HomeMy WebLinkAboutTechnical Memorandum - Woodard & Curran 4.3.26 - Miscellaneous - 0 Prescott Street 4/3/2026 -A�
Woodard
Curran
TECHNICAL MEMORANDUM
TO: Tim Willett, Town of North Andover
PREPARED BY: Taylor Christmas
REVIEWED BY: Kenneth W. Carlson, PE
DATE: April 3, 2026
RE: Zero Prescott Street Development Sewer Capacity Analysis
Preliminary Results of Flow Metering and Interceptor Sewer Model Run
1. Background and Purpose
Woodard & Curran was retained by the Town of North Andover (Town) to build a hydraulic model of a
portion of the East Side Interceptor Sewer to evaluate downstream sewer capacities under both existing
peak dry and wet weather flows and the addition of future flows from the planned development at Zero
Prescott Street. The purpose of this memo is to provide an update on the anticipated impact on sewer
capacity of the East Side Interceptor as a result of existing peak flow and future development flow.
2. Existing Peak Flow
Two temporary flow meters were installed on February 10, 2026 by Flow Assessment Services, LLC
(FAS) in order to measure existing wastewater flow in the East Side Interceptor Sewer downstream of the
proposed Zero Prescott Street Development — Meter Site #1 at MH 11002 on the East Side Interceptor
Sewer before it reaches Sutton Street, and Meter Site #2 at MH 09088 on Sutton Street. To date, Meter
Site #1 has experienced a peak flow of 4.2 mgd. This peak flow occurred on March 11, 2026 as a result
of significant rainfall and snow melt in the area. Metering is scheduled to continue for several more weeks
in order to better understand flows in the East Side Interceptor Sewer during the traditional spring high
groundwater season when wastewater flow is expected to be at its peak. This memo will only address the
flows at Meter Site#1, as the flow data at Meter Site#2 is currently being reviewed by FAS.
It should be noted that Meter Site#2 includes flow from the Sutton Street 18" main sewer, which serves a
significant part of Town, as well as the East Side Interceptor Sewer. In addition, significant flow from a
large part of Town is introduced into the East Side Interceptor Sewer at Main Street prior to the GLSD
Meter. Accordingly, the focus of this capacity evaluation is on the East Side Interceptor Sewer from the
Zero Prescott Street Development to Sutton Street, since the remaining portion of the East Side
Interceptor Sewer serves a signifcant part of the Town such that assessing the impacts of the Zero
Precscott Street Development on the rest of the interceptor sewer would be unreasonable.
3. Future Development Flow from Zero Prescott Street
Based on the Comprehensive Permit Application Package dated October 21, 2025, the future
development at Zero Prescott Street is anticipated to have a total of 457 units. Massachusetts Title 5
Guidelines recommend using 110 gpd/unit to estimate future wastewater generation. This would result in
an average dry weather flow (ADWF) of 50,270 gpd. Using a typical dry weather diurnal curve peaking
factor of 1.87, the resulting peak dry weather flow (PDWF) would be 98,549 gpd, or approximately 0.1
mgd.
4. Total Peak Metered Flow and Model Results
Based on the peak flow experienced at Meter Site #1 this spring, the interceptor sewer is anticipated to
experience a peak flow of approximately 4.2 mgd upstream of MH 09100, where a larger portion of
........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
Town of North Andover(0234962.12) 1 Woodard &Curran, Inc.
North Andover Interceptor Model Update April 3, 2026
_A�
Woodard
Curran
unmodeled sewer ties into the interceptor, prior to the Zero Prescott Street development wastewater flow
contribution. This peak flow was simulated in the modeled portion of the East Side Interceptor with the
proposed Zero Prescott Street development wastewater flow to assess impacts on the hydraulic gradeline
(HGL). The resulting HGL shows a peak d/D value of 0.59 for the one section of sewer between MH
11008 and MH 11007, meaning the interceptor sewer currently has capacity to carry the additional flow
from Zero Prescott Street without surcharging this sewer section but should be monitored in the future for
potential increases in the HGL. (see Figure 1). It should be noted that interceptor sewer capacity and flow
will be re-assessed once the flow monitoring period is complete. At that time, the model will be calibrated,
and a design storm will be simulated based on calibrated wet weather parameters, which will likely result
in a higher peak d/D value. The resulting impact of the higher d/D value of that section of the East Side
Interceptor Sewer will be assessed at that time as to whether the Zero Prescott Street Development
wastewater flow will have any significant impact on sewer capacity of that section. No significant impact
from the Zero Prescott Street Development is expected on the capacity of the remaining downstream
sewer sections of the East Side Interceptor Sewer from MH 11007 to Sutton Street.
Figure 1
PARTIALLY FULL PIPE-Flows and velocities eat various depths
Instruction:Fill out green cells,yellow cells ore results.Do not olterhlue or yellow cells.Assam e free flow condvtrons.
Diameter(in):.. 24 '..
Slope( ): 0.19 f
Flow depth(in): 14.25
d/D: 1 t1.59 33
Pipe diameter(ft) 2.11170 /
Pi pe Area gfr2): 3.142 � 1 � ,»»»»»»»»»»»»»»»»»»»»»»»»»»»»»»»»»»» »»»»,;�
Flow depth(ft): 1.188
Flowwrate gmgd): 4.21 U
Flo ww rrate(cgs): 5
t rn. 3.�7
velocity
rf`r� CI
g p)' 362
i
j
d......... d)tt) d/2 d...)tt) ANGLE A(rad,) c)tt) AREA B(fr2) AREA A+AREA B(tt2) AREA A)tt2) wetted perimeter)tt) Floww)cts) Velocity(fps)
59.3% 1.186 101.185 2.715,7 1.9,65 101.193 1.394 1.941 3.516 6.524 3.3,62
59.4% 1.1818 01.18,8 2.753 1364 101.185 1.382 1345 3.520, 6.541 3.3,64
59�.5% 1.19,01 101.190, 2.759 1364 101.1;8�7 1.380, 1348 3..524 6.558 3.3,66
59.6% 1.192 101.192 2.755. 1.9�63 101.1;8,8 1.378 1.1952 3.528 6.575. 3.3,68
59�.7% 1.194 101.194 2.751 1.9�62 101.190 1.3716 1.956 3.5.32 6.5192 3.3,69
........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
Town of North Andover(0234962.12) 2 Woodard &Curran, Inc.
North Andover Interceptor Model Update April 3, 2026