3815_PGSF WMVD Pkg 2_Vol 4-2_03.03.2026_BXWA_Certified

ASPECT CONSULTING 26 FINAL PROJECT NO. AS190583A-08  MAY 21, 2025 sample tested by the U.S. Environmental Protection Agency (EPA) 418.1 method, which is not specific to petroleum. Subsequent analysis of water sample TS-29 by Modified EPA Method 8015 detected a concentration of 1,900,000 µg/L gasoline-range hydrocarbons, while kerosene was not detected. Total xylenes, ethylbenzene, and toluene were also detected in excavation water sample TS-29 at concentrations of 770,000 µg/L, 160,000 µg/L, and 4,800, µg/L, respectively. Benzene was not detected. Ethylbenzene and toluene are reportedly impurities in technical grade xylene (Landau, 1989). In addition, Landau collected a sample of water stored in the Baker tank (BT-1) for analysis of BTEX. Detected concentrations in water sample BT-1 were 120,000 µg/L total xylenes, 20,000 µg/L ethylbenzene, and 2,100 µg/l toluene; benzene was not detected. Following testing to confirm that the mill’s wastewater treatment system could adequately treat the contaminated water, and after receiving verbal approval from Ecology, the Baker tank water was discharged to the mill’s secondary wastewater treatment plant at a maximum feed rate of 15 gallons per minutes (gpm) for treatment (Scott Paper, 1990). Within the final limits of the UST No. 29/67 excavation, four discrete soil samples were collected from each of the excavation sidewalls at a depth of approximately 4 feet below ground surface (bgs). A composite soil sample was also collected from the stockpile of excavated soil. The five soil samples were submitted for laboratory analysis of TPH by EPA Method 418.1, and BTEX. As observed with the water data, the soil analytical data showed highest concentrations of xylenes with lower concentrations of ethylbenzene and much lower concentrations of toluene. In the four excavation sidewall soil samples, the lowest concentrations were detected in the eastern sidewall (0.75 mg/kg xylenes, 0.048 mg/kg ethylbenzene; and nondetect TPH, benzene, and toluene), and the highest concentrations were detected in the northern sidewall (37,000 mg/kg xylenes; 6,600 mg/kg ethylbenzene; 5,700 mg/kg TPH; and nondetect benzene and toluene). The sample of stockpiled soil contained 2,800 mg/kg xylenes, 590 mg/kg ethylbenzene, and no detectable benzene or toluene. The UST No. 29 excavation was backfilled with the stockpiled soil removed from the UST excavation (Landau, 1989). Landau then installed a test soil vapor extraction (SVE) system on top of the impacted backfill soil to passively remove vapors and for potential use as an active vacuum extraction system. The SVE piping was encased in an approximately 2-foot layer of pea gravel placed on top of the soil backfill, which was covered with a high-density polyethylene (HDPE) liner and resurfaced with asphalt. Scott Paper Company informed Ecology of the SVE system operation plans (Scott Paper, 1991). Landau initiated startup of the SVE system with two 4-hour tests conducted on November 22 and December 2, 1991. The primary purpose of the tests was to measure the expected mass discharge rate of xylenes from the SVE system to assess compliance with a 15-pound-per-day (lb/day) rate dictated by the Puget Sound Air Pollution Control Agency (PSAPCA). Based on the tests, Landau calculated an expected mass flow rate of 1.3 lbs/day from the SVE system. Following review of those results, Landau initiated continuous operation of the SVE system on January 10, 1992, and recommended that