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L & M OPERABLE UNIT- FIRST QUARTER 2012 SITE STATUS, REMEDIAL SUMMARY, <br />AND GROUNDWATER MONITORING REPORT <br />Groundwater Monitoring and Sampling <br />April 30, 2012 <br />I:\Tidewater\TW Stockton (P2A)\QMRs\2012\1Q12\1Q12 QSSR QRSR QMR Stockton_FINAL.doc 2.23 <br />In general, reported TPHg, TPHd, TPHo, benzene, MtBE, and TBA concentrations in samples <br />from the shallow zone wells were within historical ranges during 1Q12 (Figures 3 through 8). <br />TPHg concentrations increased in a few wells, but generally remained stable or non-detect from <br />the 4Q11 to 1Q12. TPHd concentrations increased in a few wells, but generally remained <br />stable or non-detect from the 4Q11 to 1Q12. TPHo, benzene, MtBE, and TBA concentrations <br />generally remained stable or non-detect from the 4Q11 to 1Q12. <br />The extent of shallow TPHg and TPHd are historically delineated except to the north where the <br />Stockton Deep Water Channel exists. During 1Q12, TPHg was delineated to the south, <br />southwest, and west. During 1Q12, TPHd was delineated to the west except for two detections <br />southwest of the Site just south of the Mormon Slough in wells MW-30 and MW-33. These <br />wells are across the Mormon Slough and are not anticipated to be associated with the historic <br />L&M OU release. The UOU and MOU wells were not sampled during 1Q12; therefore, TPHg <br />and TPHd could not be delineated to the east. TPHo, benzene, MtBE, and TBA were <br />delineated during 1Q12. TPHg, TPHd, TPHo, Benzene, MtBE, and TBA appear to be fairly <br />stable throughout the shallow zone wells. <br />2.7.2 Deep Zone <br />The following sections summarize trends for detected petroleum hydrocarbons, fuel oxygenates, <br />and observed SPH for deeper (B-, C-, and D-Zone) groundwater beneath the Site. <br />2.7.2.1 SPH <br />A summary of 1Q12 SPH thickness and SPH sheen in comparison to the 4Q11 is provided in <br />the following table. <br />Well Identification <br />(Zone) <br />SPH Thickness <br />4Q11 (Feet)* <br />SPH Thickness <br />1Q12 (Feet)* <br />Difference <br />(Feet) <br />MW-17 (B) Sheen Sheen NA <br />MW-43 (B)0.25 0.35 +0.10 <br />MW-46 (B) Sheen Sheen NA <br />MW-47 (B)0.05 Sheen -0.05 <br />MW-48 (B)0.10 0.01 -0.09 <br />MW-49 (B)0.11 0.55 +0.44 <br />MW-50 (B)26.85 7.50 -19.35 <br />MW-52 (B) Sheen Sheen NA <br />Definitions: <br />B = B-Zone wells <br />NA = Not applicable/not available <br />SPH = Separate phase hydrocarbon <br />* = SPH removal occurred prior to groundwater sampling.