1 Optimizing sampling methods for pollutant loads and trends in San Francisco Bay urban stormwater monitoring Aroon Melwani, Michelle Lent, Ben Greenfield, and Lester McKee Sources Pathways and Loadings Workgroup May 6 th 2010 Item #1b San Francisco Estuary Institute

2 Background Small Tributary Loading Strategy – Quantify annual loads or concentrations of pollutants of concern Quantify the decadal-scale loading or concentration trends Support small tributary loading monitoring plan that meets the objectives of MRP Provision C.8.e San Francisco Estuary Institute

3 Study Design Two components: Compare strategies for determining annual pollutant loads Determine the power and sample size needed to detect declining trends in concentrations Statistically sub-sampled existing empirical data sets Examined scenarios to optimize sampling designs and strategies San Francisco Estuary Institute

4 Data Used Guadalupe River Water years 2003 – km 2 (downstream from reservoirs) 80% urbanized Zone 4 Line A Water years 2007 – km 2 38% industrial

5 Approach Following Leecaster et al. (2002) Within-storm Designs Among-storm Designs Turbidity-surrogate Regression Trend Analysis San Francisco Estuary Institute

6 Best Estimate of Loads Turbidity-surrogate methods (McKee et al.) Continuous turbidity measurements ( mins) ~ grab samples per year Regressions used to determine continuous concentrations Combined with flow measurements to calculate loads = Baseline for all design comparisons San Francisco Estuary Institute

7 Within-storm Designs San Francisco Estuary Institute

8 Storm Sampling Simulated ISCO protocols Simulated ISCO protocols Flow Sampling Criteria (1:1) Flow Sampling Criteria (1:1) Flow (cfs)

9 Within-storm Designs San Francisco Estuary Institute

10 Among-storm Designs * Largest storm selected randomly from three highest discharges per water year ** MRP design San Francisco Estuary Institute

11 Turbidity Surrogate Simulations Simulated TSR using sub-sampled turbidity-pollutant data Determine mean slope and intercept to calculate loads TSR loads compared against loads from all samples San Francisco Estuary Institute

12 Trend Analysis Trends evaluated in Hg and PCBs Targets 0.2 mg Hg / kg SS mg PCBs / kg SS Used Coefficient of Variation to examine trend Power examined for trends in 10, 20, 25 or 40 years San Francisco Estuary Institute

13 Within-storm Results San Francisco Estuary Institute

14 Results Accuracy Precision Units are fractional percent bias, e.g = 5%

15 Within-storm Design Strategies San Francisco Estuary Institute

16 Among-storm Results San Francisco Estuary Institute

17 Guadalupe River (WY 2004) Hg First Flush + Random n First Flush, Largest storm + Random n Random n First Flush + Random n First Flush, Largest storm + Random n Random n First Flush + Random n First Flush, Largest storm + Random n San Francisco Estuary Institute

18 Zone 4 Line A (WY 2007) PCBs Random n First Flush + Random n First Flush, Largest storm + Random n San Francisco Estuary Institute

19 Sampling Design Results The optimal within-storm design was an equal-spacing design (1:1), n = 12 or 18, with the linear interpolation estimator The optimal among-storm design was first flush or first flush and largest storm with 10 storms total (the maximum number evaluated) Design with first flush and largest storm generally biased high when few storms sampled Random design showed less bias when few storms sampled, but very poor precision

20 Turbidity-Surrogate Simulations San Francisco Estuary Institute

21 Guadalupe River Hg

22 Zone 4 Line A PCBs San Francisco Estuary Institute

23 TSR Simulations Turbidity-surrogate results indicate that accurate loads could be obtained with significantly less samples Precision in annual loads was optimal with 7 – 10 samples per year, depending on year and pollutant San Francisco Estuary Institute

24 Trend Results San Francisco Estuary Institute

25 Guadalupe River * Hg: n = 25; n = 37; n = 52 ** PCBs: n = 21; n = 19; n = 12 San Francisco Estuary Institute

26 Zone 4 Line A * Hg: n = 30; n = 15; n = 21 ** PCBs: n = 18; n = 15; n =14 Target set to 0.05 San Francisco Estuary Institute

27 Power Results Power for current sample sizes generally high Inter-annual differences apparent Could reduce sampling effort to 10 grab samples per year without loss of power for trend detection San Francisco Estuary Institute

28 Next Steps Choice of sampling method is a compromise between Accuracy (true loads) Precision (width of confidence) Cost (field logistics, QA/QC, Reporting) Next step - cost out the recommended designs San Francisco Estuary Institute

29 Discussion Straw-man Linear interpolation estimator with 12 samples/storm and 10 wet season storms Turbidity surrogate method with 7 – 10 grab samples Trend detection need 10 grab samples Are loads estimates every year needed or are loads calculated every few years sufficient, with less intense annual monitoring for concentrations and trends San Francisco Estuary Institute

30 Appendix Slides San Francisco Estuary Institute

31 Guadalupe River Hg Flow San Francisco Estuary Institute

32 Guadalupe River Hg Turbidity San Francisco Estuary Institute

33 Z4LA Hg Flow San Francisco Estuary Institute

34 Z4LA Hg Turbidity San Francisco Estuary Institute

35 Guadalupe River (WY 2004) PCBs San Francisco Estuary Institute

36 Guadalupe River (WY 2005) Suspended Sediment San Francisco Estuary Institute

37 Zone 4 Line A (WY 2007) Hg San Francisco Estuary Institute

38 Zone 4 Line A (WY 2009) Suspended Sediment San Francisco Estuary Institute

39 Guadalupe River PCBs San Francisco Estuary Institute

40 Guadalupe River Suspended Sediment San Francisco Estuary Institute

41 Zone 4 Line A Hg San Francisco Estuary Institute

42 Zone 4 Line A Suspended Sediment San Francisco Estuary Institute