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April 23, 1998 96-1113008.80 State of California Department of the Youth Authority Facilities Planning Division Attention: Ms. Corinda Yep, Chief-Hazardous Materials and Waste Program Subject: LETTER-REPORT-Re-Sampling of Former Diesel Underground Storage Tank Locations Northern California Youth Correctional Center 7650 South Newcastle Road Stockton, California Page 5 facility in borings that extended to 50 feet bgs. Facility and County personnel have indicated groundwater is expected to be 80 or more feet bgs. Review of information on the State Department of Water Resources website shows that the depth to groundwater recorded recently in the region is approximately 70 feet bgs. DISCUSSION Given the that there were no signs of TPH-d impacted soil (i.e., no stains, no free product, no significant odors)noted by the MARK representative during the January 1998 UST removal operations, the analytical results reported by Vector 3 were judged to be in error. Therefore, MARK reviewed the analytical results, chain of custody record, and sampling program maps, and many inconsistencies were noted. Samples were mis-identified (west versus east at Dewitt Nelson and Karl Holton schools) and inappropriately collected(backfill sample instead of native soil sample at O. H. Close School). While the reasons for the TPH-d concentration differences between the initial sampling and the re-sampling are unclear,it is clear that several quality control procedures were not adhered to which could result in cross- contamination of samples and/or non-representative sampling. The re-sampling conducted by MARK at the Karl Holton School was intended to confirm the locations and concentrations of the TPH-d impacted stockpiles/backfills identified by Vector 3. MARK's re-sampling and analysis of the stockpile/backfill identified 44 mg/kg TPH-d in the west UST location [CH- 3R (4.5')] and 470 mg/kg TPH-d in the east UST location [CH-4R(4.5')]. Native soil re-sample results at Karl Holton[CH-3R(10.5)and CH4R(10')] showed no detectable TPH-d as did the Vector 3 analyses. It should be noted that the reporting limit for the re-sampling analyses (<I.0 mg/kg) is an order of magnitude lower than the Vector 3 (10 mg/kg). The re-sampling concentrations correspond to MARK's field observations. The re-sampling conducted by MARK was also intended to address the anomalous TPH-d concentrations found in the Vector 3 soil samples collected from the west UST of the O. H. Close School. MARK's re-sampling and analyses found no detectable TPH-d concentrations in either the stockpile/backfill or native soil samples. The lack of identified TPH-d impacts is in keeping with field observations. CONCLUSIONS A summary of the analytical results is presented in Table 1. Based upon the laboratory analyses,