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WPO200800086 Calculations 2008-08-20
SWM #3 SEDIMENT BASIN CALCULATIONS FOR HOLLYMEAD TOWNCENTER AREA Al EROSION December 22, 2008 LOCATION: Albemarle County, Virginia Tax Map 32, Parcels 42A & 44 Tax Map 46, Parcel 5 PREPARED BY: Dominion Development Resources, LLC 172 South Pantops Drive Charlottesville, VA 22911 P: 434.979.8121 F: 434.979.1681 Dominion Development Resources, LLC Page 1 (434) 979 -8121 Hollymead Towncenter Area A1P"' SWM #3 Sediment Basin Name: 25 -yr Sed Basin Type: Modified Rational [HYDROGRAPH INFORMATION] Peak Flow (Qp) = 144.43 (cfs) Time to Peak (Tp) = 20.00 (min) Time of Base (Tb) = 50.04 (min) Volume = 4.98 (ac -ft) Time Step = 1.00 (min) Flow Multiplier = 1.00 [RATIONAL HYDROGRAPH INFORMATION] Flow Multiplier = 1.00 Receding Limb Factor = 1.50 [APPROXIMATE STORAGE] Maximum Outflow = 0.00 (cfs) Maximum Storage = 4.98 (cu ft) [BASIN INFORMATION] [WEIGHTED WATERSHED AREA] Description Area CN Runoff Coef <None> Overall Approximation 49.76 NA 0.60 [TIME CONCENTRATION -- User Defined] Time of Concentration (Tc) = 20.00 (min) [RAINFALL DESCRIPTION] Distribution Type = Synthetic Total Precipitation = 1.60 (in) Return Period = 25 (yr) Storm Duration = 0.33 (hr) [Hydrograph Flow Values: Time vs. Flow] [TIME CONCENTRATION -- 1.00] Time Time Incremental Cumulative Incremental Design Interval Rainfall Rainfall Outflow Outflow (min) (in) (in) (cfs) (cfs) 1 1.00 0.00 0.08 0.00 7.22 2 2.00 0.08 0.16 7.22 14.44 3 3.00 0.08 0.24 7.22 21.66 4 4.00 0.08 0.32 7.22 28.89 5 5.00 0.08 0.40 7.22 36.11 6 6.00 0.08 0.48 7.22 43.33 7 7.00 0.08 0.56 7.22 50.55 8 8.00 0.08 0.64 7.22 57.77 9 9.00 0.08 0.72 7.22 64.99 10 10.00 0.08 0.80 7.22 72.21 Dominion Development Resources, LLC Page 2 (434) 979 -8121 `r° Hollymead Towncenter Area At' s' SWM #3 Sediment Basin 11 11.00 0.08 0.88 7.22 79.43 12 12.00 0.08 0.96 7.22 86.66 13 13.00 0.08 1.04 7.22 93.88 14 14.00 0.08 1.12 7.22 101.10 15 15.00 0.08 1.20 7.22 108.32 16 16.00 0.08 1.28 7.22 115.54 17 17.00 0.08 1.36 7.22 122.76 18 18.00 0.08 1.44 7.22 129.98 19 19.00 0.08 1.52 7.22 137.20 20 20.00 0.08 1.60 7.22 144.43 21 21.00 0.00 1.60 -4.62 139.80 22 22.00 0.00 1.60 -4.81 134.99 23 23.00 0.00 1.60 -4.81 130.18 24 24.00 0.00 1.60 -4.81 125.36 25 25.00 0.00 1.60 -4.81 120.55 26 26.00 0.00 1.60 -4.81 115.73 27 27.00 0.00 1.60 -4.81 110.92 28 28.00 0.00 1.60 -4.81 106.10 29 29.00 0.00 1.60 -4.81 101.29 30 30.00 0.00 1.60 -4.81 96.48 31 31.00 0.00 1.60 -4.81 91.66 32 32.00 0.00 1.60 -4.81 86.85 33 33.00 0.00 1.60 -4.81 82.03 34 34.00 0.00 1.60 -4.81 77.22 35 35.00 0.00 1.60 -4.81 72.41 36 36.00 0.00 1.60 -4.81 67.59 37 37.00 0.00 1.60 -4.81 62.78 38 38.00 0.00 1.60 -4.81 57.96 39 39.00 0.00 1.60 -4.81 53.15 40 40.00 0.00 1.60 -4.81 48.33 41 41.00 0.00 1.60 -4.81 43.52 42 42.00 0.00 1.60 -4.81 38.71 43 43.00 0.00 1.60 -4.81 33.89 44 44.00 0.00 1.60 -4.81 29.08 45 45.00 0.00 1.60 -4.81 24.26 46 46.00 0.00 1.60 -4.81 19.45 47 47.00 0.00 1.60 -4.81 14.64 48 48.00 0.00 1.60 -4.81 9.82 49 49.00 0.00 1.60 -4.81 5.01 50 50.00 0.00 1.60 -4.81 0.19 Dominion Development Resources, LLC Page 3 (434) 979 -8121 Hollymead Towncenter Area A9aw' SWM #3 Sediment Basin Name: 25 -yr routed Type: Reservoir: Modified Puls [HYDROGRAPH INFORMATION] Peak Flow (Qp) = 18.28 (cfs) Time to Peak (Tp) = 46.00 (min) Time of Base (Tb) = 1440.00 (min) Volume = 4.86 (ac -ft) Time Step = 1.00 (min) Peak Elevation = 481.29 (ft) Detention Time = NA [RESERVOIR STRUCTURE INFORMATION] Number = 1 Name = SB- NEW - CONVERT Storage Type = User - Defined Area Maximum Storage = 584081.42 (cu ft) Maximum Discharge = 470.17 (cfs) [INFLOW HYDROGRAPH INFORMATION] Number = 1 Name = 25 -yr Sed Basin Peak Flow (Qp) = 144.43 (cfs) Time to Peak (Tp) = 20.00 (min) Time of Base (Tb) = 50.04 (min) Volume = 4.98 (ac -ft) Flow Multiplier = 1.00 Dominion Development Resources, LLC Page 4 (434) 979 -8121 Hollymead Towncenter Area A1' SWM #3 Sediment Basin Type : Stand Pipe Name : Stand Pipe [RATING CURVE LIMIT] Minimum Elevation = 472.57 (ft) Maximum Elevation = 487.15 (ft) Elevation Increment = 0.20 (ft) [STAND PIPE INFORMATION] [ORIFICE INFORMATION] Diameter = 6.00 (ft) Crest Length = 18.85 (ft) Effective Crest Length = 18.85 (ft) Orifice Coefficient = 0.60 Fractional Open Area = 1.00 [ORIFICE EQUATION] Q = Co *A((2gh) /k) ^0.5 [DEFINITIONS] Co = Orifice Coefficient A = Wetted Area, (sq ft) [WEIR INFORMATION] Crest Elevation = 483.94 (ft) Weir Coefficient = 3.33 Exponential = 1.50 [WEIR EQUATION] Q = Cw * L * H ^exp [DEFINITIONS] Cw = Weir Coefficient H = Headwater depth above inlet control section invert ft L = Crest lenght ft [OPTIONAL ORIFICE INFORMATION] Structure Number : 1 Type : Circular Orifice [OPTIONAL ORIFICE INFORMATION] Diameter = 1.75 (ft) Invert Elevation = 477.92 (ft) Orifice Coefficient = 0.60 Number of Openings = 1 [ORIFICE EQUATION] Q = Co *A((2gh) /k) ^0.5 [DEFINITIONS] Co = Orifice Coefficient A = Wetted Area, (cfs) k = 1 Dominion Development Resources, LLC Page 5 (434) 979 -8121 Hollymead Towncenter Area A'r SWM #3 Sediment Basin [CULVERT INFORMATION] Type : Circular Concrete - Groove End Projecting [OUTLET STRUCTURE INFORMATION] Diameter = 48.00 (in) Invert Elevation = 472.57 (ft) Pipe Length = 92.00 (ft) Slope = 0.06 Manning's n Value = 0.01 Orifice Coefficient = 0.60 Tailwater Elevation = 467.00 (ft) Number of Barrels = 1 [UNSUBMERGED EQUATION] H /Diam = Hc/ Diam +K *(Q /(A *Diam ^0.5)) ^M -0.5 *S Coefficient K = 0.00 Coefficient M = 2.00 Q Maximum = 87.96 [SUBMERGED EQUATION] H /Diam = c *(Q /(A *Diam ^0.5)) ^2 +Y -0.5 *S Coefficient c = 0.03 Coefficient Y = 0.69 Q Minimum = 100.53 [DEFINITIONS] H = Headwater depth above inlet control section invert, (ft) Diam = Interior height of culvert barrel, (ft) He = Specific head at critical depth (dc +Vc ^2/2g), (ft) Q = Discharge, (cfs) A = Full cross sectional area of culvert barrel, (sq ft) S = Culvert barrel slope, (ft /ft) [STAND PIPE STAGE VS. DISCHARGE] Elevation Stage Weirs Orifices Stand Pipe Culvert Total (ft) (ft) (cfs) (cfs) (cfs) (cfs) (cfs) 483.97 11.40 0.00 26.34 0.33 208.91 26.66 484.17 11.60 0.00 26.84 6.92 211.28 33.76 484.37 11.80 0.00 27.33 17.70 213.62 45.03 484.57 12.00 0.00 27.82 31.39 215.94 59.21 484.77 12.20 0.00 28.30 47.47 218.24 75.76 484.97 12.40 0.00 28.77 65.62 220.51 94.38 485.17 12.60 0.00 29.23 85.63 222.76 114.86 485.37 12.80 0.00 29.68 107.34 224.98 137.02 485.57 13.00 0.00 30.13 130.63 227.19 160.76 485.77 13.20 0.00 30.57 151.73 229.37 182.30 485.97 13.40 0.00 31.01 169.32 231.53 200.33 486.17 13.60 0.00 31.44 186.92 233.67 218.36 486.37 13.80 0.00 31.86 204.51 235.79 235.79 486.57 14.00 0.00 32.28 220.69 237.90 237.90 486.77 14.20 0.00 32.69 228.93 239.98 239.98 486.97 14.40 0.00 33.10 236.88 242.05 242.05 487.15 14.58 0.00 33.46 243.82 243.89 243.89 Dominion Development Resources, LLC Page 6 (434) 979 -8121 Hollymead Towncenter Area Ate"' SWM #3 Sediment Basin [ORIFICE STAGE VS. DISCHARGE] Elevation Stage Orifice 1 Orifice 2 Orifice 3 Orifice 4 Total (ft) (ft) (cfs) (cfs) (cfs) (cfs) (cfs) 477.97 5.40 0.01 0.00 0.00 0.00 0.01 478.17 5.60 0.36 0.00 0.00 0.00 0.36 478.37 5.80 1.12 0.00 0.00 0.00 1.12 478.57 6.00 2.23 0.00 0.00 0.00 2.23 478.77 6.20 3.64 0.00 0.00 0.00 3.64 478.97 6.40 5.25 0.00 0.00 0.00 5.25 479.17 6.60 6.99 0.00 0.00 0.00 6.99 479.37 6.80 8.73 0.00 0.00 0.00 8.73 479.57 7.00 10.28 0.00 0.00 0.00 10.28 479.77 7.20 11.43 0.00 0.00 0.00 11.43 479.97 7.40 12.55 0.00 0.00 0.00 12.55 480.17 7.60 13.57 0.00 0.00 0.00 13.57 480.37 7.80 14.53 0.00 0.00 0.00 14.53 480.57 8.00 15.42 0.00 0.00 0.00 15.42 480.77 8.20 16.27 0.00 0.00 0.00 16.27 480.97 8.40 17.07 0.00 0.00 0.00 17.07 481.17 8.60 17.84 0.00 0.00 0.00 17.84 481.37 8.80 18.58 0.00 0.00 0.00 18.58 481.57 9.00 19.28 0.00 0.00 0.00 19.28 481.77 9.20 19.97 0.00 0.00 0.00 19.97 481.97 9.40 20.63 0.00 0.00 0.00 20.63 482.17 9.60 21.27 0.00 0.00 0.00 21.27 482.37 9.80 21.89 0.00 0.00 0.00 21.89 482.57 10.00 22.49 0.00 0.00 0.00 22.49 482.77 10.20 23.08 0.00 0.00 0.00 23.08 482.97 10.40 23.65 0.00 0.00 0.00 23.65 483.17 10.60 24.21 0.00 0.00 0.00 24.21 483.37 10.80 24.76 0.00 0.00 0.00 24.76 483.57 11.00 25.30 0.00 0.00 0.00 25.30 483.77 11.20 25.82 0.00 0.00 0.00 25.82 483.97 11.40 26.34 0.00 0.00 0.00 26.34 484.17 11.60 26.84 0.00 0.00 0.00 26.84 484.37 11.80 27.33 0.00 0.00 0.00 27.33 484.57 12.00 27.82 0.00 0.00 0.00 27.82 484.77 12.20 28.30 0.00 0.00 0.00 28.30 484.97 12.40 28.77 0.00 0.00 0.00 28.77 485.17 12.60 29.23 0.00 0.00 0.00 29.23 485.37 12.80 29.68 0.00 0.00 0.00 29.68 485.57 13.00 30.13 0.00 0.00 0.00 30.13 485.77 13.20 30.57 0.00 0.00 0.00 30.57 485.97 13.40 31.01 0.00 0.00 0.00 31.01 486.17 13.60 31.44 0.00 0.00 0.00 31.44 486.37 13.80 31.86 0.00 0.00 0.00 31.86 486.57 14.00 32.28 0.00 0.00 0.00 32.28 486.77 14.20 32.69 0.00 0.00 0.00 32.69 486.97 14.40 33.10 0.00 0.00 0.00 33.10 487.15 14.58 33.46 0.00 0.00 0.00 33.46 Dominion Development Resources, LLC Page 7 (434) 979 -8121 Hollymead Towncenter Area Al SWM #3 Sediment Basin Type : Trapezoidal Weir Name : Emergency Spillway [RATING CURVE LIMIT] Minimum Elevation = 472.57 (ft) Maximum Elevation = 487.15 (ft) Elevation Increment = 0.15 (ft) [OUTLET STRUCTURE INFORMATION] Crest Length = 20.00 (ft) Angle of Walls = 8.5000 Crest Elevation = 484.90 (ft) Weir Coefficient = 3.33 Exponential = 1.50 [TRAPEZOIDAL EQUATION] Q = Cw * ( L + 0.8H * tan ( ang /2.0 ) ) * H ^exp [DEFINITIONS] Cw = Weir Coefficient H = Headwater depth above inlet control section invert L = Crest lenght ang = Angle of the walls [MAXIMUM DISCHARGE] Q = 226.28 (cfs) [WEIR STAGE VS. DISCHARGE] Elevation (ft) Stage (ft) Discharge (cfs) 484.87 12.30 0.00 485.02 12.45 2.77 485.17 12.60 9.35 485.32 12.75 18.15 485.47 12.90 28.71 485.62 13.05 40.78 485.77 13.20 54.18 485.92 13.35 68.82 486.07 