2005-01-14_REVISION - M1999120 - Laserfiche WebLink

Home Browse Search

4. The Division requested that the Applicant explain any mitigation measures to be implemented if trigger points aze met. The WWE report indicates what mitigation measures should and could be taken, but does not commit the Operator to implement any single one or combination of these measures. Please commit to what measures will be taken should the trigger points be reached. 5. The Applicant has proposed to provide the baseline groundwater data to the Division via a Technical Revision, between the time that the slurry wall is installed and before mining commences below the water table. The Operator and Applicant should be aware that the slurry wall is the feature that may disrupt the groundwater r8gime, and not mining below the water table inside the slurry wall. Therefore, one yeaz's worth of groundwater data must be acquved and submitted to the Division for review, prior to installation of the slurry wall. 6. In a letter from the Operator dated January 7, 2005, the Operator has proposed to "continue to collect data for at least 12 months, or until just prior to the start of disturbance in amendment area, and the fmal pre-mining baseline averages will then be calculated from all data collected." To clarify, the Division is in agreement with the W WE report, which states, "It is recommended that LGE continue to measure groundwater in the existing monitoring wells...throughout the life of the existing mine. Groundwater should also be monitored throughout the life of the expansion area..." 7. The January 7th letter also states, "...we propose that a change in the preliminary and then final baseline average monthly groundwater level in the vicinity of the amendment azea of greater than 5 feet, and documentation of a complaint caused by this change, would trigger an investigation to confirm that L. G. Everist, Ina (LGE) was responsible for the lowering of groundwater... Further, if there is a complaint prior to reaching the 5 foot trigger, it would be investigated to determine its causes, and if it is found that that LGE operations are responsible, then LGE would work with the affected party to implement measures agreed to in order to resolve the complaint. We are basing our proposed trigger point on the preliminary pre-mining baseline average data, which has shown natural fluctuations of groundwater levels of 3 feet. With this natural fluctuation, the trigger of 5 feet is actually reduced to 2 feet of change, an amount noted as acceptable to DMG" The Division does not agree with the 5-foot trigger point proposed by the Operator. This trigger is based on an average water level and does not account for seasonal fluctuations in groundwater. The Division has approved plans that set a trigger point of a 2 foot drop in the seasonal water level, but not based on an average groundwater level, plus an additional 2 foot drop. As mentioned under item 8 in this letter, a drop of 5 feet in groundwater levels during irrigation season has a much higher potential for negatively impacting well production and subirrigation than would a two foot drop during the seasonal groundwater highs. The Division does agree with the Operator's proposal to investigate any complaint received, regardless of the change in goundwater elevation. 8. The Division requested that the Applicant describe how the shadow effect will impact, among other things, the activities, which rely on groundwater in the vicinity of the site; vegetation on or near the site, including the cottonwood trees in the riparian azea neaz the South Platte River; and the wetlands located on the site. The information contained in the WWE report raises concems with the Division regarding these issues. The WWE report indicates that the expected shadow effect north of WCR 18 is as great as four to five feet lower than current levels, versus the current shadow effect of the existing slurry wall in this area of 1 foot lower or less. In that a nursery is known to operate in this azea, and no specifics have been submitted to the Division with regard to this operation and its reliance on subirrigation and its well, the Division needs further information regarding the potential impacts to the nursery operation. The well belonging to the nursery is projected to experience a 16 percent reduction in the saturated thickness in and azound the well. The report projects that this degree of reduction may fall within the natural range of groundwater fluctuations, and therefore, should have impacts too small to impact yields from the well. The Division does not agree with the conclusion contained in the W WE report without quantified evidence. Although the 16 percent reduction may fall within the seasonal fluctuations of the groundwater level in this well, the user is more likely to rely on greater amounts of water coincident to the growing season, and therefore, the irrigation season and higher goundwater levels. Although the well may have as much as a 16 percent reduction in the saturated thickness during non-irrigation periods, the user will likely not be pumping large amounts from the well at this time. If the user did attempt to extract the same amount of water as during the irrigation season, when the water levels were lower, the well may not produce the needed quantities of water. The Division requves more quantified data regarding this well and the owner's reliance on subirrigation to assure that the user will not be negatively impacted by the operation. 9. The Division expressed concerns in the first adequacy review that there may be effects on the amount of water conveyed in the irrigation structures that aze located among and adjacent to the proposed phases. As the Division stated, if these structures leak and the groundwater level around the structures is lowered as a result of mining activities there is likely to