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i Clayton LPOUP 5-ERV [E5 I The Learner Company contracted Kleinfelder to implement the site investigation workplan in October 2000 Kleinfelder presented the results of their investigation in the document entitled Limited Soil and Groundwater Sampling Report (Kleinfelder, January 12, 2001) During the site investigation, soil samples were collected within the excavation backfill horizon that contained the impacted soil (2 ft to 5 5 ft) at boreholes GP-1, GP-2, and GP-9 The analytical results for these samples indicated diesel range hydrocarbons ranging to 39 mg/kg, and no detectable gasoline range hydrocarbons, ethylbenzene or xylenes These results indicate that the biodegradation was effective for this material and that limited concentrations of hydrocarbons remain The site investigation also detected moderate to elevated diesel range hydrocarbons in two samples, each collected from within the boundanes of the former excavation The 10-foot sample from GP-1 indicated 2,900 mg/kg and the 10-foot sample from GP-9 indicated 140 mg/kg diesel range hydrocarbons Each of these samples was collected from the pea gravel present in the bottom of the former excavation No BTEX compounds were detected in any of the soil samples and gasoline range hydrocarbons were only detected in the 10-foot sample from GP-9, at a concentration of 3 3 mg/kg Significant concentrations of diesel and gasoline range hydrocarbons persist within the bounds of the former tank excavation and have migrated laterally up to 20 feet Diesel range hydrocarbons in the groundwater beneath this area range from 5 3 mg/1 to 330 mg/1 and gasoline range hydrocarbons range from 0 15 to 0 87 mg/l Concentrations of diesel range hydrocarbons fall off rapidly to levels below 10 mg/l in the surrounding area Gasoline range hydrocarbons are not detected outside the area described above The limited migration of this material is likely due to the fine-grained nature, and related low permeability, of the soil at the site BTEX is not detected in groundwater samples collected outside the bounds of the former tank excavation The benzene concentrations in the groundwater beneath the former UST location shows a marked decrease from those reported at the time of the tank removal Current benzene concentrations range to 8 6 ug/l, whereas, at the time of the tank removal, benzene was reported at 80 ug/1 MTBE concentrations also show a significant decrease from the 3,200 ug/l reported at the time of the tank removal to a maximum of 36 ug/l during the Kleinfelder sampling The bulk of the MTBE concentrations are present within the tank excavation and immediate vicinity and also do not appear to be migrating significantly Based on the information contained in the Kleinfelder report, and summarized above, it appears that the impacts related to the former underground storage tanks at the site are attenuating naturally The PHD/EHD reviewed the Kleinfelder report and subsequent transmittals from The Learner Company and requested that a limited groundwater investigation be conducted This investigation was to include installing three groundwater monitoring wells on the periphery of the zone of impact to determine if significant migration of fuel related compounds is occurring These wells are to be monitored on a quarterly basis for a period of one year Following one year of 2 S 1Pro)1P02263\2263 workphn_0002 doc