In response to effluent limitation guidelines promulgated by the United States Environmental Protection Agency, industry has developed alternatives to the water and oil-based drilling fluids used offshore. These synthetic-based muds (SBMs), enhanced mineral oils (EMOs) and purified paraffin oils have lower toxicity and smaller environmental impacts than diesel or conventional mineral oil-based muds (OBMs). EPA is developing new guidelines for the discharge of these fluids and the associated cuttings. The decision about allowing or disallowing the discharge of cuttings with small amounts of associated SBMs, EMOs and purified paraffin oils should not be based solely on potential environmental impacts, especially those such as bioaccumulation or biodegradation that may not be directly connected to effects on populations or ecosystems. Regulatory decisions about drilling fluid discharges should also consider potential impacts associated with the alterna-tives; including occupational accidents and chemical expo-sures, impacts associated with disposal, air emissions, and transportation risks. Because these new fluids are expensive, industry will not continue to use them if the cuttings cannot be discharged offshore. The alternative to allowing the discharge of these new drilling fluids is the continuing use of OBMs in difficult drilling situations. This paper develops a framework for a comparative environmental assessment for the discharge of drilling fluids, to help support a risk-based, integrated approach to regulatory decision making.

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