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SEP-05-2003 FRI 09 26 AM BANKS AND GESSO LLC FAX N0. 303 274 8329 <br />September 4, 2003 <br />re: Haldorson and Sons, inc. Sand and Gravel Mine, hydrology issues <br />cc: Paul Gesso, Tom Smith <br />Dear (Nr. Haldorson, <br />This letter report addresses the hydrologic issues pertinent to Che Colorado State Division of Minerals <br />and Geology (DMG) review of the proposed Haldorson and Sons Inc., Sand and Gravel Mine located <br />on Spring Creek Mesa near Montrose, Colorado. These findings are based on a review of Exhibit D, <br />Mlning Plan prepared by Banks and Gesso, Exhibit G information from B nearby DMG permitted gravel <br />mining operations, results of siz test holes drilled on the site, the WestWater Associates report, as well <br />as my on-sate investigation. <br />The following issues an: addressed in this letter, <br />1. Background <br />2. Hydrologic balance <br />3. Dry versus wet pit <br />4. Storm water runoff <br />5. Water quality <br />6. Hydrologic Impacts <br />7. Remedial action <br />e. Need for a comprehensive hydrologic study <br />1. Background <br />The WestWater report presents an accurate picture of the hydrologic conditions in this area. I concur <br />with their basic findings, aRhough t have not confirmed speafic numeric values presented in the report. <br />Important conclusions are that groundwater is derived from preapitatlon, non-consumed irrigatjon and <br />leakage from ditches and canals. Groundwater flow generally moves from the southwest to the <br />northeast along the gradient set by the top surface of the Mancos Shale formaflon. This is similar to the <br />slope and direction of the surface topography. Regional groundwater levels in the gravel deposits are <br />signficantiy affected by inigatlon practices and vary, in Gme, with the irtigation cycle. Springs and ponds <br />occur in nearby gravel ptts and along the natural and manmade slopes that penetrate the gravel <br />deposits along the edge of the mesa. <br />Hydrologic effect of a gravel pit - Digging a gravel pit is analogous to drilling a weu. In either case <br />the actual hole has little effect on the shape or location of the groundwater surface. if the bottom of <br />the well (pit) is deeper than the prevailing groundwater surface, then water will flow into the well (pit). <br />The waif (pfl) will fill to the same level as the surrounding groundwater surface. Once the well (pit) <br />has filled, water will flow through the well much the same as It did before She well was drilled with nc <br />measurable efrect on the gradient or elevation of the groundwater surface. because a gravel pit is <br />much larger than a well there may be a small variation between the'~vith° and'Without" <br />groundwater surfaces. One might expect the water surface in the pit to be slightly higher than <br />without the pit due to reduced head loss in the flow over this distance. <br />With a well, the groundwater surface is not Impacted unless you pump It. Pumping draws down the <br />water surface elevation in the well, creating an altered gradient an the surrounding groundwater <br />surface that now slopes toward the welt (cone of depression}. Groundwater within the influencer of <br />this cone will flow towards the well instead of along the natural gradient (without pumping). The <br />radius of influence and the rate of flow associated with the cone of depression are dependent on the <br />amount of drawdown created by the pumping, the properties of the aquifer material and the <br />geometry of the area. <br />P, 02 <br />