2003-06-03_REVISION - M1999034 - Laserfiche WebLink

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the contaminants were carried to the site by ground water flow. These aze the areas proposed to be mined. Given the known historical contaminant plume in this area, excavation activities associated with removal of aggregate materials within the zone of water table fluctuation would produce mechanical mixing that will remobilize (desportion) contaminants that had adsorbed on the subsurface alluvial materials. This remobilization can produce an immediate threat to human health by ingestion of contaminated drinking water supplies. The potential concentrations of desorbed contaminants are dependent upon the original historical concentrations in the aquifer, the geomorphology of the aquifer, and the grain size of particles in the aquifer, among other hydrogeologic characteristics. The historical concentration of contaminants in the shallow, alluvial aquifer is unknown as the ground water plume was not investigated until 1974. Chemical production and waste disposal at the RMA had continued for 30 years prior. Recent mapping by the U.S. Geological Survey (USGS), Hydrologic Investigations Atlas HA-736 has identified a number of paleo-channels associated with the South Platte River system. These channels of thicker deposits of alluvial materials would represent preferential flow paths through the alluvial aquifer, where contaminants might be expected to "concentrate" in their absorbed phase. Figure 2 in HA-736 identifies a channel of thicker alluvial material that trends southwest-northeast through the center of section 16, the section containing the applicant's Jeronimus property and my property. Alluvial thickness of 85 and 60 feet aze documented on the driller's logs of my two alluvial wells. A copy of the appropriate portion of that figure is reproduced and enclosed as Attachment 6. Lastly, the grain size of the alluvial material will influence the amount of adsorption. Smaller grains such as silts and clays have a greater tendency to absorb contaminants. According to the USGS, the youngest alluvium in the area consists of Piney Creek and post-Piney Creek Alluvium composed of gravel, sand, silt, and clay. Due to the unknown distribution of these materials in the subsurface, the potential concentrations of desorbed contaminants may vary greatly. Upon the recommendation of the Water Quality Control Division, I request that the Division of Minerals and Geology request asste-specific review of the applicant's discharge permit from the Division for consideration of past, current, and potential future ground-water contamination from organic chemicals attributed to historical waste disposal practices at the Rocky Mountain Arsenal. Water quality monitoring, on a minimum quarterly basis, of semi- volatile and volatile organic compounds including DIMP sbould be required from mine perimeter monitoring wells, all ouNalls, and process water effluent. Ezceedance of regulatory ground or surface water standards should require implementation of mitigation measures. 3. Injury to Decreed Water Rights The residence structure and outbuilding on my property are located approximately 40-feet east of the Amendment No.l Area boundary. The storage barn is directly adjacent to the property boundary. One bedrock aquifer well (permit no. 2455), permitted for domestic water supply, and one alluvial aquifer well (permit no. 2456), permitted for lawn irrigation, are housed within the same vault structure and located approximately 30-feet east of the property boundary. Our field irrigation well, permit no. 32883, is an alluvial aquifer well that was adjudicated December 31, 1972 and is located approximately 25 feet east of the property line.