Conservation Commission Meeting Agenda/Materials 109R and 131 Clark Lane Exhibit List (linked)

Provost G Roverto, Inc.
Civil Engineering e Surveying ° Site Planning ° Structural ° Mechanical ° Architectural Engineering
P.O. Box 191 Telephone (860) 230-0856
57 East Main Street Fax (860) 230-0860
Plainfield, CT 06374 www.prorovinc.com
C-22-14
109R & 131 CLARK LANE
PUBLIC HEARING
February 9, 2023 EXHIBIT # 48
Maureen Fitzgerald, Environmental Planner
Town of Waterford
15 Rope Ferry Road
Waterford, CT 06385
RE: Kingstown Properties, LLC — Affordable Housing Development — Clark Lane
P&R Job No. 213009
Dear Ms. Fitzgerald:
We are in receipt of the February 7, 2023 secondary report prepared by Sigrun Gadwa of Carya Ecological
Services, LLC. We understand that this report as well as the previous January 26, 2023 were commissioned
by one or more abutting property owners who have expressed opposition to the proposed project. In spite of
the questionable prejudicial position that Ms. Gadwa has taken in her review of this project based on Section
10 of her report, we feel it is important to clarify several of the salient technical issues discussed in the report.
The following is offered in response to these particular issues:
1,
Section 1 of the Carya report addresses the Clark Lane drainage system discharge that is currently
proposed to be collected and treated through the project’s stormwater system. Because of the lengthy
discussion by Ms. Gadwa at the January public hearing about this proposal, we prepared a schematic
alternative plan showing a potential extension of the Clark Lane system to the easterly limits of the
project. Ms. Gadwa indicates that this plan includes “no mention of a spreader of any sort” in spite of
clearly and obviously showing a potential level spreader. We maintain our position that our
collection and treatment of this stormwater is prudent and is a direct result of: (a) following the
protocols of the Jordan Brook Watershed Management Plan; (b) requests by Town staff during the
preapplication review process that we do so and; (c) generally accepted good engineering practice.
Despite this, if the Commission would prefer this alternative approach, it is a technically feasible
alternative and can be incorporated into the final design in the manner shown on the alternate site
plan.
Section 4 of the Carya report suggests a design alternative whereby every other house is eliminated
and replaced with a small biofiltration basin or rain garden. Assuming that we would continue to
collect and treat the Clark Lane discharge because we were requested to do so, if the applicant
redesigned the project as suggested by Ms. Gadwa, the net effect would be a reduction of impervious
coverage of approximately 22% draining to the stormwater basins. While this may result in a small
decrease of the size of both the bioretention basin and detention basin, it is important to understand
that the design flow to these basins is generated by both the impervious coverage and pervious
coverage in the contributing watershed. There is not a linear relationship between impervious
coverage and size of these basins. In general terms, a 22% reduction in impervious coverage might

result in a 10% reduction in the footprint of each basin. (The exact size reduction would require a
complete and detailed stormwater analysis and iterative basin design.) We also note that given the
sensitive nature of the receiving watercourse (Fenger Brook) it would generally be desirable to
maintain the size of the basins to provide additional treatment volume and enhanced stormwater
quality. We further note that the use of rain gardens to serve each individual unit was discussed
during preapplication reviews. Because individual unit rain gardens are typically small landscape
features, there is a higher likelihood that they will be modified or removed in the future or that their
function will unknowingly be impaired. While they would provide an appropriate level of
stormwater treatment initially, any loss of function that occurred over time and without notice would
negate their benefit. Because the entire project will be owned and managed by a single entity, the
current proposal with a single larger basin was chosen because it will not slowly disappear and it can
be maintained in perpetuity to ensure future stormwater quality as intended.
Ms. Gadwa suggests that the proposed design does not meet the Stream Channel Protection criteria in
Section 7.6.1 of the 2004 Connecticut Stormwater Quality Manual in spite of the fact that the
information necessary to establish this has not been submitted to date. The proposed design not only
meets the Stream Channel Protection criteria, it far exceeds the criteria. Per the 2004 Manual, the
typical criteria is to “control the 2-year, 24 hour post-development peak flow rate to the 1 year, 24
hour predevelopment level.”
The 1 year, 24 hour predevelopment peak flow from just the Clark Lane discharge is 2.87 cfs.
