Falls Lake Stormwater Load Accounting Tool Manual
Contents
1. Land Use Type mg L mg L Reference Residential Driveway 1 44 0 39 Passeport et al 2009 using industrial values Roof 1 08 0 15 Moran 2004 and Bannerman 1993 Moran 2004 Lawn 2 24 0 44 Skipper 2008 and NCDENR Tar Pam Model Commercial Ultra Urban Parking lot 1 44 0 16 Bannerman 1993 and Passeport et al 2009 Passeport et al 2009 Roof 1 08 0 15 Moran 2004 and Bannerman 1993 Moran 2004 Open Landscaped 2 24 0 44 Skipper 2008 and NCDENR Tar Pam Model Industrial Parking lot 1 44 0 39 Bannerman 1993 Passeport et al 2009 Roof 1 08 0 15 Moran 2004 and Bannerman 1993 Moran 2004 Open Landscaped 2 24 0 44 Skipper 2008 and NCDENR Tar Pam Model Transportation High density interstate main 3 67 0 43 Wuetal 1998 urban Low density secondary feeder 1 4 0 52 Wuetal 1998 semi urban Rural 1 14 0 47 Wu etal 1998 rural Sidewalks 1 43 1 16 Bannerman 1993 Passport et al 2009 Other Woods 1 47 0 25 Line et al 2002 median Maintained grass 3 06 0 59 Skipper 2008 Pasture 3 61 1 56 Line et al 2002 median 18 Table 3 Land Use Categories and Descriptions Residential Land Use Description 2 Acre Lots Lot size ranges from 1 70 to 2 30 acres 1 Acre Lots Lot size ranges from 0 75 to 1 25 acres 1 2 Acre Lots Lot size ranges from 0 40 to 0 60 acres 1 4 Acre Lots L2. Cells shaded grey are those designated for data input tan T Lo wigs ERE JL C Coastal Plain 7 Mountains Sandhills mn Triassic Basin C Piedmont Figure 2 Map of physiographic regions within the state of North Carolina also located in the JLSLAT on the Instructions worksheet MountAiry Wentworth EI kit Siler City Elizabethtown Figure 3 Average annual precipitation map for the state of North Carolina Labeled towns cities are available in the dropdown menu for precipitation location also located in the JLSLAT on the Instructions worksheet Rockingham Alamance Alexander Alleghany Anson Ashe Avery Buncombe Burke Cabarrus Caldwell Caswell Catawba Chatham Cherokee Clay Cleveland Davidson Davie Durham Forsyth Franklin Gaston Graham Granville Guilford Halifax Harnett Haywood Henderson Iredell Jackson Johnston PIEDMONT amp MOUNTAIN Lee Lincoln Macon Madison McDowell Mecklenburg Mitchell Montgomery Moore Nash Northampton Orange Person Polk Randolph Richmond Rowan Rutherford Stanley Stokes Surry Swain Transylvania Union Vance Wake Warren Watauga Wilkes Wilson Yadkin Yancey COASTAL PLAIN Bladen Columbus Cumberland Duplin Edgecombe Halifax Harnett Hoke Johnston Jones Martin Moore Nash Northampton Pitt Richmond Robeson Sampson Scotland Wake Wayne CAMA COUNTIES Beaufort Bertie B
3. This section of the worksheet also displays outflow data for each catchment These data include outflow concentrations loadings and percent reductions for TN and TP for each catchment The last BMP in each of the series releases water of this quality and these values account for any catchment routing that is specified in the BMP Characteristics tabs Note that these values are NOT the watershed outflow values these are only pertinent to the outflow leaving each catchment treated by BMPs Overall watershed outflow information is displayed in the Watershed Summary section of the Development Summary worksheet under the post development with BMPs condition The buttons to the right of the Watershed Summary tables allow the user to navigate among the various worksheets as well as print the Development Summary worksheet The Print Summary button when clicked will print the Watershed Summary portion of the worksheet on page 1 and the BMP Summary portion of the worksheet on page 2 Note that the button will only print to the default printer Macros MUST be enabled for this button to work 15 Il Model Documentation Governing Principles and Limitations Calculations performed within the model are governed by two basic principles Simple Method for runoff volume and pollutant loading calculations and the median effluent concentration BMP efficiency metric for BMP reduction calculations Each of these principles is described below Simp
4. Open water LAND TAKEN UP BY BMPs 1 08 0 15 LAND TAKEN UP BY BMPs 1 08 0 15 Jurisdictional land uses are not included in nutrientflow calculations Figure 5 Section of Watershed Characteristics worksheet where pre and post development land use areas are entered Users may enter land use information in two sections Non residential land uses Column 1 and residential land uses Column 2 Land uses associated with commercial industrial or transportation categories are listed on the left of the screen while land uses associated with the residential category are found on the right of the screen Miscellaneous pervious land uses as well as land that is taken up by BMPs are also listed in the non residential section of this worksheet Land areas designated to BMPs whether they exist in pre development conditions or whether they will be incorporated with the development should be entered in the Land Taken Up By BMPs category Natural wetlands riparian buffers and open water dubbed Jurisdictional Land Uses are included in the model however these land uses are not considered in the runoff volume or concentration calculations nor may they be treated by BMPs Land area values do not have to be entered in only one of the columns they may be mixed among the two columns if necessary Users should enter the total area within the site development for each type of land u
5. The impervious cover data was intersected with the residential sample polygons to determine the total percentage of impervious cover on each polygon These percentages were then analyzed by residential land use type and included the mean median minimum maximum first and third 22 quartiles and standard deviation The results are represented by box and whisker plots as well as tables in the following section Results of the analysis are shown in Figure 11 below For neighborhoods older than 15 years median impervious cover coefficients were 7 296 20 296 30 396 and 36 096 for VLDR LDR MDR and HDR respectively Figure 12 Table 8 For neighborhoods newer than 15 years median impervious cover coefficients were 2 796 27 896 36 196 and 35 996 for VLDR LDR MDR and HDR respectively Figure 13 Table 9 With the exception of the VLDR land use median impervious cover coefficients were greater in developments newer than 15 years It should be noted that the number of polygons for the developments newer than 15 years is relatively small particularly for the LDR land use category Neighborhoods Older than 15 Years i w gt o o v E 2 2 i v a E c v o x v n 7 2 VLDR n 61 LDR n 19 MDR n 14 HDR n223 Residential Category Figure 11 Median 25 quartile Q1 75 quartile Q3 minimum and maximum values for neighborhoods older than 15 years Table 8 Percent Impervious Cover for Neigh
6. 0 096 1 496 1 096 20 Determining Percent Imperviousness for Residential Lots of Various Ages This section was compiled by the Center for Watershed Protection Inc the Center and presents the methodology for identifying impervious cover IC values in suburban residential land uses for a sampling of developments in four age ranges developments built prior to 1995 older than 15 years developments built after 1995 0 15 years old developments built prior to 1985 older than 25 years and developments built after 1985 0 25 years old The land use polygons used in this study were suburban in nature and most of the development was constructed after 1970 and before 2005 Although these estimates were developed using data from the Chesapeake Bay region it is assumed that these numbers provide a reasonable estimate of suburban development trends that can be transferred to other regions outside this watershed The IC estimates presented herein apply to relatively recent suburban development and may not be transferrable to ultra urban or older development areas Using GIS data from Frederick County MD the Center analyzed IC coefficients for single family residential suburban land uses Homogenous land use polygons were analyzed using Geographic Information Systems GIS data Land use polygons were defined using the descriptions presented in Table 6 Table 6 Land Use Categories and Descriptions Residential Land Use De
