Sludge disposal studies
Richard M- h w d EPA is presently developing new criteria for sewage sludge treatment and disposal. The resulting regulations are expected to affect industrial discharges to Dubliclv owned treatment works iPOTW8), largely through requiring increased wastewater pretreatment before discharge to municipal sewer systems. EPA's Science Advisory Board (SAB) has reviewed three EPA reports addressing sludge disposal and reuse and has submitted recommendations to EPA Administrator Lee M. Thomas. The first report, prepared by EPA's Office of Water Regulations and Standards (OWRS), covers four sludge-disposal options: landfilling, land application and distribution, incineration, and Ocean disposal. It addresses methodologies for evaluating the scientific validity of each option, the identification and consistency of needed data, and modeling requirements. The document represents the beginning of a framework for evaluating sludge management risks and developing national criteria, an approach endorsed by the SAB. Among other issues, the SAB review focused on the use of "reasonable worst-case" estimates; it pointed out that the report reflects many conservative, subjective assumptions in positing its reasonable worst cases. Because it could not determine whether the worstcase scenarios developed were too conservative &e., unrealistic), the SAB recommended that detailed sensitivity analyses be conducted to determine their reasonableness, the uncertainties associated with typical results, and the 746 Environ. Sci. Technol.. Val. 21, NO.8. 1987
probability distribution of exposures and risks based on specific assumptions and scenarios. The SAB also found that the OWRS risk assessment methodologies for the four sludge disposal options were not consistent, and good comparability among the alternatives was therefore lacking. Other specific comments included the need for clear distinctions between risk assessment and related concepts and methodologies such as hazard assessment. dose-response models, vulnerability analysis, riskbenefit analysis, and exposure assessment; SAB suDwrt for eood mathematical modeliig and appropriate use of quantitative evaluation for technical, economic, institutiond, political, and social dimensions: and the importance of including effects on species other than humans. The SAB recommends that the term "most-exposed individual" be replaced by "mostexposed unit" to signal EPA's concern with effects besides human health risks.
Alternatives to ocean disposal The second EPA report. prepared by the Office of Policy Planning and Evaluation (OPPE), provides a methodology for evaluating landfill and land a p plication alternatives to ocean disposal of POTW sludge. The SAB's major findings include the following: regarding OPPEs proposal that EPA analyses of dumping sites be done on a regional basis, the entire United States coastline could not be represented by six coastal sites with respect to variations in soil, climate. and hydrologic and POTW disposal conditions; the report should consider codisposal of POTW sludges in landfills, along with other municipal and industrial wastes; because conditions at individual sites may differ significantly from model predictions, the SAB recommends
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sensitivity analyses to evaluate the precision of the parameters in the models; and the documentation provided is inadequate to support the use of the Pesticide R w t Zone Model proposed to describe transport of chemicals in the soil, and there is no discussion of validation for using the Analytic Transport 1-2-3 Dimension Model or the Exposure Analysis Modeling System model for transport in surface water. Also, use of the Universal Soil Loss Equation model, developed to predict soil movement within a field, is suggested to predict sediment yield to a stream, but other models should be considered for this purpose.
Ocean dumping replations The third report reviewed by the SAB was the Office of Marine and Estuarine Protection (OMEP) technical document wpporting revisions to the agency$ ocean dumping regulations for sewage sludges and dredged materials. The two main issues are technical justification for the separate regulatory treatment of the disposal of sewage sludges and dredge materials, and consideration of both the need for ocean disposal and the availability and impacts of land-based alternatives. The SAB found that the reportk conclusions were not adequately supported by the data and that separate testing of dredged material is not always justified. It therefore recommended that a protocol be developed to identify, for each site, any differences between dredged materials and sewage sludge in order to make appropriate decisions on disposal options. Although publication of the regulations is tentatively set for the fall, the time needed to perform the additional work recommended by the SAB may require some extension of schedules.
Richard M . Dowd. Ph.D., is president of R. M. Dowd & Company, scientific and environmentalpolicy consultanrs in WashinRron. D. C.
