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Mr.Roger Doak <br /> Coal Ash Pilot Project Proposal <br /> June 26,2000 <br /> Page 6 <br /> We do not believe that "Surface Water Quality Protection' levels are warranted, even though <br /> many of these levels are higher than groundwater projection levels. Our rational for this is that <br /> the travel time for a particle of water to migrate from the proposed pilot trench to the Saint <br /> Vrain Creek is on the order of seven years if groundwater follows a straight line from the <br /> trench to the creek. If abatement activities are warranted they can be implemented long before <br /> any possible impact to off-site properties or surface waters could occur. We have proposed a <br /> very stringent monitoring schedule which provides a high degree of confidence that any <br /> degradation of groundwater quality will be detected by the proposed monitoring and "Action <br /> Level" wells. <br /> 9. We concur that a longer time frame would have more scientific validity. We agree to a one- <br /> year monitoring period. Monitoring will be performed in accordance with the QAPP and work <br /> plan presented previously. <br /> 10. We believe St. Vrain Creek is the correct terminology for the referenced drainage. <br /> 11. We agree with the permitting requirements with the following exceptions. DMG requires a <br /> technical revision to the existing MLR permit. An amended air quality permit is not required <br /> unless annual fugitive air emissions exceed one ton per year. After reviewing AP-42 and <br /> estimating particulate emissions by means of a Mechanical Erosion program provide by EPA, <br /> it is our opinion an amended air quality permit is not required for this limited project. <br /> 12. The deposition of 400 tons of coal ash will not make significant modifications to the local <br /> groundwater hydrology. As can be seen by the model results discussed previously only minor <br /> deviations to local flow directions are observed as well as minor variations in hydraulic <br /> gradient. Both impermeable and permeable barriers were modeled and model results for both <br /> scenarios yielded very little variation in groundwater flow. <br /> 13. Contrary to our initial submittal, bottom ash will not be used in the pilot test. The proposed <br /> placement of monitoring wells in the trench is depicted in Attachment F. A typical well <br /> construction detail is also provided. The variations in water quality and groundwater <br /> hydraulics in fly ash will be monitored my completing one well throughout the buried fly ash. <br /> Another well will be completed in the native soil divider. Two wells will be completed in the fly <br /> ash portion of the trench, with one well being screened within the fly ash and the other being <br /> screened below the ash in native soil. This well configuration should provide water quality data <br /> and hydraulic characteristics for the different materials. <br /> 14. The hydraulic conductivity, not seepage velocity, is estimated to vary between 97 and 147 feet <br /> per day. The resulting seepage velocity based on published hydrogeologic data is estimated to <br /> vary between 0.83 and 1.25 feet per day. The sampling frequency (weekly for the first month, <br /> biweekly for the second month, monthly for the third month and then quarterly until project <br /> termination) is sufficient to monitor variations in water quality. <br />