7. 0 50 50 Level Spreader Filter Strip 45 5 50 Permeable Pavement 38 2 60 Sand Filter 85 10 5 Wet Detention Pond 75 10 15 Wetland 65 10 25 Coastal Region Bioretention with IWS 10 10 80 Bioretention without IWS 40 10 50 Dry Detention Pond 80 10 10 Grassed Swale 90 0 10 Green Roof 0 50 50 Level Spreader Filter Strip 45 50 Permeable Pavement 38 60 Sand Filter 85 10 5 Wet Detention Pond 75 10 15 Wetland 65 10 25 Mountains Region Bioretention with IWS 40 10 50 Bioretention without IWS 55 10 35 Dry Detention Pond 90 10 0 Grassed Swale 100 0 0 Green Roof 0 50 50 Level Spreader Filter Strip 55 40 Permeable Pavement 98 0 Sand Filter 85 10 5 Wet Detention Pond 80 10 10 Wetland 70 10 20 29 Treated Outflow Bypass Overflow Volume Reduction ide Piedmont Region Bioretention with IWS 40 10 50 Bioretention without IWS 55 10 35 Dry Detention Pond 90 10 0 Grassed Swale 100 0 0 Green Roof 0 50 50 Level Spreader Filter Strip 55 40 Permeable Pavement 98 0 Sand Filter 85 10 5 Wet Detention Pond 80 10 10 Wetland 70 10 20 Sandhills Region Bioretention with IWS 10 10 80 Bioretention without IWS 40 10 50 Dry Detention Pond 80 10 10 Grassed Swale 90 0 10 Green Roof 0 50 50 Level Spreader Filter Strip 45 50 Permeable Pavement 38 60 Sand Filter 85 10 5 Wet Detention Pond 75 10 15 Wetland 65 10 25 Triassic B
8. discussed in the next four sections Page Layout Formulas Data Reven View Add ins Dno A nas Gp wap Tes Gener x d 3M N Goch ni ILE E ee Bi Merge amp Center Conditional Formatas Cell Insert Delete Format Formatting Table Styles Styles Cels Instructions 1 Watershed Characterstcs 2 BMP Characterstcs 3 Development Summary Figure 1 Methods of navigating between worksheet tabs Instructions The Instructions tab is the first worksheet one sees when opening the JLSLAT Excel file This tab contains all instructions and assumptions regarding the JLSLAT and its use Specific instructions are stated again in subsequent tabs so users can refer to them easily This worksheet contains two maps a physiographic region map Figure 2 and an annual precipitation map Figure 3 These maps are provided for users to reference when choosing their physiographic region and precipitation location on the Watershed Characteristics tab There is also a table Table 1 of counties located within or partially within each physiographic region Table 1 allows users to get a general idea of what region their site is located in For users whose county is located within multiple regions it is crucial that they determine which region the site of interest pertains to as this affects calculations and outputs from the JLSLAT This will be discussed in greater detail in the Watershed Characteristics section
9. for the LDR and MDR were greater in developments newer than 25 years Median impervious cover coefficients for the VLDR and HDR were greater in developments older than 25 years 24 Neighborhoods Older than 25 Years p v 2 o o LU 2 gt v a z ES c v o v n VLDR n 30 LDR n 9 MDR n 3 HDR n 5 Residential Category Figure 13 Median Q1 Q3 minimum and maximum values for neighborhoods older than 25 years Table 10 Percent Impervious Cover for Neighborhoods Older than 25 Years Statistic VLDR LDR MDR HDR Q1 5 4 12 2 26 6 33 9 Min 1 7 5 9 23 2 24 0 Median 8 7 16 3 30 0 41 7 Max 14 9 30 9 33 3 47 6 Q3 10 4 21 0 31 7 46 5 Mean 8 0 17 3 28 8 38 7 STD 3 4 7 9 5 2 9 8 n 30 9 3 5 Neighborhoods Newer than 25 Years v gt o o LU 3 2 gt v a E c v o p v o VLDR n 40 LDR n 13 MDR n18 HDR n 27 Residential Category Figure 14 Median Q1 Q3 minimum and maximum values for neighborhoods newer than 25 years Table 11 Percent Impervious Cover for Neighborhoods Newer than 25 Years Statistic VLDR LDR MDR HDR Q1 2 1 20 2 27 1 30 8 Min 0 9 7 5 22 1 14 6 Median 4 1 23 2 32 3 35 9 Max 16 3 32 5 41 5 53 6 Q3 7 8 27 6 36 4 41 5 Mean 5 4 23 3 31 7 35 5 STD 3 9 6 3 5 9 10 4 n 40 13 18 27 Based on changes in development patterns over t
10. that will be used to treat runoff from the development are entered in the BMP Characteristics worksheet Users may divide the development into as many as 6 catchments and each catchment may be treated with up to 3 BMPs BMPs are selected by clicking on the appropriate cell in the row of the worksheet labeled BMP Type indicated by an arrow in Figure 6 After clicking on the cell an arrow will appear on the right side of the cell Click this arrow and a dropdown menu will appear with the available BMP choices Bioretention with IWS Internal Water Storage Zone Bioretention without IWS Dry Detention Pond Grassed Swale Green Roof Level Spreader Filter Strip Permeable Pavement Sand Filter Water Harvesting Wet Detention Pond and Wetland Click on the appropriate BMP To clear a BMP choice either click on the cell and press the delete key or select the blank row in the dropdown menu If more than 1 BMP is assigned to a single catchment the BMPs are assumed to operate in series i e the outflow from BMP 1 flows into BMP 2 etc The JLSLAT allows the user to designate additional drainage areas for the second and third BMP in the series If additional drainage area was designated for BMP 2 of the series BMP 2 would treat not only the outflow from BMP 1 but also the runoff from the designated drainage area To designate this additional drainage area simply enter the square footage for each type of land use within the area in
11. the column for BMP 2 more details on how to specify land uses within BMP drainage areas will be provided later in this section CATCHMENT 2 BMP 2 CATCHMENT 1 BMP 2 f 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 Catchment 2 Catchment 3 Catchment 4 Catchment 5 Catchment 6 Figure 6 Section of the BMP Characteristics worksheet where information regarding type of BMP undersizing oversizing and catchment routing is entered Undersized BMPs The JLSLAT allows for BMPs to be undersized to a minimum of 50 of the size required to treat the water quality event When a BMP is undersized the volume reduction provided by the BMP is reduced using a 1 1 ratio i e if the BMP size required to treat the water quality event is reduced by 40 the assigned volume reduction will be reduced by 40 However the median effluent concentrations assigned to the BMP remain the same To specify that a BMP is undersized the user should enter the BMP s size relative to the design size required to capture the designated water quality depth in decimal form i e 75 of required design size 0 75 in the appropriate row of the worksheet circled in Figure 6 While the tool provides the option of un
12. 08 Commercial Parking Lot Char 0 20 1 83 Passeport and Hunt 2009 Kin1 0 10 1 13 Passeport and Hunt 2009 Kin2 0 07 1 14 Passeport and Hunt 2009 Gre 0 18 1 57 Passeport and Hunt 2009 Gold 0 20 1 52 Passeport and Hunt 2009 Comm Lot 0 19 Bannerman 1993 Roof residential roof 0 15 Bannerman 1993 commercial roof 0 20 Bannerman 1993 industrial roof 0 11 Bannerman 1993 Gold 5 6 0 35 Moran 2004 Gold 7 23 2 10 0 05 Moran 2004 Gold 9 4 1 29 0 05 Moran 2004 Gold 9 18 0 71 0 05 Moran 2004 Gold 12 10 0 80 0 05 Moran 2004 Gold 0 70 0 05 Moran 2004 Raleigh 0 93 0 17 Hunt thesis Raleigh 1 11 0 13 Hunt thesis Raleigh 0 91 0 16 Hunt thesis Raleigh 1 39 0 46 Hunt thesis Raleigh 0 83 0 18 Hunt thesis Lawn 1 42 0 28 Tar Pamlico Nutrient Loading Model 3 06 0 59 Skipper 2008 Industrial Driveway Parking Lot 0 39 Bannerman 1993 Char 1 83 Passeport and Hunt 2009 Kin1 1 13 Passeport and Hunt 2009 Kin2 1 14 Passeport and Hunt 2009 Gre 1 57 Passeport and Hunt 2009 Gold 1 52 Passeport and Hunt 2009 34 Roof residential roof 0 15 Bannerman 1993 commercial roof 0 20 Bannerman 1993 industrial roof 0 11 Bannerman 1993 Gold 5 6 0 35 Moran 2004 Gold 7 23 2 10 0 05 Moran 2004 Gold 9 4 1 29 0 05 Moran 2004 Gold 9 18 0 71 0 05 Moran 2004 Gold 12 10 0 80 0 05 Moran 2004 Gold 0 70 0 05 Moran 2004 Raleigh 0 93 0 17 Hunt thesis Raleigh 1 11 0 13 Hunt thesis Ral
13. 1903 3969 1 umi umd 3843 pdf Winston R J 2009 Field Evaluation of Level Spreader Vegetated Filter Strip Systems for Improvement of Urban Hydrology and Water Quality M S thesis Raleigh NC North Carolina State University Biological and Agricultural Engineering Wu J S C J Allan W L Saunders and J B Evett 1998 Characterization and pollutant loading estimation for highway runoff Journal of Environmental Engineering 124 7 584 592 Yu S L Earles T A Fitch G M and Fassman E A 1998 The Use of Constructed Wetlands for Controlling NPS Runoff Engineering Approaches to Ecosystem Restoration ASCE 1998 32 Appendix A Table A1 Raw data used to compute representative pollutant concentrations for various land uses Land Use Type Site TN mg L TP mg L Reference Residential Driveway industrial pl driveway 0 39 1 44 Bannerman 2003 Passeport and Hunt 2009 Roof residential roof 0 15 Bannerman 1993 commercial roof 0 20 Bannerman 1993 industrial roof 0 11 Bannerman 1993 Gold 5 6 0 35 Moran 2004 Gold 7 23 0 05 2 10 Moran 2004 Gold 9 4 0 05 1 29 Moran 2004 Gold 9 18 0 05 0 71 Moran 2004 Gold 12 10 0 05 0 80 Moran 2004 Gold 0 05 0 70 Moran 2004 Raleigh 0 17 0 93 Hunt thesis Raleigh 0 13 1 11 Hunt thesis Raleigh 0 16 0 91 Hunt thesis Raleigh 0 46 1 39 Hunt thesis Raleigh 0 18 0 83 Hunt thesis Lawn 0 28 1 42 Tar Pamlico Nutrient Loading Model 0 59 3 06 Skipper 20
