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Home My WebLink AboutDurham Tech Facilities Building - DEQ-SIA_2018.09.17-SP1707 DURHAM TECH – FACILITES BUILDING STORMWATER IMPACT ANALYSIS STORMWATER MANAGEMENT PERMIT SUBMITTAL PIN 0830-07-58-4362 Calculations By: Tiffany R. McCormack, EI Checked By: Preston B. Royster, PE Coulter Jewell Thames, P.A. 111 West Main Street Durham, NC27701 Ph: 919-682-0368 Fax: 919-688-5646 Project # 1707 July 2, 2018 Revised: September 12, 2018 Project Description and Summary The Durham Tech – Facilities Building, currently zoned OI-2, involves the re-development of the site located on the south side of Cooper Street east of the intersection with Bacon Street. Proposed improvements include a new building, paved parking, walks, and all associated infrastructure. Soils on the site are Mayodan, Pinkston (hydrologic soil group B), Chewacla (hydrologic soil group C), and White Store (hydrologic soil group D). While the distribution of soil types onsite are relatively equal, there exists slightly more B soils than any other soil type. The site is located in the Jordan Lake Basin of the Cape Fear River Basin and is not located in a Water Supply Watershed. This site is a State owned facility and will be required to meet NC DEQ regulations as well as those placed by the City of Durham. Per the City of Durham stormwater quantity control ordinance, pre-development and post- development peak flow rates for the 2-year, and 10-year storms must be calculated at discharge points from the site. Similarly the same analysis is required by the NC Department of Environmental Quality for the 1-year storm event. If post-development flow rates exceed pre- development rates, it must be shown that areas downstream from the site will not be adversely affected by the increased flow rates or on-site detention must be provided. If a downstream analysis is provided, it must follow the increased flow until there is no increase in peak flow. If on-site detention is provided, it shall attenuate the post-development peak flows from the 1-year, 2-year and 10-year storm back to the pre-development rates. Nitrogen and Phosphorous treatment will be required since the disturbance of the site will exceed one-half of an acre and the site is located in the Jordan Lake Basin. Nitrogen and phosphorus export calculations for pre-development and post-development conditions using the Jordan Lake Stormwater Nutrient Load Accounting Tool are developed and submitted as required by the City. Total Suspended Solids (TSS) Reduction is required if the stormwater runoff is conveyed in non- vegetated conveyances. The calculations for this study are based on an analysis of the site development. Pre- development conditions have been taken as the site existed prior to the effective dates. These effective dates are as follows: March 17th, 2009 for 1-year peak flow analysis, April 23rd, 1997 for 2- and 10-year peak flow analysis and December 31st, 2001 for nutrient analysis. Based on orthographic photography, there has been no change to this site between 1997 and 2009. Post- development drainage patterns are based on the proposed grading and development. Summary tables are included that detail pre-development and post-development peak flow rates from the site, along with the percentage increase or decrease, and nutrient calculations. Methodology  HydroCAD software is used to calculate the time of concentration for each sub-basin. HydroCAD uses the SCS segmental approach to estimate the time of concentration.  