FALL. El Dorado County Baseline Load Update

Transcription

1 FALL El Dorado County Baseline Load Update 2016 FINAL REVISED BASELINE LOAD REPORT 16

2 Prepared for: Prepared by: Funded by: F I N A L R E V I S E D B A S E L I N E L O A D R E P O R T

3 TABLE OF CONTENTS List of Acronyms... ii List of Tables... iii List of Attachments... iv Introduction... 1 Methodology... 2 Quality Assurance... 7 Summary Disclosure... 8 Results References EL DORADO COUNTY BASELINE LOAD UPDATE i

4 LIST OF ACRONYMS BPC Baseline Planning Catchment BMP Best Management Practice CHP Constant Head Permeameter CICU Commercial-Institutional-Communications-Utilities County El Dorado County DCIA Directly Connected Impervious Area FSP Fine Sediment Particles MFR Multi-Family Residential NHC Northwest Hydraulic Consultants NPDES National Pollutant Discharge Elimination System NRCS Natural Resources Conservation Service PLRM Pollutant Load Reduction Model SFR Single-Family Residential TMDL Total Maximum Daily Load UPC Urban Planning Catchment Lahontan Lahontan Regional Water Quality Control Board LCCP Lake Clarity Crediting Program TP Total Phosphorus TN Total Nitrogen EL DORADO COUNTY BASELINE LOAD UPDATE ii

5 LIST OF TABLES Table 1: Baseline Parcel BMP implementation rates (from the LCCPv2) Table 2: PLRMv1 and PLRMv2 baseline pollutant load estimate comparison Table 3: Impervious area changes from PLRMv1 to PLRMv2 categorized by land use EL DORADO COUNTY BASELINE LOAD UPDATE iii

6 LIST OF ATTACHMENTS Figures: El Dorado County Baseline Pollutant Load Maps Attachment 1: TRCD Stormwater Resource Plan Baseline Modeling Support: Baseline modeling approach summary Attachment 2: DCIA Justifications Attachment 3: Catchment Connectivity Justifications Attachment 4: Catchment Pollutant Loading Attachment 5: PLRM Project Files (Provided Digitally) EL DORADO COUNTY BASELINE LOAD UPDATE iv

7 INTRODUCTION In 2009, the Lahontan Regional Water Quality Control Board (Lahontan) and Nevada Division of Environmental Protection (NDEP) completed a Total Maximum Daily Load (TMDL) analysis for Lake Tahoe i. The analysis determined fine sediment particles (FSP), defined as particles less than 16 micrometers in diameter, generated from the urban areas surrounding Lake Tahoe were the primary pollutant affecting Lake Tahoe s clarity. As a result, Lahontan completed a Basin Plan Amendment and adopted an updated Municipal National Pollutant Discharge Elimination System (NPDES) permit. Local California jurisdictions are responsible for meeting the FSP pollutant load reduction targets defined by the NPDES permit and focusing water quality improvement efforts toward preventing FSP from entering Lake Tahoe. In March 2011, Lahontan issued a Order requiring local California jurisdictions to complete a Baseline Pollutant Load Estimate Report (Report) to include the calculation of annual pollutant loading estimates for pollutants of concern fine sediment particles (FSP), total nitrogen (TN), and total phosphorus (TP) under baseline (pre-2004) conditions. El Dorado County (the County) estimated these annual baseline loads by modeling catchments using the first version of the Pollutant Load Reduction Model (PLRMv1) software. The County Report ii contained the PLRMv1 model baseline pollutant load estimation results and acted as the benchmark for meeting Lake Tahoe TMDL compliance requirements in the first NPDES permit term ( ). The 2011 baseline load estimate is now considered outdated by Lahontan and the County due to updates to PLRMv1 software (version 2 was adopted by Lahontan in August 2015), incorporation of a new catchment connectivity estimation methodology, and inclusion of refined model input data (e.g., updated land use and road condition scores). In 2016, the County used the second version of the Pollutant Load Reduction Model (PLRMv2.1) to complete an updated baseline load estimate for FSP, TN, and TP. The following narrative describes the modeling parameters, assumptions, quality assurance process, and results of the baseline load estimation update. The modeling results created using these criteria will be the new benchmark for meeting Lake Tahoe TMDL compliance requirements in the second NPDES permit term ( ). EL DORADO COUNTY BASELINE LOAD UPDATE 1

