HomeMy WebLinkAboutStormwater Management Report - - 364 JOHNSON STREET Stormwater Management Report-364 Johnson Street
STORMWATER MANAGEMENT REPORT
Watershed Protection District Special Permit
Project Address: 364 Johnson Street North Andover, MA
Parcel ID: 038.0-0015-0000.0
Applicant: Gregory & Melissa Buitkus
Prepared by: John J. McDonnell, PE, PPS
Massachusetts Registration No.: 33601
Date: August 3, 2025
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StormwaterMkanagememt Report-364 Johnson Street
TABLE OF CONTENTS
1~ Project Overview ................................................................................................................4
11- Design Parameters.___'~_--~_~____`____..~-..~..-~.'--..~._-...__.-_.--_._``-'._-~__--....~~~.~5
111. Design Storm Rainfall Data..............................................................................................6
A. Y Roof Subcatchment '.-_.-.~.-.-.~--._.`_-_...—'..'.--..---......_`....~~...~~..~.6
IV. Skormwater Management System-.~.-..~.~~.~~.~~................~~.~....~..~..~..~~..~_..._..~~~..__-._~_`~~-7
B. Overview......................................................................................................................7
C. Soil Conditions............................ 7
QTest Pit .-.'.--.._..-~~~-.-.-.~...~..-...~.~~.-.-'.~~~_~'~.'.._..'..~..~...~.....~..7
2) Soil Profile ____.-._-....~.......-......~.~..~._.~.-~...-._-..._____-.-~___.~_~~~.~~~~7
3\ Subsurface Conditions.._-_.~-'.~_~.~~~^~~..`~~~~.~~~~~~...~..~_.-..._'~_____-~-.-__-.-~~~_~~'7
Do .......-.....~._..'~_`.._`..-.......a~._.o..`.........~.........8
4) System Configuration~~~~.^-~'..~~~'.~-~~.-~_~.._`'~.~~~-_~.-'~....-~'--~'~~~~`~_..^.~~~.~..'~~..8
5! Design Specifications~~~_~_~~_....... ......................................_~~_......._~,_~~~~_~~~~.~~.,~~,~~~~~~,8
6) Water Quality Performance................................................-..._....-........_-..... -..........8
71 Maintenance.~,~,,~~,,~~~,,,,.~~,,,~,.~,,.~_,~'~,`,,,~,,,,,,,,,.`~~,.~.~.,~~,._,~',~,,8
E. Infiltrat ion Chamber.~~....-........~.~......-'......`~-...............'...~~~...........~.........8
F. Site Conditions& Installation .......................................... 10
8) Groundwater and ElevationManagement:........................................ ......................10
9) System Design Criteria:......................................................~._.....0..~...0 0.4 0 6-00..0* 10
Go Performance ~~.~~...~....~~.....~~~......~~.......~...~~.~.~~-...~.~_` 80
\HN Peak Flow Reduction.``___.~....~___.~___..~-^__~_____-~~'~~~~-~-,~~~~.~~-~~-~~~~~..~..~~~.~10
11) Volume Management.................. 10
12) Drawdownn Analysis (Time to ....~..............~...........,.....,_.~.`..~~ I I
V. OPERATION AND MAINTENANCE PLAN~-...~...~~.'....~....~.......~.~..~.'.........~....... I
H. System Components and Responsibilities.................................^...���........................11
13\ System Overview........_~~~~--~~~~-~~~-................_~.-~-...................................... ...... ...11
14\ System Components Description........................................ 12
15) System Location Reference~.~.....----...-...~'.~..-~.~.~..~....~...o 12
16) Homeowner Responsibilities.........................................................
.~__-..-.~__-~~-~.�~~-
17) Routine :-~..~,~~~.~.....~__~~~.~~~~~^~.,~~~_,~,~,~~~,_,~~~,_~~_,_____13
Stormwater Management Report-364 Johnson Street
18) Professional Mal*ntenance#,,,,,,,,.,,,,,,,.........................................................................13
1. Inspection and Monitor'I Requirements.......................................................................13 ng
19) Inspection Elements-, 13
J. Maintenance Agreement..and Easements.........................................................................13
20) Maintenance Responsibility .................................................................................... 13
K. Annual Repo 1119rt* Requkements........... 13
21) 13
VI. Compliance& Benefits..................................................................................................13
VII. Recommendation...........................................................................................................14
VIII. APPENDIX A....#** 15
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Stormwater Management Report-364 Johnson Street
l. Project Overview
This report presents the stormwater management analysis for a proposed 376 square foot roof
addition at 364 Johnson Street. The infiltration system has been conservatively designed to
accommodate the addition.
