduce sediment accumulation in the deep sump catch basins. It is recommended
that sweeping occur at least once in the fall and spring prior to cleaning and
inspection of the catch basin and manhole structures.
GRADING
The impervious areas of the site shall be graded as gently as possible, generally
not more than 4% or 5% slopes to reduce runoff velocities. Steep slopes will be
permanently vegetated to dissipate energy and reduce potential erosion. No
constructed vegetated slopes should exceed 2H:1 V. Steep slopes may require soil
reinforcement and additional vegetation.
FLOW OVER VEGETATED AREAS
Wherever possible, runoff from paved areas and snowmelt shall be directed over
vegetated areas to promote settlement of suspended solids before entering a
wetland or resource area.
STRUCTURAL BEST MANAGEMENT PRACTICES
DEEP SUMP CATCH BASINS, AREA DRAINS, AND MANHOLE STRUCTURES
Catch basins shall be cleaned, in dry weather, when half of the sump capacity is
filled or at a minimum of twice a year. Cleaning will take place at the completion of
construction, in early spring after sanding of roadways has ceased, and in the fall.
All manholes shall be inspected at least once annually. Any obstructions, sediment,
and debris that could potentially cause clogs shall be removed within the
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New England Deaconess r&,,�ciation
80 Deaconess Road
Concord, Massachusetts 01742
conveyance system as necessary. Inverts, grates, and hoods shall be checked and
replaced as necessary to maintain hydraulic effectiveness.
DETENTION FACILITY WITH PARTIAL EXFILTRATION
The underground detention system has been designed with riser structures at grade
to aid the removal of sediment and debris accumulating in the structure. The
detention facility contains a multi -stage outlet structure to meet individual storm
events. Once the system goes online, inspections should occur after each storm
event for the first few months to ensure proper stabilization, function, and to ensure
that the outlets remain free of obstructions. Preventative maintenance shall be
performed at least twice per year and after every major storm event (> 1" of rainfall)
and shall include removal of accumulated sediment, inspection of the detention
structure, and monitoring of groundwater and infiltration rates to ensure proper
operation of the system. Important items to check for include differential settlement,
cracking, breakout, clogging of outlets and vents, and root infestation. Water levels
should be checked and recorded against rainfall amounts to verify that the drainage
system is working properly.
ENERGY DISSAPATORS AND LEVEL SPREADERS
During the construction phases of the project, the energy dissipaters and level
spreaders that receive significant runoff shall be inspected monthly and cleaned as
necessary and /or after major storms events (> 1" of rainfall). Thereafter, these
structures will be cleaned at least twice per year, in the spring and fall, or as needed
depending on the frequency of major storm events (> 1" of rainfall). The riprap shall
be inspected, cleaned of sediment and debris, and reinstalled as necessary to
maintain effectiveness.
GRASS -LINED SWALES
Swales shall be inspected on a semi - annual basis in the early spring and fall.
Additional inspections shall be performed during the first few months after
construction to ensure that adequate vegetation has been established. Regular
maintenance shall include mowing, fertilizing, pruning, debris removal, and
weed /pest control. Swales shall be mowed at least once per year to a minimum of
4 inches so as not to reduce the effectiveness of pollutant removal and energy
dissipation. Accumulated sediment and debris shall be manually removed at least
twice per year.
WATER QUALITY INLETS
Water quality inlets shall be inspected and cleaned in accordance with the
manufacturer's recommendations. Documentation from the manufacturer is
attached.
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