Dredge Data Evaluation

TRC Meeting March 15 2005Don Yee

Objectives Compile dredge testing data for San Francisco

Bay Compare collection and analytical methods Compare analytical results Test hypotheses on SF Bay sediment

characteristics

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 Hunter’s Point,

Alameda)

Spatial Distribution

Bay Segment Monitor DredgeCarquinez 20 16Central Bay 381 332Lower South Bay 41NA 37 73Pacific 3Rivers 11San Pablo Bay 89 6South Bay 57 20Suisun Bay 55 41

Central Bay most stations

Nondetect Issues MDLs sufficient for most trace elements…

0%

5%

10%

15%

20%

25%

30%

35%

Al

Sb

As

Ba

Be

Cd Cr

Co

Cu

Fe

Pb

Mg

Mn

Hg

Me

Hg

Mo Ni

Se

Ag Sr

Th

Sn Ti V Zn

MON

DRE

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

PAH NDs

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 20% 40% 60% 80% 100%

MON %ND

DR

E %

ND

PCB NDs

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 20% 40% 60% 80% 100%

MON %ND

DR

E %

ND

Sensitivity Issues Dredge data MDLs usually slightly higher

PAH MDLs

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10

MON MDL ug/kg

DR

E M

DL

ug/k

g

PCB MDLs

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0

MON MDL ug/kg

DR

E M

DL

ug/k

g

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

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

Hypotheses: SeasonalitySeasonality 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

Test: SeasonalityInclude 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

Result: Seasonality Wet vs dry season

As, Cd, Cu, Mn, Ni significantly (p <0.05) different, with wet > dry

Hg, Se not significant Consistency among elements and types of test

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)

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.

Test: Interannual TrendInclude dredging data over multiple years Subsets

Central Bay stations Group by collection year

Nonparametric (Kruskal Wallis) and parametric tests (Tukey HSD)

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

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

Benicia Annual Differences

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

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

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

Oakland Depth Integration

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

Suisun Depth Integration

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)

Conclusions (cont’d) 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

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