A San Antonio Case Study on the Water Quantity and Quality Benefits of LID Development Chad Richards PE, CFM, CPSWQ Brett Sachtleben PE, CFM Agenda Purpose Water Quality Processes LID Components and their Water Quality Benefits Overview of LID Design for Billy Mitchell Village Case Study Scenarios Methodology Assumptions Results Take Aways 2 1
Purpose LID Competition Goals Reduce 5-, 25-, and 100-year event runoff compared to the existing condition Treat 85th percentile storm (1.17 ) 80% TSS removal 6-Year Simulation Results % Impervious Cover Total Precipitation (ac-ft) Predevelopment Existing Conditions LID Design Conventional Design 0.0% 43.3% 43.9% 58.4% 339.5 339.5 339.5 339.5 Outflow (ac-ft) 9.6 141.2 23.9 213.5 Runoff Coefficient 2.8% 41.6% 7.0% 62.9% 83% 3 Water Quality Processes 4 2
Settling Source: City of Virginia Beach 5 Infiltration Source: Cornell University 6 3
Vegetative Filtration Source: Oregon DEQ 7 Water Quality Processes Sorption Adsorption Absorption Bioaccumulation Biotransformation 8 4
Water Quality Processes Others Biological activity Sunlight exposure Thermal mitigation 9 LID Components and their Water Quality Benefits 10 5
Bioretention/Bioswale Source: SARA San Antonio River Basin LID Technical Guidance Manual, 2013 11 Bioretention/Bioswale Source: SARA San Antonio River Basin LID Technical Guidance Manual, 2013 12 6
Permeable Pavement Source: SARA San Antonio River Basin LID Technical Guidance Manual, 2013 13 Green Roofs Source: Wikipedia 14 7
Green Roofs Source: Wikipedia 15 Cistern/Rain Barrel Source: SARA San Antonio River Basin LID Technical Guidance Manual, 2013 16 8
Filter Strips Source: www.hertslink.org 17 Removal Efficiency Matrix Bioretention Bioswale Permeable Pavement Planter Boxes Sand Filter Stormwater Wetlands Sediments Bacteria Nutrients Trash Metals Source: SARA San Antonio River Basin LID Technical Guidance Manual, 2013 18 9
Removal Efficiency Matrix Sediments Bacteria Nitrogen (Total) Phosphorus (Total) Bioretention Bioswale Planter Boxes Detention 70% 80% 70% 80% 70% 80% 78% 72% 25% 50% 25% 50% 25% 50% 25% 57% 19 Overview of LID Design for Billy Mitchell Village 20 10
San Antonio Land/Water Sustainability Forum LID Design Competition Category: Multi-Family Mixed Use Team: Atkins Ford, Powell & Carson, Inc. Rialto Studio The University of Texas at Austin 21 Methodology Mass Balance Calculation 85% Storm Volume Calculated Bacteria, TSS, Nitrogen and Phosphorus Removal Drainage Area Pollutant Load BMP Pollutants Removed Ignored Infiltration/Retention Volume From Bioswales, Bioretention, etc. Permeable Pavement Downstream Pollutant Load ( > Minimum Expected Concentration) Cisterns 22 11
Water Quality Model Considerations Hydrodynamics Temperature Solar radiation ph Sediment-water interactions Algae Nutrient cycling Pollutant build-up and wash-off NOT CONSIDERED 23 Case Study Scenarios 1. Existing Development 2. LID Development 3. Conventional Development 24 12
Case Study Scenarios Existing Development Storm water conveyed by storm sewer and streets No W.Q. BMP s 3.2 acres draining to Outfall #1 59.8 acres draining to existing storm sewer outfall (Outfall #2) Outfall #1 Outfall #2 25 Case Study Scenarios LID Development W.Q. BMP s: Bioswales Bioretention Planter Boxes 30.0 acres draining to LID Development Outfall (#1) 32.9 acres draining to existing storm sewer (Outfall #2) 10.2 acres of offsite areas drains through BMP s along Gen. McMullen Outfall #2 Outfall #1 26 13
