2023-08-03_PERMIT FILE - M2023025 (32)

Home Browse Search

Bernhardt Pit Groundwater Evaluation May 2023 Page 15 of 31 A residual is the difference between observed and modeled values. The GWV8 program calculated residuals as the difference between modeled and observed values(the modeled value is determined based on the observed point location within the modeled cell). The distribution of residuals are shown on Figure A9. Residuals for the Bernhardt pit monitoring wells range from+0.2 ft to -1.6 ft which is less than the expected seasonal fluctuation. In general,modeled water levels are higher (blue positive values) east of the SPR and less than observed values (red negative values)west of the SPR. We believe this suggests that agricultural pumping east of the SPR may have suppressed measured water levels and the modeled levels better reflect predevelopment conditions. We simply believe that the small range of residuals around the Bernhardt pit supports our belief that the model results are accurate. Mass Balance Table A3 shows the model mass balance results (Run: Bernhardt_SS7) which shows the inflow and outflow components that include alluvial aquifer inflow and outflow and river leakages in and out of the SPR. The total aquifer inflow and outflow balance at 17.98 cfs. The SPR river gains approximately 8.18 cfs (13.56—5.38)which is approximately 2.7 cfs per mile. The mass balance error is 0.01% based on the difference between inflows and outflows. This low RMS and low model error support our conclusion that the model has a high level of accuracy. Table A3 also shows the model mass balance result(Run:Bernhardt_SS8)which shows the inflow and outflow components when the pit cells are turned off. The total aquifer inflow and outflow balance is 18.05 cfs. We do not believe the small difference between the total mass balances (.07 cfs)reflects any significant source of model error. Water Level Changes Caused by the Bernhardt Slurry Wall In run <Bernhardt SS8>, we turned the pit model cells off and used the output heads from the initial run as starting heads. Figure A10 is the contoured "difference" in model output heads between the post-pit run minus pre-pit run determined using GIS grid-math techniques. Positive values on the south and east sides of the pit(left side of model)reflect mounding. Negative values on the north and east sides of the pit reflect lower water levels in the "shadow" of the pit. The maximum mounding on the upstream side is approximately+2.5 ft and the maximum shadowing is approximately-2.5 ft on the north side(right side of the figure). Mounding greater than 0.5 feet extends approximately 1,500 feet up-gradient (south), and shadowing less than -0.5 feet can be expected approximately 2000 feet downgradient(north). There are five registered wells located within modeled change between 0.5 and 1.0 ft as summarized in Table 1. Four of the wells are located in the mounding area on the up-gradient side of the pit and one well (13701-F) is located on the downgradient shadow side. Two of the four up-gradient wells belong to the Bernhardt's which are now owned by the applicant. Table 1 —Water Level Changes>0.5 ft in Re istered Wells Permit No. Well Owner Twn ling SEO LinknB Sec Qtr� r Change(ft) 14477-F KASTEN CHERYL L&CARLEN E M KASTEN 4N 67W 24 SWNW +0.5to1.0ft httDs;//dwr.state-co.us ools ellPermits0228691 42519-F BERNHARDT,DAIRY 4N 67W 24 SWNE +0.5to 1.0ft htt s: dwr.state.co.us ools ellPermits 0353174A 5-WC8 MONGOMERY,VIOLET 4N 67W 24 SENW +0.5to1.0ft httr)s://dwr.state.co.us/Tools/WeliPermits/C620005 85-RF BERNHARDT,BEN 4N 67W 24 SANE +1.0to 1.5ft https:LLdwr.state.co.us/rools ellPermits 9058262 13701-F BERNHARDT,HERBERTB 4N 67W 12 SWSW -0.5to-1.0ft htt s: dwr.state.co.us/Tools/WellPermitsQ061716 McGrane Water Engineering,LLC 1669 Apple Valley Rd. 0 Lyons,CO 80540 a Phone:(303)917-1247;email: dennis@mcgranewater.com