ARCHIVED REPORTS XR0002751 - Laserfiche WebLink

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r ' ARCO Products Company 6 ARCO 4932, 16 E HardinWa ,Stockton,CA November 9 2001 '= -• —respectively MtBE analysis was reported in-wells MW_6, MW-7, - - - — - - ' and MW-8 up to 67,000 ugll (MW-6) 1,2-DCA was reported in wells MW-5 and MW-9 at concentrations of 3 8 ugll and 8 4 ug/l, respectively ' • Groundwater flow was measured in July 2001 to the northeast with a gradient of 0 002 ft/ft, as shown on Figure 6 ' • No water supply wells were located in a 500-foot radius door-to-door well search ' CONCLUSIONS AND RECOMMENDATIONS Based on the data collected during this assessment, petroleum hydrocarbons have ' impacted both soil and groundwater beneath the site TPHg, benzene, and MtBE were vertically defined in soil through borings SB-1 and SB-2 TPHg and benzene concentrations have been defined to the limits of detection by wells MW-6, MW-7, and MW-8 Further delineation of MtBE in groundwater may be required MtBE concentrations appear to attenuate with depth near SBA and SB-2 Higher MtBE ' concentrations off-site appear to follow groundwater flow to the northeast The presence of TPHg and benzene in upgradient well MW-9 suggests an additional source(s) of petroleum hydrocarbons may be present in the area ' SECOR recommends further lateral assessment of MtBE contamination in soil and groundwater northeast of MW-6, installation of a deep well completion to 70-to 80-feet Ibgs, and a file review to identify the potential off-site petroleum hydrocarbon source(s) LIMITATIONS { ' This report presents our understanding of existing conditions at the subject site The conclusions contained herein are based on the analytical results, and professional ' judgment in accordance with current standards of professional practice, no other warranty is expressed or implied SECOR assumes no responsibility for exploratory borings or data reported by other consultants or contractors ' 077 43826 330/AddAssess doc