8 METHODOLOGY The County completed an update to modeled baseline pollutant load estimates following the general approach and considerations outlined in the TRCD Stormwater Resource Plan Baseline Modeling Support: Baseline modeling approach summary iii (Approach Summary) appended to this document as Attachment 1. Modeling was performed using PLRMv2. The Approach Summary prescribes the inclusion of a summary disclosure table, which includes documentation of catchments containing GIS modifications, best management practices (BMPs) modeled, and whether parcel scale directly connected impervious area (DCIA) was assessed. This summary disclosure table is included in the Summary Disclosure section. Catchment Boundaries The County defined the boundaries of delineated catchments to include all County rights-ofway and urban area within the Tahoe Basin (338 total catchments) as part of the 2009 Pollutant Load Reduction Strategy iv. The catchments were delineated using a combination of USGS defined watershed boundaries, information contained in the County s Existing Conditions and Analysis Memorandums (ECAMs), and field observations. While developing inputs for the PLRM as part of this baseline remodeling effort, the catchments were refined by the County. Refinements included modifying boundaries to remove urban land outside of the County s jurisdiction and control (e.g., Meek s Bay Marina, State Parks Land, and Caltrans). The County kept non-urban land use areas within hydrologically delineated catchments containing urban areas to expedite the modeling process. Determination of urban versus nonurban area was based on the 2011 GIS Land Use layer in the PLRMv2 download package. Urban and non-urban areas were defined by individual land uses: Urban: Single-Family Residential (SFR), Multi-Family Residential (MFR), Commercial/ Institutional / Communications / Utilities (CICU), and Transportation (Paved and Unpaved Roads) Non-Urban: Vegetated (includes Unimpacted, Turf, Recreational, Ski Areas, Burned, and Harvested) Hydrologic volume and pollutant load from non-urban land uses modeled in PLRMv2 is negligible compared to urban sources. Therefore, despite keeping the non-urban land uses within modeled catchments, this approach is expected to have produced results comparable to catchments delineated at the urban boundary extent. The County aggregated the original 338 catchments into 96 PLRM catchments that were explicitly modeled using PLRMv2 for this effort. The term PLRM catchment is used interchangeably with the term Urban Planning Catchment (UPC) in this report. To streamline the organization of the models and presentation of results, multiple PLRM catchments or UPCs were included in individual PLRM models to define larger Baseline Planning Catchments (BPC). All PLRM catchments comprising a BPC share geographical proximity and have the same post outfall catchment connectivity. The use of the term BPC in this report is synonymous with the term Urban Catchment, as defined by the Lake Tahoe Clarity Crediting Handbook version 2 v. A total of 24 BPCs were developed by the County, as displayed in the figures within the Results section. EL DORADO COUNTY BASELINE LOAD UPDATE 2

9 Hydrometeorology The County used Basin-wide precipitation and temperature input data included in the PLRMv2 download package. The data has 800-meter grid resolution with each cell representing a 64-hectare (158-acre) area. Some UPCs intersected more than one grid cell. In these instances, the County selected a cell intersecting the urban area of the catchment that most closely matched average annual precipitation across the catchment. This approach follows the accepted methodology for models intersecting multiple met grids per the Approach Summary described in Attachment 1. Slope The County used an average slope of five percent for all catchments. Slope is not a sensitive input parameter in PLRM, which, particularly at the baseline modeling scale, allows for approximation of the input value. The five percent slope was deemed typical for urbanized areas within the County. Land use The County used the land use shapefile provided in the PLRMv2 download package to develop land use input data. Minor land use corrections we made in BPC-20 as documented in the Summary Disclosure section. Otherwise, no adjustments were made to the land use input data generated by the land use shapefile provided with PLRMv2. Ownership Within certain areas of the County, comingling of flows with Placer County (Placer), Caltrans, and the City of South Lake Tahoe (City) occurs. However, each jurisdiction is only responsible for the pollutant load generated within their boundaries, with the exception of some land uses such as State Parks lands, Federal lands, and Marina areas. In order to focus the modeling effort solely on the County baseline load, areas within the boundaries of the City, Placer, Caltrans, State Parks Land, and Meeks Bay Marina were removed from the modeling analysis. Soil Type The County used the soil type shapefile provided in the PLRMv2 download package. The soil data were taken from the 2006 Tahoe Basin Soil Survey completed by the Natural Resources Conservation Service (NRCS) vi. The PLRMv2 GIS tool was used to extract the soils data within each of the defined PLRM catchments. Road Condition The County used the data provided in the PLRMv2 download package as a starting point for determination of road condition scores. The County originally modified the road risk shapefile data during the previous PLRMv1 modeling effort based on categorization of traffic and abrasive application levels on roads. The modifications matched the road risk determination process outlined in the PLRMv1 User s Manual vii. Modifications made by the County to better define road risk within its jurisdiction were not incorporated into the road risk shapefile NHC used to develop the PLRMv2 road condition scores (aka the default road condition scores shapefile included in the PLRMv2 download EL DORADO COUNTY BASELINE LOAD UPDATE 3

10 package). Therefore, the County modified the PLRMv2 road condition scores GIS data to reflect the road risk shapefile used for the PLRMv1 baseline modeling effort. PLRM catchments containing modified road condition scores are documented in the Summary Disclosure section and the County-modified road condition scores shapefile is available upon request. Road Shoulder Condition The County used the data included in the PLRMv2 download package as a starting point for determination of road shoulder conditions. The road shoulder condition file is based on 2011 data and required adjustment for assessing baseline (2004) road shoulder conditions. Changes were made to road shoulder conditions in this shapefile based on previous ECAMs, photographic evidence, and in-house knowledge of 2004 conditions. PLRM catchments containing GIS modifications are documented in the Summary Disclosure section and the County-modified road shoulder condition shapefile is available upon request. Road Shoulder Connectivity The County used the data provided in the PLRMv2 download package as a starting point for determination of road shoulder connectivity. This shapefile included data classifying each road shoulder within the Tahoe Basin as Directly Connected Impervious Area (DCIA) or Indirectly Connected Impervious Area (ICIA) viii : DCIA: Impervious surfaces draining to a conveyance system. ICIA: Impervious surfaces draining to pervious surfaces which promote infiltration, distribution and energy dissipation, or storage before entering a conveyance system. Changes were made to this layer based on previous ECAMs, photographic evidence, and inhouse knowledge of the pre-2004 condition. PLRM catchments containing modified road shoulder connectivity are documented in the Summary Disclosure section and the Countymodified road shoulder connectivity shapefile is available upon request. Parcel Scale DCIA The County estimated parcel scale DCIA percentage values within each PLRM catchment. The estimation method matched criteria contained within the Approach Summary. The criteria include expected DCIA percentage value ranges (DCIA) and calculated Basin-wide average percent impervious areas for SFR, MFR, and CICU land uses. For each catchment, the expected DCIA was compared to the Basin-wide average impervious area for each land use to determine a preliminary estimate of DCIA. GIS and field assessments were then used to verify and refine these percentages. Each percentage was rounded to the nearest 10 percent in accordance with the methodology outlined in the Approach Summary. This evaluation was conducted on all catchments, as documented in the Summary Disclosure section. The justification for each estimated parcel DCIA percentage value is provided in Attachment 2. EL DORADO COUNTY BASELINE LOAD UPDATE 4

