ARCHIVED REPORTS XR0004079 - Laserfiche WebLink

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Existing Known Conditions The known lithology of the site is comprised of low permeable silts and clays the first 45'feet below the . surface . The first aquifer, consisting of highly permeable sand, begins a 45' below the surface and terminates between 56' and 60' below the surface into silty sand. This aquifer is contaminated with concentrations of MTBE to 3 ug/L as of the last monitoring event. TPHg is also present in concentration to 14 mg/L,and Benzene is present to 13 ug/L,as per the last monitoring event.The groundwater surface varies seasonally from 42 to 49 feet below the surface. Existing Equipment Installed on the Site. The site has been recently developed with new building construction comprising a bank office and commercial business. During construction the developer built a 10'x 21'underground vault to contain future remediation equipment.Also during construction,a conduit was laid from the vault to a proposed extraction well location. A 6" extraction well was installed in a 15" soil bore at this location as part of the very successful pump test performed by ATC during January and February of this year (see ATC Pump Test Report Attached). Recap of the Pump Test Results Using the Theis Solution method the average Storage Coefficient (S) was 2.4E-3 and the Hydraulic Conductivity was 0.012 cm/sec. The short steady state discharge rate was 13.5 gpm with a Radius of Influence (ROT)of greater than 90 feet(the furthest monitoring well from the extraction well). At the time of the pump test the static groundwater level was+/- 49'below the surface at the extraction well. Remediation Technology Available • 1. Local remediation sites in the area of Southwest Lodi have used Activated Carbon filtration as a "Pump and Treat'filter. This type of remediation was also used to reclaim the effluent from the above referenced pump test conducted by ATC. 2.Other technologies,such as Air Sparging,are available and in common use on sites that are not limited by the following criteria: (As per EPA Publication 510•B-95-007 "How To Evaluate Alternative Technologies For Underground Storage Tank Sites") a. No free product on the surface_of the groundwater on the site: The site does not have any free gasoline product on the groundwater. b. There can not be any basements or confined spacces present or near the site: This site does not have any basements or confined spaces on the or near the site_ c. Contaminated groundwater can not be located in a confinedaquifer system: The contaminated aquifer is confined by low permeable soils above and below the contaminated aquifer.The strata above the aquifer is made up of a very impervious layer of silty clays with some hardpan to a thickness of twenty feet starting about 25 feet below the surface. The eleven foot contaminated aquifer is located directly above a strata of silts and clays. .�� C Due to the fact the contamination on this site is located in a confined aquifer,Air Sparging must be ruled out as a possible technology for remediation of this site. " Bioremediation has been tried,but has failed to remove MTBE to non detect or acceptable levels. Both Air Sparging and Bioremediation methods have found success in remediation of TPHg and BETX 2