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Fair Meadows Pit Groundwater Evaluation <br /> November 19, 2022 Page 8 of 28 <br /> this run, the model cells within the Loloff and Derr pits were turned off. This caused the water <br /> table to back up (ie. mound) behind the slurry walls as the modeled blue 4630 contour shows <br /> (convex east the down-gradient direction). The modeled (blue) 4620 ft and 4610 ft contours are <br /> slightly higher than what was observed(white contours) mostly because the observed contours are <br /> influenced by late season(September, 2022) irrigation pumping(ie. lower than average). <br /> Observed vs. Modeled Heads <br /> We compared the observed vs modeled heads at well locations in the figure below. <br /> 4670 <br /> N 4660 <br /> E v=1.0004x <br /> 4650 R'=-0.304 <br /> N <br /> • <br /> O •♦ Residual Mean =•1.66 <br /> 4640 �. ' • • Residual Standard Dev. -9.49 <br /> W 4630 • • ~ � • Absolute Residual Mean =6.93 <br /> •�•��rN• • • Residual Sum of Squares -1.01e+004 <br /> Q 4620 •Xti• RMS Error =9.64 <br /> H • •f.• • • Minimum Residual =•33.45 <br /> • Maximum Residual =29.40 <br /> 3 4610 • •i Range of Observations -81.80 <br /> O 4600 Scaled Res.Std.Dev. -0.116 <br /> m Scaled Abs.Mean =0.085 <br /> y 4590 Scaled RMS -0.118 <br /> O <br /> 4580 Number of Observations -109 <br /> 4580 4600 4620 4640 4660 4680 <br /> Observed Water Table Elevations(ft.msl) <br /> If there were perfect agreement, the data would plot on a straight line with a perfect 1:1 <br /> relationship. The best fit line shown above has a slope of 1.0004 : 1 which is a very close to perfect <br /> when considering all the data. However, observed levels are slightly higher than modeled up- <br /> gradient (>4620 ft) values, and observed values are slightly less than the modeled downgradient <br /> (<4620 ft) values. We did not spend a considerable time trying to obtain a better match heads <br /> because the ultimate objective to estimate potential mounding and shadowing is insensitive to <br /> aquifer parameters (discussed below in"Model Sensitivity" section). <br /> The "calibration" statistics are shown next to the figure above. The Root Mean Squared (RMS) <br /> error (9.64 ft) is the square of the difference between the observed and modeled values (aka <br /> "residual"). We feel this value is reasonable considering the data covers over approximately a 60- <br /> year period and recent observations have been effected by pit dewatering,slurry walls and seasonal <br /> pumping and return flows. <br /> Mass Balance <br /> Table A4 shows the model mass balance results which shows the inflow and outflow components <br /> that include alluvial aquifer inflow and outflow and river leakages in and out of the Poudre River. <br /> McGrane Water Engineering,LLC <br /> 1669 Apple Valley Rd. •Lyons,CO 80540 •Phone:(303)917-1247 <br /> E-Mail:dennis@mcgranewater.com Web:ttp://www.mcgranewaterengineering.com <br />