HydroCAD software is used to calculate the composite curve number for each sub-basin. HydroCAD uses the NRCS TR-55 method for calculation composite curve numbers.  HydroCAD software is used to calculate pre- and post-development peak flow rates for each sub- basin. HydroCAD uses the SCS TR-20 method to develop hydrographs.  The Durham County Soil Survey is used to identify the soil types located on the site.  The Jordan/Falls Lake Stormwater Nutrient Load Accounting Tool is used to calculate Nutrient Loading for Pre- and Post-Development conditions. Discussion of Results Peak Flow Analysis For peak flow analysis, the original parcel is analyzed as two basins. Basin 1 drains to the south to Rocky Creek, located along the property line. Basin 2 drains to the north, to Cooper Street which also discharges to Rocky Creek. Analysis of the 1-, 2- and 10-year storm events result in an increase in peak flow following development in Basin 1. Proposed development results in no increases in peak flows for Basin 2. (See spreadsheet Peak Flow Analysis Summary in the calculations). The Rocky Creek runs along the southern property line to the analysis point for Basin 1. The drainage area for the stream can be found in the NC Floodplain Mapping Program to compare against the Project Area associated with this development. The Project Area is insignificant in comparison to the contributing area to the creek. (See spreadsheet Site to Drainage Area Analysis in the calculations) Stormwater Pollutant Analysis Nutrient Export Load Limits: This site is located in the Jordan Lake Basin and is required to meet the Jordan Water Supply Watershed Nutrient Strategy: Stormwater Requirements for State and Federal Entities. Based on the analysis of the site, nutrient analysis after the proposed development is less than the required nutrient loading targets. (See worksheet Jordan Lake Developer Nutrient Reporting Form) No further nutrient reductions will be required for this proposed development. TSS Reduction: Per the Jordan … Nutrient Strategy, a TSS reduction for all new impervious surfaces associated with this development will be required. A Sand Filter is proposed to provide 85% TSS reduction from all impervious surfaces included in the drainage area to this facility. The drainage area to the Sand Filter is greater than summation of the new impervious areas associated with this development. (See spreadsheet TSS Reduction Summary in the calculations) Results Based on the Jordan … Nutrient Strategy and the City of Durham Stormwater Performance Standards for Development, and all applicable amendments to it, development of this site requires TSS reduction. This requirement is met with the installation of a Sand Filter. All applicable calculations and maps follow in this report. MISCELLANEOUS MAPS PEAK FLOW ANALYSIS Project Name: Durham Tech - Facilities Building By: TRM Revised: Project Number: 1707 Date: 11.20.2017 Date: Drainage area to Rocky Creek at point of interest = 0.7 square Miles = 448 acres Project area = 2.80 acres Site to Drainage Area ratio = 0.62% Site to Drainage Area Analysis A summary of the drainage area-peak discharge relationships for the flooding sources studied by detailed methods is shown in Table 13, Summary of Discharges. Table 13 - Summary of Discharges Flooding Source Discharges (cfs) Location Drainage Area (square miles) 10% Annual Chance 2% Annual Chance 1% Annual Chance 1% Annual Future Annual Chance 0.2% Annual Chance Rocky Creek Approximately 1,250 feet upstream of Bacon Street 0.70 819 1220 1530 1910 2260 Approximately 1,250 feet downstream of Briggs Road 0.60 849 1260 1540 1930 2270 Approximately 350 feet downstream of