ARCHIVED REPORTS_XR0007901 - Laserfiche WebLink

Home Browse Search

I Corrective Action Plan Montgomery Ward Auto Service Center, Stockton, CA ' Installation of Additional Air S ar in /Va or Extraction Wells The ground water plume below the Montgomery Ward Site is shown in Figures 9 (for TPH-G) and 10 (for benzene) The center of both of these plumes are north of any known ' source at the Montgomery Ward Site Further, five years of quarterly monitoring has shown that although the gradient varies seasonally (downgradient varying from east to west), the gradient has never shown north as a downgradient Therefore, the center of the plumes appears to have originated from the Former Unocal Site which can be shown to be upgradient during the summer months when Delta College pumps its irrigation well Notwithstanding the above, the system proposed herein will address all the contamination currently present beneath the Montgomery Ward Site regardless of its source ' Accordingly, 8 additional combination wells will be needed at the Montgomery Ward Site (see Figure 13) Each of these wells will be a dual-well consisting of one well screened in ' the vadose zone (around 15 to 30 feet bgs) to be used as a vapor extraction well and another well screened below the deepest known contamination at that location (around 60 ft bgs) to be used as an air sparging well The air sparging well is required for mobilizing the contaminants trapped in soil pores at depth and to strip contaminants from the ground ' water The vapor extraction wells are needed to collect the vapors that will result from air sparging Installation of ORC in Selected Wells As directed by the County, in order to test the feasibility of using oxygen releasing compounds (ORCs) to reduce contaminant concentrations in ground water, ORCs will be placed in two wells at the Montgomery Ward Site, i e , MW-3 and MW-4 These wells were selected because, depending on the season (since gradient varies by season), both MW-3 and MW-4 become upgradient wells MW-6 will be used to check if there are any observable downgradient effects of the ORC since MW-6 is downgradient to MW-1 and MW-4 when the ground water flow is to the east ORC socks will be installed in the two selected wells according to the following configuration Screened Interval ORC Interval 1 Well No (feet bgs) (feet bgs)— MW_3 47 to 67 44 to 59 1 MW-4 48 to 68 45 to 60 Installation of Piping, Well Boxes and Well-Head Connections Figure 13 shows the proposed layout for underground piping to connect the extraction wells to the remediation unit Figure 14 shows the details on the trenches that will be excavated to install the piping and the well head connections to be done to connect the ' wells to the piping manifold leading to the remediation unit Prior io trem,11i g fol the piping runs, an Unucrground Service Alert \._."MOA� rleNranre will �� be obtained All public utilities will be marked clearly on the ground surface with paint If required, geophysical methods will be used to determine if there are other unknown pipes 24 -SAProject No 1232 - 24 - SAB 6 WORD 1212CAP