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ADDENDUM TO <br /> PROBLEM ASSESSMENT REPORT <br /> SOIL AND GROUNDWATER INVESTIGATION <br /> GRANTLINE PLAZA <br /> TRACY. CALIFORNIA <br /> 1.0 INTRODUCTION <br /> This report presents the methodology and results of a soil and groundwater investigation <br /> conducted by Roy F. Weston, Inc. (WESTON) on behalf of Souza Realty at the property <br /> known as Grantline Plaza located at 350 West Grantline Road, Tracy, California. This <br /> investigation is a follow-up phase of a previous groundwater investigation performed by <br /> WESTON in February, March, and April 1991. <br /> 1.1 Site Background <br /> The subject property is located in a commercial development and consists of a 6000 <br /> square foot building and an associated lot. A 2000 gallon underground gasoline (leaded <br /> and unleaded) storage tank (UST), installed in 1968, was removed from the south side <br /> of the building in September 1986. Inventory records kept by the property owners show <br /> no evidence of gasoline inventory loss during the life of the tank. As groundwater is very <br /> shallow on the site, water was present in the excavation pit during the tank removal. <br /> Analysis of a water sample taken by Canonie Environmental from the tank excavation <br /> indicated BTXE and TPH were present in the water. Upon completion of the tank <br /> removal, the excavation was backfilled with clean fill. <br /> 1.2 Summary of Previous Work <br /> At the request of the San Joaquin County Public Health Services Environmental Health <br /> Division (EHD) and on behalf of Souza Realty, the property owner, WESTON performed <br /> a groundwater investigation in the Spring of 1991. This work consisted of installation of <br /> three groundwater monitoring wells and two rounds of groundwater sampling. <br /> Groundwater elevations in the three wells indicated that the groundwater gradient on the <br /> site was to the north-northwest with a magnitude of 0.0016 ft/ft. Results of the two <br /> sampling rounds indicated no detectable presence of hydi ocarbons in any of the three <br /> wells. These results and a recommendation for site closure were presented to the EHD <br /> in a WESTON's report entitled "Problem Assessment Report Groundwater Investigation" <br /> dated May 17, 1991. . <br /> In response to this report, the EHD noted that although all three wells appeared to be free <br /> of petroleum hydrocarbons, the site lacked a downgradient well. In a letter dated June <br /> 17, 1991, the EHD requested a work plan be submitted to propose a program to further <br /> investigate the potential for hydrocarbon presence at the site. Discussion between <br /> WESTON and the EHD indicated that a monitoring well located in a downgradient position <br /> and soil samples located along a storm drain easement northwest of the former tank site <br /> would provide the additional data necessary to make a decision on site closure. <br /> _ 1 _ <br />