Briggs Road 0.30 428 658 802 992 1180 NC Floodplain Mapping Program Print Date: November 20, 2017 http://fris.nc.gov/FRIS Page 1 of 1 Project Name: Durham Tech - Facilities Building By: TRM Revised:TRM Project Number: 1707 Date: 11.16.2017 Date:09.11.20018 Tc Area CN Q1 Q2 Q10 (min) (ac) (cfs) (cfs) (cfs) Pre-Development 8.3 29.81 --- 35.48 48.25 97.63 Post Development 8.3 29.81 --- 36.11 49.00 98.61 Post-Development with Treatment 33.92 46.47 94.84 Percent difference between Pre- Development and Post Development -4% -4% -3% Tc Area CN Q1 Q2 Q10 (min) (ac) (cfs) (cfs) (cfs) Pre-Development 5 3.01 --- 9.99 11.92 18.23 Post Development 5 3.01 --- 9.99 11.92 18.23 Percent difference between Pre- Development and Post Development 0% 0% 0% Peak Flow Analysis Summary Drainage Basin 1 Drainage Basin 2 STORMWATER POLLUTANT ANALYSIS Nutrient Export Reduction TSS Reduction Jordan Nutrient Load Reporting Form. September 12, 2012 Jordan Lake Developer Nutrient Reporting Form (Note: A separate form is available for Neuse, Tar‐Pamlico, and Falls Lake reporting.) Please complete and submit the following information to the local government permitting your development project to characterize it and assess the need to purchase nutrient offsets. Contact and rule implementation information can be found online at http://portal.ncdenr.org/web/wq/ps/nps/nutrientoffsetintro. PROJECT INFORMATION (for Jordan Lake) Applicant Name: Coulter Jewell Thames, PA Project Name: Durham Tech. – Facilities Building Project Address (if available): Street: City/Town: County: 1616 Cooper St Durham Durham Date: (mo/d/yr) 03.21.2018 Project Location : Lat: (decimal degrees) 35.969784 Long: (decimal degrees) -78.882361 Is this Redevelopment? - Yes - No Development Type (Please check all that apply) Impervious Cover (%): (Pre-Construction) 6.9 Commercial Industrial Institutional Mixed-Use Duplex Residential Single Fam. Residential Multi-Fam. Residential Impervious Cover (%): (Post-Construction) 7.9 JORDAN WATERSHED INFORMATION Small Watershed ID (6 digits): (See next page or online map.) New Development Load Requirements (See individual rules for a full description of nutrient requirements.) Jordan Subwatershed (Please check one) Loading Rate Targets Nitrogen (N) & Phosphorus (P)Offsite Thresholds Haw River 3.8 N lb/ac/yr 1.43 P lb/ac/yr 6 N lbs/ac Residential; 10 N lbs/ac Commercial (must meet all onsite treatment requirements) Upper New Hope 2.2 N lb/ac/yr 0.82 P lb/ac/yr Lower New Hope 4.4 N lb/ac/yr 0.78 P lb/ac/yr NUTRIENT OFFSET REQUEST(Must meet the offsite thresholds – see above) Nitrogen Loading / Offset Needs (A) (B) (C) (D) (E) (F) (G) (H) (I) (Where Applicable) Untreated Loading Rate (lbs/ac/yr) Treated Loading Rate (lbs/ac/yr) Loading Rate Target (lbs/ac/yr) Reduction Need (lbs/ac/yr) B - C Project Size (ac) Offset Duration (yrs) Delivery Factor (%) State Buy Down Amount (lbs) D * E * F * G Local Gov’t Buy Down Amount (lbs) 1.81 1.78 2.2 0 25.09 30 n/a 0 Phosphorus Loading / Offset Needs (A) (B) (C) (D) (E) (F) (G) (H) (I) (Where Applicable) Untreated Load Rate (lbs/ac/yr) Treated Load Rate (lbs/ac/yr) Loading Rate Target (lbs/ac/yr) Reduction Need (lbs/ac/yr) B - C Project Size (ac) Offset Duration (yrs) Delivery Factor (%) State Buy Down Amount (lbs) D * E * F * G Local Gov’t Buy Down Amount (lbs) 0.28 0.28 0.82 0 25.09 30 n/a 0 Authorizing Local Government Name: Staff Name: Staff Email: Phone: 3. Development SummaryWATERSHED SUMMARY Ver2.0Bioretention with IWS50% 0.95 0.12Bioretention without IWS35% 1.00 0.12Dry Detention Pond0% 1.20 0.20Grassed Swale0% 1.21 0.26Green Roof50% 1.08 