HomeMy WebLinkAboutStormwater Narrative - Correspondence - 122 MILLPOND 2/7/2023
21 High Street, Suite 207
North Andover, MA 01845
C IVIL D ESIGN G ROUP, LLC
Tel 978.794.5400
ENGINEERING. LAND USE. PLANNING. PERMITTING.
www.cdgengineering.com
February 7, 2023
Town of North Andover
Planning Board
120 Main Street
North Andover, MA 01845
Re:Proposed Residential Development
122 Millpond
North Andover, MA 01845
Site and Stormwater Narrative
Dear Planning Board Members:
The proposed project is a single parcel totaling 0.81± acres and is located at 122 Millpond at the
intersection of Harkaway Road and Stevens Street. The site lies in the Residence 4 zoning
district and is currently comprised of two maintenance buildings and an existing driveway on
Harkaway Road with two tennis courts. The proposed development includes the removal of the
two tennis courts and the construction of two duplex residential structures and associated
driveways with utility connections. Theparcel is proposed to be subdivided into two Approval
Not Required (ANR) parcels, whereby the westerly parcel will include the existing maintenance
structures to remain and a proposed duplex building and the easterly parcel will include one
proposed duplex building. The site is bounded to the west by the Millpond development, to the
north by a single family residence to the south by Harkaway Road and to the east by Stevens
Street.
According to FEMA flood insurance rate maps community panel number 250098C0228F,
effective date 07/03/2012, the sitedoes not lie within a floodplain. The site also does not lie
within a buffer/resource area or within an aquifer protection area. The site does not lie within an
area mapped for rare and endangered species or certified vernal pools as mapped by the State of
Massachusetts’ Natural Heritage and Endangered Species Program (NHESP) or within an Area
of Critical Environmental Concern (ACEC).
Based on the field survey,the entire parcel drains in a southerly direction via overland flow to
the intersection of Harkaway Road and Stevens Street, where it is collected via the Town’s
drainage system. As such, the stormwater study presents acomparative analysis of the pre-
development and post-development hydrologic characteristics tothe site at the intersection.
Northeast Regional Climate Center (Cornell Rates) was utilized to source the precipitation values
andTechnical Release 55 (TR-55) methodology was utilized to determine weighted curve
numbers (CNs) for each pre and post-development subcatchment area. Weighted CNs are based
on ground cover type and hydrologic soil groups (HSGs). The times of concentration (Tc's) for
each of the existing and proposed watersheds have been calculated. The areas that do not show a
Tc travel path resulted in travel times of less than 6 minutes. CN and Tc values were then
utilized to generate hydrographs using HydroCad 10.0, an industry standard software package
commercial retail residential mixed use subdivisions industrial municipal
21 High Street, Suite 207
North Andover, MA 01845
C IVIL D ESIGN G ROUP, LLC
Tel 978.794.5400
ENGINEERING. LAND USE. PLANNING. PERMITTING.
www.cdgengineering.com
that develops a hydrologic model based on the SCS method and computes peak discharges from
rainfall runoff for urban and rural watersheds.
The project results in a net reduction of impervious area totaling 6,500± square feet, therefore,
this site is considered a redevelopment. Therefore, peak flow rates will be reduced as
groundwater recharge will increase as compared to the existing condition. Additionally, a small
rain garden is proposed in betweenthe proposed duplex buildings and is designed to take the first
flush (1”) of rooftop runoff from each of thenew buildings. The overflow is a 10’ wide earthern
berm spillway behind the edge of pavement to controlthe runoff from larger storms. Peak flow
rates for the pre-development and post-development conditions are illustrated below:
TABLE 2: PEAK FLOW RATE COMPARISON
POINT 2-YEAR STORM 10-YEAR STORM 100-YEAR STORM
OF EVENTEVENTEVENT
(3.15”/24-HR)(4.83”/24-HR)(8.94”/24-HR)
ANALYIS
PRE (CFS)POST (CFS)PRE (CFS)POST (CFS)PRE (CFS)POST (CFS)
1.252.194.76
POA-10.901.774.29
Sincerely,
C IVIL D ESIGN G ROUP, LLC
Philip R. Henry, P.E.
Principal
cc.
Mr. Thomas Zahoruiko, Applicant
commercial retail residential mixed use subdivisions industrial municipal
NRCC 24-hr D 2-Year Rainfall=3.15"
NRCC 24-hr D 2-Year Rainfall=3.15"
NRCC 24-hr D 2-Year Rainfall=3.15"
NRCC 24-hr D 10-Year Rainfall=4.83"
NRCC 24-hr D 10-Year Rainfall=4.83"
NRCC 24-hr D 10-Year Rainfall=4.83"
NRCC 24-hr D 100-Year Rainfall=8.94"
NRCC 24-hr D 100-Year Rainfall=8.94"
NRCC 24-hr D 100-Year Rainfall=8.94"
NRCC 24-hr D 2-Year Rainfall=3.15"
NRCC 24-hr D 2-Year Rainfall=3.15"
NRCC 24-hr D 2-Year Rainfall=3.15"
NRCC 24-hr D 10-Year Rainfall=4.83"
NRCC 24-hr D 10-Year Rainfall=4.83"
NRCC 24-hr D 10-Year Rainfall=4.83"
NRCC 24-hr D 100-Year Rainfall=8.94"
NRCC 24-hr D 100-Year Rainfall=8.94"
NRCC 24-hr D 100-Year Rainfall=8.94"