13.50 84.58 486.22 13.65 101.40 486.37 13.80 119.22 486.52 13.95 137.99 486.67 14.10 157.66 486.82 14.25 178.20 486.97 14.40 199.57 487.12 14.55 221.75 487.15 14.58 226.28 Dominion Development Resources, LLC Page 8 (434) 979 -8121 • Hollymead Towncenter Area A .so SWM #3 Sediment Basin Name: SB- NEW - CONVERT [RATING CURVE LIMIT] Minimum Elevation = 472.57 (ft) Maximum Elevation = 487.15 (ft) Elevation Increment = 0.15 (ft) [STAGE STORAGE INFORMATION] Storage Method: User - Defined Storage Input Method: Area Number Elevation Area Ave Area Volume Cumulative Volume (ft) (sq ft) (sq ft) (cu ft) (cu ft) 1 0.00 0.00 0.00 0.00 0.00 2 477.91 0.00 0.00 0.00 0.00 3 477.92 43448.00 21724.00 217.24 217.24 4 478.50 53614.00 48531.00 28147.98 28365.22 5 480.00 56583.00 55098.50 82647.75 111012.97 6 482.00 61799.00 59191.00 118382.00 229394.97 7 484.00 67020.00 64409.50 128819.00 358213.97 8 486.00 72640.00 69830.00 139660.00 497873.97 9 487.15 75771.00 74205.50 85336.32 583210.29 [DISCHARGE INFORMATION] Structure Number: 1 Type: Name: Stand Pipe Structure Number: 2 Type: Trapezoidal Weir Name: Emergency Spillway [RESERVOIR STAGE STORAGE /DISCHARGE] Elevation Stage Area Storage Discharge (ft) (ft) (sq ft) (cu ft) (cfs) 477.82 5.25 0.00 0.00 0.00 477.97 5.40 44324.38 3324.33 0.01 478.12 5.55 46953.52 10170.17 0.23 478.27 5.70 49582.66 17410.38 0.69 478.42 5.85 52211.79 25044.97 1.36 478.57 6.00 53752.55 32992.29 2.23 478.72 6.15 54049.45 41077.44 3.26 478.87 6.30 54346.35 49207.13 4.42 479.02 6.45 54643.25 57381.35 5.68 479.17 6.60 54940.15 65600.11 6.99 479.32 6.75 55237.05 73863.40 8.31 479.47 6.90 55533.95 82171.22 9.55 479.62 7.05 55830.85 90523.58 10.59 479.77 7.20 56127.75 98920.48 11.43 479.92 7.35 56424.65 107361.91 12.28 480.07 7.50 56765.56 115851.17 13.07 Dominion Development Resources, LLC Page 9 (434) 979 -8121 Hollymead Towncenter Area Ate" SWM #3 Sediment Basin 480.22 7.65 57156.76 124395.35 13.82 480.37 7.80 57547.96 132998.20 14.53 480.52 7.95 57939.16 141659.74 15.20 480.67 8.10 58330.36 150379.95 15.85 480.82 8.25 58721.56 159158.84 16.47 480.97 8.40 59112.76 167996.42 17.07 481.12 8.55 59503.96 176892.67 17.65 481.27 8.70 59895.16 185847.61 18.21 481.42 8.85 60286.36 194861.22 18.76 481.57 9.00 60677.56 203933.51 19.28 481.72 9.15 61068.76 213064.49 19.80 481.87 9.30 61459.96 222254.14 20.30 482.02 9.45 61851.21 231502.48 20.79 482.17 9.60 62242.79 240809.53 21.27 482.32 9.75 62634.36 250175.31 21.74 482.47 9.90 63025.93 259599.84 22.19 482.62 10.05 63417.51 269083.10 22.64 482.77 10.20 63809.08 278625.09 23.08 482.92 10.35 64200.66 288225.82 23.51 483.07 10.50 64592.23 297885.29 23.94 483.22 10.65 64983.81 307603.49 24.35 483.37 10.80 65375.39 317380.43 24.76 483.52 10.95 65766.96 327216.11 25.16 483.67 11.10 66158.54 337110.52 25.56 483.82 11.25 66550.11 347063.67 25.95 483.97 11.40 66941.68 357075.55 26.66 484.12 11.55 67357.20 367147.97 31.51 484.27 11.70 67778.70 377283.16 38.99 484.42 11.85 68200.20 387481.58 48.33 484.57 12.00 68621.70 397743.22 59.21 484.72 12.15 69043.20 408068.09 71.42 484.87 12.30 69464.70 418456.18 84.83 485.02 12.45 69886.20 428907.50 102.11 485.17 12.60 70307.70 439422.04 124.21 485.32 12.75 70729.20 449999.81 149.48 485.47 12.90 71150.70 460640.80 177.41 485.62 13.05 71572.20 471345.02 207.70 485.77 13.20 71993.70 482112.46 236.51 485.92 13.35 72415.20 492943.13 264.65 486.07 13.50 72830.58 503836.56 293.92 486.22 13.65 73238.97 514791.78 324.24 486.37 13.80 73647.37 525808.25 355.01 486.52 13.95 74055.76 536885.99 375.36 486.67 14.10 74464.15 548024.98 396.60 486.82 14.25 74872.54 559225.23 418.70 486.97 14.40 75280.93 570486.74 441.62 487.12 14.55 75689.32 581809.51 465.34 Maximum Storage = 584081.42 (cu ft) Maximum Discharge = 470.17 (cfs) Dominion Development Resources, LLC Page 10 (434) 979 -8121 EROSION AND SEDIMENT CONTROL NARRATIVE FOR HOLLYMEAD TOWNCENTER AREA Al December 22, 2008 LOCATION: Tax Map 32 Parcels 44,45 Tax Map 46 Parcel 5 Rivanna District, Albemarle County, Virginia OWNER & DEVELOPER HM Acquisition Group, LLC PO Box 5548 Charlottesville VA, 22905 PREPARED BY: Dominion Development Resources, LLC 172 S Pantops Dr. Charlottesville, VA 22911 434.979.8121 (F) 434.979.1681 1 A. MINIMUM STANDARDS (MS): All applicable Virginia Erosion and Sediment Control Regulations and Minimum Standards shall be adhered to during all phases of construction. These include, but are not limited to the following: 1. STABLIZATION OF DENUDED AREAS: Permanent or temporary soil stabilization shall be applied to bare areas within seven days after final grade is reached on any portion of the site. Temporary soil stabilization shall be applied within seven days to denuded areas that may not be at final grade, but will remain dormant or undisturbed for longer than 30 days. Permanent stabilization shall be applied at areas that are to be left dormant for more than 1 year. 2. STABILIZATION OF SOIL STOCKPILES: During construction of the project, soil stockpiles shall be stabilized or protected with sediment trapping measures. The applicant is responsible for temporary protection and permanent stabilization of all soil stockpiles on site as well as soil intentionally transported from the project site. 3. PERMANENT VEGETATIVE COVER A permanent vegetative cover shall be established on denuded areas not otherwise permanently stabilized. Permanent vegetation shall not be considered established until a ground cover is achieve that, in the opinion of the county Inspector, is uniform and mature enough to survive to inhibit erosion. 4. TIMING & STABILIZATION OF SILT TRAPPING MEASURES: Sediment basins and traps, perimeter dikes, sediment barriers and other measures intended to trap sediment shall be constructed as a first step in any land disturbing activity and shall be made functional before upslope land disturbance takes place. 5. STABILIZATION OF EARTHEN STRUCTURES: Stabilization measures shall be applied to earthen structures such as dams, dikes and diversions immediately after installation. 6. SEDIMENT TRAPS AND BASINS: A sediment basin shall control surface runoff from disturbed areas that is comprised of flow from drainage areas greater than or equal to three acres. The sediment basin shall be designed and constructed to accommodate the anticipated sediment loading for the land disturbing activity. The outfall device or system device shall take into account the total drainage area flowing through the disturbed area to be served by the basin. 7. CUT AND FILL SLOPES: Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion. Slopes that are found to be eroding excessively within one year of permanent stabilization shall be provided with additional slope stabilizing measures until the problem is corrected. 8. CONCENTRATED RUN -OFF DOWN CUT OR FILL SLOPES: Concentrated runoff shall not flow down cut or fill slopes unless contained within an adequate temporary or permanent channel, flume, or slope drain structure. 2 9. WATER SEEPS FROM A SLOPE FACE: Whenever water seeps from a slope face, adequate drainage or other protection shall be provided. 10. STORM SEWER INLET PROTECTION: All storm sewer inlets that are made operable during construction shall be protected so that sediment -laden water cannot enter the conveyance system without first being filtered or otherwise treated to remove sediment. 11. STABILIZATION OF OUTLETS: Before newly constructed stormwater conveyance channels are made operational, adequate outlet protection and any required temporary or permanent channel lining shall be installed in both the conveyance channel and receiving channel. 12. WORK IN LIVE WATERCOURSES: When work in a live watercourse is performed, precautions shall be taken to minimize encroachment, control sediment transport and stabilize the work area to the greatest extent possible during construction. Nonerodible material shall be used for the construction of causeways and cofferdams. Earthen fill may be used for these structures if armored by nonerodible cover materials. 13. CROSSING A LIVE WATERCOURSE: When a live watercourse must be crossed by construction vehicles more than twice in any six month period, a temporary stream crossing constructed of nonerodible materials shall be provided. 14. APPLICABLE REGULATIONS: All applicable federal, state and local regulations pertaining to working in or crossing live watercourses shall be met. 15. STABILIZATION OF BED AND BANKS The bed and banks of a watercourse shall be stabilized immediately after work in the watercourse is completed. 16. UNDERGROUND UTILITIES: Underground utilities shall be installed in accordance with the following standards in addition to other criteria: a. No more than 500 linear feet of trench may be opened at one time. b. Excavated material shall be placed on the uphill side of trenches c. Effluent for dewatering operations shall be filtered or passed through approved sediment trapping device, or both, and discharged in a manner that does not adversely affect flowing streams or offsite property. d. Material used for backfilling trenches shall be properly compacted in order to minimize erosion and promote stabilization. e. Restabilization shall be accomplished in accordance with these regulations. f. Applicable safety regulations shall be complied with. 3 17. CONSTRUCTION ACCESS ROUTES: Where construction vehicle access routes intersect paved public roads, provisions shall be made to minimize the transport of sediment by vehicular tracking onto paved surfaces. Where sediment is transported on to a public road surface, the road shall be cleaned thoroughly at the end of each day. Sediment shall be removed by shoveling or sweeping and transported to a sediment control disposal area. Street washing shall be allowed only after sediment is removed in this manner. This provision shall apply to individual lots as well as to larger land disturbing activities. 