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Man:h 7992 Plasticity Evaluation ~ 2 <br />For the plastic limit test, the sample from [he liquid limit test is dried until the sample can be remolded and <br />rolled into a uniform thread approximately I/8-inch in diameter. Percent moisture at the point where this <br />thread begins to break into segments approximately 1/8 - 3/8 inch in length is designated az the plattic limit. <br />Plazticity index is then calculated az the numerical diHereace between the liquid and plastic limits. <br />2.0 Evaluation of Plasticity Test Results <br />ACZ will review, organize and evaluate all plazticity test data resulting from [he initial sampling. Evaluation <br />will include statistical analysis to determine minimum/maximum values, range, mean and standard deviation <br />for liquid limit, plastic limit and plazticity index Da[a will also be analyzed [o identify and determine [he extent <br />of any correlation between plazticity values (or raw and in-place samples, samples corresponding to production <br />from the two different coal seams, and samples from different placement periods. <br />Mean plasticity index value and range of values will be reviewed relative to the friction angle assumptions <br />utilized in the most recent (1/14/92) stability analysis and any previously determined or assumed values. <br />Variances between actual and assumed values will be quan[i£ed and both variances and related implications <br />relative [o [he stability analysis, swctural integrity of the existing refuse stockpile, and current and future <br />placement practices will be presented and discussed in a summary evaluation report. <br />In the unlikely event that plasticity testing indicates much higher plasticity values than assumed in the most <br />recent stability analysis, ACZ will rerun the analysis using new material strength parameters consistent with <br />representative plasticity values. Based on the results of [his new analysis, ACZ may verify that the existing <br />refuse pile configuration and placement practices conform with applicable regulatory requirements, propose <br />additional sampling and testing to more accurately define actual material strength parameters for [he existing <br />pile, or recommend spec modifications [o [he stockpile configuration and/or refuse placement practices. <br />3.0 Ongoing Plasticity Monitoring <br />The need for and scope of ongoing plasticity monitoring will be determined by the results of [he initial testing. <br />If testing indicates uniformly low plasticity index values, no additional monitoring maybe indicated. Conversely, <br />if some or all plasticity index values are high, more rigorous monitoring may be appropriate to insure [he <br />stability of portions of the refuse pile [o be constructed in [he future. It is anticipated [hat actual test results <br />will fall somewhere between these two extremes. EFC[ currently assumes that monthly sampling and testing <br />will be required over a period of six months [o one yeaz to document the normal range of plasticity values and <br />identity any significant variances. The plan for any future plasticity monitoring will be developed and submitted <br />to CMLRD along with the summary evaluation report az par[ of a technical revision submittal. <br />4.0 Criteria and 1Jesigns for Selective Placement of High Plasticity Material <br />Initial and ongoing sampling and monitoring will provide the basis for development and any necessary future <br />modification of the criteria and designs for selective refuse placement. If high plasticity materials are identiFed <br />by sampling and testing, it is anticipated [ha[ a plasticity index threshold level will be established az [he <br />quantitative determinant dictating selective placement. Based on s[andazd engineering practices and experience <br />on similar facilities, ACZ assumes that if selective placement is indicated, design plans will involve delineation <br />of critical failure zones, and specification of placement locations and practices for potentially deleterious refuse <br />materials to both keep these materials out of and prevent [hem from otherwise influencing these critical areas. <br />Criteria and designs for selective placement will be developed and submitted to CMLRD along with the <br />summary evaluation report as par[ of a technical revision submittal. <br />c:\rnrk\pn\v9\plazi pln <br />OJ/10/`~1 I lam <br />