0.15Level Spdr, Filter Strip40%1.200.15Percent Difference Between:Sand Filter5% 0.92 0.14 *Negative percent difference values indicate a decrease in runoff volume, pollutant concentration or pollutant loading. Positive values indicate an increase. *if treating commercial parking lot, TP effluent concentration = 0.16 mg/LBMP SUMMARY Ver2.0BMP 1BMP 2BMP 3BMP 1BMP 2BMP 3BMP 1BMP 2BMP 3BMP 1BMP 2BMP 3BMP 1BMP 2BMP 3BMP 1BMP 2BMP 3Sand Filter‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐0.30‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐48,606‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐5%‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐1.08‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐10.78‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐0.150‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐1.50‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐8.87‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐1.33‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐ ‐‐0.390.150.110.12Permeable Pavement*Water HarvestingWet Detention PondWetland0%user defined10%20%1.441.081.011.083%10%18%Pre‐Dev. &Post‐Dev. without BMPsPost‐Dev without BMPs &Post‐Dev with BMPs‐1%‐1%‐2%0%‐1%0%1%8%‐3%4%11%19%Pre‐Development &Post‐Development with BMPs1%7%‐‐‐‐‐‐‐‐‐‐CATCHMENT 6‐‐ ‐‐‐‐‐‐‐‐‐‐ ‐‐‐‐ ‐‐‐‐ ‐‐‐‐ ‐‐‐‐‐‐1.33511%‐‐‐‐‐‐0.1410.28Durham Tech. ‐ Facilities BldgTRMMarch 21, 2018Development:Prepared By:Date:Post‐Development w/ BMPs7.9%375,6971.411.780.220.28REGION:TOTAL DEVELOPMENT AREA (ft2):Piedmont18%Catchment Outflow Phosphorus EMC (mg/L)Percent Reduction in Nitrogen Load (%)CATCHMENT 1Total Nitrogen EMC (mg/L)Total Nitrogen Loading (lb/ac/yr)Total Phosphorus EMC(mg/L)Total Phosphorus Loading(lb/ac/yr)Total Nitrogen Loading (lb/ac/yr)Total Phosphorus EMC (mg/L)Total Phosphorus Loading (lb/ac/yr)Percent Impervious (%)Annual Runoff Volume (c.f.)Total Nitrogen EMC (mg/L)‐‐‐‐Total Inflow Phosphorus(lb/ac/yr)BMP OutflowNitrogen (lbs/ac/yr)Total Area Treated(ac)Percent Reduction in Phosphorus Load (%)‐‐CATCHMENT 2CATCHMENT 30.94‐‐Catchment OutflowTotal Nitrogen (lb/ac/yr)8.87Percent Volume Reduced(%)BMP OutflowPhosphorus (lbs/ac/yr)Total Inflow Volume(c.f.)Total Inflow Nitrogen(lb/ac/yr)Inflow Phosphorus EMC(mg/L)Catchment Outflow Nitrogen EMC (mg/L)CATCHMENT 4‐‐ ‐‐‐‐Catchment OutflowTotal Phosphorus (lb/ac/yr)Volume Reduction (%)TN Effluent Concen. (mg/L)1.471.730.200.24TP Effluent Concen. (mg/L)BMP VOLUME REDUCTIONS/EFFLUENT CONCENTRATIONSInflow Nitrogen EMC(mg/L)CATCHMENT 5Percent Impervious(%)Annual Runoff Volume (c.f.)350,959Post‐Development Conditions7.9%378,1271.421.810.221,093,052Pre‐Development Conditions6.9%‐4%Return to Watershed CharacteristicsReturn to BMP CharacteristicsPrint SummaryReturn to Instructions 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061AB C D E F G HIJK L M N O P Q R S T UWatershed Characteristics Ver2.0PART A Parking lot 1.44 0.16 55,937 47,948 ⅛‐ac lots‐‐ ‐‐ ‐‐ Roof1.08 0.1513,241 ¼‐ac lots ‐‐ ‐‐‐‐ Open/Landscaped2.24 0.44 41,559 51,594 ½‐ac lots‐‐‐‐ ‐‐ 1‐ac lots‐‐‐‐ ‐‐ Parking lot1.44 0.39 2‐ac lots‐‐‐‐ ‐‐ Roof1.08 0.15 Multi‐family‐‐‐‐ ‐‐ Open/Landscaped2.24 0.44 Townhomes‐‐‐‐ ‐‐ Custom Lot Size‐‐ ‐‐ High Density (interstate, main)3.67 0.43PART B Low Density (secondary, feeder)1.4 0.52‐‐1.4 0.52 Rural1.14 0.471.44 0.39 Sidewalk1.4 1.162,560‐‐1.44 0.39‐‐1.08 0.15 Managed pervious3.06 0.59‐‐1.41.16 Unmanaged (pasture)3.61 1.56‐‐2.24 0.44 Forest1.47 0.25 712,118 694,271‐‐3.06 0.59‐‐1.47 0.25 Natural wetland‐‐ ‐‐‐‐‐‐ ‐‐ Riparian buffer‐‐ ‐‐283,438 283,438‐‐‐‐ ‐‐ Open water‐‐ ‐‐‐‐‐‐ ‐‐LAND