18. TEMPORARY E &S CONTROL MEASURE REMOVAL: All temporary erosion and sediment control measures shall be removed within 30 days after final site stabilization or after temporary measures are no longer needed, unless otherwise authorized by the local program authority. Trapped sediment and the disturbed soil areas resulting from the disposition of temporary measures shall be permanently stabilized to prevent further erosion and sediment. 19. ADEQUACY OF RECEIVING CHANNELS: Properties and waterways downstream from the development site shall be protected from sediment deposition, erosion and damage, due to increases in volume, velocity and peak flow rates of stormwater runoff for the stated frequency storm of 24 -hour duration. B1. PROJECT DESCRIPTION: The purpose of this project is to construct 252,197 sf of retail /office space and related parking and infrastructure. Total area of disturbance is approximately 27.68 Acres. B2. EXISTING SITE CONDITIONS: The site has been rough graded under previously approved erosion control plan. The site is grassed with moderate slopes. B3. ADJACENT AREAS: The site is bounded to the South by U.S. Route 29, to the East by Towncenter Drive, to the North by future Meeting Street, and to the West by Powell Creek. B4. SOIL DESCRIPTIONS: According to the Albemarle County Soils Survey conducted by the United States Department of Agriculture Soil Conservation Service, the primary soil types that may be disturbed during this scope of work have been identified as the following: 1. Elioak Loam (27B) — Permeability is moderate, surface runoff and the hazard of erosion is moderate. Hydrologic group C, K factor .28 2. Elioak Silt Loam (28C3) — Permeability is moderate, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group C, K factor .28 3. Glenelg Loam (34C) — Permeability is moderate, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group B, K factor .43 4. Hazel Loam (39D) — Permeability is moderately rapid, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group C, K factor .24 4 5. Louisburg Sandy Loam (47C) — Permeability is rapid, surface runoff is rapid, and the hazard of erosion is severe. Hydrologic group B, K factor .24 6. Louisburg Sandy Loam (47D) — Permeability is rapid, surface runoff is rapid, and the hazard of erosion is severe. Hydrologic group B, K factor .24 7. Pacolet Sandy Loam (65B) — Permeability is moderate, surface runoff is rapid, and the hazard of erosion is severe. Hydrologic group B, K factor .28 8. Pacolet Sandy Loam (65C) — Permeability is moderate, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group B, K factor .28 B5. CRITICAL AREAS: Critical slopes, streams and wetlands are the critical areas for this project. The contractor shall take care to prevent sediment from entering into the stream and other areas to be preserved. B6. EROSION AND SEDIMENT CONTROL MEASURES: Unless otherwise indicated, all erosion and sediment control practices will be constructed and maintained according to the minimum standards and specifications as set forth in the Virginia Erosion and Sediment Control Handbook, latest edition. The minimum standards of the Virginia Erosion and Sediment Control Regulations shall be adhered to unless otherwise waived or approved by variance. TEMPORARY CONSTRUCTION ENTRANCE (CE) — 3.02 An asphalt pad shall be constructed at the entrance of the project site to provide a means of removing sediment from the tires of construction vehicles leaving the work site. The Contractor shall remove any mud from the existing road surface by means of sweeping and shoveling, in the event the stone pad is not adequate in sediment removal. SILT FENCE (SF) — 3.05 Silt fencing will be installed as a first step in construction activities. Location and details are shown on the plans. STORM DRAIN INLET PROTECTION (IP) — 3.07 A sediment filter around a storm drain drop inlet or curb inlet used to prevent sediment from entering storm drainage systems prior to permanent stabilization of the disturbed area. Location and details of inlet protection are shown on the plans. TEMPORARY DIVERSION DIKE (DD) — 3.09 Temporary diversion dikes will be installed before site grading begins, for the purposes of diverting storm and sediment -laden runoff to the appropriate outlet or trapping facility. Location and details are shown on the plans. TEMPORARY SEDIMENT TRAP (ST) — 3.13 A temporary sediment trap will be installed before site grading begins, for the purpose of detaining sediment -laden runoff from disturbed areas. Location and details of the sediment traps are shown on the plans. TEMPORARY SEDIMENT BASIN (ST) — 3.14 5 In addition to the large, existing sediment basin, SB -3, three primitive sediment basins currently exist on the property. The basin to the NW shall be removed (replaced by proposed ST -1) and the two adjacent to Rte 29 shall be upgraded to standard and remain as long as construction permits. Location and details of the sediment basin is shown on the plans. OUTLET PROTECTION (OP) — 3.18 Outlet protection will be installed according to Virginia Erosion and Sediment Control regulations. Location and details are shown on the plans. DUST CONTROL (DC) — 3.39 A variety of methods are available to prevent surface and air movement of dust from exposed soil surfaces and reduce the presence of airborne substances which may present health hazards, traffic safety problems or harm animal or plant life. B7. PERMANENT AND TEMPORARY STABILIZATION: SURFACE ROUGHENING — 3.29 Disturbed areas to be seeded and mulched shall be left in a roughened condition to help decrease runoff velocities and aid in the establishment of vegetation. TOPSOILING — 3.30 Topsoil may be stripped from the area to be graded and stockpiles for later use. All stockpiles which will be left dormant for more than 30 days shall be temporarily seeded. A topsoil stockpile may be selected onsite by the developer and shall be temporarily protected with surrounding silt fencing. TEMPORARY SEEDING — 3.31 Temporary soil stabilization shall be applied within 7 days to denuded areas that may not be at final grade, but will remain dormant (undisturbed) for longer than 30 days and Tess than 1 year. This includes, but is not limited to areas such as soil stockpiles. Seeded areas shall be limed when necessary at a rate of 2 tons per acre, and fertilized at a rate of 450 lbs. per acre of 10 -20 -20 (10 lbs. per 1,000 square feet) or equivalent. A Temporary Seeding Schedule is attached for proper seed selection. PERMANENT SEEDING — 3.32 A perennial vegetative covering shall be established on disturbed areas within 7 days of being brought to final grade on areas not otherwise protected. Selection of the seed mixture shall depend on the time of year it is to be applied according to the Permanent Seed Schedule as shown on the drawing. Seeded areas shall be limed when necessary at a rate of 2 tons per acres, and fertilized at a rate of 1,000 lbs. per acre of 10 -20 -10 (10 lbs. per 1,000 square feet) or equivalent. MULCHING — 3.35 All seeded areas shall be mulched with straw immediately following seeding operations. Straw mulch shall be applied at a rate of two tons per acre. SOIL STABILIZATION BLANKETS AND MATTING — 3.36 Soil stabilization matting shall be applied in the conveyance areas of the designed diversions to help reduce velocities and aid in the establishment of vegetation. A detail showing the proper materials and installation is shown on the plan. 6 N B8. SOIL STOCKPILES AND BORROW AREAS A soil stockpile area has been provided with this Erosion and Sediment Control Plan. Borrow and /or waste areas must have an approved Erosion and Sediment Control Plan. B9. STORM WATER MANAGEMENT: The increase in stormwater runoff will be controlled by a retention basin, SWM #3. Water quality treatment is provided by the retention basin, bio- filters, Filterra units and a Contech Stormfilter. See SWM plan for details and hydrologic /hydraulic calculations. B10. MAINTENANCE SCHEDULE: A program of maintenance for the erosion and sediment controls specified in this narrative and shown on the plans are recommended as follows: 1. The Site Superintendent or his representative shall make a visual inspection of all erosion and sediment controls on a daily basis until the site is stabilized and especially after a heavy rainfall to assure that all controls are in place and that none have been damaged. Any damaged control shall be repaired prior to the end of each workday to include re- seeding if necessary. 2. All silt trapping devices shall be cleaned out at 50 percent capacity and sediment shall be disposed of by spreading on site or hauling away if not suitable for fill. 3. Gravel outlets shall be checked regularly for sediment buildup that may prevent drainage. Controls shall be inspected and repaired after each rainfall and cleaned if sediment has accumulated to half of the device's original height. 4. All earthen structures such as diversion dikes and berms shall be checked daily during construction for breaching by equipment. Repairs shall be made immediately. 5. Silt fences shall be checked after each rainstorm to assure they have not fallen or become clogged with silt. All repairs shall be made immediately. 6. All seeded areas shall be inspected regularly to see that good stand is maintained. Areas will be re- fertilized and re- seeded as necessary. 7. After construction operations have ended and disturbed areas have been stabilized, all berms and sediment - trapping devices may be removed after removal, the ground shall be restored to its natural or proposed condition to include establishment of permanent vegetation. Removal of any control is contingent upon approval of the County Inspector. 