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

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

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

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

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 discrete samples from 2002/2003

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

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

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

Number of Samples Collected and Analyzed Date# Time samples# Flow samples 10/31/ /8/ /14/ /6/ /9/ /14/ /23/ /29/ /17/0440 Total6247

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

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

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

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

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