11 Parcel BMPs The County used baseline parcel Best Management Practice (BMP) implementation rates outlined in the Lake Clarity Crediting Program Handbook version 2 ix (Table 1). These rates have been standardized for baseline model development. The County did not make any adjustments to these numbers for catchment modeling. Table 1: Baseline Parcel BMP implementation rates (from the LCCPv2). Baseline Parcel BMP Implementation Single-Family Residential 7% Multi-Family Residential 19% Commercial/Institutional/Communications/Utilities 5% Vegetated Turf 100% All other land uses 0% Catchment Connectivity The County estimated connectivity between catchment outfalls and surface water (i.e., Lake Tahoe or a perennial tributary feeding Lake Tahoe). Outfalls with little or no down gradient pervious area intercepting flow before entering surface water were assumed to have 100 percent connectivity. All catchments with downstream areas consisting of either meadow areas expected to induce flow dispersion and retention or distributed drainage paths were analyzed for partial catchment connectivity using the criteria and recommended methods described in the Approach Summary. A group of partially connected PLRM catchments or UPCs were selected for detailed catchment connectivity modeling in SWMM as the basis for estimating connectivity of catchments with similar characteristics. The catchments modeled represented the spectrum of typical downstream conditions found in the County. The results of these models were further evaluated using GIS analysis, field assessment, and best professional judgement for overall accuracy before rounding to the nearest 10 percent per the criteria within the Approach Summary. The finalized catchment connectivity estimations for were used to extrapolate catchment connectivity estimates for catchments considered partially connected but not explicitly modeled in SWMM for catchment connectivity. Extrapolation was based on comparing downstream drainage characteristics and catchment urban area. A summary table of modeled and extrapolated catchment connectivity estimates is contained in Attachment 3. Treatment BMPs The County used its treatment BMP database to account for 2004 treatment capacity of baseline treatment BMPs. The County calculated the total treatment volumes from all treatment facilities (e.g., infiltration basins), including estimating the surface area for infiltration. This data was summed for each catchment and was modeled in PLRMv2. In the models with treatment facilities, the County needed to account for infiltration from all of its treatment BMPs installed by However, infiltration proved to be a difficult parameter to estimate on an average annual basis. The County has used the Constant Head Permeameter (CHP) developed by NRCS x to measure infiltration rates for past projects. The measured values have ranged from less than 0.05 inches per hour to greater than 20 inches per hour which represent the infiltration rate and soil condition for the time and date of the EL DORADO COUNTY BASELINE LOAD UPDATE 5

12 test. In 2016, the County measured CHP rates for all baseline basins with the results ranging from 0.2 inches per hour to greater than 20 inches per hour. The measurements greater than 1.5 inches per hour exceed the recommended range given for infiltration basins the PLRMv2 xi. Given this limitation, the County assumed an average annual infiltration rate based on the PLRMv2 default value of 0.4 inches per hour for all basins. EL DORADO COUNTY BASELINE LOAD UPDATE 6

13 QUALITY ASSURANCE NHC reviewed the County s PLRMv2 models for quality assurance purposes. The review was intended to disclose any deviations from the model development approach expectations contained in the Approach Summary. The intended result of the quality assurance was to propagate modeling approach consistency across Placer County, El Dorado County, and City of South Lake Tahoe models. Model quality assurance focused on the key approach topics described in the Approach Summary. Considerations included model boundaries, parcel-scale DCIA, edits to default shapefiles, stormwater treatment BMPs, and catchment connectivity. The Summary Disclosure table of catchment model input parameters was created by NHC during the quality assurance process. The catchments in this list have all been quality assured by NHC. Any questions or comments were catalogued and discussed with the County. Secondary quality assurance reviews were conducted as needed to satisfy any remaining questions. The quality assurance process completed for each model was as follows: 1. Open workspace in PLRM 2. Iterate through all the projects and scenarios in the workspace and enter pertinent information into the Summary Disclosure table a. The folder pathname b. The PLRM project and scenario name c. The catchment information for each catchment in the scenario i. Name ii. Any downstream BMP treatment facility (name and type) iii. Use of distributed facilities for road drainage iv. Modification to default GIS files v. Adjustment of parcel DCIA to match an estimated value d. Notes to each catchment based on model inputs 3. Review and address catchment notes with jurisdictional modeler 4. Review and discuss method and assumptions for catchment connectivity a. Assessing 100 percent or partial connectivity b. Choosing drainage path or treatment basin for partially connected catchments c. Choosing input values for modeling the downstream treatment occurring below the catchment outfall in the Storm Water Management Model (SWMM) d. Interpreting the differences in loading between the catchment outfall and the discharge point into the nearest waterbody e. Reviewing best professional judgment adjustments to the model results and consideration of hydrological connectivity in conjunction with the pollutant connectivity EL DORADO COUNTY BASELINE LOAD UPDATE 7