14. 1995 ac lots New ac lots Built after 1995 ac lots Built before 1995 ac lots New ac lots Built after 1995 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 TOTAL AREA TREATED BY BIMP ft TOTAL AREA TREATED BY SERIES ft Figure 8 Section of the BMP Characteristics worksheet where information regarding land use of BMP drainage area s is entered 13 Development Summary The final worksheet in the JLSLAT is the Development Summary it displays all outputs for the development of interest The worksheet is separated into 2 sections Watershed Summary and BMP Summary Watershed Summary The Watershed Summary section Figure 9 displays outputs for pre development and post development conditions as well as post development conditions with BMPs incorporated These outputs include percent impervious annual runoff volume TN median effluent concentration TN loading rate TP median effluent concentration and TP loading rate Values reported for the post development with BMPs condition account for portions of the watershed not treated by BMPs The Documentation porti
15. Stormwater Ordinance Appendix APPENDIX O FALLS LAKE STORMWATER LOAD ACCOUNTING TOOL Developers and designers should use the Falls Jordan Stormwater Accounting Tool spreadsheets provided by NCDENR DWQ available online at http portal ncdenr org web waq ps nps fallslake Franklin County Stormwater Ordinance Stormwater Accounting Tool Jordan Falls Lake Stormwater Load Accounting Tool Version 1 0 User s Manual revised January 31 2011 NC STATE UNIVERSITY ncdenr North Carolina Department of ENGINEERING Environment and Natural Resources Introduction This accounting tool was developed by North Carolina State University in coordination with NCDENR to be used with the Jordan Lake Nutrient Strategy Rules While the original application of this tool is the Jordan Lake Nutrient Strategy it may also be applied to any location within the state of North Carolina This tool is intended to be used for new developments NCDENR is developing a separate tool for existing developments within the Jordan Lake watershed but can be also be applied to existing developments that are incorporating retrofit best management practices BMPs Important Notes Some BMPs included in the tool may not currently be used for meeting nutrient reduction requirements Please check with the Division and the Division s Stormwater BMP Manual for more details While the tool provides the option of undersizing BMPs this option cannot curr
16. and forgetting to the clear the BMP selection The second warning is displayed if a BMP has not been selected but another catchment is being routed to it Again this is in 12 case the user forgets to clear the catchment routing after a BMP is removed To clear all entries in this worksheet both land areas as well as catchment routing and BMPs click the Clear All Values button at the top of the worksheet In order for the Clear All Values button to work macros MUST be enabled CATCHMENT1 7 7 7 7 7 7 7 7 7 7 i CATCHMENT2 BMP 2 BMP 3 BMP 2 BMP 3 Area treated Area treated Area treated Area treated Area Treated by BMP 2 that is by BMP 3 that is Area Treated by BMP 2 that is by BMP 3 that is Drainage Area Land Use by BMP not treated by BMP not treated by BMPs by BMP not treated by BMP not treated by BMPs ft 1 1 or 2 ft 1 1 or 2 ft ft ft ft COMMERCIAL Parking lot Roof 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 aclots 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 ac lots New ac lots Built after 1995 ac lots Built before
17. asin Region Bioretention with IWS 55 10 35 Bioretention without IWS 75 10 15 Dry Detention Pond 80 20 0 Grassed Swale 100 0 0 Green Roof 0 50 50 Level Spreader Filter Strip 75 20 Permeable Pavement 98 0 Sand Filter 85 10 5 Wet Detention Pond 85 10 5 Wetland 75 10 15 30 References Bannerman R T D W Owens R B Dodds and N J Hornewer 1993 Sources of pollutants in Wisconsin stormwater Water Science Technology 28 3 5 241 259 Bass K L 2000 Evaluation of a Small In Stream Constructed Wetland in North Carolina s Coastal Plain M S thesis Raleigh NC North Carolina State University Biological and Agricultural Engineering Bean E Z W F Hunt and D A Bidelspach 2007 Evaluation of four permeable pavement sites in Eastern North Carolina for runoff reduction and water quality impacts Journal of Irrigation and Drainage Engineering 133 6 583 592 Cappiella K and Brown K 2001 Impervious Cover and Land Use in the Chesapeake Bay Watershed The Center for Watershed Protection Ellicott City MD Carleton J N 1997 An Investigation of the Performance of a Constructed Wetland in Treating Urban Stormwater M S Thesis Manassas VA Virginia Polytechnic Institute and State University Department of Environmental Sciences and Engineering Center for Watershed Protection CWP 2007 Urban stormwater retrofit practices Urban Subwatershed Restoration Manual Series Ellicott City MD Chin D A 2006 Surfac
18. borhoods Older than 15 Years Statistic VLDR LDR MDR HDR Q1 3 4 16 2 26 6 32 1 Min 0 9 5 9 22 1 14 6 Median 7 2 20 2 30 3 36 0 Max 16 3 32 5 39 9 53 6 Q3 9 5 24 6 33 4 46 1 Mean 7 0 20 0 30 1 37 4 STD 3 9 7 6 5 3 9 9 n 61 19 14 23 23 Neighborhoods Newer than 15 Years v 2 o o LU 3 9 2 v a E c v o v a VLDR n 9 LDR n 3 MDR n 7 HDR n 9 Residential Category Figure 12 Median Q1 Q3 minimum and maximum values for neighborhoods newer than 15 years Table 9 Percent Impervious Cover for Neighborhoods Newer than 15 Years Statistic VLDR LDR MDR HDR Q1 1 4 24 0 29 7 21 9 Min 0 9 20 2 23 8 15 9 Median 2 7 27 8 36 1 35 9 Max 5 5 29 2 41 5 47 9 Q3 4 0 28 5 37 7 37 6 Mean 3 0 25 7 33 8 32 3 STD 1 7 4 9 6 2 10 7 n 9 3 7 9 In order to increase the sample size for newer development differences between IC values for neighborhoods newer and older than 25 years were also evaluated For neighborhoods older than 25 years median impervious cover coefficients were 8 7 16 3 30 0 and 41 7 for VLDR LDR MDR and HDR respectively Figure 14 Table 10 For neighborhoods newer than 25 years median impervious cover coefficients were 4 1 23 2 32 3 and 35 9 for VLDR LDR MDR and HDR respectively Figure 15 Table 11 For this analysis median impervious cover coefficients
19. concentration or pollutant loading Positive values indicate an increase Figure 9 Watershed Summary section of the Development Summary worksheet BMP Summary The BMP Summary section of the Development Summary Figure 10 worksheet displays information regarding the BMPs treating the development The total area treated by each BMP includes the area treated by previous BMPs in the series as well as additional area draining to the BMP itself The inflow volume is the total amount of water flowing into the BMP The percent volume reduction is the volume reduction potential assigned to the BMP types within the specified physiographic region the same value displayed in Figure 7 The inflow concentrations and loadings for TN and TP are displayed 14 for each BMP Additionally outflow loadings for TN and TP are also displayed for each BMP Details on how these are calculated may be found in the Documentation portion of this document CATCHMENT 1 CATCHMENT 2 BMP 1 BMP 2 BMP 3 BMP 1 BMP 2 BMP 3 agi n 200 200 2479 Totas a oed 319 814 319 814 828 400 Percent iru Reduced 0z 50 M 202 mo ary En 140 121 215 e em 13 98 12 05 T 449 innos dini EML 0 520 0 258 0 430 Total rna RTT 518 257 E 0 90 Pranie ra 1205 439 2 02 Becerra ME 257 074 7 0 26 eee trogen 100 121 oe ae 4 99 2 02 Percent ARR r Nitrogen 62 40 Phosphorus EMC mgl 0 148 0 56 PE raaa d 0 735 0 260 aedes s w Figure 10 BMP Summary section of the Development Summary worksheet
20. d uses The polygons used in this study were suburban in nature and most of the development was constructed after 1970 and before 2001 Although these estimates were developed using data from the Chesapeake Bay region it is assumed that these numbers provide a reasonable estimate suburban development trends that can be transferred to other regions outside this watershed However the IC estimates presented herein apply to recent suburban development and may not be transferrable to ultra urban or older development areas Using GIS data from Baltimore County MD Howard County MD James City County VA and Lancaster County PA the Center analyzed IC coefficients for single family residential suburban land uses Homogenous land use polygons were analyzed using Geographic Information Systems GIS data Land use polygons were defined using the descriptions presented in Table 3 The following criteria were used to select single family residential polygons for analysis e For residential land uses the parcel boundary information was used to first classify parcels based on acreage shown in the description in Table 3 Development patterns that most closely matched the land use category e g acre lots were selected for sampling Because most subdivisions do not have uniform lot sizes subdivisions were selected if the majority of lots or average lot size met the general criteria for the land use category e Because of difficulty in finding subd
