Concentrations and loads of PCBs and OC pesticides in
the Guadalupe River watershed
Jon LeatherbarrowJon Leatherbarrow1,21,2, Lester McKee, Lester McKee11, John , John OramOram11
11San Francisco Estuary Institute, Oakland, San Francisco Estuary Institute, Oakland, CACA
22UC Davis, Civil & Environmental UC Davis, Civil & Environmental Engineering, Davis, CAEngineering, Davis, CA
RMP Sources, Pathways, and Loadings WorkgroupDecember 12, 2007
Agenda Item #4c
LocationLocationAgenda Item #4c
Finalized load estimates
Addressed comments from May 2007 SPLWG
Further analyses on potential source activation and watershed processing
Timeline for journal article submission February 2008: draft article completion March 2008: internal review and submission May 2008 SPLWG: update on any response
Since last meeting…Since last meeting…
Agenda Item #4c
Contaminant loadingContaminant loading
Load in Load in Grams/YrGrams/Yr
WY2003
WY2004
WY2005
WY2006
Avg. Annual Load (g)
PCBsPCBs 980 770 640 1,390 950 (±330)
DDTDDT 850 670 580 1,260 840 (±250)
ChlorChlor 690 540 420 920 640 (±120)
DieldrinDieldrin 70 60 50 110 70 (±17)
Agenda Item #4c
• Annual loads on the order of 0.5 to 1.5 kg per year in Guadalupe River for PCBs, DDT, and Chlordanes;
• Extrapolation to other watersheds (by area) suggests that combined loadings from local tributaries (e.g., >10 kg/yr of PCBs) are sufficient to significantly delay recovery from legacy contamination in the Bay.
Potential sources and distribution Potential sources and distribution (hypotheses)(hypotheses)
Agenda Item #4c
• Dispersed non-point sources of legacy contamination by positive relationships between contaminant concentrations and SSC, as opposed to point sources that get diluted by increasing flows and sediment loads;
• Urban-to-rural gradient of increasing concentrations from lower to upper watershed hypothesized based on higher concentrations on rising stage of storm events compared to falling stage;
• Unique source activation hypothesized based on occurrence of PCB congener profile similar to Aroclor 1016, which varied from commonly observed patterns of Aroclor 1254 and 1260.
Agenda Item #4c
Q (cubic meters)
0 50 100 150 200
Con
trib
utio
n to
TD
DT
(%
)
0
20
40
60
80 p,p’-DDD ▼ p,p’-DDT ○
Watershed processingWatershed processing• Congener profiles of multiple-component contaminants (e.g., PCBs, DDT) help infer how mechanisms of source activation and transport differ between low and high flows.
• For example, the dominant parent component of technical DDT (p,p’-DDT) comprises ~40% of total DDT concentrations in nearly all samples collected during flows above 20 m3/s indicating the transport of relatively unweathered sediment during high flows.
Discharge (m3/s)
Modeling Hydrologic routing: where is the water coming from? Sediment transport: where is the sediment coming from? Contaminant transport: link evolving contaminant profiles to
sources of water and sediment.
Information gathering on other tributaries Monitoring other selected tributaries Extrapolation/modeling methods
Evaluate treatment options Source reconnaissance Structural treatment selection, design, and placement
Further study and information needsFurther study and information needs
Agenda Item #4c
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