Monitoring Project. Status of the UNRBA Monitoring and Credits Projects 3/28/2016. WRRI Annual Conference March 17 & 18, 2016

Transcription

1 Status of the UNRBA Monitoring and Credits Projects WRRI Annual Conference March 17 & 18, 2016 Alix Matos, PE Monitoring Project 1

2 Objectives of the UNRBA Monitoring Program Revise lake response modeling Improve the model with additional data Recalibrate/validate Recalculate the nutrient load reduction targets Support alternative regulatory options as needed Link water quality to designated uses Identify sources of nutrients and carbon in the watershed Routine Monitoring Component 20 upland stations sampled monthly at jurisdictional boundaries Field parameters (temperature, specific conductance, DO, ph) Nutrients (nitrate plus nitrite, ammonia, total phosphorus, Total Kjeldahl Nitrogen) Total organic carbon and total suspended solids 18 lake loading stations 5 sampled twice monthly and 13 sampled monthly Same parameters as upland stations plus Dissolved organic carbon, total soluble phosphorus, orthophosphate, chlorophyll a, color, UV absorbance, and 5-day carbonaceous biochemical oxygen demand 2

3 Special Studies Address Specific Questions: How accurate are tributary loading estimates during storm events? 3

4 Special Studies Address Specific Questions How does water quality in stagnant, wetland areas change with flow? Special Studies Address Specific Questions What is the potential for the lake sediments to release nutrients into the water column? 4

5 Special Studies Address Specific Questions How do the bridge constrictions across the lake affect the hydrodynamics and transport of material? Special Studies Address Specific Questions Does historic light extinction data support the sampling methodologies in Falls Lake? 5

6 Nutrient Credits Project Objectives of the UNRBA Nutrient Credits Project Develop trapping and delivery factors for subwatersheds in the Falls Lake watershed Develop nutrient credits for practices or design variants to be used toward compliance with the Falls Rules Develop a tool to track progress towards compliance with the Falls Rules 6

7 Priority Practices for Credit Development Bioretention design variants Level spreader filter strip design variants Infiltration devices Soil improvement / pervious area nutrient management Land or forest protection Livestock Exclusion Removal of Illegal Wastewater Connection to Stormwater Systems or Surface Waters Riparian buffer restoration in developed areas Design Variants for Bioretention Cells Soil media depth Inclusion of internal water storage (IWS) Average surface ponding depth Surface storage ratio (i.e., storage volume relative to design storm volume) Drainage coefficient (default is 2 ft/d) Average Surface Ponding Depth Depth to IWS (root zone) IWS (media+gravel) Subgrade soil 7

8 Design Variants for Level Spreader Filter Strip Width (W), (i.e., flow path) Ratio of the length in ft (L) to the design flow in cfs (Q) Q = CIA Q = design flow (cfs) C is the runoff coefficient (unitless) I = 0.75 in/hr (new MDC) A = drainage area (ac) [See description of the Rational Method in Ch. 3 of the NCDEQ BMP manual] W L Modified from Winston and Hunt (2010) Volume Reduction Credits Associated with Infiltration Devices Sized for Various Design Storms Design Storm Size (inches per 24 hours) % Annual Runoff Reduction 1, Photo courtesy of NCSU-BAE 8

9 Volume Reduction Credits Associated with Soil Improvement (addition of topsoil, tillage with compost, healthy vegetation) Soil Improvements (variable depths) Increased Porosity and Storage Capacity Increased ET and exfiltration Reduced Runoff Volumes Status of Remaining Practices Working through policy issues Livestock exclusion Land conservation Developing technical approach Buffer restoration in developed areas Removal of illicit discharges to storm systems or surface waters 9

10 Jurisdictional Loads Existing Load Status Preliminary load developed for utility implementation revenue requirements Refined load developed over time Near final numbers today 10

11 Basics Data sources Other inputs Permit data Other jurisdiction approaches Imagery Draft model program Impervious area data State reviews Parcel data Calculations Jordan Falls tool Jurisdiction-developed model CATEGORIES Status of Remaining Practices Working through policy issues Livestock exclusion Residential Land conservation Non-residential Developing technical Roads approach Buffer restoration On-site in wastewater developed areas Removal of illicit discharges to storm systems or surface waters 11

12 Residential Measured or estimated impervious area based on - Lot size - Structure type (site built, singlewide, doublewide, etc) Estimated impervious area types based on lot size and structure - Roof, Sidewalk, Driveway Estimated pervious area types based on lot size and structure - Lawn, Forest Commercial Estimated impervious area types - Roof, Parking Measured Impervious Area Remaining pervious area - Open 12

13 Commercial with BMP BMP calculations through Jordan/Falls Lake Stormwater Nutrient Load Accounting Tool Identified private roads via ROADS County plats Measured length of private roads and assumed 10 lane widths Roads 13

14 On-site Wastewater Systems Failure rate from October 2013 Inventory submitted to State Loads derived from North Carolina Piedmont Nutrient Load Reducing Measures Technical Report prepared by Tetra Tech for DWQ Predevelopment Conditions Uniform Predevelopment loading initially allowed by Falls Rules State said these rates represented loading from all sources, not just surface water runoff, so not comparable with model outputs Updated model to allow for toggling between predevelopment loading rates 14

15 Model Sensitivity Rules-allowed uniform rate Resulting loads and required reduction 1,000 - (1,000) Granville County Butner Creedmoor Stem Person County (2,000) (3,000) (4,000) (5,000) (6,000) (7,000) P lb/yr Loading Diff N lb/yr Loading Diff Model Sensitivity Managed Pervious/Forest Resulting loads and required reduction 2,500 2,000 1,500 1, Granville County Butner Creedmoor Stem Person County P lb/yr Loading Diff N lb/yr Loading Diff 15

16 Questions and Discussion 16