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Small Tributaries Loading Study #2:

Zone 4 Line A, Cabot Blvd. Hayward

Year 1 – Draft FINAL report

Lester McKee and Alicia Gilbreath

Sources Pathways and Loadings WorkgroupDecember 8, 2008

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Choice of watershed to study

• TMDL reports encourage further development of loading information

• Z4LA chosen because it:– Contrasts in size to Guadalupe River– Land use– Climate– Geology and slope

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Location

• Area: 4.47 km2 Industrial: 38%• Commercial: 26% Residential: 33%

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Sampling location

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Channel

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Field equipment

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Field sampling for contaminants

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Measurement of discharge

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Results – Rainfall and runoff• 21 storm events• cumulative rainfall = 270

mm (10.6 in)• 1.6 year return• %77 % of average (45 y

record at 50dly to the south

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Nov Dec Jan Feb Mar Apr May

Dis

char

ge (

cms)

0

2

4

6

8

10

Cum

ulat

ive

Rai

nfal

l (m

m)

0

50

100

150

200

250

300

DischargeCumulative Rainfall

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Results – Suspended sediment

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Scatter plots

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Spearman partial correlations – effect of SSC removed

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• Hg not correlated with Cr, Ni, Se despite common geologic origins

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Comparisons to CA soils

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5

00

7%

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Results – Trace organics

• All <10%

• PCB 110/115, 129/138/160/163, 153/168, 180/193

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PBDEs

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• BDE 47, 99, 209 (73-88%)

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Loads of Organics

• Organic carbon: <1% SSC (Guadalupe 0.5-1.1%)

• PCB concentrations normalized to sediments (0.13 mg/kg) were 10x greater than found in the Bay

• PBDE loads were 2.8 x PCB loads

• PAH loads, despite abundant sources lower than PCBs/PBDEs, DDT and similar to chlordanes

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Z4LA concentration comparisons

• Local concentration data – Guadalupe, Coyote, San Pedro storm drain

• Hg: Z4LA = Coyote within range of San Pedro << Guadalupe

• PCB: Z4LA = Guadalupe >Coyote (*dry year)

• PBDE / DDT / chlordane, dieldrin similar trends to PCBs

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MeHg

• SSC proxy to flow

• Dilution during high flows

• More production during low flows

• Similar particle concentrations to wetlands (Heim et al., 2007)

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Which and how many watersheds should be sampled?

 

Are

a (k

m2

) 

SS

(t/km

2)

Hg

Me

Hg

Ag

Cd

Cr

Cu Ni

Pb

Zn

PC

B

PB

DE

DD

T

Ch

lord

an

e

Dield

rin

Hayward Urban

watershed(Z4LA WY

2007) 4.5 24 5.6 0.16 8.0 431,40

02,50

01,80

01,80

021,00

0 3.2 9.0 3.7 1.3 0.30

Guadalupe River

(WY 2004) 236 36 64 0.088 12.6 412,71

23,00

85,08

52,20

312,71

2 3.3 6.7 3.3 2.5 0.26

Statistically significant? yes yes maybe no no yes no yes no yes no no no maybe no

Export of POC during climatic years with ~70% mean annual runoff(units: micrograms per square meter (µg/m2) unless otherwise specified

San Francisco Estuary Institute

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Regional loads estimates(Flow method)

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Regional loads estimates(Sediment method)

• Discount estimate based on Davis et al. (2000) sediment load: we are quite certain it is too low.

• Hg: 84 – 91 kg is less than TMDL estimate (160 kg)

• PCB: 13 – 26 kg is similar to TMDL estimate (20 kg)

• PBDE: 37 – 79 kg is similar to Oram et al (2008) estimate (60 kg)

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Recommendations • Given Z4LA was sampled under dry conditions in the first year

sampling continue for either 3-4 years or until storms of <5 year return are sampled

• Given regional load estimates are crude at best, effort should be made to:– Develop regional modeling capability– Gather sample a greater variety of land types specifically as input into

models

• Improve regional data set for MeHg and HgR in the context of “high leverage watersheds”

• Given the unexpected similarity between watersheds for the trace organics, effort should be made to reject the hypothesis that imperviousness is more important than sources– An alternative hypothesis is that watershed scale is masking the source

issue