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<br />could be due to conditions other than the presence of the slurry wall, i.e. reduced precipitation and cessation of irrigation <br />of the Stegner Farms site. Though these parameters may be aggravating the drop in groundwater levels, the report does <br />not eliminate the possibility that the presence of the slurry wall may be affecting the ground water levels down gradient of <br />the site. This is a concern because according to the Colorado Revised Statues (CRS) the operator is required under the <br />permit to minimize disturbances to the prevailing hydrologic balance of the affected land and of the surrounding area both <br />during and after the mining operation and during reclamation. The additional data supplied by Aggrgate Industries from <br />LaFarge monitoring wells is also inconclusive. Based on the water levels in the Lafarge wells alone, it does appear that <br />groundwater levels south and southeast of the potentially affected land owners are relatively similar to pre-slurry wall <br />water levels. The location of these wells, however, still leaves some doubt as to the extent of the depression caused by the <br />slurry wall. <br />8. Although the conditions specified in the permit application with respect to the triggering events necessary to install a <br />french drain have not been met, it is the operator's responsibility to operate within the requirements specified in CRS 34- <br />32.5-116 (4) (h) and (i). Therefore it is necessary that Aggregate Industries submit a groundwater level analysis that better <br />delineates the extent of the mounding and shadow effects of the slurry wall in order to determine whether Aggregate <br />Industries is operating within the restrictions set forth by the CRS. As a minimum, a potentiometric map of the region <br />encompassing the areas east of the slurry wall and southwest of the slurry wall must be included, so that boundaries of the <br />depression can be identified. Additionally, the groundwater surface in the area north of the slurry wall and west of the <br />slurry wall need to be mapped so that the extent of the mounding effect can be identified. Groundwater measurements for <br />this analysis may be taken from monitoring wells, residential wells, and groundwater fed ponds and lakes. If historic data <br />is available from ponds, lakes or residential wells, this information must also be included in the analysis submitted to the <br />DMG. Alternatively, Aggregate Industries can install a french drain or other effective system to allow the water upgradient <br />of the slurry wall to circumvent the wall an<I flow unimpeded downgradient. If the french drain or other mitigation option <br />is taken, Aggregate Industries must monitor the groundwater levels in the affected regions both pre- and post-mitigation <br />system installation to identify whether the system is operating effectively to mitigate mounding and shadowing effects of <br />the slurry wall. <br />~;~~ ~ ~ <br />I & E Contact Address ~'I <br />NAME: Connie Davis /~~ x(070 DUOS ~~f~ 335 <br />OPERATOR: Aggr~a[e industries <br />STREET: P O Rnx 3121 <br />CITY/STATE/ZIP: Oreele~• C'(1 RO6't1 <br />cc ^ CE <br />^ BL <br />^ FS <br />^ HW <br />^ HMWMD (CH) <br />^ SE <br />^ WQCD (CH) <br />® OTHER: <br /> Darwin Roe, neighbor <br /> Dr. Bill Martin, neighbor <br /> Kathie Troudt Riley, P.C. <br />