21. dersizing BMPs this option cannot currently be used to meet the Jordan New Development requirements This option may potentially be used if the tool is used to calculate nutrient reductions for retrofits on existing development check with DWQ 10 Oversized BMP The JLSLAT does not include a direct method of oversizing BMPs however users can model oversized BMPs To do so users must enter two BMPs of the same type in series the outflow from the first BMP flows into the second BMP The BMP type should be that of the BMP the user wishes to oversize The percent by which the user wishes to oversize the BMP should be added to 10096 then divided by 2 This value will be entered in the same row that undersized values are entered circled in Figure 6 for both BMPs For example if a BMP was to be 5096 greater than the size required to treat the water quality depth it would be a total of 15096 of the design size Divide this value by 2 and the two BMPs in series would be assigned an undersized value of 0 75 each Catchment Routing Any catchment within the development may be routed to any other BMP or catchment The section in which this information is entered is highlighted by a box in Figure 6 To indicate that a BMP is accepting the outflow from another catchment select yes from the dropdown menu in the cell corresponding to the BMP that is accepting the outflow For example if BMP 2 of Catchment 1 is accepting the outflow from Catchm
22. e application of the IC coefficients to residential zoning classifications in North Carolina Table 4 Zoning Classifications for Durham NC City of Durham N C Durham Zoning Minimum Lot Minimum Lot Area Equivalent Land Use Code Area acre from Analysis square feet R 20 20 000 0 46 1 2 ac R 15 15 000 0 34 R 10 10 000 0 23 1 4 ac R 8 8 000 0 18 R 5 5 000 0 11 1 8 ac R 3 3 000 0 07 The results of the analysis are presented in Table 5 For single family residential categories driveways consistently made up about 496 of the polygon area while roads and buildings comprised an equal percentage that progressively increased with development density Sidewalks in residential areas composed from 196 to 296 of the polygon area and this number also increased with development density Table 5 Results of the IC Analysis by Land Use and Type of IC N T yan Total 9 Other Polygons IC Roads Buildings Parking Driveways Sidewalks Impervious 2 Acre Lots 12 10 6 3 4 3 3 0 0 3 8 0 0 0 1 1 Acre Lots 23 14 3 4 8 5 1 0 0 4 1 0 1 0 2 1 2 Acre Lots 20 21 2 7 5 7 9 0 0 4 496 1 296 0 296 1 4 Acre Lots 23 27 896 10 896 11 096 0 096 4 496 1 696 0 196 1 8 Acre Lots 10 32 696 13 496 12 296 0 096 4 796 2 296 0 096 Townhomes 20 40 996 12 6 16 496 6 496 2 196 2 796 0 696 Multifamily 18 44 496 13 1 15 996 13 096
23. e water hydrology In Water resources engineering 334 606 Upper Saddle River New Jersey Pearson Education Inc City of Durham NC No Date City County Planning Department General Zoning Districts Available online http www durhamnc gov departments planning zoneord section4 Index cfm Collins K A W F Hunt and J M Hathaway 2010 Side by side comparison of nitrogen species removal for four types of permeable pavement and standard asphalt in Eastern North Carolina Journal of Hydrologic Engineering 15 6 512 521 Hathaway J M and W F Hunt 2008 Field Evaluation of Level Spreaders in the Piedmont of North Carolina Journal of Irrigation and Drainage Engineering 134 4 538 542 Hathaway J M and Hunt W F 2009 An Evaluation of the Dye Branch Wetlands Final Monitoring Report Raleigh NC lt http www bae ncsu edu stormwater PublicationFiles Dye Branch2009 pdf gt Hathaway J M Hunt W F Johnson A 2007 City of Charlotte Pilot BMP Monitoring Program Morehead Place Dry Detention Basin Final Monitoring Report Raleigh NC Hathaway A M William F Hunt and G D Jennings 2008 A field study of green roof hydrologic and water quality performance Transactions of the ASABE 51 1 37 44 Hunt W F Jarrett A R Smith J T and Sharkey L J 2006 Evaluating Bioretention Hydrology and Nutrient Removal at Three Field Sites in North Carolina Journal of Irrigation and Drainage Engineering 132 6 600 608 John
24. eas to include within a given land use polygon Lots that were not yet built were not included as part of the subdivision Interstate state highways were not included in the polygons Interior roads e g subdivision roads were included within the land use polygons Local and arterial roads were included in the polygons if the parcels bordering each side of the road had the same land use If a local or arterial road bordering a parcel had a different land use bordering the other side of the road only half the road was included in the polygon Sample polygons were drawn by following the lot lines of contiguous parcels After delineating each polygon the appropriate land use type i e VLDR LDR MDR or HDR was assigned The owner listed in the tax map data as well as 2007 aerial photos supplied by the County were used to verify land use The age range of each neighborhood 0 15 years 0 25 years older than 25 years or older than 15 years was determined by using the build date in the County s tax map data Age range was assigned based on the most common build dates of the lots within each subdivision After the delineation of sample polygons the following methods were used to determine impervious cover based on residential land use type and age Impervious cover data was obtained from a 2007 planimetric layer provided by the County This layer included impervious cover in the form of buildings driveways roads sidewalks and parking lots
25. egion The region of a site dictates the volume reduction capabilities of BMPs Hydrologic Soil Group required The hydrologic soil group HSG is the predominant type of soil located on the site Select the appropriate HSG A B C or D from the drop down menu Users may use on site soil tests or soil maps to determine the appropriate HSG however one must be careful that the HSG does not vary throughout the site and truth checking soil maps is highly encouraged sometimes required The HSG is a reference for regulators to make sure the selected BMPs are acceptable for the given HSG Precipitation Location required Users should select a location from the drop down menu that most closely represents the rainfall patterns of the site Note that this may not necessarily be the closest location to the site Figure 3 shows trends for North Carolina regarding average annual rainfall depths and can be used to choose the most appropriate precipitation location The location selected is used to determine stormwater runoff volumes for the site Total Development Area required Enter the total number of square feet comprising the site to be analyzed It is important that this value equal the sum of all areas entered in the pre and post development land use columns In the event that these values do not match a warning will appear at the bottom of the worksheet alerting the user of this fact Development Name optional The name assigned to the site deve
26. eigh 0 91 0 16 Hunt thesis Raleigh 1 39 0 46 Hunt thesis Raleigh 0 83 0 18 Hunt thesis Lawn 1 42 0 28 Tar Pamlico Nutrient Loading Model 3 06 0 59 Skipper 2008 Transportation High Density interstate main 3 67 0 43 Wu et al 1998 Low Density secondary feeder 1 40 0 52 Wu et al 1998 Rural 1 14 0 47 Wu et al 1998 Sidewalk 1 16 Bannerman 1993 1 43 Passeport and Hunt 2009 Other Woods 1 47 0 25 Line et al 2002 median value Maintained Grass 3 06 0 59 Skipper 2008 Pasture 3 61 1 56 Line et al 2002 median value 35
