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I<_ose':iiie ?:Joiic Schools STS Project #94941- YF May 18, 1990 Page 2 Since impacted soils remained in the base of the excavation, additional work was recom- mended for the site. The Minnesota Pollution Control Agency letter dated March 27. 1990 recommended additional soil exploration and chemical analyses within the tank excavation to determine the vertical extent of contamination. Exploration Procedures On April 13, 1990, an STS environmental geologist utilized a hand auger to perform one boring (labeled B-1) to a depth of 9 feet within the backfilled tank excavation at Lexington School. The boring was sampled generally at 1 foot intervals. The boring location is shown on Figure 1. attached to this letter. Soil samples from the boring were classified in the field using the Unified Soil Classification System (USCS). An HNU photoionization detection (PID) meter calibrated to a benzene reference was employed in the soil sampling process. Specifically, it was used to detect the presence of volatile organic compounds (VOC's) in the soil samples obtained. The PID analysis was performed in general accordance with Minnesota Pollution Control Agency (MPCA) suggested practices for soil sample screening. Two soil samples were obtained for chemical analysis from the soil boring. Maximum PID meter readings were encountered between 4.5 and 6 feet. As specified in the MPCA letter. one soil sample (LEX 1) was obtained for chemical analysis between 5.5 and 6 feet. The second sample (LEX 2) was obtained at a depth of 8.5 to 9 feet. No elevated PID meter readings were detected in the second sample. Both soil samples were refrigerated and transported to Interpoll Laboratories in Circle Pines, Minnesota where they were analyzed for benzene. ethylbenzene, toluene and xylene (BETX) and total petroleum hydrocarbons (TPH) as fuel oil. Exploration Results Soils encountered in boring B-1 consisted of gravelly and silty sands (USCS Classification GM and SM) to a depth of approximately 6 feet. These soils were interpreted to be filJ material. Silty clay (CL) with some peat (Pt) was encountered in boring B-1 from 6 to 9 feet. Boring log B-1 is attached to this letter. PID meter readings of 1 to 2 parts per million (ppm) were detected in the soil samples between 0 and 8 feet. Background levels for the PID meter were 0 ppm. Very slight fuel oil odors were also detected from the surface to 7 feet. Maximum PID meter readings of 2 ppm were detected in the two samples obtained between 4.5 and 6.0 feet. No fuel oil odors or PID meter readings above background levels were encountered below 8 feet. Soil. Chemical Analysis - The chemical analysis performed on the soil samples obtained from the boring revealed no concentrations exceeding target detection limits for any of the parameters analyzed. The laboratory chemical analysis reports are included at the end of this letter.