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Ground Zero Analysis, Inc. 1172 Kansas Avenue Modesto,California 95351 't (209)522-4119/Fax(209)522-4227 r May 21, 201 j,4 Project Project No.: 425.2 G 1_z_ � Project Name: George's Service \ Ms. Vicki McCartney Sa ' County Environmental Health Department llW�� tiU 600 East Main Stockton,CA 95202 � - RE: Additional Air Sparge Well Installation Work Plan George's Service, 1600 Durham Ferry Road, Tracy, CA J1' Hello Vicki: Operation of Phase I and Phase II of the air sparging system began on March I" and August 24'h, 2012 and has been in continuous operation since. Currently, air is being injected into five (5) of the Site's wells including OS-1, OS-2, AS-1, AS-2 and AS-3. One (1) year of monthly performance groundwater monitoring has shown that the air sparging system is effective at increasing the dissolved oxygen (DO) levels in the groundwater as observed in select wells (OW- 1 & OW-2). Refer to the attached Table 1 for performance groundwater monitoring data collected from March 2012 thru May 2013. It is noted that minimal effect has been observed in the core of the groundwater plume, notably in the vicinity of AS-1 and monitoring well MW-2. Contaminant concentrations in the vicinity of the injection wells are also being reduced, as observed in OW-1. Refer to the attached Table 2. Some of the special relationship of sparge wells to observation wells do not readily lend to measuring the effectiveness of the air sparge system. For example— AS-1 with MW-1 & 101; these monitoring wells are not ideally spaced for measuring the results of sparging. To address the contaminants in the core of the plume, Ground Zero Analysis, Inc. (GZA) recommends that three (3) additional air sparge wells be installed within the high concentration portion of the groundwater plume(>5,000 pg/L TPH-G) as shown in Figure 2. Figure 1 is a site map including the TPH-G concentration contours created using the 2nd Quarter 2013 groundwater monitoring data collected on May V, 2013. Figure 2 is a site map including the locations of the three (3)proposed air sparge wells (AS-4, AS-5 & AS-6).