14 SUMMARY DISCLOSURE Folder Pathname PLRM Name Catchment Name Distributed Facilities GIS Modifications Treatment BMPs Parcel DCIA BPC01\Project1\Scenario1 BPC01\BaselineBPC01 plrmupc01 Road Shoulder; Road Connectivity IB1 (Infiltration Basin) Yes BPC01\Project1\Scenario1 BPC01\BaselineBPC01 plrmupc02 IB2 (Infiltration Basin) Yes BPC01\Project1\Scenario1 BPC01\BaselineBPC01 plrmupc03 Road Shoulder IB3 (Infiltration Basin) Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc04 Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc06 Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc07 Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc08 Road Shoulder; Road Connectivity IB8 (Infiltration Basin) Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc09 Road Connectivity Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc0a IB44 (Wet Basin) Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc0c Road Shoulder; Road Connectivity Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc10 Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc11 Road Shoulder; Road Connectivity IB11 (Infiltration Basin) Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc12 Road Connectivity IB12 (Infiltration Basin) Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc13 Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc14 Road Shoulder; Road Connectivity IB14 (Infiltration Basin) Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc15 IB15 (Infiltration Basin) Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc16 Yes BPC02\Project2\Scenario1 BPC02\BaselineBPC02 plrmupc17 Yes BPC03\Project3\Scenario1 BPC03\BaselineBPC03 plrmupc19 Road Shoulder IB19 (Infiltration Basin) Yes BPC03\Project3\Scenario1 BPC03\BaselineBPC03 plrmupc20 Yes BPC03\Project3\Scenario1 BPC03\BaselineBPC03 plrmupc21 IB21 (Infiltration Basin) Yes BPC24\Project5\Scenario1 BPC24\BaselineBPC24 plrmupc22 Road Connectivity Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc23 Road Shoulder IB23 (Infiltration Basin) Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc23laketahoeblvd Road Condition IB23 (Infiltration Basin) Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc24 Road Shoulder; Road Connectivity Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc25 Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc25laketahoeblvd Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc26 Road Connectivity Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc26laketahoeblvd Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc27laketahoeblvd Road Condition Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc29 IB29 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc30 Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc31 IB31 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc32 IB32 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc33 IB33 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc34 Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc35 Road Condition IB35 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc35pioneer Road Condition IB35 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc36pioneer Road Condition IB36 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc37 Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc38 Road Shoulder; Road Connectivity Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc39 Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc40 Road Shoulder; Road Connectivity IB40 (Infiltration Basin) Yes BPC05\Project2\Scenario1 BPC05\BaselineBPC05 plrmupc40pioneer Road Condition IB40 (Infiltration Basin) Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc41 Yes EL DORADO COUNTY BASELINE LOAD UPDATE 8

15 Folder Pathname PLRM Name Catchment Name Distributed Facilities GIS Modifications Treatment BMPs Parcel DCIA BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc42 Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc43 Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc44 Road Shoulder IB44 (Wet Basin) Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc44pioneer Road Condition IB44 (Wet Basin) Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc45 Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc46 Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc47 Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc48 Road Shoulder Yes BPC06\Project3\Scenario1 BPC06\BaselineBPC06 plrmupc48pioneer Road Condition Yes BPC07\Project4\Scenario1 BPC07\BaselineBPC07 plrmupc49 Yes BPC07\Project4\Scenario1 BPC07\BaselineBPC07 plrmupc50 Yes BPC07\Project4\Scenario1 BPC07\BaselineBPC07 plrmupc51 Yes BPC07\Project4\Scenario1 BPC07\BaselineBPC07 plrmupc52 Yes BPC08\Project1\Scenario1 BPC08\BaselineBPC08 plrmupc53pioneer Road Condition Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc54pioneer Road Condition; Road Shoulder Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc55 Road Condition; Road Shoulder Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc56 Road Condition; Road Shoulder IB56 (Infiltration Basin) Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc57 Road Condition; Road Connectivity IB57 (Infiltration Basin) Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc58 Road Condition; Road Shoulder; Road Connectivity Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc59 Road Condition; Road Shoulder; Road Connectivity Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc60 Road Condition; Road Shoulder; Road Connectivity Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc60pioneer Road Condition; Road Shoulder; Road Connectivity Yes BPC10\Project1\Scenario1 BPC10\BaselineBPC10 plrmupc60washoandr Road Condition; Road Shoulder Yes BPC11\Project1\Scenario1 BPC11\BaselineBPC11 plrmupc61 Road Shoulder Yes BPC07\Project1\Scenario1 BPC07\BaselineBPC07 plrmupc62 Road Shoulder Yes BPC12\Project1\Scenario1 BPC12\BaselineBPC12 plrmupc63 Road Shoulder; Road Connectivity IB63 (Infiltration Basin) Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc64 Road Condition; Road Shoulder; Road Connectivity Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc64pioneer Road Condition; Road Shoulder Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc65 IB65 (Infiltration Basin) Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc65pioneer Road Condition IB65 (Infiltration Basin) Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc66 IB66 (Infiltration Basin) Yes BPC15\Project2\Scenario1 BPC15\BaselineBPC15 plrmupc68 Yes BPC18\Project6\Scenario1 BPC18\BaselineBPC10 plrmupc69 Road Shoulder; Road Connectivity Yes BPC15\Project2\Scenario1 BPC15\BaselineBPC15 plrmupc70 Road Condition; Road Shoulder; Road Connectivity IB70 (Infiltration Basin) Yes BPC15\Project2\Scenario1 BPC15\BaselineBPC15 plrmupc70pioneer Road Condition; Road Shoulder; Road Connectivity IB70 (Infiltration Basin) Yes BPC13\Project2\Scenario1 BPC13\BaselineBPC13 plrmupc71 Road Shoulder; Road Connectivity Yes BPC13\Project2\Scenario1 BPC13\BaselineBPC13 plrmupc71elksclubdr Road Condition Yes BPC14\Project2\Scenario1 BPC14\BaselineBPC14 plrmupc72 Road Shoulder; Road Connectivity IB72 (Infiltration Basin) Yes BPC14\Project2\Scenario1 BPC14\BaselineBPC14 plrmupc72elksclubdr Road Condition IB72 (Infiltration Basin) Yes BPC15\Project2\Scenario1 BPC15\BaselineBPC15 plrmupc73 Road Condition; Road Shoulder; Road Connectivity Yes BPC15\Project2\Scenario1 BPC15\BaselineBPC15 plrmupc73elksclubdr Road Condition Yes BPC16\Project1\Scenario1 BPC16\BaselineBPC16 plrmupc74ws258 Road Condition; Road Shoulder; Road Connectivity IB74 (Infiltration Basin) Yes BPC16\Project1\Scenario1 BPC16\BaselineBPC16 plrmupc74ws258apacheave Road Condition; Road Shoulder IB74 (Infiltration Basin) Yes BPC17\Project1\Scenario1 BPC17\BaselineBPC16 plrmupc74ws259 Road Condition Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc75 Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc75elksclubdr Road Condition Yes BPC09\Project1\Scenario1 BPC09\BaselineBPC09 plrmupc75pioneer Road Condition Yes BPC23\Project1\Scenario1 BPC23\BaselineBPC23 plrmupc76 Road Shoulder; Road Connectivity Yes EL DORADO COUNTY BASELINE LOAD UPDATE 9

