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' Royal Oak Savings & Loan Page 2 SIO N. Main Street, Manteca, Ca4fornia ' Quarterly Ground Water Sampling Report October, 1992 -January, 1993 Previous investigations had shown that relatively low level contamination of ground I water had occurred. ' MW-1, dulled in the area where the underground tank was removed, showed an initial l concentration of 11 mg/l, and 10 months later, a concentration of 37 mg/1 of total Petroleum hydrocarbons (IPH). The soil samples taken, at the time of the well installation, showed a maximum level of 4,800 mg/kg of total hydrocarbon. Wells MW-2, 3 and 4 were all installed at a later date by Harding & Lawson Associates. All were sampled uutially on January 26, 1989. Monitoring Well 2 (MW- 2) showed a substantial increase from the initial sampling to the second sampling seven (7) months later MW-3 showed a decrease to a "none detected" level and MW-4 showed a slight increase in the benzene level. MW-5, 6 and 7 were installed in December of 1990, by WHF. Wells 5 and 6 showed "none detected" levels, and MW-7 showed significant levels of BTX&E. Minor hydrocarbon contamination was visually detected in soils at a 20 foot depth in MW-7. After the pump test and well development, a sampling round was conducted and all wells showed "none detected" in Febntary of 1991. A subsequent round was taken in March of 1991, and this round showed all wells "none detected", except Well 2. Well 2 had Benzene in it at 1.1 ppb Groundwater gradient has been measured in wveral directions over the life of this protect These measuremertts show swings from southeast to east to northeast. The Regional Water Quality Control Board (RWQCB) and the San Joaquin County Environmental Health Department had determined That down gradient is northeast and had asked for a monitoring well to be installed to the ' northeast. On May 2, 1991, MW-8 was installed, northeast of the remedial excavation. This well was installed at the direction of the RWQCB to determine if groundwater had migrated to the northeast portion of the site. Soil and groundwater samples tested negative for IBTXE and gasoline. In the July, 1991, sampling round, all wells (MW-2, MW-4, MW-5, MW-6, MW-7 and MW-8) showed "ND" for BTXE and gasoline. In October and November of 1991, MW-2 and MW-7 had low levels of some compounds. The January, 1992 sampling showed low levels of Be ne and Xylene in MW-2. In the April l and July, 1992 samplings, MW-2,<Zj!Nand MW-7 were tested. All three (3) wells showed "ND" levels for BTXE and gasoline Q � �°� _ rn �A)