The 2 year, 24 hour post-development peak flow from our entire developed site, including Clark Lane
is 1.98 cfs.
Clearly, the Stream Channel Protection criteria have been met and exceeded based on this simple
analysis alone.
Related to this point is the assertion by Ms. Gadwa that in spite of the proposed level spreader design,
the presence of an existing stone wall immediately down gradient thereof and the stable existing soil
conditions between the detention basin discharge and Fenger Brook there will be significant erosion
of channels caused by this discharge. Expanding on the above analysis:
The 25 year predevelopment peak flow from just the Clark Lane discharge is 8.34 cfs.
The 25 year post-development peak flow from our entire developed site, including Clark Lane is 7.60
ois.
Considering that the existing Clark Lane discharge has no scour protection at all and the proposed
detention basin discharge has a large level spreader and more gentle slopes immediately down
gradient, we reiterate our confidence that there will not be persistent erosion problems associated
with the detention basin outlet and level spreader.
Ms. Gadwa provides a detailed critique of the biorentention basin design in Appendix 1 of her report.
It appears that this critique is based primarily on outdated information from 2009 and 2012 from the
UNH SWC and a lack of understanding of how the system will function. The proposed design is
based on 2020 criteria provided by the UNH SWC which differ from the older criteria. A typical
detail for the enhanced bioretention basin prepared by the UNH SWC is attached and annotated to
specifically address the concerns raised by Ms. Gadwa. The following corresponds to each specific
comment:

Pretreatment is provided by the Stormceptor unit, however we take no exception to the addition
of a forebay to capture additional sediment.
The 18” thick media layer conforms with the 2020 UNH SWC standard detail. The basin is
designed to provide a minimum residence time of 24 hours in the subsurface ISR system.
The media mix proposed conforms with the 2020 UNH SWC requirements which specifically
state that compost should not be used in the filter media.
The ISR system below the basin filter media specifically requires anaerobic (saturated)
conditions to function properly. The ISR is essentially a subsurface gravel wetland which offers
a second stage of treatment below the biofiltration bed.
Given that Ms. Gadwa is not an engineer, there may be a lack of understanding of the hydrologic
analysis calculations and the design and function of the water quality diversion weir manhole.
This structure has been designed specifically to avoid excessive flows through the bioretention
basin even during large storm events by limiting headwater depths on the 12” CPP pipe to the
biotention basin by maximizing the length of the overflow weir. The weir elevation corresponds
to the headwater elevation at which the water quality flow (WQF) is reached and because of the
weir length, the headwater does not increase significantly during large storm events.
The bioretention basin underdrain will not have an adverse impact on the hydrologic regime of
down gradient wetlands.
If you have any questions or need additional information, please do not hesitate to contact us at your
convenience.
Sincerely,
David J.
co Um
eld, P.E., L.S.
Provost & Rovero, Inc.

SEED WITH GRASSES AT RATE SPECIFIED
BY MANUFACTURER AND STABIUZE WITH
‘STRAW TO A DEPTH OF 1”
—p~<
1
vy
Vv
FOR APRON DESIGN GUIDANCE, PLEASE
T U py wy
‘mez x Ls sy. v. x
ay = 3 v
¥ ¥ v
N_] SMOOTH-LINED v
HOPE PIPE ay TM
v
wv Vv
vy
vy v
PERFORATED OR SLOTTED SUBDRAIN
(NUMBER AND SPACING DETERMINED —s4
BY THE ENGINEER, 6” MIN.)
v
@ Vv
PVC CLEAN-OUT RISER! TWO 45°
ELBOWS TO CONNECT ——j
CLEAN-OUT RISER TO SUBDRAIN
Vv
v
ve
es
"5 HEC wv DOME GRATE AND
REFER TO THE FHWA’S 
INLINE’ DRA
‘SMOOTH—LINED
v gy HOPE PIPE
v v C: BIORETENTION °.
[ R x y v sv SYSTEM FOOTPRINT x!
aa v
_ | [Ve [Vf WovEN GEOTEXTILE (MIRAFI? v — ».
FLow SVHP270 OR EQUIVALENT) . ¥ FLOW 4 a
GS ouT >
NOTE 1: BOTTOM
PERMEABILITY AND_LINER
IF A NATIVE, LOW HYDRAULIC CONDUCTIVITY SOIL
{xs0.05tt/doy) IS NOT PRESENT BELOW THE PEA
cH
4.