TAKEN UP BY BMPs1.08 0.150‐‐1.08 0.15*Jurisdictional land uses are not included in nutrient/flow calculations.Total Post‐Development Calculated Area (ft2):1,093,0521,093,0521,093,052Custom Lot Size (ac) Forest Managed perviousTotal Development Area Entered (ft2):LAND USE AREA CHECKLAND TAKEN UP BY BMPs Lawn Sidewalk/Patio Roof Natural wetland* Riparian buffer* Open water*INDUSTRIALTRANSPORTATIONCOMMERCIAL Parking lot Driveway RoadwayPERVIOUSJURISDICTIONAL LANDS*Total Pre‐Development Calculated Area (ft2):InstructionsAdditional Guidelines 1. Select your physiographic/geologic region. (see map on 'instructions' page)Physiographic/Geologic Region:TP EMC(mg/L)Pre‐Development(ft2) 2. Enter the area of the entire development in square feet (ft2). 4. For each applicable land use, enter the total area of that land use that lies within the development under pre‐development conditions. 5. For each applicable land use, enter the total area of that land use that lies within the development under post‐development conditions, before BMP implementation. ‐ Unless runoff flowing onto the development from offsite is routed separately around or through the site, the offsite catchment area draining in must be included in the acreage values of the appropriate land use(s) and treated. 6. Ensure that the sum of pre‐ and post‐development areas entered equal the orginal development area. Post‐Development(ft2)TRMPost‐Development(ft2)CarrboroTotal Development Area (ft2): 1,093,052Soil Hydrologic GroupBPrecipitation location:Age(yrs)TN EMC(mg/L)TN EMC(mg/L)TP EMC(mg/L)Pre‐Development(ft2)COLUMN 2 -- RESIDENTIAL LAND USESCOLUMN 1 -- NON-RESIDENTIAL LAND USESModel Prepared By: 7. Continue to "BMP Characteristics" tab. 3. Select the location that is most representative of the site's precipitation characteristics. (see map on 'instructions' page)Durham Tech. ‐ Facilities BldgPiedmont ‐ Residential areas may be entered by average lot size (column, part A), or may be separated into individual land uses (column 2, part B) ‐‐ do NOT list out individual land uses within an area already described by lot size. ‐ For non‐residential watersheds, indicate acreages of each land use type in Column 1 for both pre‐ and post‐development conditions. ‐ For residential watersheds, complete the required information in Column 2 for both pre‐ and post‐development conditions. ‐ If a given land use is not present in the given watershed, leave the cell blank or enter a zero. ‐ Ensure that land use areas entered for both pre‐ and post‐development conditions match the total development area entered in cell O21.Development Name:Clear All ValuesReturn to InstructionsProceed to BMP CharacteristicsSkip to Development SummaryClear All ValuesReturnto InstructionsProceed to BMP CharacteristicsSkip to Development SummaryClear All ValuesReturn to InstructionsProceed to BMP CharacteristicsSkip to Development Summary BMP Characteristics Ver2.0 Instructions 1. Select the type of BMP for each catchment. 2. Enter the area of each land use type in the contributing drainage area for each BMP. 3. Continue to "Development Summary" tab. Additional Guidelines ‐ This spreadsheet allows the development to be divided into as many as 6 smaller catchments. ‐ BMPs 1, 2, and 3 for a given catchment are assumed to operate in series, with the outflow from 1 serving as the inflow to 2, etc. ‐ Not all BMP or catchments must be utilized. Simply leave fields blank in the columns not needed. ‐ Leave cells blank or insert zeroes if a land use is not present in the area draining to the BMP. ‐ For water harvesting BMPs, be sure to enter the percent