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March 17, 2016 Page 5 in the unit. Younger more recently infiltrated water may be transitional between precipitation and a fully evolved calcium carbonate groundwater. This evolution may be somewhat accelerated if the precipitation comes into contact with fine grained(crushed)limestone. In addition,the water quality may be affected by any other units that the water moves through. However,this is no different than any natural groundwater movement in the area. Exposure and crushing the limestone as the result of quarrying will not result in conditions that lead to accelerated metals release such as what might occur due to oxidation and the development of acid-rock drainage. The lack of any significant quantities of oxidizable minerals(e.g.,sulfides)along with the alkaline environment associated with the limestone will, in general, limit the dissolution and mobility of most of the metals of concern. However,both arsenic and selenium(metalloid and non-metal,respectively)can be mobile in alkaline conditions. Arsenic concentrations are not unique in the Fort Hayes,and the MEP suggests low mobility(Table 1). Selenium may be slightly elevated in the Fort Hayes compared to other limestones,and there were detected concentrations in the MEP extract(but at levels well below the Federal MCL of 0.05 mg/L). Therefore,if groundwater monitoring is conducted,selenium should be considered for the analyte list. Barium,an alkali earth element,may also be slightly above average in the Fort Hayes Limestone. However,based on the geochemistry of the element, including significant solubility limits,and the results indicating that the MEP results are much lower than the MCL,this element should not be a concern. GCC plans to beneficially use kiln feed material from the main kiln baghouse as reclamation pit backfill. Table 2 presents the available analytical data for this material. It is noted that for most of the analyte concentrations(RCRA metals),the total and leachate concentrations are generally similar to the unprocessed or minimally processed limestone(Table 1). For cadmium,lead and silver,total and MEP/TCLP(Toxicity Characteristic Leaching Procedure)concentrations for the kiln feed and limestone are similar. The TCLP method is similar to MEP,but slightly more aggressive(e.g.,more acidic than MEP). Total arsenic concentrations are slightly lower in the kiln feed while TCLP/MEP concentrations are similar. Similarly, total barium concentrations are slightly lower in the kiln feed,but slightly more leachable. Chromium is slightly higher in the kiln feed with similar leachable concentrations. Total selenium concentrations appear similar,but the leachable component may be marginally higher in the kiln feed. The most significant difference is noted for mercury. Total mercury concentrations are up to 1,000 times greater in the kiln feed, with the leachable fraction also higher(i.e.,detectable in the kiln feed). The MEP concentration was equal to the Federal drinking water standard(MCL)of 0.002 mg/L in one sample. The paste pH of the dust is highly alkaline at 11.3 to 11.4. The kiln feed material will represent only a very small fraction(less than 2%)of pit backfill,and will be placed under three feet of topsoil. Therefore,the pH and potential mercury concentrations would be highly mitigated. In both cases,attenuation during groundwater transport is also likely to be significant. Nonetheless,mercury would be a potential analyte at groundwater monitoring locations,along with the standard field measurements of pH,temperature,and specific conductance. Close Consulting Group LLC