Lusmy
—*Sing Rouyy
. pone
i
NVEL ELEVATION, A LOW PERMEABILITY LINER OR
‘SOIL SHOULD BE USED TO MINIMIZE INFILTRATION AND
PRESERVE HORIZONTAL FLOW IN THE STONE. THIS
UNER EXTENDS FROM THE BASE OF THE EXCAVATION
TO ABOVE THE TOP OF THE BIORETENTION SOIL MEDIA
LAYER. IF GEOTECHNICAL TESTS CONFIRM THE NEED
FOR A UNER, ACCEPTABLE OPTIONS INCLUDE:
SOIL COMPACTION; 6-12 in CLAY SOIL (MINIMUM
15% PASSING THE $200 SIEVE AND A MAXIMUM
PERMEABILITY OF 1x10-5 cm/s)
. A 40 mil PVC LINER WITH SAND BEDDING AND/OR
NON-WOVEN GEOTEXTILE. PVC LINERSEAMS MAY BE
WELDED, TAPED (WATERPROOF ROOFING TAPE), OR
OVERLAPPED (MINIMUM ONE FOOT). THE
PERFORMANCE OBJECTIVE IS TO CREATE AND
MAINTANN AN ANAEROBIC ZONE IN THE STONE®
‘A BENTONITE LAYER WITH MINIMUM THICKNESS OF 4
in
USE OF CHEMICAL ADDITIVES (SEE NRCS
AGRICULTURAL HANDBOOK #386, DATED 1961)
e, OR AN OTHERWISE PREPARED DESIGN BY A
PROFESSIONAL ENGINEER
‘IF ENGINEER BEUEVES THE PVC LINER IS AT RISK OF
PUNCTURE, THE LINER MAY BE SANDWICHED BETWEEN
NON-WOVEN GEOTEXTILE OR SAND (3 in THICKNESS)
RISER ELEVATION SET TO WOV
ELEVATION OR DESIGN VOLUME
O: WATER
~~ _QUALITY VOLUME
—
CAPPED PVC
CLEAN-OUT RISER:
(WITH TWO 45° BENDS)
“St
BIORETENTION.-
SOIL MIXTURE
NON-WOVEN GEOTEXTILE TO LINE EXCAVATION WALLS
IF NECESSARY TO PREVENT FINES LATERALLY
INFILTRATING SYSTEM; PVC LINER NEEOED ALONG
SIDES IF IN HYDROLOGIC SOIL GROUP A SOILS
SEE NOTE 1 (Lert) _/
PVC UNER
PERFORATED OR SLOTTED SUBDRAIN
(NUMBER AND SPACING DETERMINED BY THE
ENGINEER); SUBDRAIN IS AN OUTLET
MANIFOLD, WITH A CLEAN-OUT AT ONE END
NA
ABOUT BOTTOM
SECTION Y-Y'
NOTE: ADDITIONAL OUTLET STRUCXTURES ABOVE
THE ELEVATION OF THE WQV OR DESIGN VOLUME
MAY BE NECESSARY TO CONVEY LARGE FLOWS.
APPENDIX 1A
PLAN VIEW.
ra
8.
9.
The
dim
are
or omissions shall be reported to UNHSC without
delay. The Copyrights to all designs and drawings
for any purpose other than that authorized by
UNHSC is forbidden.
NOTES:
1
FOR FULL BIORETENTION STORMWATER SYSTEM\SPECIFICATIONS, PLEASE REFER TO THE
UNH STORMWATER CENTER'S BIORETENTION SPEOIFICATIONS PUBLICATION, DATED
FEBRUARY 2017, FOUND AT:
https://www.unh.edu/unhse/sites/default files /medio/ ynhsc_bsm_spec_2-28~17_0.pdf
SYSTEM FOOTPRINT NEED NOT BE RECTANGULAR. AN)\SHAPE IS POSSIBLE. THESE
DETALS USE THE RECTANGULAR SHAPE AS AN EXAMPLE.
THESE DETALS ARE NOT TO SCALE; FOR DIMENSIONS
EACH LETTER TO THE TABLE OF METRICS.
