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)"ATE OF CALIFORNIA-Environmental Pro tect=ency ` PETE WILSON, Governor <br /> CALIFORNIA REGIONAL WATER QUALI t CONTROL BOARD <br /> CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A 4 <br /> Sacramento, CA 95827-3098 <br /> PHONE: (916)255-3000k` '� <br /> FAX: (916) 255-3015 <br /> kr ki'r yaa <br /> 10 December 1992 E C a , <br /> DEC 15 1992 <br /> ENVIRONMENTAL HEALTH <br /> Margaret Lagorio PERMIT/SERVICES <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> P.O. Box 2009 <br /> Stockton, CA 95201 <br /> UNDERGROUND TANK INVESTIGATION, FORMER AMERICAN FOREST PRODUCTS (AFPC) SITE, <br /> 2801 N. WEST LANE, STOCKTON, SAN JOAQUIN COUNTY <br /> As you requested, I have reviewed the file for this site. The review revealed <br /> that soil contamination was defined and two underground tanks and piping were <br /> excavated. Excavated soil was bioremediated on site. Prior to excavation, <br /> soil , predominantly interbedded layers of silty sand and sandy silt with some <br /> clay, contained up to 28,000 ppm TPH as diesel . The excavation of soil was <br /> limited to contamination above 10,000 ppm TPHd and after excavation, soil <br /> samples from the bottoms of the pits contained up to 9200 ppm TPHd at a depth <br /> of 26 feet and 8300 ppm TPHd at 22 feet. <br /> None of the wells on site has shown ground water contamination since they were <br /> first installed in 1987 at which time, depth to ground water was about 35 <br /> feet. When last sampled in July 1991, depth to water was about 68 feet. The <br /> water level has dropped approximately 33 feet from 1987 to 1991 . <br /> If ground water returns to its former level , 9 feet of soil will separate the <br /> bottom of the excavation from ground water. The soil contamination left in <br /> place poses a threat to ground water. Therefore, additional soil remediation <br /> should be conducted. Alternatively, a feasibility study, to determine whether <br /> the contamination left in place poses a threat to ground water, including mass <br /> balance equations, chromatograms, and other necessary data, may be conducted. <br /> The results of the feasibility study may indicate that additional soil <br /> remediation is necessary. <br /> If left in place, this contamination must be considered waste under Chapter 15 <br /> of the Health and Safety Code and, therefore, the soil must be disposed or <br /> contained on-site in the appropriate waste management units under the <br /> necessary waste discharge requirements and fees. <br /> The existing monitoring wells must be maintained, or replaced, and monitored <br /> annually until soil has been successfully remediated as necessary, a formal <br /> closure request has been made, and the Regional Board concurs with the request <br /> for closure. <br />