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9 PnRnGON CONSULTING GROUP i ~ i ~ °SERVICE, QUALITY, AND INNOVATION° SENT VIA CERTIFIED MAIL 1107 Oak Pad Dive, S,ea 110 Fa.a coma.. co eoszs Certified Number 7001 1940 0006 0581 4341 Phan (990)1TA1600 Ev c9~ol7vv.Ieso ~.wmm May I, 2002 Dnv~x M. IUU, P.E., DEE Scow A. Rurxrntono, P.E Ba,cc Surtx, P.E Jnwes M. Txonus, P.E. Ms. Kate Pickford Bn..o c. wox~a Colorado Division of Minerals and Geology STPVex A M.uug P.E Anrc D. WraFx, EI.T. 1313 Sherman Street, Room 215 u~n,ms'A,~~MU, Denver, Colorado 80203 RE: April 2002 Quarterly Monitoring Report_ /Request for Site Closure Aggregate Industries F Street Facility 4509 F Street Permit#: /ri-I«i~-G~/ Confidental?: Greeley, Colorado Class: / - Type-Seq . . From: Project Number 1001018 To~ t/z Doc. Name: /~F,r~` ,~» k ' ! ~~~~ .~ lJ - ~ P~,~ Doc. Date (if no date stamp): / T Dear Ms. Pickford: X~,~ Enclosed are two (2) copies of The April 2002 Quarterly Monitoring Report for the above- referenced site. Petroleum hydrocarbon concentrations were not observed above the laboratory detection limits or were observed at relatively low concentrations in groundwater samples collected from the site in April 2002. The April 2002 sampling episode was the fourth event in which benzene-toluene-ethylbenzene-xylenes concentrations were not observed above the Maximum Contaminant Levels in groundwater samples collected fiom the site. Therefore, it is our opinion that additional monitoring, assessment or abatement is not warranted at the site at this time and site closure should be granted by the Colorado Division of Minerals and Geology for the 2001 diesel-fuel release. As summarized in previous reports. the volume of the diesel-fuel spill was estimated to be approximately 10,840 gallons based on information provided by Aggregate Industries. We attempted to perform a mass balance to compare the amount of diesel fuel released versus the amount of diesel fuel recovered during the soil and groundwater abatement activities. Due to the limited number of impacted samples analyzed from the site, the mass balance indicated that much more diesel fuel was recovered than released. Based on experience and professional judgement, a release of 10,840 gallons would be expected to cause greater impacts than have been observed at the site. The apparent lack of significant impacts appears to indicate that the abatement activities were highly successful in cleaning up the spill or that the spill amount was much lower than estimated by Aggregate Industries. Possible explanations for an erroneous spill estimate could be fuel theft or short fuel deliveries. ENVIRONMENTAL ENGINEERING AND GEOHYDROLOGY