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Castro Valley Creek Stormwater Quality Monitoring

Castro Valley Creek Stormwater Quality Monitoring. Brake Pad Partnership Meeting June 22, 2005. BPP Technical Studies. Air Deposition Monitoring (SFEI). Representative Sample of Brake Pad Wear Debris (BMC/Link Test Labs). Air Deposition Modeling (AER). Physical & Chemical

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Castro Valley Creek Stormwater Quality Monitoring

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  1. Castro Valley Creek Stormwater Quality Monitoring Brake Pad Partnership Meeting June 22, 2005

  2. BPP Technical Studies Air Deposition Monitoring (SFEI) Representative Sample of Brake Pad Wear Debris (BMC/Link Test Labs) Air Deposition Modeling (AER) Physical & Chemical Characterization of Wear Debris (Clemson University) Copper Source Loading Estimates (Process Profiles) Watershed Modeling(U.S. EPA) Water Quality Monitoring (ACCWP) Bay Modeling (URS) Final Report Data Assessment Conclusions Steering Committee, Scientific Advisory Team, and Stakeholder Involvement Process (Sustainable Conservation)

  3. Scope of Work • Collect runoff samples from Castro Valley Creek during five to ten storm events • Analyzes samples for total copper and total suspended solids. • Obtain rainfall and stream flow data

  4. Background • Castro Valley Creek Watershed • 5.51 square miles • Predominantly low-density residential w/ some commercial development and open space • Mean Annual Rainfall: 21 inches • Rainy season: October through May • Elevation: 200 to 500 feet above sea level • Mean Annual Stream Flow: 123 million cu. ft. • Stream channels mostly incised or culverted

  5. BACKGROUND (Cont.) • Long history of monitoring watershed • USGS stream flow from 1971 • Hourly rainfall from 1970 • Extensive Water Quality sampling • USGS from 1971 to 1989 • Flow-weighted composite sampling 1990-95 • 90 discrete samples from 2002/2003

  6. Overview of Sampling Effort • Sampled Nine Storm Events from October 2003 through February 2004 • Time-weighted: composites of four hourly samples • Flow-weighted discrete samples: every 240,000 cubic feet of flow • Consistent with previous sampling regime • First flush as discrete sample

  7. Overview of Sampling (cont.) • Samples collected using an ISCO automated sampler located at USGS gaging station • Bubbler records stage at two-minute intervals • Converts to flow using USGS rating curve

  8. Overview of Sampling (cont.) • Samples analyzed by ToxScan Laboratories • Total Copper: EPA Method 160.2 • Total Suspended Solids: EPA Method 200.8 • 109 samples Analyzed • 62 time-weighted samples • 47 flow-weighted samples

  9. Number of Samples Collected and Analyzed

  10. Overview of Sampling (cont.) • 5-minute instantaneous flow record for entire season: USGS • One-hour rainfall record for four gauges: ACFC&WCD

  11. Issues Raised in Peer Review • Potential bias due to fixed-point sampling • Appropriateness of suspended sediment analytical method

  12. Fixed–Point Sampling • Issue: Fixed-point sampling with an automated sampler may introduce a bias. • Larger grain sizes not evenly distributed • Magnitude: ? • Potential Resolution: • Simultaneous fixed point and equal width integrated sampling. • Drawbacks • Difficult logistically / expensive. • Not consistent with previous data/calibration

  13. Total Suspended Solids Analysis • Issue: • Total suspended solids analysis may underestimate suspended sediment concentrations. • Magnitude: ? • Potential Resolution: • TSS and suspended sediment concentration (SSC) analysis on split samples. • Drawback: • Previous data: TSS

  14. Summary • Samples were collected during nine storm events • 109 Flow and Time-weighted samples collected and analyzed • Good coverage of storm flow during first half of wet season • Some uncertainty regarding potential bias

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