7 BIOFILTERS #3 & #4 100 -YR ROUTING FOR HOLLYMEAD TOWNCENTER (AREA Al) December 17, 2008 LOCATION: Tax Map 32, Parcel 44 Albemarle County, Virginia OWNER: HM Acquisition Group, LLC 126 Garrett Street Charlottesville, Virginia 22902 DEVELOPER: Octagon Partners 126 Garrett Street Charlottesville, Virginia 22902 PREPARED BY: Dominion Development Resources 172 South Pantops Road Charlottesville, VA 22911 434.979.8121 (F) 434.979.1681 Name: 100 -yr post Type: Modified Rational [HYDROGRAPH INFORMATION] Peak Flow (Qp) = 30.84 (cfs) Time to Peak (Tp) = 6.60 (min) Time of Base (Tb) = 16.56 (min) Volume = 0.35 (ac -ft) Time Step = 0.10 (min) Flow Multiplier = 1.00 [RATIONAL HYDROGRAPH INFORMATION] Flow Multiplier = 1.00 Receding Limb Factor = 1.50 [APPROXIMATE STORAGE] Maximum Outflow = 0.00 (cfs) Maximum Storage = 0.35 (cu ft) [BASIN INFORMATION] [WEIGHTED WATERSHED AREA] Description Area CN Runoff Coef <None> Overall Approximation 4.16 NA 0.82 [TIME CONCENTRATION -- User Defined] Time of Concentration (Tc) = 6.60 (min) [RAINFALL DESCRIPTION] Distribution Type = Synthetic Total Precipitation = 1.00 (in) Return Period = 100 (yr) Storm Duration = 0.11 (hr) 'tr. t rr Type : Rectangular Weir Suppressed Name : Weir [RATING CURVE LIMIT] Minimum Elevation = 507.00 (ft) Maximum Elevation = 518.00 (ft) Elevation Increment = 0.25 (ft) [OUTLET STRUCTURE INFORMATION] Crest Length = 15.71 (ft) Crest Elevation = 517.00 (ft) Weir Coefficient = 3.33 Exponential = 1.50 [MAXIMUM DISCHARGE] Q = 52.31 (cfs) [WEIR STAGE VS. DISCHARGE] Elevation (ft) Stage (ft) Discharge (cfs) 517.00 10.00 0.00 517.25 10.25 6.54 517.50 10.50 18.49 517.75 10.75 33.97 518.00 11.00 52.31 Name: BF #3 [RATING CURVE LIMIT] Minimum Elevation = 507.00 (ft) Maximum Elevation = 518.00 (ft) Elevation Increment = 0.25 (ft) [STAGE STORAGE INFORMATION] Storage Method: User - Defined Storage Input Method: Area Number Elevation Area Ave Area Volume Cumulative Volume (ft) (sq ft) (sq ft) (cu ft) (cu ft) 1 0.00 0.00 0.00 0.00 0.00 2 515.99 0.00 0.00 0.00 0.00 3 516.00 6066.00 3033.00 30.33 30.33 4 518.80 6066.00 6066.00 16984.80 17015.13 2 wr Nair Name: 100 -yr rtd Type: Reservoir: Modified Puls [HYDROGRAPH INFORMATION] Peak Flow (Qp) = 17.41 (cfs) Time to Peak (Tp) = 11.00 (min) Time of Base (Tb) = 94.80 (min) Volume = 0.20 (ac -ft) Time Step = 0.10 (min) Peak Elevation = 517.48 (ft) Detention Time = NA [RESERVOIR STRUCTURE INFORMATION] Number = 1 Name = BF #3 Storage Type = User - Defined Area Maximum Storage = 12890.25 (cu ft) Maximum Discharge = 52.31 (cfs) [INFLOW HYDROGRAPH INFORMATION] Number = 4 Name = 100 -yr post Peak Flow (Qp) = 30.84 (cfs) Time to Peak (Tp) = 6.60 (min) Time of Base (Tb) = 16.56 (min) Volume = 0.35 (ac -ft) Flow Multiplier = 1.00 3 N✓ w Name: 100 -yr post Type: Modified Rational [HYDROGRAPH INFORMATION] Peak Flow (Qp) = 23.09 (cfs) Time to Peak (Tp) = 5.40 (min) Time of Base (Tb) = 13.56 (min) Volume = 0.22 (ac -ft) Time Step = 1.00 (min) Flow Multiplier = 1.00 [RATIONAL HYDROGRAPH INFORMATION] Flow Multiplier = 1.00 Receding Limb Factor = 1.50 [APPROXIMATE STORAGE] Maximum Outflow = 0.00 (cfs) Maximum Storage = 0.22 (cu ft) [BASIN INFORMATION] [WEIGHTED WATERSHED AREA] Description Area CN Runoff Coef <None> Overall Approximation 2.93 NA 0.83 [TIME CONCENTRATION -- User Defined] Time of Concentration (Tc) = 5.40 (min) [RAINFALL DESCRIPTION] Distribution Type = Synthetic Total Precipitation = 0.86 (in) Return Period = 100 (yr) Storm Duration = 0.09 (hr) 4 low , 4000 Type : Rectangular Weir Suppressed Name : Weir [RATING CURVE LIMIT] Minimum Elevation = 499.00 (ft) Maximum Elevation = 516.00 (ft) Elevation Increment = 0.25 (ft) [OUTLET STRUCTURE INFORMATION] Crest Length = 15.71 (ft) Crest Elevation = 512.50 (ft) Weir Coefficient = 3.33 Exponential = 1.50 [RECTANGULAR SUPRESSED EQUATION] Q = Cw * L * H ^exp = 342.50 (cfs) [WEIR STAGE VS. DISCHARGE] Elevation (ft) Stage (ft) Discharge (cfs) 512.50 13.50 0.00 512.75 13.75 6.54 513.00 14.00 18.49 513.25 14.25 33.97 513.50 14.50 52.31 513.75 14.75 73.10 514.00 15.00 96.10 514.25 15.25 121.09 514.50 15.50 147.95 514.75 15.75 176.54 515.00 16.00 206.76 515.25 16.25 238.54 515.50 16.50 271.80 515.75 16.75 306.47 516.00 17.00 342.50 Name: BF #4 [RATING CURVE LIMIT] Minimum Elevation = 498.00 (ft) Maximum Elevation = 516.00 (ft) Elevation Increment = 0.25 (ft) [STAGE STORAGE INFORMATION] Storage Method: User - Defined Storage Input Method: Area Number Elevation Area Ave Area Volume Cumulative Volume (ft) (sq ft) (sq ft) (cu ft) (cu ft) 1 0.00 0.00 0.00 0.00 0.00 2 511.49 0.00 0.00 0.00 0.00 3 511.50 5972.00 2986.00 29.86 29.86 4 516.00 5972.00 5972.00 26874.00 26903.86 5 Name: 100 -yr rtd Type: Reservoir: Modified Puls [HYDROGRAPH INFORMATION] Peak Flow (Qp) = 6.10 (cfs) Time to Peak (Tp) = 11.00 (min) Time of Base (Tb) = 89.00 (min) Volume = 0.06 (ac -ft) Time Step = 1.00 (min) Peak Elevation = 512.73 (ft) Detention Time = NA [RESERVOIR STRUCTURE INFORMATION] Number = 1 Name = BF #4 Storage Type = User - Defined Area Maximum Storage = 27620.50 (cu ft) Maximum Discharge = 342.50 (cfs) [INFLOW HYDROGRAPH INFORMATION] Number = 8 Name = 100 -yr post Peak Flow (Qp) = 23.09 (cfs) Time to Peak (Tp) = 5.40 (min) Time of Base (Tb) = 13.56 (min) Volume = 0.22 (ac -ft) Flow Multiplier = 1.00 6 WATER QUALITY ANALYSIS FOR HOLLYMEAD TOWNCENTER (AREA Al) August 8, 2008 Revised: December 22, 2008 LOCATION: Tax Map 32, Parcel 44 Albemarle County, Virginia OWNER: HM Acquisition Group, LLC 126 Garrett Street Charlottesville, Virginia 22902 DEVELOPER: Octagon Partners 126 Garrett Street Charlottesville, Virginia 22902 PREPARED BY: Dominion Development Resources 172 South Pantops Road Charlottesville, VA 22911 434.979.8121 (F) 434.979.1681 PERFORMANCE -BASED METHOD The performance -based water quality criteria state that for land development, the calculated post - development non -point source pollutant runoff load shall be compared to the calculated pre - development Toad based upon the average land cover condition or the existing site condition. This approach requires the designer to calculate the pollutant load to be removed, implement a BMP strategy, and then calculate the performance of that strategy, based on the effectiveness or pollutant removal efficiency of the selected BMP(s). REMOVAL RATE CALCULATION The simple method was used in determining the required pollutant removal for Area A -1. The existing impervious for the site is Tess than 20 %, putting the project in the New Development category. The parcel in question is not in a drinking water watershed or other rural lands. The post - developed condition will result in 859,341 SF of impervious surfaces. The resultant removal rate for New Developments in Development Areas is 69% (see attached BMP Computation). Proffer #9 (ZMA 2007 -001) requires that, to the extent practicable, additional stormwater management measures be utilized to achieve a removal rate 20% better than would otherwise be requires, up to a maximum of 80% removal rate. Therefore, the target removal rate for this project is 80 %. BMP SELECTION The site contains an existing stormwater management basin which is designed to provide stormwater quantity control for the site. The basin is currently serving as a sediment basin, but is now designed to ultimately become a retention basin with an aquatic bench. The new retention basin contains 4 *WQV and is sized to provide 65% removal of pollutants for existing Area B -1, Area A -1, future Block D and a portion of Towncenter Drive and Meeting Street. Most of the runoff from the site is collected and pre- treated prior to reaching the existing basin at one of two points, the existing storm sewer outfall from Area B1 at the south end of the basin near Route 29 and a new storm sewer outfall at the north end of the basin. A small portion of the site drains directly to the basin without pre- treatment. In order to reach the 80% target removal rate, treatment trains were proposed for each outfall. These consist of new bio- filters and a ConTech StormFilter system. Two Filterra units have been included to treat runoff not flowing through one of the other pre- treatment devices before entering the retention basin. The majority of the runoff entering the basin through the existing pipe system is treated in new bio- filters (BF -1 through BF -4) or Filterra units sized to achieve a 65% removal rate. The resultant effluent is then further treated in the retention basin for an additional 65% removal of the remaining pollutant load. All of the runoff entering the existing basin at the northern outfall is routed through the ConTech StormFilter system which outfalls to the new retention basin. This treatment train achieves a removal rate of 50% at the Stormfilter, 65% at the retention basin. Nearly 100% of the runoff from the new impervious surface is captured and treated in one or more BMP's resulting in removal of 80% of the pollutant load as shown in the treatment matrix shown on Sheet C7 of the Stormwater Management Plan. 1992 3.14 TEMPORARY.. SEDIMENT BASIN: DESIGN DATA SHEET (with or without an emergency spillway) Project I-4 ©ll M c 0.at - T t_e k a r /kr e K A - Basin # 3 Location S o ,,, k\A vr-., r Total area draining to basin: y c 1. acres. Basin Volume Design Wet,Storage: 1.. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres). 67 cu. yds. x 4 L 1 L acres = 3 , 3 ..ei z . cu. yds. 2. A v a i l a b l e basin volume = i W 2Z cu. yds. at elevation h 1 Lso ' . .(From • storage - elevation curve) 3. Excavate Z 111 cu. yds. to obtain required volume *. * Elevation corresponding to required volume = invert of the dewatering orifice. 4. Available volume before cleanout required. 