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10. "It is assumed that the liner material will be placed in horizontal lifts with some type of keying or benching <br />into the adjacent alluvial sand and gavel. Is there a maximum loose or compacted lift thickness? What type <br />of compaction equipment will be used? Will moisture/density tests be required on the compacted liner, and <br />if so at what frequency?" (Colorado Department of Transportation; March 26, 2005) <br />Division of Minerals and Geology (DMG) Response- According to the pemrit application, the claystone <br />will be processed in place to within t2% of optimum moisture. The claystone will be ripped in place to a <br />depth of approximately 1' by shanks on a D-8, or comparable. Water will be injected into the ripped zone <br />through tines on a water truck that will also mix the claystone. The processed bedrock will be transported to <br />the slope liner by graders that will strip approximately 4" of the material over a lazge azea, further mixing the <br />bedrock. The weathered claystone bedrock shall be stripped to a depth of at least 1' beneath the slope liner/ <br />weathered claystone contact. The entire foundation shall be rolled and compacted with a sheepsfoot <br />compactor prior to placement of the first lift of slope liner soil. <br />The applicant states that the earthfill material shall be placed in the slope liner in continuous and <br />approximately horizontal layers, not more than 9" loose lift thickness. The combined excavation and placing <br />operations shall be such that the materials will be sufficiently blended to secure the best practicable degree <br />of compaction and stability. The material will be compacted to a minimum of 95% of the Standazd Proctor <br />as described in ASTM D698. Self-propelled tamping sheepsfoot type rollers shall be used for compacting. <br />The rollers shall be capable of effectively achieving the required density for the entire depth of the lifts being <br />placed. If, in the opinion of the Engineer, the surface of the prepazed foundation or the compacted surface of <br />any layer of earthfill is too dry or smooth to bond properly with the layer of material to be placed thereon, <br />the applicant stated that it will be moistened and/or worked with harrow, scarifier, disc, or other suitable <br />equipment, in an approved manner to a sufficient depth to provide a satisfactory bonding surface before the <br />next succeeding layer of earthfill material is placed. If in the opinion of the Engineer, the compacted surface <br />of any layer of the earthfill in-place is too wet for proper compaction of the layer of earthfill material to be <br />placed thereon, it shall be removed, allowed to dry; or be worked with harrow, scarifier, disc, or other <br />suitable equipment to reduce the moisture content to the required amount; and then it shall be recompacted <br />before the next succeeding layer of earthfill material is placed. <br />Application Exhibit G -Water Information: <br />11. "Our drinking water comes from a well located approximately 150 feet from the proposed gravel pit. The <br />construction of the gravel pit, which borders our property on three sides, will lower the groundwater table <br />and perhaps even impact water quality. We as landowners have not given the gravel pit company <br />permission to do this to our only source of drinking water." (Georgia and Jerry Landrus; March 6, 2005). <br />Division of Minerals and Geology (DMG) Response- The applicant is required by law to minimize <br />disturbances to the prevailing hydrologic balance of the affected land and of the surrounding area and to the <br />quantity or quality of water in surface and groundwater systems both during and after the mining operation and <br />during reclamation (Rule 3.1.6). A groundwater mode] was submitted to the Division during the adequacy <br />review period to assess potential impacts to the goundwater system in the affected land and surrounding azea <br />and to propose mitigation measures. The impacts to groundwater due to de-watering were modeled using 6 <br />different phases, each approximately 60-acres in size. The operator is required to line the first two units of <br />mining or a maximum disturbance of 50 acres before mining in the next unit. Modeling of the 60-acre phases <br />assumed a maximum extent of drawdown and mitigation measures to limit the azea of de-watering impact. <br />Primary mitigation measures included in the model include 4 groundwater injection well sites, each with 500 <br />gallons per minute (gpm) of mine water recharge to the aquifer for a total rechazge of 2,000 gpm. The recharge <br />azeas will be installed and operating in advance of the mining activity in each area. The water will be delivered <br />by pipe to a rechazge site that will contain a vertically oriented perforated pipe to be installed approximately I S <br />to 20 feet below the ground surface with approximately 15 to 20 feet of 3 foot thick gavel pack surrounding the <br />pipe. Each rechazge site is located in the proximity of an existing piezometer that is monitored monthly for water <br />levels and will allow the applicant to monitor the effects of the mitigation measures. Additional rechazge to <br />groundwater is expected from the silt ponds, but was not considered in the model. <br />