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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 4 ANALYTICAL RESULTS The soil samples were delivered by the MARK geologist to McCampbell Analytical of Pacheco, California, a state-certified laboratory. The samples were analyzed within appropriate holding times for TPH-d per EPA Test Method 8015m. The analytical results from the nineteen Advanced samples and the six primary MARK samples are summarized in Table 1. The analytical results from the re-sampling are included in Attachment C. Of the four re-samples collected from the two Karl Holton School UST locations, non-detectable TPH-d conditions were confirmed for the two native soil samples [CH-3R (10.5') and CH-4R (10')]. Similar TPH-d concentrations,470 mg/kg in CH-4R(4.5')versus 586 mg/kg in SP-CH-F, were found in the east UST stockpile (now backfill) soil samples. However, only 44 mg/kg was detected in re-sample CH-3R (45) which corresponds to Advanced stockpile/backfill sample SP-CH-H which reportedly contained 8,528 mg/kg TPH-d. Of the two re-samples collected from the O. H. Close School UST location, MARK re-samples OH-5R (10') (native soil) and OH-5R (4') (backfill/stockpile soil) contained no detectable TPH-d concentrations, while Advanced samples YA-5 (native soil) and SP-YA-I (stockpile/backfifl soil) reportedly contained 7,994 mg/kg and 2,454 mg/kg, respectively. HYDROGEOLOGIC CONDITIONS The site is underlaid by flood basin deposits consisting silty and fine sandy soils associated with the San Joaquin-Sacramento River. These deposits are estimated to be as much as 100 feet thick. Trenches excavated to depths of 10 to 14 feet bgs during the UST removal operations, and the borings advanced to 11 feet bgs during the re-sampling, exposed native soil consisting of stiff to hard, moist, and reddish-brown clayey silt/silty clay. Three borings drilled the day before the re-sampling for another UST assessment within the facility exposed silt(clayey, sandy, gravelly, and slightly organic) and sands (clayey, silty,and at depth,poorly graded and fine-to medium-grained). Copies of these boring logs are included in Attachment B. The observed soil types are consistent with the anticipated flood plain sediments. Surface water runoff is via ephemeral streams that flow westward toward the San Joaquin River located about 7 miles west of the facility. While groundwater might be expected in isolated lenses of fine- grained sand units of old stream channels, or within peat/organic-rich soils of the delta deposits, groundwater was not encountered during the previous day's assessment investigation elsewhere within the