33 cu. yds. x /-113 G acres = L, og cu. yds. 5. Elevation corresponding to cleanout level =- . (From Storage - Elevation Curve) 6. Distance from invert of the dewatering orifice to cleanout level = 6.2)0 ft. (Min. = 1.0 ft.) Dry Storage: 7. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres). 67 cu. yds. x yl.'1c. acres = 3, 3 Z cu. yds. III - 112 1992 3.14 8. Total available basin volume at crest of riser* = lj vir cu. yds. at elevation V t 3 .Prf . (From Storage - Elevation Curve) Minimum = 134 cu. yds./acre of total drainage area. 9. Diameter of dewatering orifice = 1 & in. 10. Diameter of flexible tubing = in. (diameter of dewatering orifice plus 2 inches). Preliminary Design Elevations 11. Crest of Riser = g 3.19 Top of Dam = 14(41, 1 Design High Water = 4 » r. • Upstream Toe of Dam = & / • D Basin Shape 12. Length of Flow L = z_eto Effective Width We 0‘? If > 2, baffles are not required Z. If < 2, baffles are required Runoff 13 . Q2 = 1 3. cfs (From Chapter 5) 14. Q = \ 2- Lk • 2 cfs - (From Chapter 5) Principal Spillway Design 15. With emergency spillway, required spillway capacity Q = Q2 = - 13. cfs. (riser and barrel) Without emergency spillway, required spiliway capacity Q = Q = t 24. 2 cfs. P 25 (riser and barrel) M - 113 1992 3.14 16. With emergency spillway: Assumed available head (h) = \ : d ft. (Using Q h = Crest of Emergency Spillway Elevation Crest of R iser Elevation Without emergency spillway: Assumed available head (h) = ft. (Using .Q h = Design High Water Elevation - Crest of Riser Elevation 17. Riser diameter (D = E )-- in. Actual head (h) = , t • t C ft. (From Plate 3.14 -8.) Note: Avoid orifice flow conditions. 18. Barrel length (1) = . q 2 ft. Head (H) on barrel through embankment. = 2 . s2 ft. (From Plate 3.14 -7). 19. Barrel diameter = 4 s in. (From Plate 3.14 -B [concrete pipe] or Plate 3.14 -A [corrugated pipe]). 20. Trash rack and anti- vortex device Diameter = l L inches. Height = 3 c. inches. (From Table 3.14 -D). Emergency Spillway Design 21. Required spillway capacity Q = Q25 - Op = S • C . cfs. 22. Bottom width (b) = 30 ft.; the slope of the exit channel (s) = 0. 3 r ft. /foot; and the minimum length of the exit channel (x) = yq ft. (From Table 3.14 -C). III - 114 ',roe 1992 3.14 Anti-Seep Collar Design 23. Depth of water at principal spillway crest (Y) = ft. Slope of upstream face of embankment (Z) = :1. Slope of principal spillway barrel (S = Length of barrel in saturated zone (L = ft. 24. Number of collars required = dimensions = , (froth Plate 3.14-12). Final Design Elevations 25. Top of Dam = 41,1.1(S Design High Water = Emergency Spillway Crest = Loq,q, ' • Principal Spillway Crest '= 4%3, 99' Dewatering Orifice Invert = qt. se Cleanout Elevation = 1 411.1 Elevation of Upstream Toe of Dam or Excavated Bottom of "Wet Storage Area" (if excavation was performed) = 410, 00 III - x.. Amoy ‘ftieue 1992 3.14 TEMPORARY.. SEDIMENT BASIN, DATA SHEET (with, or without an emergency spillway) Project kr21l - To,r cc ".k-.r Ara.,, A -1 Basin # Location L . k Total area draining to basin: 6,1 2 acres. Basin Volume Design Wet, Storage: 1. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres). 67 cu. yds. x z acres = 45o .24 . cu. yds. 2. Available basin volume = (.$.L4 cu. yds. at elevation s&o,$0 . (From storage - elevation curve) 3. Excavate 0 cu. yds. to obtain required volume *. * Elevation corresponding to required volume = invert of the dewatering orifice. 4. Available volume before cleanout required. 33 cu. yds. x G . - acres = 1 cu. yds. 5. Elevation corresponding to cleanout level = 5 o g. S S . (From Storage - Elevation Curve) 6. Distance from invert of the dewatering orifice to cleanout level = ic ft. (Min. = 1.0 ft.) Dry Storage: 7. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres). 67 cu. yds. x . z acres = 59 . zy cu. yds. III - 112 • • • • • 1992 3.14 • 8. • Total available basin volume at crest of . riser* = G3 cu. yds. at elevation 511. c . (From Storage - Elevation Curve) ,„. * Minimum = 134 .cu„ yds./acre of total drainage area. 9. Diameter of dewatering orifice = in. 10. Diameter of flexible tubing = in. (diameter of dewatering orifice plus 2: inches). • , Preliminary Design Elevations • 11. Crest of Riser = , 5o -- Top of Dam = 5 s ' Design High Water = Upstream Toe of Dam =• . (" Basin Shape • 12. Length of Flow L • = • Effective Width We 5 3 /10 If > 2, baffles are not required If < 2, baffles are required 0 .16 ei.44 ker ft eek Runoff 13 . Q2 = • g cfs (From Chapter 5) 14. Q = 12 cfs (From Chapter 5) • .1 Principal Spillway Design . 15. With emergency spillway, required spillway capacity Q = Q2 = 3 cfs. (riser and barrel) • Without emergency spillway, required spillway capacity Q = Q25 = 17. cfs. • (riser and barrel) IIJ -113 . 1992 3.14 16. With emergency spillway: Assumed available head (h) = nr I P ft. (Using Q h = Crest of Emergency Spillway Elevation Crest of Riser Elevation Without emergency spillway: Assumed available head (h) = 1 ft. (Using . Q25) h = Design High Water Elevation - Crest of Riser Elevation 17. Riser diameter (Di) = '40 in. Actual head (h) = O, ft. (From Plate 3.14 -8.) Note: Avoid orifice flow conditions. 18. Barrel length (1) = . (. ft. Head (H) on barrel through embankment. = I ) • 4 3 ft. (From Plate 3.14 -7). 19. Barrel diameter = 3c. in. (From Plate 3.14 -B [concrete pipe] or Plate 3.14 -A [corrugated pipe]). 20. Trash rack and anti- vortex device Diameter = inches. Height = /1 inches. (From Table 3.14 -D). Emergency Spillway Design 21. Required spillway capacity Q = Q25 - Qp = cfs. 22. Bottom width (b) = l A ft.; the slope of the exit channel (s) = Op ft. /foot; and the minimum length of the exit channel (x) = rr I n ft. (From Table 3.14 -C). III - 114 1992 3.14 Anti -Seep Collar Design 23. Depth of water at principal spillway crest (Y) = ft. Slope of upstream face of embankment (Z) = :1. Slope of principal spillway barrel (S = N l' % Length of barrel in saturated zone (L = ,./14 ft. 24. Number of collars required = r l A dimensions = w l A (froth Plate 3.14 -12). Final Design Elevations 25. Top of Dam = s ki. s fl Design High Water = s 13 AS Emergency Spillway Crest = r r I A Principal Spillway Crest • 5 i 3 o _ Dewatering Orifice Invert = 510. g ' Cleanout Elevation = Sop gc' Elevation of Upstream Toe of Dam or Excavated Bottom of "Wet Storage Area" (if excavation was performed) = s u 6, • • I1I - 115 1992 3.14 TEMPORARY.. SEDIMENT BASIN DATA SHEET (with or without an emergency spillway) Project k t..1 t M tw Jl "tom N L J c, A =1 Basin # Location S E c 1, k Total area draining to basin: 5. c acres. Basin Volume Design Wet, Storage: 1. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres). 67 cu. yds. x s : s . acres = 311 . (c . cu. yds. 2. Available basin volume = o s . cl.t, cu. yds. at elevation .1 . (From storage - elevation curve) 3. Excavate "Q r cu. yds. to obtain required volume *. (' . * Elevation corresponding to required volume = invert of the dewatering orifice. 4. Available volume before cleanout required. 33 cu. yds. x S - s acres = 1%3 _ g, cu. yds. 5. Elevation corresponding to cleanout level = s ‘∎ . % A' . (From Storage - Elevation Curve) 6. Distance from invert of the dewatering orifice to cleanout level = t 5a ft. (Min. = 1.0 ft.) Dry Storage: 7. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres). 67 cu. yds. x acres = X73 e t cu. yds. III - 112 1992 3.14 8. Total available basin volume at crest of . riser* = - 114 , r y cu. elevation SCS s d' . (From Storage - elevation Cury yds. at ( S e) *Minimum = 134 cu. yds. /acre of total drainage area. 9. Diameter of dewatering orifice = C in. 10. Diameter of flexible tubing = , 9, in. (diameter of dewatering orifice plus 2. inches). Preliminary Design Elevations 11. Crest of Riser = S I S _ s o Top of Dam = SIB s Design High Water = 5 \ S • `) Upstream Toe of Dam = s, o , a Basin Shape 12. Length of Flow L = Effective Width We If > 2, baffles are not required 1 If < 2, baffles are required o , S p. i f r Q„ t , , Runoff 13. Q = (. . O cfs (From Chapter 5) 14. Q 25 = ` 1.1 cfs - (From Chapter 5) Principal Spillway Design 15. With emergency spillway, required spillway capacity Q = Q = 6. 0 cfs. (riser and barrel) Without emergency spillway, required spillway capacity Q = Q 25 = °[ - cfs. (riser and barrel) III - 113 1992 3.14 16. With emergency spillway: Assumed available head (h) = (P ft. (Using Q h = Crest of Emergency Spillway Elevation Crest of Riser Elevation Without emergency spillway: . Assumed available head (h) = 00 ft. (Using .Q25) h = Design High Water Elevation - Crest of Riser Elevation 17. Riser diameter (D = 0 in. Actual head (h) = 0,34 ft. (From Plate 3.14 -8.) Note: Avoid orifice flow conditions. 18. Barrel length (1) = . 69 . ft. Head (H) on barrel through embankment. = 8S ft. (From Plate 3.14 -7). 19. Barrel diameter = 3 '0 in. _ (From Plate 3.14 -B [concrete pipe] or Plate 3.14 -A [corrugated pipe]). 20. Trash rack and anti- vortex device Diameter = ,q 0, inches. Height = 2.I inches. (From Table 3.14 -D). Emergency Spillway Design 21. Required spillway capacity Q = Q25 - Qp = N ( P cfs. 22. Bottom width (b) = 1 P ft.; the slope of the exit channel (s) = Iv ((A ft. /foot; and the minimum length of the exit channel (x) = w 114 ft. (From Table 3.14 -C). III - 114 .4. 1992 3.14 Anti-Seep Collar Design 23. Depth of water at principal spillway crest (Y) = N in ft. Slope of upstream face of embankment (Z) = (414 :1. Slope of principal spillway barrel (S = 1 p Length of barrel in saturated zone (L = Af Ip ft. 24. Number of collars required = J IA dimensions = (from Plate 3.14-12). Final Design Elevations 25. Top of Dam = siis 5 Design High Water = st 5, 9 s Emergency Spillway Crest = 1 Principal Spillway Crest •= $ is .30 Dewatering Orifice Invert = t Cleanout Elevation = 5 ti ol • Elevation of Upstream Toe of Dam • or Excavated Bottom of "Wet Storage Area" (if excavation was performed) = s P • G-1 • - . 