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CONSULTANTS, INC. <br /> G E O T E C H N I C A L ■ ENVIRONMENTAL ■ MATERIALS _ <br /> Project No. S9200-06-45 <br /> June 26, 2008 ( f1 VIP,D <br /> Mr. Terrence Fox lJ ll II U <br /> California Department of Transportation-District 6 JUL a 7 2008 <br /> Hazardous Waste Branch ENVIRbi',,0E*N I HEALTH <br /> 2015 E. Shields Avenue, Suite 100 PER-MIT/SE.R,M-ES <br /> Fresno, California 93726 <br /> Subject: STOCKTON YARD MAINTENANCE STATION <br /> 1604 B STREET, STOCKTON,CALIFORNIA <br /> CONTRACT NO. 06A1141 <br /> TASK ORDER NO. 45, EA NO. 10-ON8300 <br /> WELL INSTALLATION AND WELL DESTRUCTION WORKPLAN <br /> Dear Mr. Fox: <br /> In accordance with the California Department of Transportation Contract No. 06A1141, Task Order <br /> No. 45, Geocon Consultants, Inc. has prepared this Workplan for well installation and well destruction <br /> activities to be conducted at the Stockton Yard Maintenance Station (the Site) located at 1604 B Street <br /> in Stockton, California. This Workplan describes the scope of services requested by Caltrans and <br /> outlines procedures and methods to be employed by Geocon to complete the well installation and well <br /> destruction activities. The site location is depicted on the Vicinity Map,Figure 1. <br /> BACKGROUND AND PURPOSE <br /> In December 1989, one 5,000-gallon diesel underground storage tank (UST) and one 10,000-gallon <br /> gasoline UST, two pump islands and associated product piping were removed from the Site. Analytical <br /> results of soil samples collected from the UST excavation indicated total petroleum hydrocarbons as <br /> gasoline and diesel (TPHg and TPHd) concentrations up to 2,000 and 58 milligrams per kilogram <br /> (mg/kg), respectively. In September 1993, one 115-gallon backup diesel generator UST was removed <br /> from the Site. Soil discoloration and odors were not noted during the 1993 UST removal activities. <br /> TPHd, benzene, toluene, ethylbenzene and total xylenes (BTEX) were not reported for the soil <br /> samples collected from the UST excavation and stockpile. The former UST locations are presented on <br /> Figure 2. <br /> Twelve groundwater monitoring wells (MW-1 through MW-12) and two vapor extraction wells <br /> (VW-1 and VW-2) were installed at the Site between 1992 and 1996. Groundwater monitoring has <br /> been conducted at the Site since April 1992 for wells MW-1, MW-2 and MW-3, since May 1995 for <br /> wells MW-4 through MW-8 and VW-1, and since February 1996 for wells MW-9 through MW-12 and <br /> VW-2. TPHg, TPHd and benzene concentrations up to 54,000, 11,000 and 13,700 micrograms per liter <br /> (pg/1), respectively, have been reported for the groundwater samples. Historical groundwater flow <br /> beneath the Site is directed toward the east and southeast. <br /> Groundwater levels have risen approximately 20 feet since the wells were installed, resulting in <br /> submerged screens in wells MW-1 through MW-12. In correspondence dated August 16, 2007,the San <br /> Joaquin County Environmental Health Department (SJCEHD) expressed concern regarding the well <br /> screen intervals at the Site, and concern that the current monitoring data may not be providing accurate <br /> information regarding the groundwater impacts in shallow groundwater beneath the Site. In a phone <br /> 3160 Gold Valley Drive, Suite 800 0 Rancho Cordova, California 95742 ■ Telephone (916) 852-9118 ■ Fax(916) 852-9132 <br />