27. ent 3 the cell corresponding with the column for BMP 2 of Catchment 1 and the row for Catchment 3 should be changed to display yes instead of no To route one catchment to another catchment simply route the catchment outflow to the first BMP within the catchment accepting the outflow Water Harvesting BMP Water harvesting is a BMP given as an option within the JLSLAT Users must enter a volume reduction for the water harvesting BMP in the appropriate row within the BMP Characteristics worksheet This is the volume reduction used to calculate volume and nutrient outputs from the system It is important to note that the water harvesting BMP is NOT modeled as a catch and release system in the JLSLAT it is assumed that volumes reduced by the system are NOT released to the stormwater network It is up to the developer to prove that this is in fact the case and that the reported volume reduction is accurate To aid with the selection of BMPs a table BMP Details is located at the top of the worksheet and displays the volume reduction and median effluent concentrations for each type of BMP for the physiographic region indicated in the Watershed Characteristics page Note the values will change if the region is changed Figure 7 shows this table with the Coastal physiographic region as the selected region Users may use this table to determine which types of BMPs would provide the most treatment for their development As permeable pavement green
28. ently be used to meet the Jordan New Development requirements This option may potentially be used if the tool is used to calculate nutrient reductions for retrofits on existing development Using the Client Master Files To prevent manipulation of the Jordan Falls Lake Stormwater Load Accounting Tool JLSLAT and its outputs a system has been developed involving two Excel files a Client file and a Master file The Client file will be distributed to the general public and the Master file will be distributed to regulators by NCDENR The Master file is NOT designed to run scenarios and analyze developments Its only use is for regulators to extract input data from the Client file and view results To ensure that both files function properly and produce accurate results do NOT attempt to change any formatting data or formulas within the files Client File Developers or anyone submitting the results from the JLSLAT for regulatory review may use the Client file to run any and all scenarios for a given development When they are ready to submit a given scenario development for review they will save the Client file and send it to the appropriate regulatory agency The agency s Master file will extract the input data from the Client file and produce its own results Regulators will use these results to review the development Master File The Master file extracts the input data from a specified Client sheet and produces its own set of results Agai
29. fficacy of three wet detention ponds Journal of Environmental Quality 31 2 654 660 Moran Amy Christine 2004 A North Carolina Field Study to Evaluate Greenroof Runoff Quantity Runoff Quality and Plant Growth A thesis published by the Graduate School of North Carolina State University under the direction of Dr William F Hunt Ill and Dr Greg Jennings Passeport W and W F Hunt 2009 Asphalt parking lot runoff nutrient characterization for eight sites in North Carolina USA Journal of Hydrologic Engineering 14 4 352 361 Passeport E Hunt W F Line D E Smith R A and Brown R A 2009 Field study of the ability of two grassed bioretention cells to reduce storm water runoff pollution Journal of Irrigation and Drainage Engineering 135 4 505 510 Pitt R R Field M Lalor and M Brown 2005 Urban stormwater toxic pollutants assessment sources and treatability Water Environment Research 67 3 260 275 Skipper Gabrielle Marie 2008 Watershed Scale Stormwater Monitoring of a Mixed Land Use Watershed in the North Carolina Piedmont A thesis published by the Graduate School of North Carolina State University under the direction of Dr William F Hunt Ill Stagge J H Field Evaluation of Hydrologic and Water Quality Benefits of Grass Swales for Managing Highway Runoff 2006 M S Thesis College Park MD University of Maryland Department of Civil and Environmental Engineering http www lib umd edu drum bitstream
30. g the efficiency of a best management practice BMP The method used by the JLSLAT is based upon a median effluent concentration of a given pollutant for a given BMP This value will vary based upon the pollutant and the type of BMP The concentrations used for the JLSLAT application will be explained in detail in the Watershed Characteristics section of this document To apply this BMP efficiency method one must know the volume of water flowing into a BMP the inflow concentration of the pollutant of interest the percent of inflow volume that leaves the BMP as treated outflow and untreated overflow as well as the outflow pollutant concentration for both of these outflow components Assumptions made regarding these variables for the JLSLAT are discussed in detail in the Watershed Characteristics section of this document Equation 4 is used to calculate total mass of pollutant leaving the BMP and Equation 5 is used to calculate the percent mass removal by the BMP MasSout ECouttiow Volume outtiow 6 2297E 5 ECoverflow A VolUMEoverfiow 6 2297 5 4 where Mass average annual mass of pollutant leaving the BMP Ibs ECouttlow event median concentration for treated outflow portion of outflow mg L Volume outflow volume of water leaving the BMP as treated outflow ft ECoverflow event median concentration for untreated overflow portion of outflow mg L and Volume overflow volume of water leaving the BMP as untreated overflo
31. he years the results showed that older developments were likely to have lower IC than newer developments however this was only true for the MDR and LDR land use categories This may be due in part to the range of ages sampled nothing prior to 1970 or to changes made by Frederick County MD as a result of a Site Planning Roundtable in 2000 or the nature of the VLDR category estate homes Further analysis is needed to hypothesize the specific reason for the lack of IC increase for the newer VLDR and HDR land use categories The data provided by the Center for Watershed Protection regarding the breakdown of different types of impervious surfaces within residential land uses were used to calculate a composite pollutant concentration The concentrations assigned to a specific land use coupled with the percent of watershed comprised of that particular land use allowed for a weighted average concentration to be calculated These results are displayed in Table 12 26 Table 12 Representative pollutant concentrations for residential land uses of various ages After 1995 Before 1995 TN TP TN TP 2 ac lots 2 22 0 44 2 19 0 43 1 aclots 2 12 0 43 2 15 0 43 ac lots 2 06 0 43 2 11 0 43 ac lots 2 00 0 42 2 07 0 43 ac lots 1 98 0 43 2 02 0 43 Townhomes 1 94 0 42 1 94 0 42 Multi family 1 92 0 41 1 92 0 41 BMP Efficiency Median Effluent Concentration Method There are several methods for quantifyin
32. ivisions that met the above criteria for polygon delineation no minimum area was set for the polygon size for residential areas Instead it was decided that each residential polygon must include a minimum of 5 lots e Polygons were drawn by following the lot lines of contiguous parcels and excluding areas of unbuildable land located in the interior of the polygon Stream valleys that did not originate within the subdivision were excluded from the land use polygons as were other unbuildable lands such as floodplains wetlands and conservation areas The basis behind this rule is that not all development sites include these types of characteristics When predicting future impervious cover a planner could estimate the areas based on existing mapping and based on local codes and ordinances that determine unbuildable acreage This acreage could then be removed from the total acreage of the planning area e Stormwater ponds and open water were not considered to be impervious cover because they are generally small in area and are not always associated with a single land use While water surfaces do act as impervious surfaces in a hydrologic sense they do not generally have similar consequences on stream quality watershed health or pollutant loading as more conventional impervious cover such as roads parking lots and rooftops 17 Table 2 Representative TN and TP concentrations for various land uses TN TP
33. le Method The Simple Method is a method for estimating the volume of stormwater runoff and the pollutant load exported within that runoff leaving a small urban catchment Volume calculations are based upon impervious cover of a catchment which is represented by the runoff coefficient Rv R 0 05 0 009 I 1 where R Simple Method runoff coefficient and percent impervious cover of the catchment 96 The volume is a function of the runoff coefficient Rv the area of the catchment and the annual rainfall amount Some variations of the Simple Method are applied on an individual storm basis in which case the precipitation value would be the depth of rainfall that one wishes to estimate runoff for For JESLAT applications annual precipitation values are used V R A P 12 2 where V volume of runoff ft A area of catchment ft and P average annual rainfall depth in To estimate the mass of pollutant that leaves the catchment on an annual basis Equation 3 is used L P Pj R 12 C A 2 72 3 where L average annual pollutant load Ibs Pj fraction of rainfall events that produce runoff and C event mean concentration of the pollutant mg L CWP 2007 recommends a Pj value of 0 9 indicating that 90 of rainfall events produce runoff However for the JLSLAT a value of 1 0 was used in order to provide a conservative estimate of the pollutant load leaving the site The event mean concentratio