16 Folder Pathname PLRM Name Catchment Name Distributed Facilities GIS Modifications Treatment BMPs Parcel DCIA BPC23\Project1\Scenario1 BPC23\BaselineBPC23 plrmupc76sawmillrd Road Condition Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc77 Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc77laketahoeblvd Road Condition Yes BPC04\Project1\Scenario1 BPC04\BaselineBPC04 plrmupc77sawmillrd Road Condition Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc78 Road Shoulder; Road Connectivity IB78 (Infiltration Basin) Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc78laketahoeblvd Road Condition IB78 (Infiltration Basin) Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc79 Road Shoulder; Road Connectivity Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc79laketahoeblvd Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc80 Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc80laketahoeblvd Road Condition; Yes BPC21\Project10\Scenario1 BPC21BaselineBPC21 plrmupc81 Road Shoulder; Road Connectivity IB81 (Infiltration Basin) Yes BPC21\Project10\Scenario2 BPC21BaselineBPC21 plrmupc81nuppertruckee Road Condition IB81 (Infiltration Basin) Yes BPC21\Project10\Scenario3 BPC21BaselineBPC21 plrmupc82 Road Shoulder; Road Connectivity IB82 (Infiltration Basin) Yes BPC21\Project10\Scenario4 BPC21BaselineBPC21 plrmupc82nuppertruckee Road Condition IB82 (Infiltration Basin) Yes BPC21\Project10\Scenario5 BPC21BaselineBPC21 plrmupc83 Road Shoulder; Road Connectivity IB83 (Infiltration Basin) Yes BPC21\Project10\Scenario6 BPC21BaselineBPC21 plrmupc83nuppertruckee Road Condition IB83 (Infiltration Basin) Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc84 Road Shoulder; Road Connectivity IB84 (Infiltration Basin) Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc84nuppertruckee Road Condition IB84 (Infiltration Basin) Yes BPC22\Project7\Scenario1 BPC22\BaselineBPC22 plrmupc84laketahoeblvd Road Condition IB84 (Infiltration Basin) Yes BPC19\Project8\Scenario1 BPC19\BaselineBPC19 plrmupc85 Road Connectivity Yes BPC15\Project2\Scenario1 BPC15\BaselineBPC15 plrmupc86 Road Condition; Road Shoulder Yes BPC15\Project2\Scenario1 BPC15\BaselineBPC15 plrmupc86apacheave Road Condition Yes BPC19\Project8\Scenario1 BPC19\BaselineBPC19 plrmupc87 Yes BPC19\Project8\Scenario1 BPC19\BaselineBPC19 plrmupc88 Road Shoulder ib88 (Infiltration Basin) Yes BPC19\Project8\Scenario1 BPC19\BaselineBPC19 plrmupc89 Road Shoulder; Road Connectivity Yes BPC19\Project8\Scenario1 BPC19\BaselineBPC19 plrmupc90 Road Shoulder; Road Connectivity Yes BPC19\Project8\Scenario1 BPC19\BaselineBPC19 plrmupc90suppertruckee Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc91 Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc91suppertruckee Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc92 Road Shoulder; Road Connectivity: Reclassified Caltrans yard from MFR to CICU (0.43 acres) Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc92suppertruckee Road Condition Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc93 Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc93suppertruckee Road Condition Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc94 Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc94suppertruckee Road Condition Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc95 Yes BPC20\Project9\Scenario1 BPC20\BaselineBPC20 plrmupc95suppertruckee Road Condition Yes EL DORADO COUNTY BASELINE LOAD UPDATE 10

