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

ATTACHMENT B. Stormwater Management Resources.
New York State Stormwater Management Design Manual
Appendix A
Table A.2 Pollutant Concentrations from Source Areas
Constituent | TSS! TP? TN’ | FColi Cu! Pb! Zn!
1,000
mg/l mg/L mg/l etm ug/l ug/l ug/l
Resid Roof 19 0.11 15 0.26 20 21 312
Comm Roof 9 0.14 Bel. 1.1 7 17 256
Indust Roof 17 - - 5.8 62 43 1,390
C/R Parking 27 0.15 1.9 1.8 ol 28 139
late 228 ‘ : 27 34 5 | 224
Parking
Res Street 172 0.55 14 37 25 51 173
Commn Street 468 - - 12 73 170 450
Rema) 51 - 2 - 22 80 80
Highway
aa 142 0.32 3.0 : 54 400 329
Highway
Lawns 602 Qed 9.1 24 17 17 50
Landscaping 37 - - 94 94 29 263
Driveway 173 0.56 Dal 17 17 - 107
Gas Station 31 - - - 88 80 290
Auto Recycler | 335 - - - 103 182 520
Heavy
Industrial 124 - - - 148 290 1600
1: Claytor and Schueler (1996)
2: Average of Steuer et al. (1997),Bannerman (1993) and Waschbusch (2000)
3: Steuer et al. (1997)
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109R & 131 CLARK LANE
PUBLIC HEARING
EXHIBIT # 23
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Attachment B: to Carya E.S. Review
of Proposed Clark Lane Residential
A$
FEB 06 2023
Development, January 2023.

New York State Stormwater Management Design Manual Appendix A
A.3 Impervious Cover Data
The Simple Method uses different impervious cover values for separate land uses within a subwatershed.
Representative impervious cover data, are presented in Table A.3. These numbers are derived from a
recent study conducted by the Center for Watershed Protection under a grant from the U.S.
Environmental Protection Agency to update impervious cover estimates for a variety of land uses.
(Cappiella and Brown, 2001). In addition, some jurisdictions may have detailed impervious cover
information if they maintain a detailed land use/land cover GIS database.
Table A.3 Land Use and Impervious Cover Estimates
Land Use Category Mean Impervious Cover
Agriculture 2
Open Urban Land* 9
2 Acre Lot Residential 11
1 Acre Lot Residential 14
1/2 Acre Lot Residential 21
1/4Acre Lot Residential 28
1/8 Acre Lot Residential 33
Townhome Residential 41
Multifamily Residential 44
Institutional** 31-38%
Light Industrial 50-56%
Commercial 70-74%
* Open urban land includes developed park land, recreation arcas, golf
courses, and cemeteries.
** Tnstitutional is defined as places of worship, schools, hospitals,
government offices, and police and fire stations
iA.4 Limitations of the Simple Method
The Simple Method should provide reasonable estimates of changes in pollutant export resulting from
urban development activities. However, several caveats should be kept in mind when applying this
method.
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New York State Stormwater Management Design Manual
A.5 SMP Pollutant Removal
Appendix A
The removal efficiencies of various SMP practices also help determine final annual pollutant loads. Table
A provides estimates of the average pollutant removal efficiency of the five SMP categories.
Table A.4. Suggested Removal Rates for SMPs
TSS TP TN | Metals' | Bacteria
Wet Ponds 80 50 (51) | 35 (33) | 60 (62) 70
Stormwater Wetlands 80° (76) | 50 (49) 30 40 (42) 80 (78)
Filtering Practices 85 (86) | 60(59) | 40(38) | 70(69) | 35 (37)
Infiltration Practices ‘ 90° (95) 70 50 (51) | 90° (99) 90°
Water Quality Swales 85 (84) | 40(39) | 50° (84) 70 0 (-25)°
L Average of zinc and copper. Only zinc for infiltration
2 Many wetland practices in the database were poorly designed, and we consequently
adjusted sediment removal upward.
3. It is assumed that no practice is greater than 90% efficient.
4, Data inferred from sediment removal.
Ss Actual data is based on only two highly performing practices.
6. Assume 0 rather than a negative removal.
Note: Data in parentheses represent median pollutant removal data reported in the National
Pollutant Removal Database - Revised Edition (Winer, 2000). These data were adjusted for
convenience and to reflect biases in the data.
These efficiencies represent ideal pollutant removal rates that cannot be achieved at all sites, or at a
watershed level. Typically, they need to be “discounted” to account for site constraints, and other factors
that reduce practice efficiency. For example, the removal rate should be adjusted to reflect the fraction of
runoff captured by a practice on an annual basis (90% if this guidance is followed). For more detail on
how to apply these discounts, consult Caraco (2001).
One particularly important consideration is how to account for practices applied in series (e.g., two ponds
applied in sequence). If the volume within the practices adds up to the total water quality volume, they
are assumed to act as a single practice with that volume. Otherwise, total pollutant removal should be
determined by the following equation:
R=L [(E))+(1- Ey)Ext(1-(E1)+(1- E,)E2)Est...]
Where:
R= Pollutant Removal (Ibs)
L= Annual Load from Simple Method (Ibs.)
E; = Efficiency of the ith practice in a series
Another adjustment can be made to these removals to account for loss of effectiveness and “irreducible
concentrations.” Evidence suggests that, at low concentrations, SMPs can no longer remove pollutants.
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New York State Stormwater Management Design Manual Appendix A
Steuer, J., W. Selbig, N. Hornewer, and J. Prey. 1997. “Sources of Contamination in an Urban Basin in
Marquette, Michigan and an Analysis of Concentrations, Loads, and Data Quality.” U.S. Geological
Survey, Water-Resources Investigations Report 97-4242.
Waschbusch. 2000. Sources of phosphorus in stormwater and street dirt from two urban residential basins
in Madison, Wisconsin, 1994-1995. In: National Conference on Tools for Urban Water Resource
Management and Protection. US EPA February 2000: pp. 15-55.
Winer, R. 2000. National Pollutant Removal Database - Revised Edition. Center for Watershed
Protection, Ellicott City, Maryland.
Attachment B. Part Il. UNH Stormwater Managment Resources on
Biofiltration Basins(2009 and 2012 UNH Biennial Reports, pp 20 to 21in both.
Hard copies have been provided separately to the Conservation Commission.
NOTE: Both the 2009 and 2012 UNH Reports are available on line:
Performance Testing Results and design guidance for biofiltration
basins published by the University of New Hampshire Stormwater Center.
PDF’s may be downloaded from https:/Avww.unh.edu/unhsc/pubs-specs-info
and ac company the electronic submission of this report.
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