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• I i1 . ADDENDUM NO. 2 TO PROM'FM ASSESSMENT REPORT SOIL. AND« GROUNDWATER 1NVFSTIGATION GRANT LIN1'1- PLAZA 'TRACY, CALIFORNIA 1 .0 INTRODUCTION This report presents the methodology and results of a followup groundwater sannpling � program conducted by Roy F. Weston, Inc. (WESTON) on behalf of Souza Realty at the property known as Grantline Plaza located at 3.50'West Grantline Road, Tracy, California. This investigation is a second followup to a groundwater investigation previously performed by WESTON in February, March, and April 1991, 1A Site Background I The subject property is located in a commercial development and consists of a 6000 square foot building and' an associated 'lot. A 2000 gallon underground gasoline (leaded and unleaded):storagetank (UST), installed in 1968, was removed from tht: south side of the building in September 1986. Inventory records kept by the property owners show no zwidence of gasoline inventory loss during the life of the tank. As groundwater is very shallow on the site, water was present in the excavation pit during the tank removal. Analysis of a water sample taken by Canonie Environmental from the tank excavation indicated gasoline components of benzene, toluene,.xylene and ethylbenzene (BTXE) and total petroleum hydrocarbons (TPH) were present in the water. Upon completion of the tank removal, the'excavation was backfilled with clean fill. I.2 Summary of Previous Work At the request of the San Joaquin County Public Health Services Environmental Health Division (EHD) and onbehalf of the property owner, Souza Realty, WESTON perfomied a groundwater investigation in the Spring of 1991. This work consisted of installation of three groundwater monitoring wells (MW-1, 2 and 3 as sho,,vn on Figure 1) and completion of two rounds of groundwater sampling and analysis. Groundwater elevations in the three wells indicated that the groundwater gradient ari the site was to ,he north-northwest with a magnitude of 0.0016 ft/ft. Results of the two sampling rounds indicated no detectable presence of hydrocarbons in any of the three wells. These results and a recommendation for f site closure were presented to the EHD in WESTON's report entitled."Problem Assessment F Report Groundwater Investigation" dated May 17, 1991. In response to this report, the EHD noted that although all three wells appeared to be free of petroleum hydrocarbon components and MW-1 was directly over the former tank site location, the site lacked a downgradient well. In a letter dated June 17, 1991, the EHD' requested a work plan be submitted to propose a program to further investigate the potential ` for hydrocarbon presence at the site. Discussion between WESTON and the EHD indicated that groundwater samples and analyses from a new. monitoring well located in a downgradient position and soil samples locateu along a storm drain easement nortliwvest of { the former tank site would provide: the additional data nece*.sary to make a decision on site s closure. Krrs�WIA,2 run l Fj ;