nhc Study overview Literature Stormwater Loading Field BMP Review - PowerPoint PPT Presentation

Infiltration BMP Design and Maintenance Optimization Preliminary Results Lake Tahoe Basin Science Conference May 23, 2012 nhc

Study overview Literature Stormwater Loading Field BMP Review Simulations Survey 2 nhc

Field data collection Study Sites Concentrated in the South Lake area • Coordinated with TRPA and landowners • 45 Sites • 45% Single and Multi Residential • 45% Commercial • 10% other • 3 nhc

Field data collection Sub-surface Observations and Infiltration Trenches Measurements: Infiltration Systems BMP design, condition, performance Drainage size, surfaces, 45 2 condition Infiltration Basins Dry Wells Pervious Pavement 15 2 6 4 nhc

Infiltration BMP Media Condition Field data analysis Normal 14 Mean 3.064 StDev 1.082 N 56 12 10 Frequency Condition: Visual 8 estimate of sediment 6 accumulation 4 2 0 1 2 3 4 5 Condition Score Average Condition Score 1 3 5 5 nhc

Field data analysis Drainage Surface and Infiltration Performance Performance diagnostic - time for infiltration of 1L water. Histogram of Imp1LInfilTime, Roof1LInfilTime 20 Surface Impervious Roofs 15 Frequency 10 5 0 -160 0 160 320 480 640 1L Infiltration Time (seconds) 6 nhc

Field data analysis Field Survey Insights • Visual condition estimate is a poor indicator of performance • Non-design runoff results in severe declines 7 nhc

BMP stormwater loading simulations Approach Load stormwater with typical • Tahoe Basin FSP mg/L Vary stormwater composition • and BMP designs Quantify infiltration • performance changes 8 nhc

BMP stormwater loading simulations Experimental Challenges 9 nhc

BMP stormwater loading simulations Clogging Mechanisms 10 nhc

BMP stormwater loading simulations Infiltration Performance Decline 100 Replicate measurements 90 < 1SD of the mean Infiltration Rate (in/hr) 80 70 60 50 40 30 20 10 0 0 25 50 75 100 125 150 175 200 225 FSP Load (grams) 11 nhc

BMP stormwater loading simulations Scaling up to In-Situ BMPs Assumptions: • Stormwater with constant FSP concentrations • Rain = 30 in/yr, RO coef = 1 • BMP = No depth, 12.8 in/hr soil BMP/ BMP/ 3 year Infiltration Surface Type Surface Type FSP (mg/L) FSP (mg/L) Drainage Drainage Decline (%) Roof Roof 5 1:9 1:12 5 Parking Lot Parking Lot 100 1:9 1:12 100 12 nhc

BMP stormwater loading simulations Roof @ 3 yrs = 25% decline Parking Lot @ 3 yrs 99.7% decline 13 nhc

Conclusions Findings that we should care about • All surface types not equal in clogging potential • Results may indicate severe performance declines within 3 years • Severe declines also results in loss of stormwater volume reduction benefits 14 nhc

Conclusions Next steps • Continue loading simulations • Lateral infiltration • Stormwater composition • BMP designs • Field verification of performance declines • Draft BMP design and maintenance recommendations 15 nhc

Questions ? (www.2ndnaturellc.com ) 16 nhc