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Stormwater Management Report-364 Johnson Street
i. Design Parameters
Table 1. Design parameters for current roof addition, total managed area, design storm, and
surface type.
Parameter Value
Current Roof Addition 376 sq ft (Subcatchment 1 S)
Total Managed Area 376 sq ft
Design Storm I 00-year, 24-hour event (T.97 inches rainfall per NO AA Atlas 14)
Surface Type 100% impervious (CN - 98)
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S.174)tormwater Management Report-364 Johnson Street
Ill. Design Storm Rainfall Data
The system has been designed using the 100-year, 24-hour event rain fall data from
NOAA Atlas 14 (?. 711)
A. 1 00-year Roof Subcatchment
Summary for Subcatchment I S: Roof
Runoff 0,,07 cis 0 12.03 hrs, Volume= 0,006 af, Depth= 7,73"
Routed to Pond 2P -- Infultration Chamber
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0,00-25,,00 hrs,
PF—Depth_English—PDS 24-hr S1 1 00-yr Rainfall=7,97""
ion
376 98 Roof
376 100.00% Impervious Area
Tc Length Slope Velocity Capacity Description
5'0 22 0.07 Direct Entry. Ridge to Outter
Subcatchment I S: Roof
Hydrograph
Q,W CfS
0075
PF 13 th_;�'En lisOiLp S -h# S
007 ps
0065
006 Riona VC luo'',
0�055 R 3110 1, a.
P"
005 en
1
Y�
I............ ........ .....
0 CkOE5
00-4
.................................. ...................... .......
�r
O�035
003
Figure 1. In a 1 00-year, 24 hour storm event, the peak runoff rate for proposed roof is 0.07 ds.
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Stormwater Management Report-364 Johnson Street
IV. Stormwater Management System
B. Overview
The proposed system utilizes a subsurface infiltration chamber(Cultec 1 -180HD) as the primary
means of storage and infiltration.
The proposed system utilizes a mini dry well (Shea Mini-Dry Well) as the primary means of
pretreatment.
The System Flow Path is the Following:
0 Roof---+ Gutters --+ Downspouts --+ Pretreatment--+ Infiltration ---+ Groundwater
C. Soil Conditions
1) Test Pit Investigation:
• Performed by: John McDonnell P.E., C.S.E
Date: June 7, 2025
0 Test Pelt: TH-1
0 Surface Elevation: 255.8 feet
2) Soil Profile Description:
* off -10": Horizon A, Fine Sandy Loam (FSQ, 10YR 3/4 (dark yellowish brown)
0 10" -23": Horizon Bw, Fine Sandy Loam (FSQ, 1 OYR 6/8 (brownish yellow)
& 23" -74": Horizon C, Sandy Loam (.SLR, 2.5Y 5/6 (light olive brown)
3) Subsurface Conditions
0 Mottling observed at 48" depth (Elevation 251.8 feet)
a Water weeping at 71" depth (Elevation 249.9 feet)
0 Soil texture: Predominantly sandy loam throughout profile
0 Infiltration capacity: Good infiltration potential based on soil texture
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Story water Management Report-364 Johnson Street
D. Pre-treatment System
4) System Configuration
A Shea Concrete Mini Dry Well (160-gallon capacity) provides pretreatment upstream of the
Cultec infiltration system.
5) Design Specifications
•
Capacity: 160-gallon precast concrete chamber
• Access: Cast iron grate with 24" round frame for maintenance
• Filtration: Filter fabric and crushed granular media
• Outlet: 4"diameter connection to distribution system
6) Water Quality Performance
The system achieves 85% Total Suspended Solids (TSS) removal in the main infiltration
chamber, exceeding the 80% regulatory requirement. Per the TSS Removal Calculation
Wort sheet from the Massachusetts Stormwater Handbook, the Shea mini dry well provides
initial treatment (25% TSS removal) through settling with the designed 24 in sump, with the
Cultec infiltration system providing additional treatment (80% of remaining load).
Location:1364 Johnson St,Now Andover,MA 01845
B C D E
TSS Removal Starting TSS Amount I
GIMP' Rate' Load* Removed C*D I"
0
04%V Sump and Hooded
Catch Basin 1 0.25 1.00 0.25
M Dry Well 0.80 0.76 0.60
> 0.00 0.15 0.00
0 0
E0)
cen 0.00 0.15 0.00
U)
U)
0.00 0.00
0.16
Separi-,
ha r.no
7) Maintenance
The 24"access cover allows for periodic inspection and cleanout of the mini dry well chamber to
maintain system performance.
