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May- 13. 2004 2: I1PM Neil 0• Anderson & Assoc . No- 5095 P. 13 �- 19 March 2004 AGE-NC Project No. 02-0886 Page 2 of 8 The Modesto, Riverbank and Turlock Lake Formations and overlying recent alluvium are the ., principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River. The closest surface water feature to the site is the Mormon Slough and Stockton Diverting Channel, located approximately 1,500 feet southand 2,000 feet eastofthe site,respectively.Water from Canals drains into the San Joaquin River Deep Water Channel and is primarily used for commercial and recreational boating. .. Based upon ground water monitoring well information obtained from Main Street and Oro Avenue (50 feet north of the site),ground water flow direction is southeast to eastemly and currently occurs at a depth of approximately 55 feet bsg within ground water wells.The sedimentary units are thought to be relatively horizontal and continuous over the area. .. 2.3. UNDERGROUND STORAGE TANK REMOVAL On 06 March 2002,three USTs,two dispenser islands and associated piping were removed from the site under AGE supervision. Six samples were collected beneath the USTs and three laboratory- composited/discrete soil samples were collected from the excavated soil. Total petroleum hydrocarbons quantified as gasoline(TPH-g)were detected at concentrations up to 86 milligram per kilo gr ( g/kg). Toluene, ethyl benzene and xylenes (TEX)were detected at concentrations of up to 13 nl g{xylene);benzene was not detected in the excavation soil samples. The highest concentrations of contaminants were present in the southern samples from tanks#2 and #3; this location was the fill area to both USTs. Approximately 200 tons of soil were excavated during removal of the USTs. Two laboratory- composite and one-discrete samples were collected from the stockpiled soil prior to placement back into the excavation after completion of UST removal;the soil was placed back into the excavation because oftheproximity to amajor roadway(adjacent).Subsequent analytical results of the discrete soil sample from one stockpile of approximately 25 yards of soil detected TPH-g at 13 mg/kg and benzene at 0.023 mg/kg.,also o,03k3 e+t1,11 0, 1/I.ryllc� +o}ai xy+� s. J 411-/ Fuel additives were not detected in the samples. Analytical results of soil sample are summarized in Tables 1 and 2.— So";�i r,$04S 4rtm,41,L 14 41G rr ni"a,✓';, arti, n&f_ IrdZ&1,a"eJrt 2.4. PREVIOUS SITE ASSESSMENT In April 2003,three soil borings(Bl,B2 and B3)were advanced and sampled at the site(Figure 2). .. Each boring was advanced to a depth of approximately 65 feet below surface grade(bsg). Soil and Adma"d Ce EnAmnm tal,Inu rr