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Holl~~ Belbiumd • <br />klu6i/e Premi.c Concrete, /nc. <br />Findings and Conclusions <br />• Page 5 <br />Mar 22, 2000 <br />The southern portion of the Tanabe property is located within a fringe area of the RMA <br />DIMP plume that flows northwest from the RMA within the alluvial aquifer. The <br />northern half of the Tanabe property does not contain detectable concentrations of <br />DIMP in the ground water beneath it. DIMP is the only chemical of concern to be <br />detected in the most frequently sampled ground water well on the property (485A). The <br />Tanabe property is located near the First Creek paleochannel hydrologically cross- <br />gradient from the northern DIMP plume, the only area off of the RMA that, according <br />to 1997 data. exceeds the DIMP CGWS. <br />According to interviews with TCHD and South Adams County Water and Sanitation <br />District representatives, [he containment/[reatment systems have been effective at <br />preventing additional DIMP from leaving the RMA and the only DIMP that remains in <br />the Offpost Study Area is historical DIMP that has been in the ground water since <br />before corrective action commenced. Historical DIMP located in the fringe areas is <br />hydrologically connected to the South Platte River. The reduction in size of [he overall <br />plume and the consistent decrease in DIMP concenn'ations in monitoring wells both on <br />and hydrologically upgradient from the property is consistent with the original design <br />intentions of the RMA corrective action. U.S. Army DIMP concentration maps show a <br />consistent decrease in the size of both the DIMP plume anti the area of detectable DIMP <br />concentrations between 1995 and 1997. In addition, the only established human <br />exposure pathway for DIMP has been eliminated throughout the Offpost Study Area of <br />the DIMP plume by providing alternative sources for drinking water. <br />Monitoring wells adjacent and hydrologically upgradient From the Tanabe property <br />contain DIMP concentrations below the CGWS, with concentrations decreasing since <br />the installation of the containment and treatment systems. No DIMP concentrations <br />above the CGWS have been found in ground water wells on the property since 1985. <br />Additionally, discharge from dewa[ering operations northwest of the Tanabe property. <br />within DIMP plume fringe areas, has not contained concentrations of DIMP above <br />CGWS. <br />Should you have any questions concerning this research or findings, please feel free to <br />contact me at (303) 830-I 188. Thank you for allowing ERO to assist you with this <br />project. <br />Sincerely, <br />ack Denman <br />Environmental Scientist <br />Enclosures <br />cc: Jeffrey W. Schwarz, Massey, Semenoff, Stern, & Schwarz, P.C. <br />ERO <br />Resources <br />Corporation <br />