115 SUBPOENA FOR WITNESS (CIVIL) — Case No.: CL07- 0600413 -00 ATTORNEY ISSUED VA. CODE §§ 8.01 -407; 16.1 -265; Supreme Court Rules 1:4, 4:5 Commonwealth of Virginia February 23, 2011/9:30 a.m. HEARING DATE AND TIME Albemarle County Circuit Court 501 East Jefferson Street, Charlottesville, Virginia 22902 ADDRESS OF COURT River Heights Associates, L.P. v. Regency Centers Corporation, et al. TO THE PERSON AUTHORIZED BY LAW TO SERVE THIS PROCESS: You are commanded to summon Ray Lilly. c/o Greg Kamptner, Es q u ire, Co unty Attorne NAME 401 McIntire Road STREET ADDRESS Charlottesville Virginia 22901 CITY STATE ZIP TO the person summoned: You are commanded to appear ® in the Court x at County Office Bldg, 401 McIntire Road, Room 320„ Charlottesville, Virginia 22902 ADDRESS (DEPOSITION USE IN CIRCUIT COURT ONLY) on December 15, 2010 at 10:00 a.m. to testify in the above -named case. This subpoena is issued by the attorney for and on behalf of River Heights Associates, LP PARTY NAME Joseph W. Wright, III 30347 NAME OF ATTORNEY VIRGINIA STATE BAR NUMBER 675 Peter Jefferson Parkway Suite 190 (434) 979 -5515 OFFICE ADDRESS TELEPHONE NUMBER OF ATTORNEY Charlottesville, Virginia 22911 (434) 295 -7785 OFFICE ADDRESS FACSIMILE : OF ATTORNEY � 4 DATE ISS ED , SIGNATURE OF AT ORNEY Notice to Recipient: See page two for further information. RETURN OF SERVICE (see page two of this form) FORM DC -497 (W) 7/00 Page 1 TO the person summoned: If you are served with this subpoena less than 5 calendar days before your appearance is required, the court may, after considering all of the circumstances, refuse to enforce the subpoena for lack of adequate notice. If you are served with this subpoena less than 5 calendar days before your appearance is required, you may wish to contact the attorney who issued this subpoena and the clerk of the court. TO the person authorized to serve this process: Upon execution, the return of this process shall be made to the clerk of court. NAME: ADDRESS: n PERSONAL SERVICE Tel. No. Being unable to make personal service, a copy was delivered in the following manner: n Delivered to family member (not temporary sojourner or guest) age 16 or older at usual place of abode of party named above after giving information of its purport. List name, age of recipient, and relation of recipient to party named above: et n Posted on front door or such other door as appear to be the main entrance of usual place of abode, address listed above. (Other authorized recipient not found.) n not found ,Sheriff Z1 i DATE by , Deputy Sheriff CERTIFICATE OF COUNSEL I, Joseph W. Wright, III, counsel for Plaintiff, hereby certify that a copy of the foregoing subpoena for witness was mailed to William T. Freyvogel and Jonathan T. Blank, counsel of record for Defendants, on the /e, day of December 2010. + SIG • TURE OF ATTORNEY FORM DC -497 (W) 7/00 Page 2 EROSION AND SEDIMENT CONTROL NARRATIVE FOR HOLLYMEAD TOWNCENTER AREA Al December 22, 2008 LOCATION: Tax Map 32 Parcels 44,45 Tax Map 46 Parcel 5 Rivanna District, Albemarle County, Virginia OWNER & DEVELOPER HM Acquisition Group, LLC PO Box 5548 Charlottesville VA, 22905 PREPARED BY: Dominion Development Resources, LLC 172 S Pantops Dr. Charlottesville, VA 22911 434.979.8121 (F) 434.979.1681 1 A. MINIMUM STANDARDS (MS): All applicable Virginia Erosion and Sediment Control Regulations and Minimum Standards shall be adhered to during all phases of construction. These include, but are not limited to the following: 1. STABLIZATION OF DENUDED AREAS: Permanent or temporary soil stabilization shall be applied to bare areas within seven days after final grade is reached on any portion of the site. Temporary soil stabilization shall be applied within seven days to denuded areas that may not be at final grade, but will remain dormant or undisturbed for longer than 30 days. Permanent stabilization shall be applied at areas that are to be left dormant for more than 1 year. 2. STABILIZATION OF SOIL STOCKPILES: During construction of the project, soil stockpiles shall be stabilized or protected with sediment trapping measures. The applicant is responsible for temporary protection and permanent stabilization of all soil stockpiles on site as well as soil intentionally transported from the project site. 3. PERMANENT VEGETATIVE COVER A permanent vegetative cover shall be established on denuded areas not otherwise permanently stabilized. Permanent vegetation shall not be considered established until a ground cover is achieve that, in the opinion of the county Inspector, is uniform and mature enough to survive to inhibit erosion. 4. TIMING & STABILIZATION OF SILT TRAPPING MEASURES: Sediment basins and traps, perimeter dikes, sediment barriers and other measures intended to trap sediment shall be constructed as a first step in any land disturbing activity and shall be made functional before upslope land disturbance takes place. 5. STABILIZATION OF EARTHEN STRUCTURES: Stabilization measures shall be applied to earthen structures such as dams, dikes and diversions immediately after installation. 6. SEDIMENT TRAPS AND BASINS: A sediment basin shall control surface runoff from disturbed areas that is comprised of flow from drainage areas greater than or equal to three acres. The sediment basin shall be designed and constructed to accommodate the anticipated sediment loading for the land disturbing activity. The outfall device or system device shall take into account the total drainage area flowing through the disturbed area to be served by the basin. 7. CUT AND FILL SLOPES: Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion. Slopes that are found to be eroding excessively within one year of permanent stabilization shall be provided with additional slope stabilizing measures until the problem is corrected. 8. CONCENTRATED RUN -OFF DOWN CUT OR FILL SLOPES: Concentrated runoff shall not flow down cut or fill slopes unless contained within an adequate temporary or permanent channel, flume, or slope drain structure. 2 9. WATER SEEPS FROM A SLOPE FACE: Whenever water seeps from a slope face, adequate drainage or other protection shall be provided. 10. STORM SEWER INLET PROTECTION: All storm sewer inlets that are made operable during construction shall be protected so that sediment -laden water cannot enter the conveyance system without first being filtered or otherwise treated to remove sediment. 11. STABILIZATION OF OUTLETS: Before newly constructed stormwater conveyance channels are made operational, adequate outlet protection and any required temporary or permanent channel lining shall be installed in both the conveyance channel and receiving channel. 12. WORK IN LIVE WATERCOURSES: When work in a live watercourse is performed, precautions shall be taken to minimize encroachment, control sediment transport and stabilize the work area to the greatest extent possible during construction. Nonerodible material shall be used for the construction of causeways and cofferdams. Earthen fill may be used for these structures if armored by nonerodible cover materials. 13. CROSSING A LIVE WATERCOURSE: When a live watercourse must be crossed by construction vehicles more than twice in any six month period, a temporary stream crossing constructed of nonerodible materials shall be provided. 14. APPLICABLE REGULATIONS: All applicable federal, state and local regulations pertaining to working in or crossing live watercourses shall be met. 15. STABILIZATION OF BED AND BANKS The bed and banks of a watercourse shall be stabilized immediately after work in the watercourse is completed. 16. UNDERGROUND UTILITIES: Underground utilities shall be installed in accordance with the following standards in addition to other criteria: a. No more than 500 linear feet of trench may be opened at one time. b. Excavated material shall be placed on the uphill side of trenches c. Effluent for dewatering operations shall be filtered or passed through approved sediment trapping device, or both, and discharged in a manner that does not adversely affect flowing streams or offsite property. d. Material used for backfilling trenches shall be properly compacted in order to minimize erosion and promote stabilization. e. Restabilization shall be accomplished in accordance with these regulations. f. Applicable safety regulations shall be complied with. 3 17. CONSTRUCTION ACCESS ROUTES: Where construction vehicle access routes intersect paved public roads, provisions shall be made to minimize the transport of sediment by vehicular tracking onto paved surfaces. Where sediment is transported on to a public road surface, the road shall be cleaned thoroughly at the end of each day. Sediment shall be removed by shoveling or sweeping and transported to a sediment control disposal area. Street washing shall be allowed only after sediment is removed in this manner. This provision shall apply to individual lots as well as to larger land disturbing activities. 18. TEMPORARY E &S CONTROL MEASURE REMOVAL: All temporary erosion and sediment control measures shall be removed within 30 days after final site stabilization or after temporary measures are no longer needed, unless otherwise authorized by the local program authority. Trapped sediment and the disturbed soil areas resulting from the disposition of temporary measures shall be permanently stabilized to prevent further erosion and sediment. 