4.26 CEPRMP Sediment Core Plan

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4.26 CEP/RMP Sediment Core Plan

• Draft Comments
• CFWG Sept 2005

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General Objectives (for CEP RMP)

• Build understanding of ecosystem characteristics
  and processes
• To provide sufficient (better) basis for deciding
  among possible management alternatives

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Specific Objectives (for this Study)

• Estimate future loads from eroding buried
  contaminants
• Estimate historic loadings of contaminants
  (especially recent decades)
• Characterize contamination with depth to assess
  current status and likely future changes
• Provide data for parameterization and evaluation
  of the multi-box model

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If 20 Cores Budgeted

• Random sampling
• Pros aim to be representative of studied system
• Cons muddy signal, may need many samples before
  important factors IDd
• Deterministic sampling
• Pros build process with relatively few samples
• Cons selected samples often not characteristic
  of larger system (e.g. USGS depositional cores)

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Sediment Core Sampling Strategy

• Hybrid Approach
• Some samples specifically to understand loading
  history (deposition only zones)
• Remainder of sites to begin representative
  characterization of Bay sediments

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Initial Effort Timeline

• One cruise 1 year (not 2 years)
• Relatively few stations spaced widely apart
• Long lived isotopes, pollutants, 1 yr storage
  not too bad if stored properly
• Not enough samples (e.g. 10 in yr 1) for info to
  change stratification midstream

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Sampling Effort Distribution

• Use general Bay segmentation scheme
• Suisun, San Pablo, South, Lower South Bay
• Areas with bathymetric change history mapped
• Different sediment and pollutant loading
  quantities and sources
• Cores from each segment
• 1 depositional (wetland or deep Bay?)
• 1 erosional
• 2 more characteristic of that segment
• Depositional, neutral, or erosional

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Modeling Other Needs

• Hybrid approach seeks some of each
• Assumes near 0 possibility that any model can do
  without verification of loading histories or
  process outcomes
• ? Is how much of each ?
• 20 samples not a large number
• Numbers likely not definitive of loading or
  representativeness
• Collect excess samples of each type?
• Will we be able to get around to analyses soon
  enough?

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Example Stratification

0
-
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Distribution of Sites
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Future loads from erosion

• Unmixed buried sediments become mixed
• Pollutant profiles at depth lt gt mixed layer?
• Introduced and averaged into mixed layer
• Widespread characterization preferred
• Rate of erosion
• Extrapolate recent history (Jaffe rates)
• Predicted from model (calibrated to Jaffe?)

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Future Loads w/ no More Cores

• Assume a range of profiles from existing data?
• Pollutant profiles at depth lt or or gt mixed
  layer
• How much higher or lower is reasonable?
• Trend is likely depth gt or surface
• USGS cores depth gt surface
• Many others suggest depth surface
• Guessing time scale of change much harder

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Historic Contaminant Loadings

• Depositional cores reflect past conditions
• Potential limitations
• Ambiguous chronology multiple tracers?
• Natural or manmade disturbances choose sites
  carefully?
• Not representative of Bay what does it reflect?
• Deep bay or wetland?

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Historic Contaminant Loadings

• Deep bay cores
• Proslikely less hot spot influence, more
  representative of segment conditions
• Cons integrate more processes more degrees of
  freedom (mixing w/ other seds, long response
  time), location history uncertain
• Wetland cores
• Prosrespond more quickly to changes, reflective
  of local sources (hotspot, effluent or
  tributary), better mapped, history
• Cons more reflective of local sources, slow
  accretion

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Alternatives Historic Loadings

• Assume Breivik close enough?
• Revise Breivik with upper and lower bounds?
• How low/high is reasonable?
• Monitor current loads with time series
• Currently _at_ Guadalupe river, Mallard Island
• Representative enough?
• Project trends backward for hindcast?

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Contaminant Profiles w/ Depth

• System status not just in surface 5cm sediments
• Dominant sedimentation regimes in each segment
  sampled ( - 0 sedimentation)
• Spatially variable but representative in long
  term
• (must start somewhere)
• Alternatives (?)
• Assume concentration lt or gt surface sediments
• Even larger uncertainties

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Data for Model

• (Multi box or other)
• Past future loads, current system status are
  needed to model
• (input parameters, initial or final conditions)
• Loads and status data needed independent of model
• Relative priority somewhat model dependent
• Which is more important?

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Comments on Plan to Date

• Too expensive (much of CEP budget)
• Underfunded for objectives
• Too little of budget for interpretation/reporting
• Any geologic cores for sediment transport
  perspective?
• Why not Cs137 or mix of other tracers?
• Can cores be collected and stored for later
  analysis?
• Why wetland cores (not in model)?

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Comments on Plan to Date

• Expect high of useless cores
• Use screening analyses
• Need more sections per core for temporal trends
  (fewer cores more sections)

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Regional Board Wish List

• Some Central Bay sites
• Trade OC pesticides for other organics in some
  samples?
• Selenium (for a background baseline?)
• PCDD/Fs
• Background PCB levels