E. Infiltration Chamber
Table 2. System components and specifications of proposed subsurface infiltration chamber
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Stormwater Management Report-364 Johnson Street
System Specification
Component
Configuration 3 chambers in stone field
Dimensions 9.33' x 12.00' x 2-83'deep
Storage Capacity 166.7 cubic feet (0.004 acre-feet)
Infiltration Rate 12 inches/hour(derived from field percolation test yielding 24
inches/hour with factor of safety of 2.0 applied)
Emergency Emergency overflow pipes installed per manufacturer specifications.
Overflow System design prevents surface discharge during 1 00-year, 24-hour
storm events through adequate storage capacity and infiltration rates.
Pond 2P,., Infultration Chamberw Ch,amber Wizard Stone F
Chamber Model 411W Cultec R-180HD (For resildential use only)
Effective Size= 33,.6W' x 20.0H => 3.44 sf x 6,33L = 21.8 cf
Overall Size= 36.0"W x 20.5"'H x T33"L with 1,00" Overlap
Row Length Adjustment= +1.00" x 3-44 sf x 3 rows
36.0'tWide + 6-0"" Spacing = 42.0" C-C Row Spacing
1 Chambers/Row x 6-33" Long " Row Adjustment = 7.33" Row Length +12.0" End
Base Length
3 Rows x 36-0"' Wide -#- 6.0"' Spacing x 2 + 12.0" Side Stone x 2 = 12.00" Base Width
6.0" Stone Base + 20.5"" Chamber Height + 6-0""l Stone Cover = 2 71" Field Height
3 Chambers x 21,,8 cf +1.00" Row Adjustment x 3,44 sf x 3 Rows 75.6 cf Chamber
303.2 cf Field - 75,,,,6 cf Chambers = 227.6 cf Stone x 40.0% Voids 91.0 cf Stone Stol
Chamber Storage + Stone Storage = 166.7 cf = 0-004, af
Overall Storage Efficiency = 55.0%
Overall System Size = 9.33" x 12.00* x 2-71
3 Chambers
11.2 cy Field
8.4 cy Stone
Figure 3. Modeled Infiltration Chamber System Embedded in Stone Field
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for water Management Report-364 Johnson Street
F Site Conditions & Installation
•
8) Groundwater and Elevation Management-,
Seasonal high groundwater: Estimated at elevation 251.8 feet (based on mottling
observed in Test Pit TH-1)
• Stone field bottom elevation: Set at elevation 254.0 feet to ensure minimum 2-foot
clearance above groundwater
• Actual groundwater separation: 2.2 feet(exceeds CEP minimum requirement)
Final turf elevation: 257.16 feet above system installation
Site regrading-, Area will be regraded post-construction to achieve proper drainage
patterns
9) System Design Cntena,*
• Groundwater protection: System design maintains adequate separation from seasonal
high groundwater to prevent contamination and ensure proper infiltration
• Drainage design: System design maintains adequate slope for proper drainage and
conveyance to treatment components
G. Performance Analysis
The HydroCAD analysis demonstrates excellent system performance-.
10)Peak Flow Reduction
Table 4. Pre-and post-treatment peak flow (in cfs)
Flow Parameter Value
Pre-treatment Peak Inflow 0.07 cfs
Post-treatment Peak Outflow 0.03 ds
Flow Attenuation 67.1%
1 I)Volume Management
Table 5. Volume parameters related to surface discharge to watershed
Volume Parameter Value
Total runoff volume (100-year storm) 0.008 acre-feet
Runoff infiltration All runoff infiltrated through subsurface system
Surface discharge to watershed None
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Stormwater Management Report-364 Johnson Street
Pond 2Ps,, Infultration Chamber
Hydrograph
r r a
.m.
.......
w e
tnoo
0.075
e r f
0.0 _ ae� _ _ _ e mm eed:4'..0 0-1#
tD
e n _ m......(
0.055
r � �
05, ae �e. mm
r
0 0.045,
j
ae �,
� �eeem
.... �.
i � r
..... .
r
0.035,
�o LL
o,,03--
o
..0.025-
e �� �.
.,.ed
,
j
nn
Figure 4. Infiltration Chamber Hydrograph shows all runoff Infiltrated through subsurface
system
1 Drawdown Analysis (Tian to Empty
• 2-year storm: 6.5 minutes
• 10-year storm: 11.7 minutes
• 2 -year storm: 15.4 minutes
• 100-year storm: 21.9 minutes
V. OPERATION AND MAINTENANCE PLAN
H. System Components and Responsibilities
. . .
13)System Overview
The stormwater management system consists of four primary components working in series to
capture,pretreat, and infiltrate roof runoff from the 376 square foot addition.