volume reduction that will be achieved by your system. Volume detention (catch‐and‐release mechanisms) will not be considered ‐ only proven volume reductions are valid inputs. ‐ The BMP undersizing option should only be used for existing development or retrofit sites. ‐ IMPORTANT: for the land area calculation checks to occur, you MUST press enter after entering a value for area to be treated by a BMP (not just click on the next cell). ‐ See User's Manual for instructions on modeling oversized BMPs. BMP #1 BMP #2 BMP #3 BMP #1 BMP #2 BMP #3 BMP #1 BMP #2 BMP #3 Type of BMP:Sand Filter If BMP is undersized, indicate the BMP's size relative to the design size required to capture the designated water quality depth (i.e. 0.75 = BMP is 75% of required design size): *For water harvesting BMP, enter percent volume reduction in decimal form. Catchment 1:‐‐‐‐‐‐no no no no no no Catchment 2:no no no ‐‐‐‐‐‐no no no Catchment 3:no no no no no no ‐‐‐‐‐‐ Catchment 4:no no no no no no no no no Catchment 5:no no no no no no no no no Catchment 6:no no no no no no no no no COMMERCIAL Parking lot Roof 13,241 Open/Landscaped INDUSTRIAL Parking lot Roof Open/Landscaped TRANSPORTATION High Density (interstate, main) Low Density (secondary, feeder) Rural Sidewalk MISC. PERVIOUS Managed pervious Unmanaged (pasture) Forest RESIDENTIAL 2‐ac lots (New) 2‐ac lots (Built after 1995) 2‐ac lots (Built before 1995) 1‐ac lots (New) 1‐ac lots (Built after 1995) 1‐ac lots (Built before 1995) ½‐ac lots (New) ½‐ac lots (Built after 1995) ½‐ac lots (Built before 1995) ¼‐ac lots (New) ¼‐ac lots (Built after 1995) ¼‐ac lots (Built before 1995) ⅛‐ac lots (New) ⅛‐ac lots (Built aŌer 1995) ⅛‐ac lots (Built before 1995) Townhomes (New) Townhomes (Built after 1995) Townhomes (Built before 1995) Multi‐family (New) Multi‐family (Built after 1995) Multi‐family (Built before 1995) Custom Lot Size (New) Custom Lot Size (Built after 1995) Custom Lot Size (Built before 1995) Roadway Driveway Parking lot Roof Sidewalk Lawn Managed pervious Forest LAND TAKEN UP BY BMP 0 TOTAL AREA TREATED BY BMP (ft2):13,24100 000 000 TOTAL AREA TREATED BY SERIES (ft2): ‐ Volume reduction efficiencies for undersized BMPs are calculated based on a 1:1 ratio (a BMP that is 60% smaller than the required design size is assigned a removal efficiency equal to 60% of the standard efficiency value). Effluent concentrations remain the same as full‐sized BMPs. ‐ If the outflow from an entire catchment (including outflow from selected BMPs) drains to another BMP, indicate this in the drop down menu below the BMP type and leave all cells for individual land uses blank. ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 2 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Area Treated by BMP (ft2) ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 3 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Area treated by BMP #3 that is not treated by BMPs #1 or #2 (ft2) Area Treated by BMP (ft2) Area treated by BMP #2 that is not treated by BMP #1 (ft2) 13,241 00 Does BMP accept the outflow from another Catchment? If so, indicate which one(s). (Land use are Area treated by BMP #2 that is not treated by BMP #1 (ft2) Area treated by BMP #3 that is not treated by BMPs #1 or #2 (ft2) Drainage Area Land Use Area treated by BMP #2 that is not treated by BMP #1 (ft2) Area treated by BMP #3 that is not treated by BMPs #1 or #2 (ft2) Area Treated by BMP (ft2) ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 1 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Clear All Values Return to Instructions Return to Watershed Characteristics