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Mr. Douglas M. Ikenberry, P.E. <br />Page 4 <br />October 27, 2012 <br />Doty & Associates, LLC <br />Key conclusions that can be drawn from the monitoring conducted to -date are as follows. <br />1. Background has been adequately established for statistical analyses. <br />2. Other than equilibration with the chemistry of the comminuted overburden backfill, <br />there have been no significant groundwater quality changes and certainly no <br />changes indicative of a release from the disposal facility. <br />SUMMARY & CONCLUSIONS <br />In our opinion, a reduced sampling frequency is appropriate and justifiable for this site. <br />1. The regulatory requirement that background be established through collection of <br />a minimum of eight quarterly samples has been satisfied. <br />2. There is no evidence of a release from the ash backfill areas and constituent <br />concentrations have been quite stable during the period of record. <br />3. Rapid transport of dissolved contaminants associated with a release (that might <br />otherwise warrant more frequent monitoring) is highly unlikely given the low <br />hydraulic conductivity of the subsurface materials and the relatively slow <br />groundwater flow velocity. <br />4. The site poses little risk because the materials being placed are limited to a few <br />well characterized relatively inert materials and they are effectively isolated from <br />the environment by the disposal cell design. <br />5. There are essentially no downstream receptors due to the low population density <br />and very limited use of shallow groundwater in the area. <br />Therefore, we request that the groundwater monitoring frequency for this facility be <br />changed to semi - annual, as allowed at B4(B) of the solid waste regulations. <br />LOGISTICAL CONSIDERATIONS <br />Because the Keenesburg site is also regulated under the mining rules, a technical <br />revision to the reclamation permit will be prepared and submitted to DRMS after receipt <br />of approval of the monitoring schedule change from your Division and from Weld County. <br />We will continue the currently approved quarterly monitoring program until such time as <br />we have approvals from your Division, Weld County and DRMS. In addition, after all <br />approvals have been received, we will notify the three regulatory groups of our schedule <br />for implementing semi - annual monitoring. <br />