System Flow P'ath.*Roof--► Gutters--+Downspouts MU'U' Drywv`ell(Pretreatment) --*Cuitec
Infiltration Chambers -- Groundwater
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Stormwater Management Report-364 Johnson Street
14)System Components Description
1. Collection System
• Roof gutters and downspouts: Collect and convey roof runoff through 4-inch PVC
connections
• Underground piping: 4-inch Schedule 40 PVC pipes transport water between system
components at minimum 1% slope
2. Settlement and Distribution System (Mini Drywell)
• Component: Shea Concrete Mini Dry Well, 160-gallon capacity
• Function: Provides initial treatment through sedimentation in the 24-inch sump
• Access: Cast iron grate with 24-inch round frame for * ection and maintenance
Insp
• Performance: Achieves 25%Total Suspended Solids(TSS)removal through settling
3. Primary Treatment System (Infiltration Chambers)
• Component: Three (3) Cultec R-1 80HD chambers in engineered stone field
• Dimensions: 9.33x 12.00' x 2.83'deep
• Storage: 166.7 cubic feet total storage capacity
• Function-, Final treatment and infiltration to groundwater at 12 inches/hour design rate
• Performance: Achieves additional 80% TSS removal for combined system efficiency of
85%
4. Emergency Overflow System
• Component: Emergency overflow pipes per manufacturer specifications
• Function: Prevents surface flooding during extreme events exceeding design capacity
15)System Location Reference
Attached hereto as Appendix A is a view from thesite plan showing the precise location of
all stormwater system components. This drawing is provided for the homeowner's future
reference to locate system components for "inspection and maintenance activities.
16)Homeowner Responsibilities
The property owner is responsible for maintaining the storm water management system in proper
working condition to ensure regulatory compliance and system performance. Specific
responsibilities include.
• Routine inspection of roof gutters and downspouts
• Seasonal cleaning of debris from system inlets
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for water Management Report-364 Johnson Street
• Annual inspection of pretreatment chamber
• Prompt repair of any system deficiencies
17)Routine Maintenance (Homeowner)-,
• Quarterly: Visual inspection of surface conditions
• Bil-annually: Gutter and downspout cleaning
• Annually: Pretreatment chamber inspection and cleaning
40 As needed:, Debris removal and minor repairs
18)Professional Maintenance*.
• Every 3-5 years: Comprehensive system evaluation
• As needed: Infiltration rate testing and system rehabilitation
1. Inspection and Monitoring Requirements
19)Ins pection Elements:
• Roof drainage system condition
• Pretreatment chamber sediment levels
• Evidence of system backup or overflow
• Infiltration performance observations
J. Maintenance Agreement and Easements
20)M ant enance Responsibility
• Property owner responsible for system maintenance
• Access maintained for inspection and cleaning
• Documentation of maintenance activities
• Professional assistance as needed
K. Annual Reporting Requirements
21)Documentation
• Annual maintenance log
• Inspection findings and recommendations
• Any repairs or modifications made
• System performance observations
Note: The attached I" = 10' site plan(Appendix A)provides precise component locations and
shall be referenced for all future inspection and maintenance activities. This drawing is essential
for locating buried system components and should be retained with property maintenance
records.
V1. Compliance & Benefits
1. Watershed Protection: The system eliminates all surface runoff, providing 100%
volume control and significant peak flow reduction.
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Stormwater Management Report-364 Johnson Street
2. Conservafive Design: The system is sized for 340% more impervious area than the
current roof addition, ensuring adequate capacity for future development. Infiltration rate
based on site-specific testing with a conservative safety factor.
3. Groundwater Recharge:All stormwater is returned to the groundwater system through
infiltration, maintaining natural hydrology.
V11. Recommendation
The proposed infiltration system exceeds typical stormwater management requirements by
providing complete volume control and substantial peak flow attenuation for both current and
anticipated future development. The system design ensures no adverse impact to the
watershed and supports the Town's stormwater management objectives.
Analyst's prepared using HydroCAD@ software following SCS TR-20 methodology
Prepared By: John J McDonnell,PE, PLS
..0 F
III
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OHNJ.
WDONNELL
CIVIL
No.41157
119 T F.
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Page 14 of 15
Stormwater Management Report-364 Johnson Street
VII L APPENDIX A
ttn
mm
F
EXISTING EXISTING
C) 2 STORY 1 STORY
BUILT IN 1964
PROP PROP
ENTRANCE 2 STORY
812"X49
ADDITION Ilk,
f -PROP.
16'px23168* r DECK:
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nwmi 6#6*x4#611
PROP,BASEMENT'
WALKOUT
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. . . . . . . . . .
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CD . . . . . . .
PROP.,"
RECHARGER
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