Bacteria Concentration (#/100 ml) 9/12/2014 Case Study Scenarios Conventional Development Storm water conveyed by storm sewer and streets W.Q. BMP s: Detention Facility at Outfall 30.0 acres draining to Outfall #1 32.9 acres draining to existing storm sewer outfall (Outfall #2) Outfall #1 Outfall #2 27 Results Bacteria Concentrations at Combined Outfall 30000 25000 20000 31.8% 15000 10000 63.4% 5000 0 Existing LID Conventional 28 14
Nitrogen Concentration (mg/l) TSS Concentration (mg/l) 9/12/2014 Results TSS Concentrations at Combined Outfall 180 160 140 120 34.8% 100 80 60 64.6% 40 20 0 Existing LID Conventional 29 Results Nitrogen Concentrations at Combined Outfall 1.80 1.60 10.8% 1.40 1.20 30.0% 1.00 0.80 0.60 0.40 0.20 0.00 Existing LID Conventional 30 15
Concentration (#/100 ml) Phosphorus Concentration (mg/l) 9/12/2014 Results Phosphorus Concentrations at Combined Outfall 0.45 0.40 0.35 0.30 22.2% 0.25 45.1% 0.20 0.15 0.10 0.05 0.00 Existing LID Conventional 31 Results Bacteria Concentrations at Outfall #1 30000 Avg. ContributingBacteria Concentration = 26854 25000 20000 15000 10000 72.0% 5000 0 96.8% LID Conventional 32 16
Concentration (mg/l) Concentration (mg/l) 9/12/2014 Results TSS Concentrations at Outfall #1 180 Avg. ContributingTSS Concentration = 168 160 140 120 100 80 60 40 20 0 95.1% LID 77.8% Conventional 33 Results Nitrogen Concentrations at Outfall #1 2.00 1.80 Avg. Contributing Nitrogen Concentration = 1.66 1.60 1.40 1.20 1.00 45.8% 26.7% 0.80 0.60 0.40 0.20 0.00 LID Conventional 34 17
Concentration (mg/l) 9/12/2014 Results Phosphorus Concentrations at Outfall #1 0.50 0.45 0.40 Avg. Contributing Phosphorus Concentration = 0.38 0.35 0.30 0.25 42.5% 0.20 0.15 0.10 75.1% 0.05 0.00 LID Conventional 35 Take Aways One BMP doesn t fit all Treatment at the source is best LID is an emerging technology 36 18
References City of Austin. 2013. Stormwater Control Measures in Austin, TX: Data Report. City of Austin, Watershed Protection Department, Environmental Management Division, Stormwater Quality Evaluation Section. Report Number CM-13-01. September 2013. Center for Watershed Protection. 2007. National Pollutant Removal Performance Database Version 3. Center for Watershed Protection. Ellicott City, MD. September 2007. Federal Highways Administration. 2004. Stormwater Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring. U.S. Department of Transportation, Federal Highways Administration, Washington, D.C. James Miertschin & Associates, Inc. 2010. BMP Assessment Report Update Development of an Implementation Plan for Bacteria for: Segment 1910 Salado Creek Segment 1920A Walzem Creek Segment 1911 Upper San Antonio River, Prepared for San Antonio River Authority and Bexar Regional Watershed Management Partnership. September 2010. San Antonio River Authority. 2013. San Antonio River Basin Low Impact Development Technical Guidance Manual, v1. San Antonio River Authority. San Antonio, TX. Texas Commission on Environmental Quality. 2013. Implementation Plan for Four Urban Watersheds in the City of Austin. Water Quality Planning Division, Office of Water, Texas Commission on Environmental Quality. Austin, Texas 37 Contact Information Chad Richards : Chad.Richards@atkinsglobal.com Brett Sachtleben: Brett.Sachtleben@atkinsglobal.com 38 19