SITE INFORMATION AND CORRESPONDENCE_FILE 1

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r � wy STATE QV-'AUPORNIA-Environmental Protection Age1*y F EC LSON,Governor �AL�FORNEA REGIONAL WATER DUALITY CONTROL BOARD ,,.,��, uEN T FAL VALLEY REGION 34a�Routier,"load, Suite A Sacramento, CA 95a273098 PHONE: (918)2553000 FAX: (916)255,3015 10 December 1992 Margaret Lagorio San Joaquin County Public Health Services Environmental Health Division P.O. Box 2009 Stockton, CA 95201 UNDERGROUND TANK INVESTIGATION, FORMER AMERICAN FOREST PRODUCTS (AFPC) SITE, 2801 N. .WEST,LANE, STOCKTON, SAN JOAQUIN COUNTY As you requested, I have reviewed the file for this site. The review revealed that soil contamination was defined and two underground tanks and piping were excavated. Excavated soil was bioremediated on site. Prior to excavation, soil , predominantly interbedded layers of silty sand and sandy silt with some clay, contained up to 28,000 ppm TPH as diesel . The excavation of soil was limited to contamination above 10,000 ppm TPHd and after excavation, soil samples from the bottoms of the pits contained up to 9200 ppm TPHd at a depth of 26 feet and 8300 ppm TPHd at 22 feet. None of the wells on site has shown ground water contamination since they were first installed in 1987 at which time, depth to ground water was about 35 feet. When last sampled in July 1991, depth to water was about 68 feet. The water level has dropped approximately 33 feet from 1987 to 1991. If ground water returns to its former level , 9 feet of soil will separate the bottom of the excavation from ground water. The soil contamination left in place poses a threat to ground water. Therefore, additional soil remediation should be conducted. Alternatively, a feasibility study, to determine whether the contamination left in place poses a threat to ground water, including mass balance equations, chromatograms, and other necessary data, may be conducted. The results of the feasibility study may indicate that additional soil remediation is necessary. If left in place, this contamination must be considered waste under Chapter 15 of the Health and Safety Code and, therefore, the soil must be disposed or contained on-site in the appropriate waste management units under the necessary waste discharge requirements and fees. The existing monitoring wells must be maintained, or replaced, and monitored annually until soil has been successfully remediated as necessary, a formal closure request, has been made, and the Regional Board concurs with the request for. closure.