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Dredge Data Evaluation TRC Meeting March 15 2005 Don Yee.

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Presentation on theme: "Dredge Data Evaluation TRC Meeting March 15 2005 Don Yee."— Presentation transcript:

1 Dredge Data Evaluation TRC Meeting March 15 2005 Don Yee

2 Objectives Compile dredge testing data for San Francisco Bay Compare collection and analytical methods Compare analytical results Test hypotheses on SF Bay sediment characteristics

3 Compiled Data State effort to develop sediment quality guidelines occurred concurrently, including compilation of selected dredged material testing data Draft database released November 2004 ~40 dredging studies in SF Bay 11 monitoring studies (includes Hunters Point, Alameda)

4 Spatial Distribution Central Bay most stations

5 Nondetect Issues MDLs sufficient for most trace elements…

6 Nondetect Issues Many NDs for organics (esp. dredge data)

7 Sensitivity Issues Dredge data MDLs usually slightly higher

8 Reported Organics Subset of common PAHs reported Reported PCBs as Aroclors or congeners, study specific Total PCBs differ (ND=0 case) Dredge data most sum Aroclors or sum congeners = 0 Monitoring data avg Aro/cong = 1.7

9 Comparing Data Large % of organics NDs challenging for comparison ND assumptions have large influence particularly on sums Non-parametric statistics more resistant to NDs, but MDL/RL differences and non reporting among different studies can bias outcome

10 Hypotheses: Seasonality Seasonality in historic RMP sediment data (5cm surface grabs) found not significant, therefore… Seasonality in dredge cores even less likely Cores composited for analysis Relatively infrequent revisits in dredging may leave gaps

11 Test: Seasonality Include areas dredged multiple times, perhaps covering different times of year Relatively infrequent revisits in dredging = poor seasonal coverage Deeper coring and compositing may dilute seasonal signal Wilcoxon and Tukey HSD test Comparing Dec-May wet vs Jun-Nov dry Central Bay stations alone

12 Result: Seasonality Wet vs dry season As, Cd, Cu, Mn, Ni significantly (p dry Hg, Se not significant Consistency among elements and types of test

13 Seasonality (Alternative) Oakland 38 and 42 ft projects large portion of dry data (50 ft project split in both seasons) Deeper sediments include relatively uncontaminated Bay muds Excluding data still showed significant wet and dry differences (both tests, same metals)

14 Hypotheses: Interannual Trend Negligible interannual trends in sediment concentrations RMP surface sediments show few/ no significant interannual trends for most contaminants Interannual dredge trends likely confounded by differences in sampled locations & signal diluted by compositing.

15 Test: Interannual Trend Include dredging data over multiple years Subsets Central Bay stations Group by collection year Nonparametric (Kruskal Wallis) and parametric tests (Tukey HSD)

16 Result: Interannual Trend Significant (p <0.05) differences among years for various metals. No consistency among metals for years with significant differences Compare enough categories, and significant differences will be found

17 Alternative: Interannual Trends Use smaller scale: Benicia Harbor only Small well defined area, expect less variation 3-4 samples per year for 3 years Significant differences 1996 > 1997 or 2000: As, Cd, Cr, Hg (p < 0.05) 1996 frequently nigher than other stations

18 Benicia Annual Differences

19 Hypotheses: Depth Integration Sediment contaminant concentrations at depth are not significantly different from surface concentrations Deep dredging will encounter clean Bay sediments and average lower contaminant concentration than surface samples

20 Test: Depth Integration Subset to focus on area around Oakland Dredge data in port dominated by deepening project samples Latitude & longitude from all Oakland dredging projects Monitoring data for surface sediments in same box Wilcoxon and Tukey HSD test

21 Result: Depth Integration Concentrations for nearly all metals Oakland monitoring > dredge data As, Cd, Cu, Pb, Hg, Ni, Se, Ag, Zn statistically significant difference Cr only metal higher in dredge sediment Generally consistent among metals Significant differences on As, Cd, Se, Zn even removing BPTCP, LEMP, Alameda NAS data

22 Oakland Depth Integration

23 Result: Depth Integration Part 2 Examine differences in dredge vs monitoring in Suisun Bay. Hg statistically significantly higherin monitoring (surface sediment) data Cr only metal higher in dredge sediment Differences hold even dropping LEMP, BPTCP data

24 Suisun Depth Integration

25 Conclusions Dredge data analytical methods sufficient for most trace elements Organics analyses usable only for PAHs due to extensive ND results Dredge data may show seasonality in Central Bay Larger number of samples provides power Similar trends among metals evidence of real effect Significance holds even removing obviously biasing data sets (e.g. Oakland deepening projects)

26 Conclusions (contd) Segment scale dredge data show no interannual trends (Central Bay) Significant results found in many comparisons, but inconsistent among trace elements Significance may be artifact of numerous (year) categories Smaller scale dredge data may show trends Narrower sampling focus reduces lateral and vertical variability

27 Dredge Data Useful (with care) Awareness of collection, analytical, and reporting conventions Selecting the right subset to reduce biases Inconsistent significance may not be significant

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