17 RESULTS The PLRMv2 modeling update estimated an increase in the total FSP pollutant load generated by urban runoff when compared to the PLRMv1 baseline pollutant load estimation xii. However, after adjusting for post outfall catchment connectivity, the County s final PLRMv2 FSP baseline pollutant load is less than the PLRMv1 baseline pollutant load. A comparison of pollutant load estimates is contained in Table 2: 1) previously modeled PLRMv1 baseline load without consideration for catchment connectivity, 2) PLRMv2 pollutant load prior to considerations of catchment connectivity, and 3) PLRMv2 baseline pollutant load adjusted to consider catchment connectivity. Table 2: PLRMv1 and PLRMv2 baseline pollutant load estimate comparison. Pollutant Load Total Area 1 Surface Runoff Pollutant Loading FSP TP TN (iteration) (ac) (ac-ft/yr) (lbs/yr) (#/yr) 2 (lbs/yr) (lbs/yr) PLRMv1 Baseline 19,738 1, , E+19 2,300 9,000 PLRMv2: without catchment connectivity 18, , E+19 1,980 7,000 PLRMv2 Baseline: with catchment connectivity 18, , E+19 1,170 4, Both Urban and Non-Urban land uses (as defined for the Lake Tahoe TMDL) were included in the total area. Upon further inspection of the total area during PLRMv2 modeling, some areas (State Parks, Meeks Bay Marina) were determined to be outside of County s authority, and were removed from the analysis Kg FSP = 1.1x10 14 particles FSP xiii The changes from PLRMv1 to PLRMv2 models results (lines one and two in Table 2) are a decrease in surface runoff, increase in FSP, and decreases in TP and TN. The decrease in surface runoff, TP, and TN correlates with a decrease in modeled impervious area and a reduction in total urban area modeled (e.g., removal of land area associated with State Parks and Meeks Bay Marina). The update from the PLRMv1 to PLRMv2 included a refined and more accurate land use layer for the Tahoe Basin using the 2010 TRPA LiDAR data, which resulted in changes to impervious area within the County as categorized in Table 3 by urban land use. Table 3: Impervious area changes from PLRMv1 to PLRMv2 categorized by land use. Impervious Area by Land Use Units SFR MFR CICU Roads Aggregate PLRMv1 (ac) PLRMv2 (ac) (ac) Change (as decrease) (%) 4% 54% -21% 20% 15% In PLRM, the MFR, CICU, and Roads land uses are the biggest sources of urban area runoff reaching the catchment outfall for two reasons: 1) impervious to pervious area ratios are typically high; and 2) DCIA to ICIA ratios are typically high. The reduction in surface runoff, TP, and TN reaching the catchment outfalls between PLRMv1 and PLRMv2 models primarily results from the 20 percent decrease in road impervious area. EL DORADO COUNTY BASELINE LOAD UPDATE 11

18 The increase in FSP pollutant loading reaching the catchment outfalls between PLRMv1 and PLRMv2 models is due to the translation of road risk (PLRMv1) to road condition score (PLRMv2), which resulted in roads being assigned, on average, higher characteristic runoff concentrations (CRCs) for FSP in the baseline condition. This is the expected cause of the increase in generated FSP in the PLRMv2 results. The final reported runoff volume and pollutant load numbers included consideration for post outfall catchment connectivity. The PLRMv1 reported numbers assume all catchments are fully connected to surface water. Adjustments made to consider catchment connectivity reduced the reported runoff volume and pollutant load to surface waters. The final total baseline pollutant loads decreased in this update when compared to reported values from the PLRMv1 modeling: approximately 26 percent for FSP, approximately 50 percent for TP, and approximately 54 percent for TN. EL DORADO COUNTY BASELINE LOAD UPDATE 12

19 REFERENCES i Lahontan Regional Water Quality Control Board (LRWQCB) and Nevada Division of Environmental Protection (NDEP) Final Lake Tahoe Total Maximum Daily Load. ii El Dorado County (EDC), Baseline Pollutant Load Estimate Report, September iii NHC, TRCD Stormwater Resource Plan-Baseline Modeling Support: Baseline modeling approach summary, September iv EDC, Pollutant Load Reduction Strategy, December 2009 v Lahontan Water Quality Control Board and Nevada Division of Environmental Protection. December Lake Clarity Crediting Program Handbook: for Lake Tahoe TMDL Implementation v2.1. Prepared by Environmental Incentives, LLC. South Lake Tahoe, CA. Pg A-4. vi United States Department of Agriculture, Natural Resources Conservation Service. 2007, Soil Survey of the Tahoe Basin Area. California and Nevada. Accessible online at: vii viii NHC, PLRM User s Manual, December Pg NHC, PLRM User s Manual, May Pg 67. ix Lahontan Water Quality Control Board and Nevada Division of Environmental Protection Lake Clarity Crediting Program Handbook: for Lake Tahoe TMDL Implementation v2.0. Prepared by Environmental Incentives, LLC. South Lake Tahoe, CA. Pg A-6. x National Resource Conservation District (NRCS), June Constant Head Permeameter (CHP) Construction and Implementation Guide. USDA, South Lake Tahoe Field Office. xi NHC, PLRM User s Manual, May Pg 76. xii El Dorado County (EDC), Baseline Pollutant Load Estimate Report, September EL DORADO COUNTY BASELINE LOAD UPDATE 13

20 FIGURES EL DORADO COUNTY BASELINE POLLUTANT LOAD MAPS

21 01 Idaho Oregon va Ne da _ ^ Utah 02 rn Arizona lifo Ca ia Location V U 89 N C a ev a lifo da rn ia U V V U 89 U V V U 88 V U BPC Number Miles 89 Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community Map Author: Cara Moore PLRM v2.1 Baseline Pollutant Load BPC Map Prepared for: Prepared by:

22 BPC01 Idaho Oregon va Ne da _ ^ rn Arizona lifo Ca TAHOMA MAP Utah BPC02 ia Location V U 89 N C a ev a lifo da rn ia BPC03 50 BPC05 BPC24 BPC07 BPC04 BPC22 BPC06 BPC12 BPC23 BPC10 BPC13 BPC14 PIONEER BPC17 TRAIL MAP BPC15 BPC21 BPC16 BPC20 MEYERS, SAWMILL, & TAHOE MT MAP 50 BPC19 V U 89 U V V U 88 V U FSP (lbs/acre/year) Miles 89 Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community Map Author: Cara Moore PLRM v2.1 Baseline Pollutant Load Overview Map Prepared for: Prepared by:

23 Idaho Oregon Utah va Ne 01 da _ ^ 02 BPC01 lifo Ca 03 rn ia Location BPC BPC BPC V U 89 Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, MilesAEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community Map Author: Cara Moore UPC Number FSP (lbs/acre/year) PLRM v2.1 Baseline Pollutant Load Tahoma Map Prepared for: Prepared by:

24 a BPC BPC07 52 BPC BPC V U 89 BPC07 BPC11 BPC BPC BPC BPC09 _ ^ 73 lifo Ca 74ws259 rn BPC17 ia BPC15 70 BPC16 Location 74ws Miles UPC Number FSP (lbs/acre/year) 0 da 72 va Ne 75 BPC14 Utah BPC13 71 Idaho Oregon Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community Map Author: Cara Moore PLRM v2.1 Baseline Pollutant Load Pioneer Trail Map Prepared for: Prepared by:

25 Idaho Oregon 51 Utah va Ne 26 BPC24 da _ ^ BPC04 22 lifo Ca 24 rn BPC ia 0c Location BPC BPC09 BPC BPC06 42 BPC06 BPC08 BPC07 BPC BPC12 60 V U BPC07 BPC13 BPC BPC BPC18 82 BPC21 74ws259 74ws258 BPC16 BPC BPC BPC19 92 V U Miles UPC Number FSP (lbs/acre/year) Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community Map Author: Cara Moore PLRM v2.1 Baseline Pollutant Load Meyers, Sawmill, Tahoe Mt Map Prepared for: Prepared by:

26 ATTACHMENT 1 TRCD STORMWATER RESOURCE PLAN BASELINE MODELING SUPPORT: BASELINE MODELING APPROACH SUMMARY

27 TRCD Stormwater Resource Plan-Baseline Modeling Support Baseline modeling approach summary October 2016 PURPOSE The following memorandum contains a summary of guidelines for baseline pollutant load development using version 2 of the Pollutant Load Reduction Model (PLRM). This document was created as part of the TRCD s Stormwater Resource Plan Development Project. The guidelines represent a combined effort by the development team: California urban jurisdictions (Placer County, El Dorado County, and the City of South Lake Tahoe), TRCD, Lahontan RWQCB, and NHC. The final product is intended to provide consistent baseline modeling approach criteria for California urban jurisdictions in the Tahoe Basin. Approaches employed by each jurisdiction fit a consistency governed by the criteria outlined within this document. The consistency in approach methodologies is expected to help streamline model development (California urban jurisdictions), review (California TMDL program manager), and project benefit comparison (project funding agencies). The guidelines were developed for use by the California urban jurisdictions and TRCD (assisting the jurisdictions). Other users (e.g., Nevada urban jurisdictions and NTCD) may choose to use the guidelines contained in this approach, as well. However, only feedback from the California TMDL program manager has been incorporated into this memorandum. KEY APPROACH TOPICS This document has been split into a list of key approach topics to address when creating baseline models in PLRM. The entire model development process is not contained within this memorandum. Each key topic was chosen based on having some or all of the following effects: communicating model inputs or outputs and generating or reducing pollutant load. Other model input factors and parameters also have significant impacts on pollutant estimations, but those should be automatically generated as catchment attributes using the PLRM GIS tool and shapefiles. Users should be familiar with creation of models in PLRM before applying this guidance. The topics covered focus on criteria and suggested methods to attain the goal of a consistent baseline modeling approach across California urban jurisdictions. Each topic within the checklist (below) is hyperlinked to the corresponding topic section and users may consider using the checklist to track their internal quality assurance process when creating each baseline model. Checklist of key approach topics 1. Managing files 2. Determining model boundaries 3. Estimating parcel-scale DCIA 4. Editing default shapefiles 5. Representing stormwater treatment BMPs 6. Estimating catchment connectivity 7. Annotating model input parameters TRCD Stormwater Resources Plan Baseline Modeling Support PAGE 1

28 1. MANAGING FILES 1.1. Concept The development team anticipates each user will apply a file management method best suited to their jurisdiction or client. Additionally, users among the jurisdictions will change during the course of the Lake Tahoe TMDL program implementation timeline. Given this reality, as a user, consider the transferability of each model and associated data to other users when developing a file management structure. File management structures are expected to vary by user with the following criteria considered to help ease navigation Criteria Recommended Folder Structure A diagram of the recommended folder structure is shown in Figure 1.1. Appropriate names should be filled into the bracketed text. Inclusion of at least one readme file is recommended. The file should be located within the primary PLRM files directory to ensure any future user can easily find it. The contents of the readme file should include an explanation of contents within each folder and subfolder. [Root Directory] [Jurisdiction Name] Baseline Workspace GIS ReadMe (File) Project[X] XML Baseline Default Scenario1 Figure 1.1 Illustration of the recommended file management for baseline models Organizing Files The PLRM installation package includes default GIS shapefiles. Users may need to modify these default shapefiles based on their own evaluation of their jurisdictional baseline conditions and quality assurance review. Users should make a copy of a default shapefile before modifying it. After modification, final baseline shapefiles should be kept separated from the default shapefiles to minimize future confusion and to allow for comparison. Users may modify specific shapefiles for individual projects or scenarios. Similarly, users may create xml output files from the PLRM GIS tool for specific projects or groups of catchments. Consistent naming conventions for crosslinking these files is recommended. Implementation of this concept could be TRCD Stormwater Resources Plan Baseline Modeling Support PAGE 2