Proceed to Development Summary Project Name: Durham Tech - Facilities Building By: TRM Revised:TRM Project Number: 1707 Date: 11.20.2017 Date:03.19.2018 Pre‐Development 6.9% Post‐Development 7.9% Additional Impervious to be treated =0.18 acres Imervious area Treated by SCMs for TSS = 0.30 acres Site Impervious Percentage TSS Reduction Summary SAND FILTER DESIGN Project Name: Durham Tech Building Addition By: TRM Revised: Project Number: 1707 Date: 03.19.2018 Date: Drainage Area =0.30 ac Impervious Area =0.30 ac Water Quality Volume: Simple Method WQV = 3630*Rd*Rv*Ad WQV = Runoff Volume (cf)Rv = Runoff coefficient (unitless) Rd = Design storm rainfall depth = 1.0 in Ad = Drainage area (ac) Rv = 0.05+0.9*Ia Ia = Impervious fraction = 1.00 Rv = 0.95 Required runoff Volume Adusted Water Quality Volume: WQV = 1,035 cf WQV(adj) = (0.75)*WQV WQV(adj) = 776 cf Required Surface Areas: Maximum head on the Sandfilter hMaxFilter (ft) = hMaxFilter =4 ft AS (sf) + Af (sf) = 194 sf Storage volume in each chanmber must be equivalent Minimum surface area of sediment basin As = 97 sf Minimum surface area of sand filter bed Af = 97 sf Design Summary As (Provided) =105 sf Af (Provided) =105 sf hMaxFilter (ft) =4ft Volume Provided V = 840 cf Sand Filter Sizing WQVAdj (cf) AS (sf) + Af (sf) Project Name: Durham Tech Building Addition By: TRM Revised: Project Number: 1707 Date: 07.02.2018 Date: Water Quality Volume = 776 cf Drainage Time = 40 hrs Q = Water Quality Volume/Drainage Time Q = 19.40 cf/hrs = 0.01 cfs Apply Safety Factor of 10; Q= 0.05 cfs 2. Use the following equation:D = 16((Q*n)/S0.5)3/8 Where D = Diamter of single pipe (in.) n = roughness factor (recommeded to be 0.011)n = 0.011 S = internal slope (recommended to be 0.5%)S = 0.5 Q = flow rate through soil media (cfs)Q = 0.05 D = 1.12 in Closest equivalent Standard Pipe Size = inch Number of Pipes Required in the Underdrain = 24" Pipes Underdrain Design The number of pipes needed for the underdrain system is determined using the following 3-step process. 1. Determine flow rate through the soil media and apply a safety factor of 10 (this is now the underdrain design flow, Q). 3. The only unknown is D. This is the diameter of a single pipe that could carry all the water were it to be the only underdrain. Pipe diamters are typically either 4 inches or 6 inches. Table 5-1 below converts "D" (in inches) to an equal number of 4 or 6 inch underdrains at 0.5% slope. Project Name: Durham Tech - Facilities Building By: TRM Revised: Project Number: 1707 Date: 09.12.2018 Date: Outlet Structure Dimension Inside Chamber Width:7 ft Outside Width:8.00 ft Inside Chamber Length:15 ft Outside Length:16.00 ft Wall Thickness:6 in Number of Chambers:2 Lid Top Elevation:338.86 ft InsideTop Elevation:338.19 ft Invert Elevation:330.19 ft Bottom Elevation:329.19 ft Extended Base Horizontal: in 256 sf Extended Base Vertical: in Ext Base Depth:0 ft SHWT Elevation:336.75 ft Displaced Volume:1,935 cu ft Displaced Weight:120,766 lbs Volume of Concrete (Chambers):819 cu ft Weight of Concrete Structure:122,830 lbs Volume of Media:214 cu ft Weight of Media:25,632 lbs Weight of Earth over Sand Filter:56,320 lbs Weight of Extended Base:- lbs Total Weight of Structure:204,782 lbs Factor of Safety:1.70 OK Anti-Flotation Sizing Calculations Structure: Sandfilter Ext. Base Surface Area: SAND FILTER1 Drainage area number1 Total coastal wetlands area (sq ft) - Parking / driveway (sq ft)47948 sfTotal surface water area (sq ft)62866 sf - Sidewalk (sq ft)2560 sfTotal drainage area (sq ft)1093052 sf - Roof (sq ft)13241 sfBUA associated with existing