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AGGREGATE <br />Kaze Pickford, Environmental Specialist, Division of Minerals and Geology u+ousTaies <br />October 26, 2001 <br />Page Two <br />plume exist that has not yet been identified, continued monitoring will alert us to any need to further <br />identify and monitor the plume. <br />2. In the event that contamination is identified in the groundwater and a Corrective Action Plan is <br />warranted, Aggregate Industries will consult with Paragon for an evaluation of remedial options. <br />Possible remedial options for dissolved petroleum hydrocarbon contamination at the site may include <br />natural attenuation; in-situ bioremediation; air sparging; and/or groundwater extraction, treatment and <br />reinjection of treated groundwater. The selection of a remedial action, if necessary, would be based <br />on the contaminant characteristics, extent of contamination requiring remediation, results of risk- <br />based modeling, results of on-site pilot tests, costs and length of time estimated for remediation. <br />3. With regard to groundwater samples collected from the monitoring wells, the statewide interim <br />organic pollutant standards published in "The Basic Standards for Ground Water" Regulation 41, <br />(SCCR1002-41) will be used as an indicator of contamination for BTEX. Those standards for BTEX <br />are 5; 1,000; 680; and 10,000 micrograms per liter (µg/L), respectively. TEPH is not regulated by a <br />numeric standard in Colorado at this time; however; the presence of free-phase product in the <br />monitoring wells would also serve as an indicator of significant contamination at the site and the <br />possible need for additional assessment and/or remediation. Effluent parameter concentrations for oil <br />and grease, as set forth in the NPDES permit for the site, will serve as the indicator of contamination <br />in the dewatering trench; i.e. a visible sheen or floating oil, which may indicate an exceedence of the <br />daily maximum effluent parameter concentration of 10 mg/I. <br />4. In order to avoid a similar incident in the future, all piping from the diesel fuel tank to [he fuel- <br />dispensing unit has been installed above ground. The tank and piping are inspected on a weekly <br />basis. A record of fuel deliveries, fuel usage and tank volume measurements is maintained and <br />reconciled on a monthly basis. <br />5. The monitoring plan for the dewatering trench will be in accordance with the NPDES permit for this <br />site. The NPDES permit requires a weekly visual observation for oil and grease monitoring which, <br />according to the permit, is observing the discharge to check for the presence of a visible sheen or <br />floating oil. In the event an oil sheen or floating oil is observed, a grab sample will be collected, <br />analyzed and reported. In addition, corrective action shall be taken immediately to mitigate the <br />discharge of oil and grease. <br />6. If contamination of groundwater is discovered, Aggregate Industries will contact DMG immediately. <br />7. In the DMG's October 15, 2001 letter, it was requested that "prior to [he cessation of dewatering <br />activities, the remainder of contaminated soils will be excavated in order to avoid contact with <br />groundwater when the groundwater rebounds." Our observations regarding this issue are described <br />below and are based on information contained in Paragon's July 6, 2001 Soil and Groundwater <br />Abatement Report, <br />• Soil contamination is already in contact with the goundwater table. TEPH contamination was <br />observed at and below the water in the Bottom # I soil sample collected near the source area and <br />Connie Nickle Davis, Support Services <br />P. O. Box 337231, Greeley. CO 80633 <br />970-3366526 Fez: 970.3786856 <br />