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ARCO Service Station No. 2186 Page 2 3212 North California Street December 3,2008 Stockton, California 94570 for the presence of volatile organic compounds using a photo-ionization detector and selected soil samples will be analyzed by an environmental laboratory certified by the State of California. Instead of advancing two shallow wells to approximately fifty-five feet bsg with a twenty-foot screened interval between approximately thirty-five and fifty-five feet bsg, the EHD believes the shallow wells should be continuously cored beginning at approximately thirty feet bsg, and based on this information, the wells should be screened between approximately thirty-eight and fifty-eight feet bsg to avoid connecting two sand units. Stantec proposes to advance deep well MWAD initially to approximately sixty-five feet bsg using eight-inch diameter hollow-stem augers followed by advancing the soil boring to the same depth of approximately sixty-five feet using eighteen-inch diameter hollow- stern augers centered on the eight-inch pilot boring. Stantec proposes to collect soil samples at five-foot intervals as described for the shallow wells. Following this, an eight and five-eighths-inch diameter, flush-threaded steel conductor casing will be installed to sixty-five feet bsg; then eight-inch diameter hollow-stern augers will be used to advance the boring down the inside of the conductor casing to total depth of approximately eighty- five feet bsg, setting deep well MW-11) screened between sixty-five and eiglity-five feet bsg. Instead, the EHD believes deep well MW-113 should be continuously cored beginning at approximately sixty feet bsg, and based on the lithological information, conductor casing should be installed to approximately seventy feet bsg instead of the proposed sixty-five feet bsg with MW-11) screened between approximately seventy and eighty-five feet bsg. Based on field logs, it appears that boring MW-1 has a potential aquitard approximately fifty-eight to sixty-seven feet bsg and nearby boring BH-2/AW-1 has a potential aquitard beginning at approximately sixty-five feet bsg. Based on soil lithology for boring log MW-1, placing the screened interval at approximately seventy feet bsg will target the large sand unit beginning at approximately sixty-seven feet bsg. San Joaquin County requires monitoring wells to be constructed following the Well Standards in accordance with San Joaquin County Ordinance Code Section 9-1115.6. Well Standards' Section 13.9.2 specifically states that the monitoring well borehole diameter shall be at least four inches greater than the outside diameter of the conductor casing. The inner diameter of the permanent conductor casing shall in turn be at least four inches greater than the outside diameter of the well casing. Because the work plan does not give specifies as to the inside and outside diameters of the conductor casing, the EHD can not determine whether this work plan meets these requirements. Please submit an addendum to this work plan by January 26, 2009, that addresses the recommendations presented above. Include a well construction diagram of the shallow and deep wells along with specific dimensions for the borehole, conductor casing, and well casing.