Estimation of Contaminant Loads from the Sacramento-San Joaquin River Delta to San Francisco Bay.

Contaminant concentrations from the Sacramento-San Joaquin River watershed were determined in water samples mainly during flood flows in an ongoing effort to describe contaminant loads entering San Francisco Bay, CA, USA. Calculated PCB and total mercury loads during the 6-year observation period ranged between 3.9 and 19 kg/yr and 61 and 410 kg/yr, respectively. Long-term average PCB loads were estimated at 7.7 kg/yr and total mercury loads were estimated at 200 kg/yr. Also monitored were PAHs, PBDEs (two years of data), and dioxins/furans (one year of data) with average loads of 392, 11, and 0.15/0.014 (OCDD/OCDF) kg/yr, respectively. Organochlorine pesticide loads were estimated at 9.9 kg/yr (DDT), 1.6 kg/yr (chlordane), and 2.2 kg/yr (dieldrin). Selenium loads were estimated at 16 300 kg/yr. With the exception of selenium, all average contaminant loads described in the present study were close to or below regulatory load allocations established for North San Francisco Bay.

Characteristics of road sediment fractionated particles captured from paved surfaces, surface run-off and detention basins.

This study presents the results of evaluating changes in properties of road sediment fractionated particles at the source (dry pavement), during transport (highway runoff) and after deposition (dry detention basin). A total of 38 solid particle samples were collected from paved surface, highway runoff, and from three locations within detention basins. Each sample was size-fractionated ranging from 38 µm to 1000 µm. Key results were that: (i) less than 2% of total particle mass in four vacuumed solid samples was associated with the <38 µm fraction compared to 47 to 82% in centrifuged highway runoff samples and 25% for detention basin sediments, (ii) based on number concentrations more than 90% of particles from all sources were smaller than 38 µm, (iii) the densities of fractionated particles were generally within the range from 1.5 to 2.2g/cm(3); (iv) all collected particles were predicted to resist aggregation in solution with a typical measure of surface potential, the zeta potential, typically ranging from -15 to -30 mV, (v) metal concentrations increased with decreasing particle size for vacuumed samples from the highway shoulder and parking lot, however, size dependent trends in metal concentrations were less apparent in centrifuged highway runoff samples and detention basin sediment samples; (vi) the distributions of metal mass across sieved size fractions generally followed patterns of particle mass distribution in which less than 10% of the total Cu, Pb, and Zn mass was associated with particles <38 µm; (vii) metal mass distributions tended toward increasing metal fractions in finer particle fractions along a gradient from the inlet to the outlet of the detention basins; and (viii) individual particle morphology (1 < d(p) < 10 µm) showed that particles were not smooth or spherical, clearly deviating from the assumptions typically used in estimating particle settling velocities using Stokes' Law.