BIORETENTION SOIL MIX SHALL NOT BE PLACED UNTIL AFTE]
rere REFERENCE
ENGINEERING APPROVAL
BIORETENTION SYSTEM IS RECOMMENDED TO HAVE PRETREATMENT (FOREBAY,
TONOP SE RMIEHNIC
PLANT THE SYSTEM AS SPECIFIED; AT A MINIMUM, SEED THE SYSTEM FLOOR AND SIDE
SLOPES WITH RYE GRASS MIXTURE CONTAINING PERENNIAL AND WINTER RYES, AT A
RATE SPECIFIED BY THE MANUFACTURER. STABILIZE THE SLOPES WITH STRAW TO A
DEPTH OF 1”,
GENERAL CONSTRUCTION GUIDELINES:
7.1, VERIFY THAT NO FOREIGN OR DELETERIOUS MATERIAL OR LIQUID SUCH AS PAINT,
PAINT WASHOUT, CONCRETE SLURRY, ASPHALT/CONCRETE LAYERS OR CHUNKS,
CEMENT, PLASTER, OILS, GASOLINE, DIESEL FUEL, PAINT THINNER, TURPENTINE, TAR,
ROOFING COMPOUND, SOLID WASTE, OR ACID HAS BEEN DEPOSITED IN PLANTING
SOIL (BIORETENTION MEDIA OR LOAM ON SIDE SLOPES).
7.2, PROCEED WITH PLACEMENT OF ANY SUBSURFACE MATERIALS ONLY AFTER
UNSATISFACTORY CONDITIONS HAVE BEEN CORRECTED.
7.3. COMPACT EACH BLENDED LIFT OF BIORETENTION SOIL MEDIA TO 75% OF MAXIMUM
STANDARD PROCTOR DENSITY ACCORDING TO ASTM D698.
7.4. GRADE SOIL MEDIA TO A SMOOTH, UNIFORM SURFACE PLANE WITH LOOSE,
UNIFORMLY FINE TEXTURE. ROLL AND RAKE, REMOVE RIDGES, AND FILL
DEPRESSIONS TO MEET FINISH GRADES.
7.5. UGHTLY COMPACT FINISHED FLOOR ELEVATION AND FINISHED SLOPES USING THE
BUCKET OF AN EXCAVATOR, NON-MOTORIZED ROLLER, HAND TAMP, OR OTHER:
MEANS, THEN ROUGHEN SURFACE WITH A RAKE TO LOOSEN SOILS BEFORE
‘SEEDING.
7.6. 00 NOT COMPACT THE SUBGRADE AT THE BOTTOM OF EXCAVATION UNLESS
PERMEABILITY EXCEEDS 1x10°> cm/s
BIORETENTION SOIL MEDIA (BSM) MIXTURE SPECIFICATIONS:
8.1, STICKS AND ROOTS SHOULD BE MINIMIZED IN THE BSM MIXTURE, AND PREFERABLY
LIMITED TO NOTHING LARGER THAN 4.76 mm (0.187 in).
8. DEBRIS AND OTHER FOREIGN MATERIALS SHOULD BE MINIMIZED.
8. ORGANIC MATTER SHOULD MAKE UP A MINIMUM OF 3% BY VOLUME AND A MAXIMUM
8% BY VOLUME OF THE BSM.
8.4, BSM MIXTURE SHOULD HAVE A SOIL REACTION pH OF 6 TO 7.
8.5. CATION EXCHANGE CAPACITY (CEC) OF BSM SHOULD BE A MINIMUM OF 10 meq
PER 100 ml AT A pH OF 7.0.
