No abstract

Assessing the hazard posed by sediments contaminated with hydrophobic organic compounds is difficult, because measuring the freely dissolved porewater concentrations of such low-solubility chemicals can be challenging, and estimating their sediment-water partition coefficients remains quite uncertain. We suggest that more accurate site assessments can be achieved by employing sampling devices in which polymers, with known polymer-water partition coefficients, are used to absorb the contaminants from the sediment. To demonstrate the current accuracy and limitations of this approach, we compared use of three polymers, polydimethylsiloxane, polyoxymethylene, and polyethylene, exposed to a single sediment in two modes, one in which they were exhaustively mixed (tumbled) with the sediment and the other in which they were simply inserted into a static bed (passive). Comparing porewater concentrations of specific polychlorinated biphenyl (PCB) congeners with results obtained using air bridges, we found the results for tumbled polymers agreed within 20%, and the passive sampling agreed within a factor of 2. In contrast, porewater estimates based on sediment concentrations normalized to f(OC)K(OC), the weight fraction of organic carbon times the organic-carbon normalized partition coefficient, averaged a factor of 7 too high. We also found good correlations of each polymer's uptake of the PCBs with bioaccumulation by the polychaete, Neanthes arenaceodentata. Future improvements of the passive sampling mode will require devices that equilibrate faster and/or have some means such as performance reference compounds to estimate mass transfer limitations for individual deployments.

No abstract

This work analyzes a database of 31 existing CO 2 enhanced oil recovery (EOR) projects that was compiled for the estimation of oil reserves to better understand the CO 2 retention, incremental oil recovery, and net CO 2 utilization for these oil fields. The measured data begin at the start date of the CO 2 flood and extend through the year 2007. Cumulative CO 2 retention (in the formation), incremental oil recovery factors, and net CO 2 utilization factors were calculated for each of the sites. To express all site data on a common dimensionless scale, the data were extrapolated to 300% cumulative hydrocarbon pore volume (HCPV) by fitting nonlinear functions. Summary statistics were then calculated from 0% to 300% HCPV. Across all 31 sites, the 10th, 50th (median), and 90th percentile values for the three factors at 300% HCPV were:

Samples from a former manufactured gas plant (MGP) site in Santa Barbara, CA, were tested to evaluate the environmentally acceptable endpoints (EAE) process for setting risk-based cleanup criteria. The research was part of an ongoing effort to develop and demonstrate a protocol for assessing risk-based criteria for MGP sites that incorporates the availability of polycyclic aromatic hydrocarbons (PAHs). Six samples were tested:  source soil, treated source soil, aged soil, lampblack soil, background soil, and spiked soil. The samples were subjected to a battery of physical and biological tests that focused on determining the “availability” of the soil-bound contaminants to groundwater, ecological receptors, and human receptors. Different assays yielded similar qualitative results, but the magnitude of the effects differed significantly. Each assay has unique inherent limitations, but the earthworm uptake assay is preferred because it is reliable, inexpensive, and sensitive at meaningful soil concentrations. Results demonstrated that sorption to soil, matrix effects, aging, and treatment can significantly reduce chemical availability. Including these reduced availability results in risk assessment calculations yielded environmentally protective cleanup levels almost 3−10 times greater than levels derived using California default risk assessment assumptions. Using an EAE-based approach for MGP soils, especially those containing lampblack, could provide more realistic risk assessments.