SITE INFORMATION AND CORRESPONDENCE_FILE 2

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.. Former Exxon Service Station No. 73942 Page 2 of 3 4444 North Pershing Avenue April 3, 2015 Stockton, California 95207 • Analyzing selected soil samples from B2 (aka B15) for total petroleum hydrocarbons (TPH) as gasoline (TPHg), TPH as diesel (TPHd), and the Environmental Protection Agency Method 8260 suite of compounds that include: benzene, toluene, ethylbenzene and total xylenes (BTEX); methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether (ETBE), di-isopropyl ether (DIPE), tertiary-amyl methyl ether (TAME), and tertiary butyl alcohol (TBA); • Installing one off-site monitoring well, MW15, using hollow-stem-auger drill technology, to approximately forty feet bsg, on the north side of Rosemarie Lane at the location illustrated on Plate 2 of the Addendum after obtaining an access agreement from the property owner; • Collecting soil samples at five-foot intervals to depths of approximately twenty-five feet bsg, then collecting continuous soil samples "across the anticipated screened interval" from approximately twenty-five to forty feet bsg for lithologic evaluation; • Shortening the proposed well screen-interval length if "multiple, distinct course-grained layers are encountered"; • Based on field criteria listed in bullet three above, submitting a minimum of four soil samples from the well borehole for chemical analyses listed in bullet four above; and • Submitting a report of findings following the field work that includes the advancement of two soil borings and one monitoring well. The following are EHD's responses to the Addendum: • The EHD is concerned that the proposed depth of sixty feet bsg for B2 (aka B15) may not satisfy the objective of defining the vertical extent of petroleum hydrocarbon contamination. This is based on historical soil analytical data indicating significant concentrations of contaminants of concern at approximately forty feet bsg in boreholes IP3 and V1, approximately ten feet northeast and southwest, respectively, of proposed boring B2 (aka B15), and detection of contaminants of concern in soil samples collected at approximately ninety-nine feet bsg in down-gradient well MW14. The EHD approves the advancement of B2 (aka B15) with the condition that field criteria listed in bullet three be employed to identify petroleum hydrocarbon contamination and determine the total depth of the borehole. • The EHD suggests that, going forth, 61 (aka B14) and B2 (aka B15) be renamed SB14 and S1315, respectively. This proposed nomenclature conforms to the historical naming of boreholes at this site and will assist in identifying the sequential order of these borings for future reference. • Although Cardno proposes to install off-site well MW15, the Addendum lacks specifics concerning the construction of the well. The EHD approves the installation of MW15 with the conditions that eight-inch augers are used for advancing the borehole; two-inch- diameter Schedule 40 casing is employed, No. 3 sand is used for the filter pack for 0.020-inch casing slots or No. 2/12 sand is used for the filter pack for 0.010-inch casing slots; the filter pack extends from total depth of the borehole to at least two feet above the screened interval; a three-foot bentonite seal is placed above the filter pack using