HomeMy WebLinkAboutSUB201700091 Calculations 2017-06-05 OLD TRAIL CREEKSIDE V- CONCEPTUAL STORMWATER
MANAGEMENT CALCULATIONS PACKET
Date of Calculations
JUNE 5, 2017
PREPARED BY:
COLLINS ENGINEERING
200 GARRETT STREET, SUITE K
CHARLOTTESVILLE, VA 22902
434.293.3719 PH
434.293.2813 FX
www.collins-engineering.com
Lots 1-5 Soil Mapping
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Lots 1-5 Soil Types
Albemarle County,Virginia(VAO03)
Map Map Unit Name Percent
Unit of AOI
Symbol
7B Braddock loam,2 to 7 percent 87.8%
slopes
8C3 Braddock clay loam,7 to 15 8.9%
percent slopes,severely
eroded
81B Thurmont loam,2 to 7 3.3%
percent slopes
Totals for Area of Interest 100.0%
Note:The soils' properties for this development are predominantly composed of hydrologic group type B.
Lots 6-12 Soil Mapping
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Lots 6-12 Soil Types
Albemarle County,Virginia(VAO03)
Map Unit Map Unit Name Percent
Symbol of AOI
78 Braddock loam,2 to 7 100.0%
percent slopes
Totals for Area of Interest 100.0%
Note:The soils' properties for this development are predominantly composed of hydrologic group type B.
DEQ Virginia Runoff Reduction Method
Water Quality Calculations
(COMPLIANCE IS MET THROUGH THE BEST MANAGEMENT PRACTICES OF PROTECTING
FOREST & OPEN SPACES, A CONTRIBUTION TO THE LICKINGHOLE BASIN FUND AND
THROUGH THE PURCHASING OF NUTRIENT CREDITS)
Summary of Phosphorous Removal Compliance:
Total Phosphorous (TP) Load Reduction Required: 3.23 lbs/yr.
TP Load Removed Through Protected Forest & Open Space Easements 0.31 lbs/yr.
TP Load Removed Through Contribution to the Lickinghole Basin Fund 0.88 lbs/yr.
TP Load Removed Through Purchasing Nutriet Credits 2.04 lbs/yr.
3.23 lbs/yr.
DEQ Virginia Runoff Reduction Method Nest,Development Compliance Spreadsheet-Version 3.0
F:2011 BMP Standards and Specifications 02013 Draft BMP Standards and Specifications
Project Name: Old Trail Creekside V-Preliminary Subdivision Plat CLEAR ALL data input calls
Date: 6/5/2017 _ constant values
BMP Design Specifications List:2011 Std s&Specs akuletion ells
Site Information final results
Post-Development Project(Treatment Volume and Loads)
Land Cover(acres)
A Soils B Soils C Soils D Soils Totals
Forest/Open Spate lanes)--undisturbed,
protected forest/open space or reforested land 0.00 aoo
Managed Turf(acres)--disturbed,graded for
yards or other turf to be mowed/managed 7.33 7.33
Impervious Cover(acres) 1 82 1.82
9.15
Constants Runoff Coefficients(Rv)
Annual Rainfall(inches) 43 A Soils B Soils C Soils D Soils
Target Rainfall Event(inches) 1.00 Forest/Open Space 0.02 0.03 0.04 0.05
Total Phosphorus(TP)EMC(mg/L) 0.26 Managed Turf 0.15 0.20 0.22 0.25
Total Nitrogen(TN)EMC(mg/L) 1.86 Impervious Cover 0.95 0.95 0.95 0.95
Target TP Load(lb/acre/yr) 0.41
PI limitless correction factor) 0.90
Post-Development Requirement for Site Area
TP Load Reduction Required(Ib/yr) 3.54
LAND COVER SUMMARY-POST DEVELOPMENT
Land Cover Summary Treatment Volume and Nutrient Loads
Forest/Open Space Cover(acres) 0.00 Treatment Volume 0.2663
(acre-ft)
Weighted Rv(forest) 0.00 Treatment Volume(cubic feet) 11,598
%Forest 0% TP Load(lb/yr) 7.29
TN Load(lb/yr)
Managed Turf Cover(acres) 7.33 Ilnforma[ional Purposes Only)
52.13
Weighted Rv turf) 0.20
If Managed Turf 80%
Impervious Cover(acres) 1.82
Rv(impervious) 0.95
%Impervious 20%
Site Area(acres) 9.15
Site Rv 0.35