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PM14 Statistical Analyses for Toxicology
(PM209) Variability in the sediment test used to measure the toxicity of synthetic-based drilling muds.
Louallen, J1, Rabke, S2, Dorn, P1, Wong, D.1, Purcell, T3, Hood, C4, Glickman, A5, 1 Shell, Houston, TX2 MI Drilling, Houston, TX3 Am. Petroleum Inst., Washington, D.C.4 Baker Hughes Inteq, Houston, TX5 ChevronTexaco, Richmond, CA
ABSTRACT- The USEPA regulates the sediment toxicity of synthetic-based drilling muds (SBM) discharged from offshore oil and gas exploration and development activities in the Western Gulf of Mexico. EPA promulgated a Best Available Technology (BAT) limitation and New Source Performance Standard (NSPS) to control the maximum sediment toxicity of SBM at the point of discharge. Sediment toxicity is measured by a modified ASTM 96 hr sediment toxicity test using Leptocheirus plumulosus. Contrary to the traditional use of a numerical limit, EPA promulgated a sediment toxicity ratio of less than 1.0 to determine the pass/fail of a field sample compared to the C16-C18 internal olefin reference SBM. A field SBM, which may contain olefins, esters or a blend of fluids, can be equally or less toxic, but not more toxic than the reference. A single toxicity test is used to determine satisfactory laboratory performance and whether an SBM can be discharged. The ratio rejects a field mud sample only if the toxicity ratio is still greater than 1.0 after test variability is considered, by using a 0.25 multiplier initially recommended in 2001 based on very limited test data. Over the past several years, an industry work group has sponsored studies to further develop and understand the sediment toxicity test as a compliance tool. Among such studies were round robin tests aimed to develop the competency of laboratories and to understand intra- and inter-laboratory variability. With compliance testing currently underway, a coded database of over 400 tests is available that allows a robust statistical evaluation of the variability associated with the sediment tests with field and reference SBM. Results of this statistical evaluation and recent laboratory round robin testing will be presented.
Key words: sediment toxicity, drilling mud, oil and gas drilling
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