2005-01-24_REVISION - M1999120 - Laserfiche WebLink

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RE: L. G. Everist, Inc., Fort Lupton Sand and Gravel Mine, DMG #M-1999-120; Second Adequacy Response Letter been collected. Wells will continue to be monitored at least monthly by LGE once mining starts (and/or slurry wall construction starts) and 3-month running average groundwater levels that represent post-mining conditions will be calculated for each well. These post-mining/post- disturbance averages will be compared to the pre-mining averages for each well. If the post- mining/post-disturbance average varies by more than 2.0 feet, then this portion of the trigger will be met. The other portion of the trigger that has to be met is that a complaint must be received or if monitoring of vegetation indicates a hydrologic imbalance. LGE will commit to the 2.0 foot trigger, although we would still like to state for the record that we believe that 2.0 feet is too small when taking into account the natural fluctuations in groundwater levels due in part to precipitation or drought and/or irrigation. Further, if the 2.0 foot trigger is reached, but LGE has not started any new mining or slurry wall construction, it can be assumed that LGE is not the cause, and the pre-mining groundwater baseline may have to be adjusted via a Technical Revision. Refer to Number 5 for actions taken if a trigger is met. Also refer to Numbers 12-14 for details on monitoring of vegetation. 8. Nursery, N side of CR18, nursery well and the owner's reliance on sub-irrigation. We have observed that the nursery flood irrigates, and does not rely on sub-irrigation. The trees at the nursery are in raised rows, allowing the owner to flood-irrigate, by pumping from the well. Therefore, the mitigation would be the same as for any well -after determining that LGE is the cause, and discussions with the nursery, we would deepen, modify, or replace this well. 9. Lupton Bottom Ditch LGE has an agreement with the Lupton Bottom Ditch Company (LBDC), which ensures that LGE will mitigate any damage (including water loss) that LGE's operation causes the LBDC. (A copy of the agreement was included in the first adequacy response, dated January 3, 2005.) LGE has experienced very little leakage from the East Lateral of the Lupton Bottom Ditch in the area of the current mine. The analysis in the WWE report that concludes that there will not be excessive seepage from the East Lateral is consistent with observations and data. Records show 4-5 gallons per minute of inflow into the existing pit that is attributable to seepage from the approximately 0.25 mile reach of ditch through the site. This is a very low rate of seepage. Slurry walls will be constructed around the ditch prior to mining in the amendment area. This will create a seal around the ditch which will prevent excessive seepage. Also, we have consulted with WWE regarding the statements concerning recharge assumptions in the model. WWE did not include any recharge to groundwater from any ditches in the vicinity of the proposed expansion in the model. Also, what WWE meant by the statement, "Recharge from the East Lateral of the Lupton Bottoms Ditch, in particular, will maintain groundwater levels north of the expansion." was that the East Lateral will recharge groundwater levels from irrigation from the ditch, not from ditch seepage. Historically, water has been diverted from the East Lateral for irrigation of the land north of the expansion. Because there is very little leakage from the ditch, and because we have an agreement with the Ditch Company, LGE feels that additional monitoring is not required. LM/FL-Resp2ndAdegRev-dmgKP-012105.doc 4