19. ADEQUACY OF RECEIVING CHANNELS: Properties and waterways downstream from the development site shall be protected from sediment deposition, erosion and damage, due to increases in volume, velocity and peak flow rates of stormwater runoff for the stated frequency storm of 24 -hour duration. B1. PROJECT DESCRIPTION: The purpose of this project is to construct 252,197 sf of retail /office space and related parking and infrastructure. Total area of disturbance is approximately 27.68 Acres. B2. EXISTING SITE CONDITIONS: The site has been rough graded under previously approved erosion control plan. The site is grassed with moderate slopes. B3. ADJACENT AREAS: The site is bounded to the South by U.S. Route 29, to the East by Towncenter Drive, to the North by future Meeting Street, and to the West by Powell Creek. B4. SOIL DESCRIPTIONS: According to the Albemarle County Soils Survey conducted by the United States Department of Agriculture Soil Conservation Service, the primary soil types that may be disturbed during this scope of work have been identified as the following: 1. Elioak Loam (27B) — Permeability is moderate, surface runoff and the hazard of erosion is moderate. Hydrologic group C, K factor .28 2. Elioak Silt Loam (28C3) — Permeability is moderate, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group C, K factor .28 3. Glenelg Loam (34C) — Permeability is moderate, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group B, K factor .43 4. Hazel Loam (39D) — Permeability is moderately rapid, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group C, K factor .24 4 5. Louisburg Sandy Loam (47C) — Permeability is rapid, surface runoff is rapid, and the hazard of erosion is severe. Hydrologic group B, K factor .24 6. Louisburg Sandy Loam (47D) — Permeability is rapid, surface runoff is rapid, and the hazard of erosion is severe. Hydrologic group B, K factor .24 7. Pacolet Sandy Loam (65B) — Permeability is moderate, surface runoff is rapid, and the hazard of erosion is severe. Hydrologic group B, K factor .28 8. Pacolet Sandy Loam (65C) — Permeability is moderate, surface runoff is rapid and the hazard of erosion is severe. Hydrologic group B, K factor .28 B5. CRITICAL AREAS: Critical slopes, streams and wetlands are the critical areas for this project. The contractor shall take care to prevent sediment from entering into the stream and other areas to be preserved. B6. EROSION AND SEDIMENT CONTROL MEASURES: Unless otherwise indicated, all erosion and sediment control practices will be constructed and maintained according to the minimum standards and specifications as set forth in the Virginia Erosion and Sediment Control Handbook, latest edition. The minimum standards of the Virginia Erosion and Sediment Control Regulations shall be adhered to unless otherwise waived or approved by variance. TEMPORARY CONSTRUCTION ENTRANCE (CE) — 3.02 An asphalt pad shall be constructed at the entrance of the project site to provide a means of removing sediment from the tires of construction vehicles leaving the work site. The Contractor shall remove any mud from the existing road surface by means of sweeping and shoveling, in the event the stone pad is not adequate in sediment removal. SILT FENCE (SF) — 3.05 Silt fencing will be installed as a first step in construction activities. Location and details are shown on the plans. STORM DRAIN INLET PROTECTION (IP) — 3.07 A sediment filter around a storm drain drop inlet or curb inlet used to prevent sediment from entering storm drainage systems prior to permanent stabilization of the disturbed area. Location and details of inlet protection are shown on the plans. TEMPORARY DIVERSION DIKE (DD) — 3.09 Temporary diversion dikes will be installed before site grading begins, for the purposes of diverting storm and sediment -laden runoff to the appropriate outlet or trapping facility. Location and details are shown on the plans. TEMPORARY SEDIMENT TRAP (ST) — 3.13 A temporary sediment trap will be installed before site grading begins, for the purpose of detaining sediment -laden runoff from disturbed areas. Location and details of the sediment traps are shown on the plans. TEMPORARY SEDIMENT BASIN (ST) — 3.14 5 In addition to the large, existing sediment basin, SB -3, three primitive sediment basins currently exist on the property. The basin to the NW shall be removed (replaced by proposed ST -1) and the two adjacent to Rte 29 shall be upgraded to standard and remain as long as construction permits. Location and details of the sediment basin is shown on the plans. OUTLET PROTECTION (OP) — 3.18 Outlet protection will be installed according to Virginia Erosion and Sediment Control regulations. Location and details are shown on the plans. DUST CONTROL (DC) — 3.39 A variety of methods are available to prevent surface and air movement of dust from exposed soil surfaces and reduce the presence of airborne substances which may present health hazards, traffic safety problems or harm animal or plant life. B7. PERMANENT AND TEMPORARY STABILIZATION: SURFACE ROUGHENING — 3.29 Disturbed areas to be seeded and mulched shall be left in a roughened condition to help decrease runoff velocities and aid in the establishment of vegetation. TOPSOILING — 3.30 Topsoil may be stripped from the area to be graded and stockpiles for later use. All stockpiles which will be left dormant for more than 30 days shall be temporarily seeded. A topsoil stockpile may be selected onsite by the developer and shall be temporarily protected with surrounding silt fencing. TEMPORARY SEEDING — 3.31 Temporary soil stabilization shall be applied within 7 days to denuded areas that may not be at final grade, but will remain dormant (undisturbed) for longer than 30 days and less than 1 year. This includes, but is not limited to areas such as soil stockpiles. Seeded areas shall be limed when necessary at a rate of 2 tons per acre, and fertilized at a rate of 450 lbs. per acre of 10 -20 -20 (10 lbs. per 1,000 square feet) or equivalent. A Temporary Seeding Schedule is attached for proper seed selection. PERMANENT SEEDING — 3.32 A perennial vegetative covering shall be established on disturbed areas within 7 days of being brought to final grade on areas not otherwise protected. Selection of the seed mixture shall depend on the time of year it is to be applied according to the Permanent Seed Schedule as shown on the drawing. Seeded areas shall be limed when necessary at a rate of 2 tons per acres, and fertilized at a rate of 1,000 lbs. per acre of 10 -20 -10 (10 lbs. per 1,000 square feet) or equivalent. MULCHING — 3.35 All seeded areas shall be mulched with straw immediately following seeding operations. Straw mulch shall be applied at a rate of two tons per acre. SOIL STABILIZATION BLANKETS AND MATTING — 3.36 Soil stabilization matting shall be applied in the conveyance areas of the designed diversions to help reduce velocities and aid in the establishment of vegetation. A detail showing the proper materials and installation is shown on the plan. 6 B8. SOIL STOCKPILES AND BORROW AREAS A soil stockpile area has been provided with this Erosion and Sediment Control Plan. Borrow and /or waste areas must have an approved Erosion and Sediment Control Plan. B9. STORM WATER MANAGEMENT: The increase in stormwater runoff will be controlled by a retention basin, SWM #3. Water quality treatment is provided by the retention basin, bio- filters, Filterra units and a Contech Stormfilter. See SWM plan for details and hydrologic /hydraulic calculations. B10. MAINTENANCE SCHEDULE: A program of maintenance for the erosion and sediment controls specified in this narrative and shown on the plans are recommended as follows: 1. The Site Superintendent or his representative shall make a visual inspection of all erosion and sediment controls on a daily basis until the site is stabilized and especially after a heavy rainfall to assure that all controls are in place and that none have been damaged. Any damaged control shall be repaired prior to the end of each workday to include re- seeding if necessary. 2. All silt trapping devices shall be cleaned out at 50 percent capacity and sediment shall be disposed of by spreading on site or hauling away if not suitable for fill. 3. Gravel outlets shall be checked regularly for sediment buildup that may prevent drainage. Controls shall be inspected and repaired after each rainfall and cleaned if sediment has accumulated to half of the device's original height. 4. All earthen structures such as diversion dikes and berms shall be checked daily during construction for breaching by equipment. Repairs shall be made immediately. 5. Silt fences shall be checked after each rainstorm to assure they have not fallen or become clogged with silt. All repairs shall be made immediately. 6. All seeded areas shall be inspected regularly to see that good stand is maintained. Areas will be re- fertilized and re- seeded as necessary. 7. After construction operations have ended and disturbed areas have been stabilized, all berms and sediment - trapping devices may be removed after removal, the ground shall be restored to its natural or proposed condition to include establishment of permanent vegetation. Removal of any control is contingent upon approval of the County Inspector. 