Modeling Copper Runoff in San Francisco Bay Area

Watersheds

Jim Carleton

US EPA

BPP Technical Studies

Copper Source Loading Estimates (Process Profiles)

Physical & ChemicalCharacterization of

Wear Debris (Clemson University)

WaterQuality

Monitoring (ACCWP)

Steering Committee, Scientific Advisory Team, andStakeholder Involvement Process (Sustainable Conservation)

AirDepositionModeling

(AER)

WatershedModeling

(U.S. EPA)

BayModeling (URS)

Final ReportData Assessment

Conclusions

Air Deposition

Monitoring (SFEI)

Representative Sample of Brake PadWear Debris

(BMC/Link Test Labs)

Castro Valley street TCu deposition/accumulation post-rain (Pitt,1981)

0

0.02

0.04

0.06

0.08

0 20 40 60 80 100 120

day

TC

u lb

/cur

b m

ile

data first-order f it

tkek

kM 21

2

1

Copper Build-up on Impervious Surfaces

Copper on Suspended Sediment in Bay Area Streams

All simultaneous TCu & TSS Data (log scale)

1

10

100

1000

10000

100000

0.000 10.000 20.000 30.000 40.000 50.000 60.000

% imperviousness

TC

u/T

SS

(m

g/k

g)

Geometric mean140 mg/kg

Soil background25 mg/kg

Key Questions for Watershed Modeling

• What are deposition rates of copper on pervious and impervious surfaces in the San Francisco Bay area?

• How much of the deposited copper comes from brake pads?

• How much of the copper that is deposited on pervious surfaces ends up transported to streams (and the bay) in runoff?

Watershed Modeling with HSPF

• Castro Valley watershed model used to estimate build-up and washoff parameters.– First calibrate stream flow using local precipitation data

as input.

– Next calibrate suspended sediment and copper against monitoring data.

• Using build-up/washoff parameters from Castro model, run simulation of greater Bay area (multi-watershed) to estimate total loads to Bay.

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Baysheds83.shpCastro_watershed.shpGuadaulperiver.shp

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20 0 20 40 Miles

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Castro Valley watershed

Guadalupe River watershed

Bay Area Watersheds

Castro Valley HSPF Initial Calibration

Using annualized loadings from initial

air deposition monitoring

Guadalupe River HSPF Initial Validation

Using annualized loadings from initial

air deposition monitoring

Future Activities

• Incorporation of modeled source loadings, and will need to look at:– Importance of suspended sediment (which is hard to

model)– Uncertainties in apportioning pervious and impervious

land loadings to copper in stream water column– Sensitivity of model results to choice of model

parameters• Approaches

– Calibration using current data– Checking against historical data– Staying within literature ranges of parameters– Best professional judgment