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• Contained within this report are evaluations of the chemical and physical data, locations and extends <br />of suitable and unsuitable overburden, and proposed methods of mitigation. Spoil mixing <br />phenomenon is discussed and core variability is documented. A sampling program immediately after <br />mining is proposed to investigate and evaluate mining methods, overburden mixing, and reclamation <br />success (see Section 2.05.4(2)(d), Topsoil (Redistribution). These investigations and proposals are <br />intended to optimize postmine vegetation growth and ground water aquifer characteristics. <br />Conclusions and recommendations are based on the interpretation of laboratory data and lithological <br />descriptions developed during the sample collection and analysis. <br />Overburden Sampling Schedule <br />A two phase overburden sampling program was utilized within the proposed New Horizon 2 permit <br />area to prepare the overburden assessment. Similar phased sampling techniques have been <br />described by USDA (1979), Barrett et al. (1980), Dollhopf et al. (1981), Barth et a1. (1981), Dollhopf <br />(1983), Montana Department of State Lands (1983), and Wyoming Department of Environmental <br />• Quality (1985). Phased drilling programs can decrease overburden, interburden, and underburden <br />(OIU) characterization costs substantially without jeopardizing the quality of data obtained. <br />The following tasks were accomplished during the two phases of OIU analyses: <br />Phase I: The first phase drilling was implemented in 1988 to determine OIU characteristics <br />over the entire study area and to obtain representative core hole locations from which <br />cross sections could be developed. Following the initial data analysis and <br />interpretation, general areas and percentages of suitable and unsuitable material <br />were identified. The site specific horizontal and vertical variability and discontinuities <br />of strata were evaluated. <br />Phase It: Three additional sampling locations were approved for the New Horizon 2 study area <br />on August 7, 1987 by CDMG (Peter O'Connor's letter to J. Lunan). Phase II drilling <br />converged on the OIU problem areas to better define and confirm the extent of <br />suitable, marginally suitable, and unsuitable material. Constituents which approached <br />Revised 9/99 2.oa.s-s <br />