ARCHIVED REPORTS_XR0012617 - Laserfiche WebLink

Home Browse Search

-,�, i � 7 �-� m-� ,.,,yam. �� ,�" � •�'` �. within one mile of the site in the downgradient direction that put;mp water either from a shallow perched zone or from a deeper water-bearing zone. Water supply wells in the area are typically more than 345 feet deep and at-e screened at depths greater than 144 feet. 1.3 SITE HISTORY Exxon RS 7-3942 dispensed gasoline froi-3 three single-walled steel underground storage tanks until 24 July 1986,when they were removed. An underground used oil tank was also removed and the buildings demolished at lhat time. Associated piping was removed from time site 11 December 1986. 1.4 PREVIOUS I\VESTIGA717IONS petroleum hydrocarbons were detected ill closure samples collected from excavations when the tanks and piping were removed (Table 1). 1 larding Lawson Associates(MLA)and EA Engineer- ing, Science,and Technology(EA) have been irmvestigating the subsurface of the site since then. Seven groundwater monitoring wells (f=igure 3) have been installed on the site to investigate iter monitoring wells have been installed off the site to soils and groundwater; three groandw: define the extent of the dissolved petroleum hydrocarbon plume. Because the water table has been dropping, three groundwater recovery wells have been recently installed in the northwest corner of the site from which groundwater caul be extracted. E Varying concentrations of petroleum hydrocarbons have been defined in soils from immediately below the contact of backfill and native soils (EX-2 at 20 feet,Table 1)down to a depth of 28.5 feet, in MW8, which wits more chalk S feet below static water at the time. Soil and soil vapor sampling and chemical analyst:;have defined petrolc,im hydrocarbons in a soil column extending from 16 feet below ground surface to well bclo%%, the existing water table. Groundwater has also been satmmpled and chemically analyzed regularly as part of the continuing investigation. Analytical results of groundwater;aam,plitlg (Table 2) have defined a dissolved constituent plume that appears la originate in Clic area of the old tank field and extends off the site to the northwest, having dispersed will, groundwater flow into Rosemarie Lane. Offsite " sources south of former Exxon RS 7-3942 have also been implicated. Gasoline has also been intermittently detected and mcastu•caI on the groundwater ill MW3. .As noted earlier, groundwater flows to the northwest. When monitoring first began is 1987, groundwater was 17 to 19 feet below ground surface (Table 3). The water table has since de- clined almost 10 feet to 28.5 t� 29.5 feet hclow ground surface,but groundwater has continued flowing to tl,e northwest. Various wells have been tested with slug/bail and pumping tests to characterize the aquifer and provide parameters useful in proposing and designing a retmmediatian system. estinm;tted hydraulic parameters(Table 4)characterize a transnmii sive aquifer from which yells can successfully exlr:tct enough groundwater to control further migration of tl,e 2 Mi.'11w L++ W