GENERAL31792 - Laserfiche WebLink

Home Browse Search

~. "Applicmu shall e.rtend pumping tunes and othenvise regulate pumping practices to reduce potential impacts on neighboring wells. " Division Response: The applicant submitted a hydrologic evaluation of potential impacts to nearby wells prepared by Leonard Rice Consulting Water Engineers, Inc. This report evaluates impacts to lowered water levels in wells resulting from the dewatering of [he I-acre pit sites for dredge construction. The 1-acre starter pit will cause a maximum drop of 5 feet, 2000 feet from the starter pit site if located above [he most permeable portion of the aquifer. [n addition, mitigation effects of aquifer subflow and recharge will reduce the effects by 50 percent. [f this occurs, the impacts [o nearby well users will be insignificant. Platte Sand & Gravel will also begin mining as far away from existing wells and as close to the river as allowed. Any change to this plan will need to be submitted as a revision to the permit. The Division believes that impacts to the surrounding well owners will be minimized. 6. "Once the dredge has been assembled, dewatering activities shall cease. " Division Response: In a letter dated April 4, 2001, the Applicant committed to mining only I acre (as stated in [he original plan) to assemble the dredge and then stop pumping thus allowing water to flow back in the pit and float the dredge. 7. "Tire Applicant shall install two measuring weirs and clocks prior to the comtnencement of dewatering to measure the effect of dewatering on the Ditch. Both the Applicant and Westem Mutual Ditch Personnel shall have ready access to these structures and records. " Division Response: Mining in each lake area will be done as far from off site wells as possible and as close to the river as practical for the lake azea development. The closest dewatering distance to the Westem Mutual Ditch will be greater than 1000 feet. In addition, the Westem Mutual Ditch is situated at an elevation higher than the mining operation and the groundwater table is over seven feet below the surface. Based on [he limited dewatering activity to no greater than one acre in size, the predicted cone of depression will not extend to the ditch, however, since the ditch is simated at an elevation higher than the groundwater surface, whether the cone of depression will extend to the ditch is irrelevant. Once the 1-acre dewatering pit is completed, the remainder of the site will be wet mined. Therefore, the Division does not believe that measuring weirs and clocks are necessary. 8. "Mining depth shall be limited to fifteen jeer below the static water level." Division Response: In a letter dated March 30, 2001, the Applicant committed to the limit the depth of mining to 15 feet below the static water level or less during set up of the dredge, to reduce the impacts to the surrounding wells. 9. "The Applicant must demonstrate an ability to augment ground water evaporation losses from the pits at full build out. Applicant cterrently owns insufficient water for augmentation. A !12 permit should be made contingent upon Applicant's demonstration of ownership or control of water sttffcient to augment evaporation losses and adjudication of a decreed augmentation plan. " Division Response: Platte Sand & Gravel predicts that 2,274.23 acre-feet of water to evaporate from the exposed lake areas each year. This assumes a lake surface of 768.32 acres with an average net annual evaporation of 2.96 acre-ft/surface acre. The applicant states they have no current water rights to use for make up water. The applicant may not expose groundwater until the Colorado Division of Water Resources, Office of the State Engineer ("OSE") issues a well permit. The applicant states that a Temporary Substitute Supply Plan ("TSSP") and well permit application have been filed with the OSE. In the TSSP, the applicant states that it has committed to buying water from Longmont to cover the industrial and evaporative uses associated with the apera[ion during the first five years. The applicant has committed that groundwater will not be exposed until they have received necessary approvals from the OSE.