34. lopment to be analyzed This name will appear on the summary sheet with the JLSLAT outputs Model Prepared By optional The name of the person using the JLSLAT for a site development This name will appear on the summary sheet with the JLSLAT outputs The lower section of the Watershed Characteristics worksheet Figure 5 is where users enter land use data for pre and post development conditions COLUMN 1 NON RESIDENTIAL LAND USES COLUMN 2 RESIDENTIAL LAND USES Pre Post TN EMC TP EMC Custom Lot Age TN EMC TP EMC Development Development mg L mg L 2 2 Size ac yrs mg L mg L ft fc COMMERCIAL PARTA Parking lot 1 44 0 16 Yeac lots Roof 1 08 0 15 ac lots Open Landscaped 2 24 0 44 Y ac lots ind d INDUSTRIAL 1 ac lots New 2 15158 0 42966 Parking lot 1 44 0 39 2 ac lots Roof 1 08 0 15 Multi family Open Landscaped 2 24 0 44 Townhomes TRANSPORTATION Custom Lot Size T High Density interstate main 3 67 0 43 PARTB Low Density secondary feeder 14 0 52 Roadway 14 0 52 Rural 1 14 0 47 Driveway 10 1 44 0 39 Sidewalk 14 1 16 Parking lot 1 4 0 39 PERVIOUS Roof 1 08 0 15 Managed pervious 3 06 0 59 Sidewalk Patio 14 1 16 Unmanaged pasture 3 61 1 56 Lawn 2 24 0 44 Forest 1 47 0 25 Managed pervious 3 06 0 59 JURISDICTIONAL LANDS Forest 1 47 0 25 Natural wetland Natural wetland Riparian buffer Riparian buffer Open water
35. lygons using GIS For IC types not available as planimetric data e g sidewalks driveways the following major assumptions were made Other Impervious Surfaces Orthophotos were used to digitize an impervious cover layer that included tennis courts garages and other impervious surfaces not included in the buildings parking lots roads driveways or sidewalks layers This layer was included in the processing and calculation of total impervious cover Sidewalk Estimation Sidewalks were identified only as lines in the GIS layers so orthophotos were used to measure the length of sidewalks in each polygon which was then multiplied by 4 feet assumed sidewalk width The resulting numbers were added to the data table for calculation of total impervious cover 19 Driveway Estimation Driveway data was not available so GIS orthophotos were used to determine an average driveway size for each polygon which was then multiplied by the number of homes within the polygon The resulting numbers were added to data table for calculation of total impervious cover Results for each land use polygon were used to compute an average IC by type for various suburban residential land uses More detailed information on the sampling protocol and impervious cover measurement can be found in Cappiella and Brown 2001 The current zoning code classifications for the City of Durham NC are shown in Table 4 The information in this table can be used to guide th
36. mation users must specify the age of the development in the column labeled Age of Development It is expected that the majority of developments analyzed with the JLSLAT will be new developments however should the JLSLAT be applied to existing developments users have the option of choosing an age of Before 1995 and After 1995 For new developments users should select New Results will not be displayed if a development age is not selected Users may clear all entries by clicking the Clear All Values button at the top of the worksheet The other buttons Return to Instructions Proceed to BMP Characteristics and Skip to Summary Page allow users to navigate among the different worksheets In order for the Clear All Values button to work macros MUST be enabled An additional note regarding the Clear All Values button When using the Client and Master files clicking the Clear All Values button in the Master file will only clear values that were entered in the Master file in addition to those values carried over from the Client file All values that were entered in the Client file and thus carried over to the Master file will remain To clear these values the user must click the Clear All Values button in the Client file To avoid confusion it is best to work entirely within the Client File It is unnecessary to perform any actions within the Master file BMP Characteristics All details pertaining to the BMPs
37. n the Master file is NOT designed to run scenarios and analyze developments It is strongly recommended that the regulatory agency use the Save As feature to have a separate Master file for each Client file To establish the connection between the Master and Client files go to the Instructions worksheet and click on Data gt Connections gt Edit Links Browse files and select the client sheet you want to extract the data from Click on the Update Values button The files should update automatically and any time the Master Sheet is opened it will extract the data from the specified Client file You may check the status of the connection by clicking Data gt Connections gt Edit Links gt Check Status If for some reason the link is broken simply repeat the steps described above Glossary of Terms water quality depth The depth of rainfall that a BMP is designed to capture and treat generally 1 inch for all regions except CAMA for CAMA it is generally 1 5 inches physiographic region Broad scale subdivision based on terrain texture rock type and geologic structure and history In North Carolina there are five main physiographic regions coastal plain sandhills piedmont Triassic basin and mountains In the JLSAT the region CAMA refers to the region of the state where Coastal Area Management Act applies see NCDENR s website for more information about this region and the stormwater requirements hydrologic soil grou
38. n was used to first classify parcels based on acreage shown in the description in Table 6 Development patterns that most closely matched the land use category e g acre lots were selected for sampling Because most subdivisions do not have uniform lot sizes subdivisions were selected if the majority of lots or average lot size met the general criteria for the land use category Because of difficulty in finding subdivisions that met the above criteria for polygon delineation no minimum area was set for the polygon size for residential areas Instead it was decided that each residential polygon must include a minimum of 5 lots unless it was in the very low density residential category Stormwater ponds and open water and pools were not considered to be impervious cover because they are generally small in area and are not always associated with a single land use While water surfaces do act as impervious surfaces in a hydrologic sense they do not generally have similar consequences on stream quality watershed health or pollutant loading as more conventional impervious cover such as roads parking lots and rooftops Once a development area was selected the following methods were used to delineate land use polygons Residential polygons generally included individual lots as well as common land owned by the homeowner s association or developer The subdivision names in the County s subdivision layer were used to determine which residential ar
39. ns used for certain land uses will be discussed in detail in the Watershed Characteristics section of this document Several assumptions limitations accompany the Simple Method taken from CWP 2007 1 The Simple Method should be used on catchments with areas of 1 square mile 640 acres or less and 2 The Simple Method only estimates pollutants loads leaving the catchment via stormwater runoff 16 Determining Representative Pollutant Concentrations for Various Types of Land Uses A literature review was conducted to establish representative pollutant concentrations for various land use types Only peer reviewed literature was considered in this endeavor however geographic limitations were not imposed Only data that were reported for the specific land use of interest i e not multi use watersheds were used If multiple data were available the average of the data was taken as the representative pollutant concentration unless otherwise noted Table 2 displays the representative TN and TP concentration values for various land uses as well as the references from which the values were derived Raw data from individual studies used to compute these values may be found in Appendix A Determining Percent Imperviousness for Various Residential Lot Sizes This section was compiled by the Center for Watershed Protection Inc the Center and presents the methodology for identifying types of impervious cover IC in suburban residential lan
