SITE INFORMATION AND CORRESPONDENCE (2)

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CONSULTANTS, INC. E N V I R O N M E N T A L ■ G E O T E C H N I C A L ■ M A T E R I A L SM) Project No. 58643-06-01 February 18,2004 Mike Infurna FEB San Joaquin County 2 3 2��4 Environmental Health Department ENVIRONMENI NtALTH 304 East Weber Avenue, Third Floor PERMIT/SERVICES Stockton, CA 95202 RE: FREE PRODUCT DISCOVERY AND PROPOSED ACTIONS RANCH MARKET SITE 23569 SOUTH SANTA FE ROAD RIVERBANK,CALIFORNIA Dear Mr. Infurna: During the First Quarter 2004 Groundwater monitoring event, Geocon encountered free product in one well (MW-3) at the Ranch Market site in Riverbank, California. The purpose of this letter is to document the discovery of the free product and present our proposed actions. Underground storage tanks were removed from the site in 1991. The site has not operated as a fueling facility since that time. In more than five years of groundwater monitoring at the site (1998-2004)free product has not been encountered until the first quarter of 2004 Attached is a series of Monitoring Well Logs gathered for MW-3 prepared during the First Quarter 2004. The location of MW-3 is shown on the attached Figure 2 from the Fourth Quarter 2003 Groundwater Monitoring Report. As indicated by the logs from the Quarterly monitoring event of January 9, 2004 to the most recent measurement obtained on February 9, 2004, free product has been persistent within this well. Upon discovery of the free product, Geocon personnel began frequent monitoring of the product levels and bailing to remove it. Observed product levels ranged from an initial high of 0.5 foot on January 9, 2004 to 0.012 foot on February 9, 2004. On January 30, 2004, Geocon personnel purged the well in an attempt to create a cone of depression and draw additional product into the well. No enhancement of the free product thickness was noted from the pumping effort. As of February 9, 2004 approximately one half gallon of product has been removed from MW-3. The product odor, color, and apparent viscosity are consistent with that seen in weathered gasoline. The discovery of the free product after a significant period of remedial activity could be indicative of additional Underground Storage Tanks (USTs) on the site. Geocon proposes to conduct a records search and a geophysical investigation of the site to confirm the existence of any additional USTs at the location. The geophysical investigation will consist of Magnetometer, Electromagnetic, and Ground Penetrating Radar methods to attempt to define the locations of unknown USTs on the property. In addition to this, free product levels will continue to be monitored and bailed as needed. 2356 Research Drive ■ Livermore, CA 94550-3848 0 Telephone (925) 371-5900 ■ Fax (925) 371-5915