IF BSM IS PURCHASED FROM A MANUFACTURER, BSM MIXTURE SHALL NOT CONTAIN THE
FOLLOWING:
9. UNACCEPTABLE MATERIALS: CONCRETE SLURRY, CONCRETE LAYERS OR CHUNKS,
‘SWALE, OR
OTHER APPROVED STRUCTURE). PRETREATMENT IS REQUIRED FOR PROJECTS REQUIR! |
O; WATER:
QUALITY VOLUME
DOME GRATE AND INLINE DRAIN:
NYLOPLAST (OR SIMILAR), SIZED TO
CONVEY EVENTS EXCEEDING WQV
Contractor shall verify and be responsible for all
lensions. DO NOT scale the drawing - any errors
the property of UNHSC. Reproduction or use
UNIVERSITY OF NEW HAMPSHIRE
STORMWATER CENTER
— EXISTING GROUND
p< Lit “vs
ILS, GASOLINE, DIESEL U va ober es Z
CEMENT, PLASTER, BUILDING DEBRIS, ASPHALT, BRICKS, OILS, ; a = ; rae
FUEL, PAINT THINNER, TURPENTINE, TAR, ROOFING COMPOUND, ACID, SOLID WASTE, . ion eae \ 7
OR OTHER EXTRANEOUS MATERIALS THAT ARE HARMFUL 10 PLANTS. \ tee OR ae Cant
9.2, UNSUITABLE MATERIALS: STONES, ROOTS, PLANTS, SOD, CLAY LUMPS, OR POCKETS NON-WOVEN cEOTEXTILE, \ \ @ eee hte \ \<
OF COARSE SAND THAT EXCEED A COMBINED MAXIMUM OF 5% BY DRY WEIGHT OF TO LMS ERCWAION. NZ x We A fe
THE MANUFACTURED SOIL. WALLS, IF NECESSARY \ Th Zi : pbc WC AS Oumuer store
9.3. LARGE MATERIALS: STONES, CLODS, ROOTS, CLAY LUMPS EXCEEDING 0.187 in (4.76 “fh ids Hi = = 3 ea Moon HOPE: ad is scorafS Flow Q
iecarear SOT OED, aeasaseehes saonon se)
at mm) IN ANY DIMENSION. MS Bipebasetesese Seesosegonscess aan TER cloneoces MRtR PPE sepa | OUT (
. ———-| \, \ [Bgogekesecsees: wae)
NO COMPOST SHOULD BE USED IN THE PLANTING MIX (USED ON THE SIDE SLOPES h— APPENDIX 1C - \
‘AND SURROUNDING AREA) UNLESS SPECIFIED BY THE ENGINEER. : \ PERFORATED /SLOTTED. ne N SecTIUeD HORE
10.1. = 7 Mt CRUSHED STONE (ISR); HOPE SUBDRAIN \ Mo ORIFICE {EE} SIZED TO
OR OF GRANULAR TEXTURE WITH 100% PASSING THROUGH A 1/2-in (13 mm) \ iM REFER, TQ NOTES, BELOIK } | CREATE 242HR RESIDENCE
SIEVE, WITH A pH OF 3.4 TO 4.8. 1 iN hot TIME OF WOV
10.2. WOOD DERIVATIVES: SHREODEO WOOD, WOOD CHIPS, GROUND BARK, OR WOOD Dit =
WASTE: OF UNIFORM TEXTURE AND FREE OF STONES, STICKS, SOIL, OR TOXIC ONIN NA oe” NANA VAN ee \ CNZAN LAW
MATERIAL. ‘ T 1
11. THE CRUSHED STONE LAYER SHOULD CONSIST OF AASHTO #5 STONE (3/4-in). SEE NOTE 1, ABOVE,
12, THE VOLUME OF WATER CONTAINED ABOVE THE BSM ELEVATION AND BELOW THE HIGH ‘ABOUT’ BOTTOM
FLOW SPILLWAY IS STATISTICALLY DESIGNED TO HOLD A SPECIFIC RUNOFF VOLUME.
13, THE DESIGN VOLUME ABOVE THE BSM IS PREFERABLY THE WOV. THIS VOLUME MAY NOT _X! APPENDIX 1D
BE ACHIEVABLE FOR RETROFIT INSTALLATIONS SECTION X-X'
BIORETENTION SYSTEM DESIGN METRICS BIORETENTION SYSTEM DESIGN METRICS ACCEPTABLE PARTICLE SIZE DISTRIBUTION TERNAL SLORAGE. RESen vol SR) NUTESt
OF FINAL BIORETENTION SOIL MIX ‘+ THE HYBRID BIORETENTION SYSTEM HARBORS AN ANAEROBIC INTERNAL
1D DESIGN PARAMETER MIN | DESIGN | UNITS 1D DESIGN PARAMETER MIN | DESIGN | UNITS = Ras ERAGE RESEINOR FER WTEOGEN RENO
x SYSTEM FLOOR WIDTH AT P RISER PIPE DIAMETER é W MEDIA TYPE | SIEVE #] SIZE (in) | SIZE (mm) | % PASSING GUTEC MD RISE ee
B ‘SYSTEM FLOOR LENGTH FT Q OUTLET PIPE DIAMETER 6 IN COARSE SAND | 4 0.187 4.76 100 * THE PVC LINER SLOPES FROM THE OUTLET TOWARDS THE INLET TO
MEDIUM SAND | 10 0.079 2.00 95 MAXIMIZE STORAGE RETENTION AND PROVIDE EXTRA TREATMENT/FILTER TIME
c BIORETENTION FOOTPRINT AREA SF R INFLOW PIPE DIAMETER IN Se 0 oar aaa was VA PLUG FLOW THROUGH CRUSHED STONE.