40. on of this document explains how each of these values are calculated The watershed TN and TP loading values are those that correspond with the required target loading rates set forth by the Jordan Lake Nutrient Strategy The lower portion of the Watershed Summary section reports percent differences between the various watershed conditions including pre development and post development without BMP incorporation pre development and post development with BMP incorporation and post development without BMPs and post development with BMPs REGION Piedmont TOTAL DEVELOPMENT AREA ft 1 393 920 Pre Development Conditions Post Development Conditions Post Development w BMPs Percent Impervious 1 2 2 21 0 21 0 Annual jei Volume 375 361 1365521 1 208 257 Total Nitrogen EMC mol 2 63 1 88 1 33 Total Nitrogen Loading Iblaclyr 1 93 4 72 2 16 Total Phosphorus EMC molL 101 0 42 0 27 Total Phosphorus Loading Ibtactyr 0 74 1 06 0 31 Percent Diffarance Beery Pre Dev amp Pre Development amp BMPs amp Post Dev without BMPs Post Development with BMPs Post Development with Percent Impervious 19 19 0 Annual Runoff Volume c f 264 222 12 Total Nitrogen EMC mg L 28 50 30 Total Nitrogen Loading Iblaclyr 145 12 54 Total Phosphorus EMC malL 58 73 36 Total Phosphorus Loading Iblaclyr 44 58 71 Negative percent difference values indicate a decrease in runoff volume pollutant
41. ot size ranges from 0 20 to 0 30 acres Lot size ranges from 0 10 to 0 16 acres includes 1 8 Acre Lots duplexes 5 10 units acre attached single family units that Townhomes include a lot area 10 20 units acre residential condominiums and Multifamily apartments with no lot area associated with the units Once a development area was selected the criteria used to delineate the polygons were generally as follows e Parcel lines were used as guides for drawing the polygon boundaries e Unbuildable land such as floodplains steep slopes and conservation areas were not included in the polygons e Subdivision lots that were not built out were not included in the polygons e Large forested areas located outside parcel boundaries were not included in the polygons e Local and arterial roads were included in the polygons if the parcels bordering each side of the road had the same land use e falocal or arterial road bordering a parcel had a different land use bordering the other side of the road only half the road was included in the polygon Interstate and state highways were not included in the polygons e Parcel data such as a business or owner name was used to verify land use e Orthophotos were also used to verify land use A direct measurement technique was used to assess the IC for each land use polygon This involved clipping planimetric IC layers e g buildings roads parking lots to the land use po
42. p Soils are classified into hydrologic soil groups HSGs to indicate the minimum rate of infiltration obtained for bare soil after prolonged wetting median effluent concentration The median concentration of a given constituent that is released from a best management practice This value is independent of the inflow concentration internal water storage zone Subsurface portion of a bioretention cell that provides water storage in the bottom of the cell Water stored in this layer is principally released by exfiltration The IWS zone is created by elevating the underdrain usually with a 90 degree PVC elbow I Using the Jordan Falls Lake Stormwater Load Accounting Tool JLSLAT This section covers the use and interpretation of the JLSLAT There are four worksheet tabs within the Excel spreadsheet that users will need to access Instructions Watershed Characteristics BMP Characteristics and Development Summary The Instructions tab provides background information and general instructions for using the JLSLAT The Watershed Characteristics and BMP Characteristics tabs allow users to enter their development and BMP data Finally the Development Summary is where all outputs are displayed Users may navigate between these four tabs by either clicking the buttons at the top of the worksheets Figure 1A or by clicking on the tab name at the bottom of the screen Figure 1B Each tab and its corresponding instructions assumptions and uses are
43. roofs and water harvesting BMPs are not assigned a nutrient removal credit their effluent concentrations default to the value of the land use they are replacing parking lot roof etc Water harvesting permeable pavement and green roofs may not currently be used for meeting nutrient reduction requirements in the Jordan Lake watershed Please check with the Division and the Division s Stormwater BMP Manual for applicability details 11 BMP DETAILS TN Effluent Concen TP Effluent Concen mg L mg L Bioretention with IWS i 0 12 DryDetentionPond Grassed Swale EIE BMP Volume Reduction 96 5 40 if treating commercial parking lot TP effluent concentration 0 16 mg L Figure 7 BMP Details table displaying values for the Piedmont physiographic region blank cells indicate 096 volume reduction The lower portion of the BMP Characteristics worksheet Figure 8 allows the user to define the watershed draining to each BMP The user should enter the total area of each land use type that drains to each BMP in the appropriate column Note that when entering residential land use information the user MUST be sure to enter the land area values in the appropriate row for the age of the development New Before 1995 and After 1995 ages are listed out separately unlike the Watershed Characteristics worksheet The size of the BMP itself should be entered in the very last land use row Land taken up b
44. runswick Camden Carteret Chowan Craven Currituck Dare Gates Hertford Hyde New Hanover Onslow Pamlico Pasquotank Pender Perquimans Tyrrell Washington Table 1 List of counties located within or partially within each physiographic region TRIASSIC BASIN Durham Granville Wake Chatham Lee Moore Montgomery Richmond Anson Union Rockingham Stokes Davie SANDHILLS Montgomery Moore Lee Harnett Cumberland Hoke Robeson Scotland Richmond Watershed Characteristics On the Watershed Characteristics worksheet users enter all information pertaining to the site of interest including both pre and post developed conditions General development information is entered in the upper section of the worksheet shown in Figure 4 Physiographic Geologic Region i Total Development Area t oS Soil Hydrologic Group ae Development Name Ey Precipitation location O Model Prepared By A oo O Figure 4 General development information section of Watershed Characteristics worksheet Physiographic Geologic Region required This is the physiographic region in which the site is located Select the appropriate region from the drop down menu Regions to select from include CAMA coastal area management act Coastal Sandhills Piedmont Triassic Basin and Mountains Users may reference Figure 2 or Table 1 both located in the Instructions worksheet to determine the appropriate physiographic r
45. scription Very Low Density Residential Lot sizes greater than 1 acre less than 1 dwelling VLDR unit per acre Low Density Lot size ranges from 0 25 to 1 acre 1 to 4 dwelling Residential LDR units per acre Medium Density Residential Lot size ranges from 0 1 to 0 2 acres 5 to 10 MDR dwelling units per acre High Density Lot sizes less than 0 1 acre greater than 10 dwelling Residential HDR units per acre The current zoning code classifications for the City of Durham NC are shown in Table 7 The information in this table can be used to guide the application of the IC coefficients to residential zoning classifications in North Carolina Table 7 Zoning Classifications for Durham NC City of Durham N D Durham Zoning Minimum Lot Minimum Lot Area Equivalent Land Use Code Area acre from This Analysis square feet R 20 20 000 0 46 LDR R 15 15 000 0 34 LDR R 10 10 000 0 23 LDR R 8 8 000 0 18 MDR R 5 5 000 0 11 MDR R 3 3 000 0 07 HDR 21 The following criteria were used to select residential polygons for analysis Residential polygons were selected at random by using a Random Number Generator in Excel to assign a numerical number to each subdivision in the County s GIS data The random selection process was limited to subdivisions built after 1973 Subdivisions were then analyzed in numerical order of the random numbers For each subdivision the parcel boundary informatio
