2005-01-03_REVISION - M1999120 (5)

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Ms. Lynn Mayer January 3, 2005 Page 5 Drawing 3 shows the predicted changes in groundwater under the first scenario, without the proposed amendment azea. This drawing indicates drawdown azound 2 feet upgradient of the RJ Campbell Pit, mounding of around 4 feet upgradient of the existing lined Ft. Lupton and NCCI Pits, and a small shadow effect downgradient of these two pits. The magnitude and extent of the shadow effect is reduced by mounding from the RJ Campbell Pit, which will not be lined. Drawing 4 shows the results of predicted changes in groundwater levels with all other permitted pits and the Ft. Lupton amendment azea. Drawing 5 shows the predicted net change in groundwater due only to the LGE expansion. The model results are conservative for several reasons, including: (1) it was assumed that the proposed amendment area is one large pit when, in fact, it will be several, smaller lined cells with some groundwater flow between them, and (2) rechazge to groundwater from Little Dry Creek and imgation ditches was not included in the model, but will lessen impacts. Recharge from the East Lateral of the Lupton Bottoms Ditch, in particular, will maintain groundwater levels north of the expansion. As shown in Drawing 5, the LGE expansion is predicted by the model to result in a maximum effect of 5 feet close to the pit with the shadow attenuating to zero approximately 3,500 feet north of the pit. The expansion reduces the amount of drawdown on the upgradient side of the RJ Campbell Pit due to mounding from the increased slurry wall. Additional mounding is projected to occur on the upgradient side of the LGE expansion. Five water wells exist in the groundwater shadow from the proposed expansion (Table 1). Two are lower yield domestic wells, and three are high yield irrigation wells. All of the wells are located in the South Platte alluvium. The closest well is a domestic well approximately 300 feet north. None of the existing wells are within an azea of projected drawdown of greater than 3 feet. The saturated thickness of the five wells was determined from well permit information. The percent change (reduction) in saturated thickness resulting from the LGE expansion only, and all other permitted pits, was calculated and the results are shown in Table 1. The saturated thickness of the wells will be reduced by less than 11 percent for all wells except Permit No. 6639. The saturated thickness in this well, which is owned by Blue Ribbon Nursery, is projected to be reduced 1l to 16 percent. The projected amount of reduction in saturated thickness is likely within the natural range of groundwater fluctuations, and is likely too small to impact yields from the wells. Drawing 5 shows that the amendment area is projected to raise groundwater on the upgradient (west) side of the pit. As discussed in more detail in the following response to question #8, this mounding should not have any deleterious effects on wetlands and other features on this side of the operation.