ARCHIVED REPORTS XR0002718 - Laserfiche WebLink

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":1ii�i:7 bio i;"•{:'rr c ...5(;4:i�::3,.a'. ........_ ...... .�....,... � ... _ f concentrations, no consistent trend of hydrocarbon contamination can be determined. However, the concentrations detected are very low and most likely do not represent a threat to public health. No Maidmum Contaminant Level (MCL) or Action Level (AL) for TPH in drinlldng water have been establishedby the State of California. Furthermore, the AL for toluene is 100 ppb; toluene has been detected only once in MW-4 at 1.5 ppb, well below the AL. No benzene has been detected in any well at the site. 4A Remediation Alternatives for Hydrocarbon Impacted Groundwater The presence of impacted groundwater at the site is still uncertain. TPH as gasoline, TPH as diesel or TPH as motor oil has not been detected in any well for two consecutive ; quarters. Based upon the site conditions and concentration of impacted groundwater, most groundwater treatment methods would be ineffectual at this site. In-situ air sparging has not , been shown to be effective on motor oil; bioremediation may be difficult because.of the . �1 clayey soil; and pump and treat would not be effective because wells at the site have shown poor recharge, which would make pumping difficult. ' It is also very likely that none of the remediation alternatives considered would be cost effective. Air sparging would probably require installation of equipment crossing Hardin;: Way, which would not be logistically possible, nor permitted by the City of Stockton; bioremediation and the associated monitoring would be very costly relative to the achievable clean-up levels. Pump and treat, if at all possible, would also be very costly; furthermore, pump and treat systems rarely obtain background clean-up levels. 4.5 Site Closure Based upon the data collected from the site, the information and assumptions in this report and historical information regarding the site, GeoAudit recommends certification of the property for site closure. The following items are most important for closure consideration:- ' • The highest concentration and volume of remaining impacted soil in the vicinity of the site is located almost entirely beneath Harding Way. • The average concentration of the remaining impacted soil on-site is estimated to be 200 ppm; beneath Harding Way, the average concentration is estimated to be 1,050 ppm. • It is estimated that approximately 100 gallons of hydrocarbons remain beneath Harding Way, as compared to appro.-dmately 11 gallons remaining on-site. ' • It is likely that the source of the impacted soil on-site may have originated off-site. A.&S-A 12 1