2005-06-24_REVISION - M2000016 (13)

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~FARGE NORTH AMERICA AGGREGATES, CONCRETE Ife ASPHALT surrounding groundwater table. In the model, any inflow of groundwater to the dewatered pit wa.s assumed to be conveyed instantaneously to the South Platte River where it had no effect on the overall results of the model because the head at the South Platte River was held constant. 14. (AMEC, p. 11) Page 11 of the AMEC report indicated that registered alluvial wells within 600 feet were identified based on SEO records. Were field inspections conducted to identify ALL wells within 600 feet? Will any wells beyond 600 foot-radius be affected by the mine operations? No field investigation of wells within 600 feet of the site has been completed to date. However, as a part of the well permitting process through the State Engineer's Office, Lafarge will work with the District 2 Water Commissioner to locate any wells within 600-feet of the site that are not permitted with the SEO. Ba<ed on the SEO's well permit database, there are permitted wells that may be affected by the mining operation. As stated previously, based on the modeling this impact will be less than 5 to 10 feet of drawdown for wells outside 200 feet of the site. 15. (AtLfEC, pp.ll-12) Regarding Well Permit No. 2216, the report concludes, "The estimated drop in groundwater level at this well should have a minimal impact to the historic use of the well. " Table 5 shows that the modeled water level change at this well during mining is -3.0 feet. What is the basis for this conclusion? Please see the enclosed Well Permit for this well. 16. (AMEC p.ll) The necessary agreement Ivith the owner of Well Permit No. 13697, which is expected to be unusable during the life of Phase 6 Cell 1, must be prior to approval of this amendment. Although the AMEC report recommends otherwise, our opinion is that an agreement with the landowner is not necessarily required fot approval of the amendment. Any concerns that the well owner may have about the effects of the mining operation on the well will be addressed through the well permitting process with the SEO. The owner of the well has been notified of this amendment and has not objected to issuance of the permit. 17. (Ah1EC p.12) Well Permit No. 7280 was identified as within 600 feet, but opposite the South Platte River from the mining activities, so not expected to be significantly affected. The Division agrees that impacts are not likely. However, to verify this assumption, the applicant must install or identify a monitoring well in the vicinity of this well suitable for establishing a baseline and monitoring for potential impacts. See also the Groundwater Monitoring Plan section of this memo. An additional monitoring well on the opposite side of the South Platte River from the mining operation is not necessary. If the DMG agrees that impacts to the well are unlikely, we suggest that the well itself serves as additional way to monitor any effects the mining operation maybe having on the groundwater table on the o.~posite side of the well If the mining operation is having an effect on the well on the opposite side of the river, Lafarge will work with the owner to LAFARGE NORTH AMERICA INC. -Lafarge Construction Materials 10170 Church Ranch Way. Suite 200, Westminster, Colorado 80021 Telephone: (303) 657000 Facsimile: (303) 657-4037