ARCHIVED REPORTS XR0004094 - Laserfiche WebLink

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• Findings From Water Sample Analysis EW -1 shows all constituents to be non -detect except for xylene at 1ppb. Monitoring well GMX-1 continues to have trace amounts of TPHg (.49ppm), Benzene(.7ppb) and MTBE (13ppb). MW -2 has shown an increase in TPHg(8.8ppm,+300%), Benzene(9ppb, +112%) and Ethyl-Benzene(848ppb, +1021%). The increase in concentration at MW -2 is most likely attributed to lack of purge volume before sampling. MW -3 continues to have a clean history. MW -4 was dry and not sampled. For the three wells with a contaminant history (EW -1, GMX-1, and MW -2), the average of each contaminant is below drinking water health limits. MW -2 and MW -3 are confined samples because they are not in contact with the surrounding groundwater. The distance from the inside of the cone tip to the first slot of the 2" PVC screen pipe is 0.91 foot (10 718"). From DelTech's field report, it is seen that the standing water column for MW -2 and MW -3 is only 0.40 foot and 0.78 foot, respectively. The standing water column is below the first screen slot on MW -2 and MW -3. The analytical results from MW -2 and MW -3 should not be relied on. The proposed clean up levels from the approved "Final Remedial Plan" and the average remaining concentrations are as follows: Compound Concentration Goals Average Remaining_ Concentrations Benzene 0.005mg/L 0.0032mg/L MTBE 0.001 mg/L 0.0043mg/L TPHg 2.Omg/L 3.1 Omg/L iThe direction of flow is South West with a gradient of s=0.0058. A gradient of .0058 is extremely steep and is questionable. Foothill Engineering does not recommend relying on this value, especially since there was only two wells with good levels of water. Conclusions Pumping has brought the plume to the surface for treatment and disposal. All regulated constituents have been brought within the EPA's drinking water standards. In MW -2, the three fold increase of the Total Petroleum Hydrocarbons as Gasoline from when pump and treat stopped is unexpected. Due to the lack of available water for purging in MW -2, Foothill Engineering believes the increase in concentration found during this event should not be relied on. Recommendations Foothill Engineering continues to recommend that the San Joaquin County Public Health Services, Environmental Health Department issue a letter stating no further action is required for this site. Please contact Mike Vlach at (916) 729-5184 if any questions arise concerning this report. Respectfully submitted w�Ro�ss�o�y� Foothill Enginee ing Ui C 57 07 v P.12-31-05 Mike Vlach, P.E. LP clw_ Attachments: Groundwater s Eiralyv§i cap, Site Map, Del -Tech Field Report, Laboratory Reports cc: Diana Maragos, Attorney for Sun West Liquors, W. T. Mitchell Group