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Response to Exhibit B. Comment 4 <br />The Uncompahgre River through the area of the proposed <br />ZMK Gravel Pit is a loosing stream. That is, the water table <br />adjacent to the river is below the level of the streambed. The <br />attached sketch shows a cross-section drawn through the Webb <br />domestic well, Monitoring Well No. 3, and the river. <br />The Webb well was drilled to a depth of 97 feet in <br />August of 1974. At the time of drilling, the water depth was 40 <br />feet below the ground surface. Monitoring Well No. 3 was <br />installed to a depth of 15 feet below the ground surface during <br />January of 1992. The monitoring well is about 95 feet away from <br />the creek bed and did not encounter groundwater. Neither did <br />Monitoring Well No. 2 which is 70 feet from the river. <br />On February 1, 1992, the water depth in the Webb well <br />was 82 feet below the ground surface. According to Mr. Webb, <br />there is no variation in water taste, turbidity, or color during <br />the year. <br />The cross-section shows probable water table <br />configurations as they may have existed in 1974 and 1992. If the <br />permeability of the streambed and subsoil is high, water lost <br />from the river could cause a small mound in the water table. If <br />the permeability is relatively low, there may be little or no <br />mounding. The movement of water seeping through the s~reambed is <br />primarily downward with very little lateral spreading. The <br />amount of water loss is related to the wetted peri~eter of the <br />streambed and is independent of water table depth. <br />It seems reasonable, based on the above, to assume that <br />the water table beneath the proposed gravel pit will vary in <br />depth from about 20 feet in early summer following the spring <br />recharge to at least 40 feet during the late winter months. It <br />is probable that seepage from the river is primarily downward and <br />that the seepage causes some water table mounding. <br />Since the gravel mining operation will be suspended <br />during high flow periods, it is extremely unlikely that <br />groundwater will be encountered during mining. The monitoring <br />wells that have been installed extend to a depth of 5 feet below <br />the deepest mining. Therefore, monitoring can verify the <br />position of the groundwater and insure that the mining operations <br />always remain well above the water table. <br />1Tolman, C.F., "Ground Water," McGraw-Hill, 1937. <br />2Bouwer, Herman, "Groundwater Hydrology," McGraw-Hill, 1978 <br />Page 1 <br />