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• The statistical method proposed to document and quantify the asymptotic condition is published in an American Petroleum Institute (API) publication entitled Technological Limits of Groundwater Remediation A Statistical Evaluation Method(Publication No 4510, 1991) Generally, the API method dc5nes an asymptotic condition as one in which some concluding time period in a time series data set exhibits a negligible trend or slope that is not statistically different than zero Additionally, both the upper and lower bounds on the slope (at the 95 percent confidence interval) should be small Sequential regression is used to identify data subsets which are asymptotic The data subset (concluding time period) which has a regres- sion slope not different from zero (upper and lower bounds straddle zero) and for which the absolute value for the lower or upper bound slopes (the largest of the two) is smallest for all subsets analyzed, is defined as the most trendless data subset It is proposed that SVE is terminated when a trendless data subset is identified for a time period of 3 months Again, it should be remembered that termination of SVE does not mean termination of remedial action Groundwater monitoring and WQLZ maintenance will continue, and intrinsic remediation mechanisms (i e, biodegradation) will be relied upon to continue the restoration process and maintain plume stability 5.4 Alternative Evaluation Technical, institutional, environmental safety, and economic criteria were used to evaluate the . alternatives Because some remedial alternative elements were common to both alternatives, only the characteristic elements (described above) were considered during the evaluation process It was determined that Alternative 2 was the most feasible for long-term application Alternative 2 was chosen on the following basis • Technical. Technical criteria considered included short- and long-term effectiveness, reduction in the toxicity, mobility, and volume of affected media, and implementability With regard to implementability, Alternative 2 is favored because implementation is not expected to significantly disrupt the site, or the community In terms of effectiveness, Alternative 1 is anticipated to be more effective in the short-term This is because affected soil would be immediately removed and hydrocarbon mass removal would be more extensive than would be using Alternative 2 It should be noted the EPA suggests that the volume of soil considered by this plan is greater than the volume limit considered technically feasible to handle using excavation Between Alternatives 1 and 2, long-term effectiveness is expected to be essentially the same because capillary fringe and groundwater impact would be reduced by intrinsic mechanisms For example, the conditions that limit the biodegradation rate ( i e , compound availability for biodegradation, compound solubility, molecule branching, and molecular weight) would be 3201337B/1918REV 24 August 31, 1995