29 through use of a matching suffix or prefix. Figure 1.2 provides a screenshot example of the recommended file management structure illustrated in Figure 1.1 for baseline model development. Figure 1.2 Example of the suggested file management for baseline models TRCD Stormwater Resources Plan Baseline Modeling Support PAGE 3

30 2. DETERMINING MODEL BOUNDARIES 2.1. Concept This topic considers possible conditions affecting modification of previously delineated catchments when used as model inputs. For example, a user may combine several delineated catchments into one model to reduce the total number of baseline models for the jurisdiction or a user may remove Caltrans right-of-way area located within a delineated catchment from the modeled catchment Criteria Caltrans Right-of-Way Urban jurisdictional catchments may contain Caltrans right-of-way. Caltrans is responsible for pollutants and runoff generated within this area; therefore, users should remove Caltrans right-of-way from the urban jurisdiction s catchment shapefile before modeling PLRM. Removal of the Caltrans area from catchments may create multiple polygon features with the same catchment attributes. Users should merge any separated catchment polygons into the same GIS polygon feature as separate parts, as shown in Figure 2.1. Figure 2.1 Example of catchments split into multiple parts of a single polygon feature by the Caltrans right-of-way Stormwater Routing The internal and external routing of stormwater runoff should be considered when delineating catchments in GIS and grouping those catchments in PLRM models. Delineating a catchment should include consideration of local surface topography and the stormwater infrastructure. Grouping catchment should be based on the expected catchment connectivity to Lake Tahoe. All catchments in any given model must have the same catchment connectivity to properly assess pollutant loading estimates. Details on how to estimate catchment connectivity are contained within Section 6. TRCD Stormwater Resources Plan Baseline Modeling Support PAGE 4

31 Hydrometeorological Data MetGrid files Users should determine which PLRM meteorological grids, if more than one, are intersected by catchment(s) within the model. Models with multiple catchments should be assigned MetGrids_PLRM.kml MetGrid_Precip.kml the meteorological grid most representative of the average Notes: Double click to open each file. annual precipitation rate within their model. Users can open the PLRM meteorological grid files provided within this document in Google Earth or other kmz file compatible software to determine the most appropriate meteorological grid based on this guidance. TRCD Stormwater Resources Plan Baseline Modeling Support PAGE 5

32 3. ESTIMATING PARCEL-SCALE DCIA 3.1. Concept Urban parcel land uses in PLRM are defined to include commercial land uses (CICU), single family residential (SFR), and multi-family residential (MFR). Parcel-scale directly connected impervious area (DCIA) is one of the few primary model inputs not automated by the PLRM GIS processing tool. PLRM catchments automatically default to 50 percent parcel DCIA values (Figure 3.1). Users must determine and adjust (as needed) input parcel-scale DCIA values in catchments with urban parcel land uses to reflect the estimated baseline conditions and avoid misestimating parcel loading. Completion of this step should be communicated to the Lake Tahoe TMDL program manager using the summary table described in Section 7. Figure 3.1 Default parcel DCIA values requiring assessment and manual input 3.2. Criteria Users must change DCIA percentages for urban parcel land uses (SFR, MFR, and CICU) in PLRM models. The attached DCIA assessment workbook can be used when estimating DCIA percentage for each urban parcel land use. The workbook processes the PLRM GIS tool output xml file into a summary table of catchment urban parcel land uses. Each catchment urban parcel land use is assigned attributes after processing the xml file: DCIA assessment workbook DCIA_Assessment.xl sm Notes: 1. Double-click to open the file 2. Enable macros when prompted 3. Read instructions on the ReadMe worksheet 1. The calculated impervious area percentage 2. The qualitative assessment of the impervious area relative to the basin-wide average (see Table 3.1 for basin-wide impervious area averages listed by urban parcel land use) 3. A typical expected DCIA percentage value for that land use type (see the Typical column in Table 3.1) TRCD Stormwater Resources Plan Baseline Modeling Support PAGE 6

33 Table 3.1 Expected ranges for parcel DCIA percentages and the calculated basin-wide impervious area percentage for each urban parcel land use DCIA Impervious Area Land Use Low Typical High Basin-wide SFR 10% 30% 50% 17% MFR 30% 50% 70% 25% CICU 50% 70% 90% 37% The land use attributes contained within the DCIA assessment workbook (after processing) are expected to be used as a starting point for final estimations of urban parcel land use DCIA values within each catchment modeled in PLRM. The typical DCIA percentage value for each land use type is an estimated value expected to correlate to the basin-wide average impervious area for that land use. The qualitative assessment of catchment impervious area relative to the basin-wide average helps inform users whether to adjust the model s DCIA percentage for each land use up (based on assessment of above typical ) or down (based on assessment of below typical ). Final estimated DCIA percentage values for each land use are expected to typically fall between the numbers contained in the Low and High columns shown in Table 3.1. If the user estimates a DCIA percentage value outside this range, then the user should report a justification for determination of that value. Users are expected to fulfill the following criteria when estimating DCIA percentage and justifying any values outside the expected range for each land use: Consider connectivity to the adjacent right-of-way (e.g., driveway slopes, roof drainage to driveway or parking lot) Consider land use connectivity to the outfall (i.e., does the land use flow to roads with high or low connectivity to the outfall?) Conduct a limited amount of field work including in-person observation of sample catchment sections Approximate estimates to the nearest 10 percent (e.g., 20 percent, 60 percent) TRCD Stormwater Resources Plan Baseline Modeling Support PAGE 7