Dredge Data Evaluation

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 (ND0 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 lt0.05)
  different, with wet gt 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 lt0.05) 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 gt 1997 or 2000 As, Cd, Cr, Hg (p lt 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 gt 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