development (sq ft) - Roadway (sq ft)Proposed new BUA (sq ft)63749 sf - Other, please specify in the comment box below (sq ft) Percent BUA of drainage area6%Total BUA (sq ft)63749 sfDesign rainfall depth (in)1.0 inMinimum volume required (cu ft)776 cfDesign volume of SCM (cu ft)840 cf#1 Is the SCM sized to treat the SW from all surfaces at build-out? Yes#7 If applicable, with the SCM be cleaned out after construction?Yes#2 Is the SCM located on or near contaminated soils? No#8 Does the mainetenance access comply with General MDC (8)?Yes#3 What are the side slopes of the SCM (H:V)? n/a#9 Does the drainage easement comply with General MDC (9)?Yes#3 Does the SCM have retaining walls, gabion walls or other engineered side slopes? No#10 If the SCM is on a single family lot, does the plat comply with General MDC (10)?#4 Are the inlets, outlets, and receiving stream protected from erosion (10-year storm)? Yes#11 Is there an O&M Agreement that complies with General MDC (11)?Yes#5 Is there a a bypass for flows in excess of the design flow? Yes#12 Is there an O&M Plan that complies with General MDC (12)?Yes#6 What is the method for dewatering the SCM for maintenance?Pump (preferred)#13 Was the SCM designed by an NC licensed professional?Yes #1 SHWT elevation (fmsl)lower than 336.75' #3 Volume of stormwater from drainage area during design storm (cubic feet) 776 cf#1 Type of sand filter (open or closed) Closed #3 Total volume that can be stored above the sediment and sand chambers (cubic feet) 840 cf#1 If closed, describe if the filter will be pre-cast or pour-in-place: #3 Is this sand filter designed to attenuate peak flows? No#3 Elevation of the bypass device (fmsl) 337 ft#1 If closed, top of grate elevation (fmsl) 341 ft#2 Volume that can be retained in the sediment chamber (cubic feet) 420 cf#2 Will there be a permanent pool in the sediment chamber? Yes#2 Bottom of the sediment chamber (fmsl)331 ft#4 Ponding depth from the top of the sand to the bypass device (ft) 5 ft#2 Area of the sediment chamber (square feet)105 sf#2 Physical depth of the sediment chamber (inches) 90 in#2 Ponding depth in the sediment chamber, above any permanent pool (inches)54 in#2 Elevation of top of weir between chambers (fmsl)333 ft#2 Volume that can be retained in the sand chamber (cubic feet) 420 cf#2 Bottom of the sand chamber (fmsl) 331 ft #7 Depth above underdrain pipe (inches) 12 in#2 Area of the sand chamber (square feet)105 sf#8 Will the media be maintained to drain at least two inches per hour at the sand surface? Yes#2 Physical depth of the sand chamber (inches) 90 in #9 Is at least one clean-out pipe provided at the low point of each underdrain line? Yes#2 Ponding depth in the sand chamber, above any permanent pool (inches)54 in#9 Will clean-out pipes be capped? YesTHE DRAINAGE AREAGENERAL MDC FROM 02H .1050Break down of BUA in the drainage area (both new and existing):COMPLIANCE WITH THE APPLICABLE STORMWATER PROGRAMStormwater program(s) that apply (please specify):Phase II and Jordan Lake RulesPlease use this space to provide any additional information about this sand filter that you think is relevant to the review:SAND FILTER MDC FROM 02H .1056ADDITIONAL INFORMATIONWeir from Sediment chamber to Sand chamberpre-cast#3 Describe the bypass device:#5 Describe the mechanism for distributing flow over the sand surface:#6 Sand specification for sand chamber Cleaned, washed, coarse masonry sand, such as ASTM C33. The sand particles shall be less than 2mm average diameter.Splitter box with weir set at water quality elevationDurham Tech Facilites BuildingSand Filter13:47 PM 9/17/2018