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-32-1998 1 23PH FPOM P 4 • Frank's Exxon#4 .2- 26 May 1998 San Joaquin County MW-7 The maxx;murn concentration of contaminants occurred to. W-1,MVw-2,and MW-3 with 120 �sg/l TPH-g, 1 1 µg11 toluene,4 8 LL_o 1,2-DCA, and 19 99f1 MTBE(EPA Method 8020). Since shutting-off the remediation system, quarterly ground water momtortng in 1997 has shown some rebound with contamination be.mg detected to all monitoring wells except MW-5 The concentrations of contamination, and their maximum concentration limit(MCL) and taste wed odor threshold are as follows. Contaramant/concentration(µg11) MCL (µg/1) Taste&Odor(µb11) Momtonng Well affected TPH-g 53 - 59 5 MW-7, 8, & 9 TPH-d 610 --- 100 MW-3 Toluene 0.72 I50 42 MW-3 Xylene 2.0- 2 7 1750 17 MVV-6, 7, 8,9 1,2-DCA 0 9 to 5.7 05 7,000 MW-1,2, 3,4 MTBE 5 1 to 16 (EPA Method 8250) CA St. 15 -95 ND to 43 (EPA 8020) Action (SNARL 20 to 40) MW-1, 2,3,4, & 8 Level 35 SNARL.- Suggested no adverse respons:levels Although the concentration of petroleum contaminants have decreased 3-4 orders of maWtude, 1,2-DCA and MTBE have decreased 1-2 orders ofmagnitude However, 1,2-DCA continues to remain above the MCL,TPH-g,TPH-d and MIKE conttmttes to remain above the taste and odor dueshoid,and MTBE may be above the California State Action Level Two domestic wells, one oa site and a L-a;tler park well approximately 100 ft off-site,were unpacted by the contamination. From March 1996 to August 1997,the on-site Well had ND to 51 ug11 T1'H-g and ND to 3 2 µg/1 1,2-DCA From February to November 1997,the trailer park well had ND to 62 µg/l TPH-g, 2 0 µ$/1 1%DCA, and 10µg/1 MTBE. In response to the detection of contaminants m the on-site well,the owner had a new well installed in October 1997 to a depth of 360 ft with a200 ftgrout seal 'Me November 1997 ground water mormtonng data shows the contamination has not impacted the well at thnts lower depth. However,fat= sampling events may detect contammabon at this lower depth The geologic log snows interbedded clay and sand units with no confining units throughout the boring. Therefore,the pumping of the water from this well will just tmcrease the flow luxes,possibly causing the contamination to spread downward to the 200 to 360 ft level The site owner has been asked to install anew well at the trailer park If installed, . the pumping of thts well could cause the eontammation to spread laterally and eventually imzpaet the