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Groundwater Monitoring and Mitigation Plan for <br />Heit Aggregate Resource Operation-Weld County <br />Aquatic and Wetland Nursery and Coyle Properties <br />4.1 Trigger Definition <br />Groundwater levels should continue to be monitored on a monthly basis for at least the first year <br />of mining, starting when de-watering operations for mining commence. This post-mining data <br />should be compazed to baseline data to assess whether the operation is affecting groundwater. <br />It is proposed to define a level of change in baseline groundwater levels that would "trigger": <br />]) Immediate cessation of dewatering operations, <br />2) An evaluation of the data and factors causing the decline in readings (to confirm that the <br />mining operation was responsible), and <br />3) Implementation of mitigation measures. <br />For the purposes of this plan, it is proposed that potential impact to groundwater will result and <br />the above actions will be triggered from post-mining data that show: 1) a lowering of the average <br />(growing or non-growing season) groundwater by more than 2 feet, or 2) lowering of two or <br />more consecutive readings by more than 2 feet compazed to data taken at the same time of year <br />prior to mining. Two feet is recommended as the limit of change in groundwater since the <br />preliminary modeling indicates that this is the maximum change that will occur and since <br />lowering of groundwater any further could limit sub-irrigation in the growing season. <br />5.0 RECOMMENDED MITIGATION MEASURES <br />The mitigation measures described in this section could be used to alleviate an impact to <br />groundwater where monitoring data triggers a determination of impact, as defined in the previous <br />section. The mitigation measures have been evaluated at a conceptual level in terms of <br />feasibility. The exact measure or combination of measures used should be determined based on <br />consultation with the affected party. The cost for construction and maintenance of mitigation <br />measures will be borne by the owner of the Heit Pit. <br />' 021-110.030 Wright Water Engineers, Inc. Page 4 <br />July 2003 <br />