7 WATER QUALITY ANALYSIS FOR HOLLYMEAD TOWNCENTER (AREA Al) August 8, 2008 LOCATION: Tax Map 32, Parcel 44 Albemarle County, Virginia OWNER: HM Acquisition Group, LLC 126 Garrett Street Charlottesville, Virginia 22902 DEVELOPER: Octagon Partners 126 Garrett Street Charlottesville, Virginia 22902 PREPARED BY: Dominion Development Resources 172 South Pantops Road Charlottesville, VA 22911 434.979.8121 (F) 434.979.1681 PERFORMANCE -BASED METHOD The performance -based water quality criteria state that for land development, the calculated post - development non -point source pollutant runoff load shall be compared to the calculated pre - development load based upon the average land cover condition or the existing site condition. This approach requires the designer to calculate the pollutant load to be removed, implement a BMP strategy, and then calculate the performance of that strategy, based on the effectiveness or pollutant removal efficiency of the selected BMP(s). REMOVAL RATE CALCULATION The simple method was used in determining the required pollutant removal for Area Al. The existing impervious for the site is less than 20 %, putting the project in the New Development category. The parcel in question is not in a drinking water watershed or other rural lands. The post - developed condition will result in 859,360 SF of impervious surfaces. The resultant removal rate for New Developments in Development Areas is 69% (see attached BMP Computation). Proffer #9 (ZMA 2007 -001) requires that, to the extent practicable, additional stormwater management measures be utilized to achieve a removal rate 20% better than would otherwise be requires, up to a maximum of 80% removal rate. Therefore, the target removal rate for this project is 80 %. BMP SELECTION The site contains an existing stormwater management basin which is designed to provide stormwater quantity control for the site. The basin is currently serving as a sediment basin, but is designed to ultimately become a bio- filter comprising 38,105 SF. This bio - filter also treats runoff from Area B1, which utilizes 23,610 SF of the bio- filter area — leaving 14,495 SF for treatment of runoff from Area Al. This existing bio- filter area will provide 50% removal of pollutants for 579,800 SF of impervious surface. Most of the runoff from the site is collected and pre- treated prior to reaching the existing basin at one of two points, the existing storm sewer outfall from Area B1 at the south end of the basin near Route 29 and a new storm sewer outfall at the north end of the basin. A small portion of the site drains directly to the basin without pre- treatment. In order to reach the 80% target removal rate, treatment trains were proposed for each outfall. These consist of new bio- filters and a ConTech Storm Filter system. The majority of the runoff entering the basin through the existing pipe system is treated in new bio- filters (BF -1 through BF -4) sized to achieve a 65% removal rate. The resultant effluent is then treated a second time in the existing basin for an additional 50% removal of the remaining pollutant Toad. All of the runoff entering the existing basin at the northern outfall is routed through the ConTech StormFilter system which outfalls to a new bio- filter (BF -5) prior to entering the existing basin. This treatment train achieves a removal rate of 50% at the Stormfilter, 65% at the bio- filter. After accounting for the treatment of the runoff at the other outfall, there is some remaining pollutant removal capacity in the existing bio- filter, allowing for triple treatment of a portion of the runoff from the site. Runoff from 99.7% of the new impervious surface is captured and treated in one or more BMP's resulting in removal of 80% of the pollutant load as shown in the attached treatment matrix. Short Version BMP Computatioi is For Worksheets 2 - 6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Hollymead Towncenter Area Al Water Resources Area: Development Area Preparer: JDB Date: 30-Jun-08 Project Drainage Area Designation Area Al L storm pollutant export in pounds, L = [P(Pj)Rv /12 ] [ C(A)2.72 ] Rv mean runoff coefficient, Rv = 0.05 + 0.009(1) Pj small storm correction factor, 0.9 percent imperviousness P annual precipitation, 43" in Albemarle A project area in acres in subject drainage area, A = 25.30 C pollutant concentration, mg /I or ppm target phosphorus f factor applied to RR V required treatment volume in cy, 0.5" over imperv. area = A(I)43560(0.5/12)/27 RR required removal , L(post) - f x L(pre) %RR removal efficiency , RR100 /L(post) Impervious Cover Computation (values in feet & square feet) Item pre development Area post - development Area Roads Length Width subtotal Length Width subtotal 0 01 0? 0 0 --u 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0' Driveways Length Width no subtotal Length Width no subtotal and walks 0 0 1 0 0 0 1 0 , 0 0 0 0 0 0 0 0 0 0 1 0 0 'Parking Lots 1 2 3 4 1 1 2 3 4, 0 0 0 1 0 0 Gravel areas Area 1 Area x070= 0 x 0.70= 0 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Actively-grazed A r ely - grazed pasture & Area Area Y and cultivated turf 0 x . 0.08 = 0 :1_, .... VI x 0.08 = _._. . 0 Active crop land Area i Area �x 0.25 = i 01 Other Impervious Areas .,,,....... _ __ .._.._._ x 0.25 - 0L ........................ � mm ...._. .,..__ _...._.; j 0 859360 Impervious Cover O% :' ,(pre) .. I(post) Rv(post) V 0.75 1326.2 New Development (For Development Areas, existing impervious cover <= 20 %) C f I (pre) * Rv(pre) L(pre) L(post) RR 1 % RR Area Type 0.70 1.00 20% 0.23 ° 35.72 116.77 81 04' '' 69 Development Area irk 0.35 1.00 0% 0.05 3.88 58.38 54.50 93% Drinking Water Watersheds 0.40 1.00 1% 0.06 5.24 66.72 61.49 92% Other Rural Land * min. values Redevelopment (For Development Areas, existing impervious cover> 20 %) C f I (pre) * Rv(pre) L(pre) L(post) 1 RR % RR Area Type 0.70 0.90 20% 0.23 35.72 116.77 84.62 72% Development Area 0.35 0.85 0% 0.05 ; 3.88 58.38 55.08 94% Drinking Water Watersheds 1 0.40 0.85 1% 0.06 5.24 66.72 62.27 93% Other Rural Land Interim Manual, Page 70 rev. 16 Feb 1998 GEB 0 . C f. O o 0 0 d 0 f4 M N d LL L 1 H O m C LQ O O 1 >, o 71::2 p O 110 ( > O Lc) E E O N cf) N o V d LO CO O O) CO t To M .X O R n. 0 0 0 ∎ 0 E O O O m rY . 0 _ co fti Q (6 N N o o U E R 2 O O LO N m LO (0 0 (0 E _ Es LPL O ' w% d o 0 o II o I— E f6 2 O LO O O 0 N m l f") (0 Lo O LO W Q fx 0 (n R . Z H d o o o 0 W Z Q o r- Q co °o U Z E 2 o O Q N Q W O co O co N O ( (0 0 O W W L o o co M W Q I .L E Q 7r � N 00 E W J a co o N. 2 W < O N 0 W O oo rn o M M CO C L6 � N C .- L 0 O Ll. O_ i5 m _ O) LL E O () L m - O o) W L= 0 O _ u-) m X jL LL _O m Z 0 0 W 0 D LT Z Q ., _O c m LL CD � cn E c m 1-1- LE J E E < R 3 1- F W Z c u) O1- TEMPORARY SEDIMENT BASIN PROJECT HTC AREA A -1 PROJ NO. 8.0175 / BASIN # ! 5 DATE 8/8/2008 y + LOCATION NORTHWEST CORNER OF LOT BY DEG INPUT DRAINAGE AREA 9.18 ac BASIN VOLUME DESIGN WET STORAGE 1. MINIMUM REQUIRED VOLUME 615.06 cy 2. AVAILABLE BASIN VOLUME 3. MINIMUM REQUIRED VOLUME + 25% 768.83 cy AVERAGE END AREA - BASIN VOLUME ESTIMATES ELEVATIOF AREA VOLUME VOLUME TOTAL ft sf cf cy cy 481 8,837.00 9,247.00 342.48 482 9,657.00 342.48 46,082.00 1,706.74 486 13,384.00 2,049.22 29,076.00 1,076.89 488 15,692.00 ✓ 3,126.11 3r4 02 716 REQUIRED WET STORAGE VOLUME 615.06 cy REQUIRED WET STORAGE VOLUME + 25% 768.83 cy APPROX. ELEVATION 483.10 3. EXCAVATE CUBIC YARDS 4. AVAILABLE VOLUME BEFORE CLEANOUT REQUIRED 302.94 cy 4A. AVAILABLE VOLUME BEFORE CLEANOUT REQUIRED + 25% 384.41 cy 5. ELEVATION CORRESPONDING TO CLEANOUT LEVEL 482.10 6. DISTANCE FROM DEWATERING ORIFICE TO CIO LEVEL INVERT DEWATERING ORIFICE R'QD 483.10 INVERT DEWATERING ORIFICE USED 483.10 APPROX. VOLUME AT INVERT USED 815.03 cy DISTANCE FROM INVERT TO CIO LEVEL 1.00 ft DISTANCE ACCEPTABLE WET STORAGE VOLUME ACCEPTABLE DRY STORAGE 7. MINIMUM REQUIRED VOLUME 615.06 cy 7A. MINIMUM REQUIRED VOLUME + 25% 768.83 cy 8. TOTAL AVAILABLE VOLUME AT CREST OF RISER CREST OF RISER 485.00 APPROX. AVAILABLE TOTAL VOLUME 1686.40 cy TOTAL MINIMUM REQUIRED VOLUME + 25% f 1537.66 cy ADEQUATE DRY STORAGE VOLUME 9. DIAMETER OF DEWATERING ORIFICE Q 1.09 cfs d(1ST ITERATION) 6.53 In d(2nd ITERATION) 7.10 in d(3rd ITERATION) 7.16 in d(4th ITERATION) 7.17 In USE d 8 in 10. DIAMETER OF FLEXIBLE TUBING 10 in !STANDARD SIZE Page 1 SEDIMENT BASIN A1- EP.XLS TEMPORARY SEDIMENT BASIN PROJECT HTC AREA A -1 PROJ NO. 8.0175 BASIN # 2 1 DATE 8/8/2008 LOCATION NORTHWEST CORNER OF LOT BY DEG PRELIMINARY DESIGN 11. PRELIMINARY DESIGN ELEVATIONS: CREST OF RISER 485.00 ft TOP OF DAM 488.00 ft DESIGN HIGH WATER 484.41 ft UPSTREAM TOE OF DAM 481.00 ft BASIN SHAPE 12. LENGTH OF FLOW / EFFECTIVE WIDTH: SURFACE AREA OF NORMAL POOL 10606 sf LENGTH OF FLOW PATH 72 ft EFFECTIVE WIDTH 80 ft L/We 0.90 BAFFLES REQUIRED RUNOFF (RATIONAL METHOD CALCULATION) USE MAXIMUM C VALUE DURING CONSTRUCTION AND MINIMUM Tc VALUE 13. FLOW FROM 2 -YEAR STORM C: 0.65 Tc: 14.0 I: 3.6 in /hr 21.5 cfs 14. FLOW FROM 25 -YEAR STORM C: 0.65 Tc: 14.0 I: 5.7 in /hr Q= 34.0 cfs PRINCIPAL SPILLWAY DESIGN See Attached Calcs 15. REQUIRED SPILLWAY CAPACITY: EMERGENCY SPILLWAY? (Y /N) N REQUIRED SPILLWAY CAPACITY: N/A CFS 16. ASSUMED AVAILABLE HEAD: ELEV. OF CREST OF E.S. IF USED: N - ASSUMED AVAILABLE HEAD= N/A ft 17. RISER DIMENSIONS: RISER DIAMETER: 48.00 in lFrom Plate 3.14-8 or Calcs) ACTUAL MAX. ELEV.: 484.41 ft l (From Calcs if appropriate) ACTUAL HEAD: -0.59 ft (From Plate 3.14 -8 or Calcs) • 18. BARREL LENGTH: - BARREL LENGTH: 38.00 BARREL INVERT OUT: 4 8T! EO " ft HEAD H ON BARREL: 3.41 ft (From Plate 3.14 -7) 19. BARREL DIAMETER: 1 BARREL DIAMETER: 36 in (From Plate 3.14A or 3.14B) 20. TRASH RACK AND ANTI- VORTEX DEVICE: Pre - Manufactured Trash Rack Refer to Plans for Detail Page 2 SEDIMENT BASIN A1- EP.XLS TEMPORARY SEDIMENT BASIN PROJECT HTC AREA A -1 PROJ NO. 8.0175 BASIN # 2 DATE 8/8/2008 LOCATION NORTHWEST CORNER OF LOT BY DEG EMERGENCY SPILLWAY DESIGN 1 21. REQUIRED SPILLWAY CAPACITY: Qe = Q(25) -Qp = N/A CFS 22. DIMENSIONS: 1 BOTTOM WIDTH (b): N/A ft (From Table 3.14 - C) SLOPE OF EXIT CHANNEL (s): N/A ft/ft (From Table 3.14 - C) MIN. LENGTH EXIT CHANNEL (x): N/A ft (From Table 3.14 - C) ANTI -SEEP COLLAR DESIGN Existing Structure FINAL DESIGN ELEVATIONS 23. ELEVATIONS: TOP OF DAM: 488.00 ft DESIGN HIGH WATER: 484.41 ft EMERGENCY SPILLWAY CREST: N/A ft PRINCIPAL SPILLWAY CREST: 485.00 ft DEWATERING ORIFICE INVERT: 483.10 ft CLEANOUT ELEVATION: 482.10 ft Page 3 SEDIMENT BASIN A1- EP.XLS