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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.

Predicting the rate and extent of decomposition of residues at the soil surface is necessary to evaluate the impacts of minimum‐tillage practices on erosion control and thus ensure the most effective use of residues. A mechanistic model simulating the decomposition of surface‐managed winter wheat residues was developed and model predictions were compared to results from field studies of decomposition rates. The model consists of two submodels. The first simulates decomposition of the various components of wheat residues (straw, leaves, and chaff) under constant conditions. This submodel requires input on the N content of the residue, and is based on results of laboratory experiments in which respiration was measured. The second submodel uses meteorological data to simulate environmental conditions in the residue layer. This information is combined with laboratory derived estimates of the effects of temperature and moisture to calculate the cumulative decomposition days. To apply the model to field situations, the relationships between respiration and mass loss were estimated experimentally. The effects of added microarthropods and nematodes were also measured, but no effects on respiration were observed in either case. Model predictions agreed well with data from field experiments in which bundled straw was used, but decomposition of straw in litter bags was slower than predicted. When grab samples were used to measure the loss of residues containing leaves, chaff, and straw, the model performed well even across climatic regions until early summer (32–36 wk after residue placement in the field), when residues began to disappear more rapidly than predicted.

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