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Mr Steve Schneider . SJCPHS October 8, 1992 Page 2 3_ Proposed Individual Target Criteria for BTEX You requested that individual target criteria be proposed for benzene, toluene, ethylbenzene, and total xylenes in the stockpiled sod In addition, you asked that these criteria be based on the guidelines posited by Jon Marshack of the California Regional Water Quality Control Board, Central Valley Region, in his paper entitled Designated Lev I Methodology for Waste Classification and Cleanup Level D t rmrn tin dated October 1986 Therefore, we have revised our proposed target criteria for BTEX The revised target criteria for individual constituents is shown in the following table These target criteria are considered quite conservative, and therefore more than adequate to meet SJPHS and RWQCB concerns, because no environmental attenuation has been assumed, and groundwater beneath the tank excavation is already impacted above the water quality goals TARGET CRITERIA FOR SOIL TO BE RETURNED TO THE TANK EXCAVATION CONSTITUENT WATER QUALITY LEACHABILITY TARGET CRITERIA GOAL FACTOR IN SOIL BENZENE 0 7 ug/I 10 0 007 mg/kg TOLUENE 100 ug/I 10 10 mg/kg ETHYLBENZENE 680 ug/I 10 6 8 mg/kg TOTAL XYLENES 1,750 ug/1 10 17 5 mg/kg 4 Placement of a Buffer Zone In the Bottom of the Excavation You requested that other soil stockpiled on the Manna Pro site from recent excavations on the northern property boundary be used as a 'buffer zone" between stockpiled sod returned to the tank excavation and the highest groundwater observed at the site We have found that the depth to groundwater beneath the site typically is approximately 40 feet below grade According to SJCPHS, during a recent flood season, groundwater was observed as high as 30-35 feet below grade To establish a reasonable buffer zone to prevent tank pit soils from contacting high groundwater, we propose the following i) Before any stockpiled soil meeting target criteria is placed in the excavation, a "buffer zone" of clean fill from the excavation at the northern end of the site will be placed in the bottom of the excavation to a depth of 10 feet below grade Notwithstanding the above, stockpiled soil represented by composite samples showing concentrations of petroleum hydrocarbons below laboratory detection levels may, in lieu of sod from the northern boundary (or alternative sources), be used to fill the excavation to 10 feet below grade Manna Pro, however, will not be required to obtain additional soil from alternative off-site sources if there is not enough soil from the northern boundary or from the stockpile to fill the excavation up to 10 feet below grade (Manna Pro is informed that at least 1,700 cubic yards of sod from the northern boundary currently exist on the site) GROUNDWATER EEETECHNOLOGY,INC