BD WATER QUALITY VOLUME Cr Ss PERFORATED SUBDRAIN LENGTH fT ~ - * DESIGN GUIDELINES FOR THE SUBSURFACE GRAVEL WETLAND SPECIFICATIONS
E WOV AND RISER CAP ELEVATION FT T OUTLET PIPE LENGTH FT SILTS 200 0.003 0.075 10-20 (UNHSC, 2016) IDENTIFIED THAT THE WATER VOLUME IN THE ISR BE AT
CLAYS <200 PAN PAN 0-5 LEAST 0.26¢WQV [WATER QUALITY VOLUME), OR 26% OF THE WOV,
us sie HART a 4 Let) = * PVC LINER THICKNESS OF 40 TO 60 mil, PREFERABLY SEAMLESS. IF SEAMS
6 BOTTOM BSM ELEVATION FT V_| SLOPE GRADE (RUN PER Ift RISE) T “+ ARE UNAVOIDABLE, THE SEAMS SHOULD BE SEALED.
a BOTTOM STONE ELEVATION fT W ROCKCAPRON WOOT fT BIORETENTION SOIL MEDIA COMPONENTS:
= AMOUNTS MIXED BY TOTAL VOLUME
|__| TOP _STONE/OUTLET INVERT ELEVATION APPENDIXIB x ROCK APRON LENGTH 1 © 60-85% — SAND (0.5 TO 2.0 mm) (SEE SPECS ABOVE)
J WOV PONDING DEPTH N Y RISER DOME GRATE DIAMETER N # 15-25% — LOAM OR TOPSOIL
+ 3-8% — ORGANIC MATTER
Ls BSM_MEDIA_DEPTH 18 ba £ PYG LAER SLOPE x * 0-5% — WATER TREATMENT RESIDUALS OR IRON FILINGS**
Ui_| INLET END PEA GRAVEL DEPTH N AA OUTLET PIPE SLOPE %
Lo | OUTLET END PEA GRAVEL DEPTH 3 N 8B ‘CLEAN-OUT RISER DIAMETER 1 ‘ALTERNATELY, USE MEDIA SPECIFIED IN THE ALTERATION OF TERRAIN
= RULES, Env-Wq 1508,07(k)
Mi_| INLET END CRUSHED STONE DEPTH N ce CLEAN-OUT RISER ELEVATION T SFIHIS IS AN AVENDMENT USED FOR ENHANCED PHOSPHORUS ADSORPTION
Mo [OUTLET END CRUSHED STONE DEPTH| 14 N oD PVC_LINER GAP 0.1%8 T
N | SUBDRAIN DEPTH ABOVE BOTTOM | 4 N EE | OUTLET PIPE ORIFICE DIAMETER | 1 iN
oO PERFORATED SUBDRAIN DIAMETER 6 IN
os 7 Project: B
University of New Hampshire GRAPHIC SCALE : Date:
35 Colovos Road 02 | 10 Sept 2019 | DES Revisions STAN DAR D D ETAI L 21 FEB 2020
Durham, NH03824 01 |12.Mar 2079. lintel design N/A - DRAWING NOT TO SIZE
one (603) 862. a BIORETENTION ISR
( ) No. | Date Revision Sheet No.
Fax (603) 862-3957 .
http:/Awww.unh.edu/unhsc Designed: Checked: Approved: O 1 f O 1
. ~_ JCB TPB/JJH TPB/JJH_ | Original Drawing Size = 34 x 22 in. STORMWATER SYSTEM O
——