46. se This should be done for both pre and post development conditions If a particular land use is not present on the site the cells may be left blank or a zero may be entered The TN EMC and TP EMC values listed beside each land use are the representative concentrations of total nitrogen TN and total phosphorus TP found in stormwater runoff leaving that particular land use The methods used to establish percent impervious assignments and representative pollutant concentrations for individual land uses are discussed in Part II of this document The percent impervious value for the driveway land use is adjustable This value defaults to 1 10096 impervious however uses may adjust this in the gray shaded cell in the Age of Development column Note that the percent impervious value entered must be validated and may or may not be accepted by the reviewing agency It is important that the areas entered for both the pre and post development condition sum to equal the Total Development Area entered in the upper section of the Watershed Characteristics worksheet A chart displaying the totals for each of these values is located below Column 1 Land Use Area Check If these values do not equal each other a warning will be displayed below Column 2 to alert the user that there is a discrepancy Residential Land Uses There are two options for entering land use information for residential sites The first option is entering area values in Part A of Col
47. son J L 2006 Evaluation of Stormwater and Wet Pond Forebay Design and Stormwater Wetland Pollutant Removal Efficiency MS Thesis Raleigh NC North Carolina State University Department of Biological and Agricultural Engineering Lenhart Hayes Austin 2008 A North Carolina field study to evaluate the effect of a coastal stormwater wetland on water quality and quantity and nitrogen accumulation in five wetland plants in two constructed stormwater wetlands A thesis published by the Graduate School of North Carolina State University under the direction of Dr William F Hunt III Li H Sharkey L J Hunt W F Davis A P 2009 Mitigation of impervious surface hydrology using bioretention in North Carolina and Maryland Journal of Hydrologic Engineering 14 4 407 Line D E and Hunt W F 2009 Performance of a bioretention area and a level spreader grass filter strip at two highway sites in North Carolina Journal of Irrigation and Drainage Engineering 135 2 217 224 Line D E G D Jennings M B Shaffer J Calabria and W F Hunt 2008 Evaluating the Effectiveness of Two Stormwater Wetlands in North Carolina Transactions of the ASABE 51 2 521 528 31 Line D E N M White D L Osmond G D Jennings and C B Mojonnier 2002 Pollutant export from various land uses in the Upper Neuse River Basin Water Environment Research 74 1 100 108 Mallin M A S H Ensign T L Wheeler and D B Mayes 2002 Pollutant e
48. umn 2 This section gives several lot size options including 2 1 and 2 acre lots as well as multi family and townhome lots If the site conforms to one of these specific lot sizes the appropriate area may be entered in the gray shaded cells next to the appropriate land use Average percent impervious values and representative TN and TP concentrations for these lot sizes are built in to the JESLAT The method by which these values were determined is discussed in Part Il of this document If the site s lot sizes fall between the given lot sizes users may use the Custom Lot Size option To do so the user will enter the lot size for the development in the gray shaded cell in the Custom Lot Size column This value must fall between acre and 2 acres as the JLSLAT linearly interpolates the percent imperviousness and representative pollutant concentrations from the given lot sizes If the values fall outside this range or the user prefers or is required to report individual residential land uses within a development Part B of Column 2 should be used Part B lists out all types of land uses that may be found within a residential area and allows the user to enter the total number of acres of each land use present for the site of interest To avoid inaccurate results do NOT list out individual land uses in Part B within an area already described by lot size in Part A When using Part A of Column 2 to enter land use area infor
49. w ft BMPyrem ECinftow VOlUMeintiow 6 2297E 5 MasSout ECinflow VOlUMEinfiow 6 2297E 5 100 5 where ECintiow event median concentration for inflow mg L and Volume inflow Volume of water entering the BMP ft 27 There are some assumptions regarding this BMP efficiency metric 1 The effluent concentration is the median value of the concentrations exiting the BMP This metric does not take into account maximum or minimum concentrations and the representative EC does not vary with storm size or intensity 2 3 volume 4 Due to the nature of the metric the pollutant removal is controlled primarily by the This metric assumes the BMP is designed and constructed appropriately to capture and treat the first flush 1 inch for non CAMA locations 1 5 inch for CAMA locations The outflow EC is not dependent upon the inflow EC nor the inflow volume or outflow volume reduction provided by the BMP thus BMPs with higher volume reductions will have greater pollutant removal capabilities Determining BMP Median Effluent Concentrations A literature review was conducted to establish representative effluent concentrations for the BMPs in the JLSLAT Only peer reviewed literature was considered in this endeavor and only studies conducted in the Mid Atlantic states were used Georgia South Carolina North Carolina Virginia Maryland Outliers were excluded from data sets for each BMP t
50. y BMP as all of the rainfall that falls on the BMP enters the BMP The areas entered in a given land use MUST be less than or equal to the total area of that land use entered in the Watershed Characteristics worksheet To ensure this is the case there is a built in check in the worksheet If the user enters a value that exceeds the total available area of that particular land use the model displays an error message However in order for this check to function users must press the Enter key on the keyboard after entering the land use area clicking on a different cell will NOT trigger the check to occur The two columns to the right of the Catchment 6 area show the user how many acres of a given land use are available and how many are currently being treated The two rows below the grey shaded cells shows how many total acres are being treated by each BMP as well as by the series Remember that entering land areas for BMPs 2 or 3 in a series indicate that the BMP is accepting runoff from this area IN ADDITION TO the outflow from the previous BMP Not all of the watershed must be treated by a BMP the Jordan Lake Nutrient Strategy requirements will dictate how much treatment needs to be included Two other checks have been incorporated into the BMP Characteristics worksheet The first displays a warning message if a BMP is specified but there are no land areas entered This prevents the user from inadvertently erasing land use areas
51. ype and the median of the reported effluent concentrations was calculated Green roofs permeable pavement and water harvesting effluent values were assumed to be the same as the concentrations entering the BMP These results are shown in Table 13 Table 13 Median effluent concentrations assigned to BMPs BMPs TN EMC mg L TP EMC mg L Bioretention with IWS 0 95 0 12 Bioretention without IWS 1 00 0 12 Dry Detention Pond 1 20 0 20 Grassed Swale 1 21 0 26 Green Roof 1 08 0 15 Level Spreader Filter Strip 1 20 0 15 Permeable Pavement 1 44 0 39 Sand Filter 0 92 0 14 Water Harvesting 1 08 0 15 Wet Detention Pond 1 01 0 11 Wetland 1 08 0 12 f replacing commercial parking lot value is 0 16 mg L Volume reductions were an integral part of calculating effluent loads from a given BMP The volume reduction values assigned to each BMP type varied based upon the physiographic region These assignments are displayed in Table 14 and are expressed as percent of the inflow volume 28 Table 14 Fate of BMP inflow in terms of treated outflow overflow and loss via ET infiltration Treated Outflow Bypass Overflow Volume Reduction jadis CAMA Region Bioretention with IWS 10 10 80 Bioretention without IWS 40 10 50 Dry Detention Pond 80 10 10 Grassed Swale 90 0 10 Green Roof
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