Laserfiche WebLink
4 <br /> In February 1987, ARCO retained Brown Md. Caldwell (BC) to conduct a site <br /> investigation at Station 434_ In March 1987, the County approved BC's work plan to <br /> install three on-site groundwater monitoring wells. In April 1987, BC installed monitoring <br /> wells W-1, W-2, and W-3. The locations of these monitoring wells are shown on Figures <br /> 2 and 3. Figure 3 also shows the locations of all existing on-site and off-site monitoring <br /> wells, benzene concentrations in groundwater sampl s collected from these wells in January <br /> 1989, the seasonal range of groundwater flow directions, and the locations of additional <br /> proposed off-site monitoring wells. Monitoring well construction details for all existing <br /> monitoring wells are shown on Figure 4. Also shown on Figure 4 -are the highest and <br /> lowest groundwater levels measured since April 1987. <br /> April 1987, minor benzene, toluene; d- xylene .(BTX). .concentrations were_) <br /> 9idendfied_,in..soil samples-collected from 'borehole- -2. Laboratory results of soil samples <br /> collected from on-site boreholes are shown in Table 1. BTX and total Petroleum <br /> hydrocarbons� (TPH) were' identified in groundwater samples collected from monitoring <br /> wells W-1, W-2, and W-3. Lahoratory results of groundwater samples collected :from on- <br /> andx off-site monitoring wells are shown in Tabl 2. Groundwater flow direction was <br /> south=southwest sunder;aTMgradient .of:approxirriately._b feet per....mile. EDepth­to–_.groundwater <br /> was approximatelyT49-ifeet-below..gioun`d,.sur-facer A Problem Assessment Report describing <br /> the results of the April 1987 work was issued on qay 21, 1987. Copies of this .and later <br /> reports issued have been sent to ARCO, the Regional Board, the County, the City, and to <br /> the Stockton Engineering Branch of the Department of Health Services. <br /> By July 1987, BC had obtained a City enc r achment permit to install a monitoring <br /> well next to Well 12 and permission from American Savings to install two downgradient <br /> monitoring wells on their property. The County approved BC's work plan for the <br /> installation of these three off-site monitoring wells and for two on-site soil boreholes. BC <br /> installed off-site monitoring wells W-4, W-5, and -6 (Figure 3) and on-site soil ;boreholes <br /> B-1 and B-2 (Figure 2) in July 1987. No hydrocarbon constituents were identified in soil <br /> samples collected from boreholes W-4, W-5, and -6. High concentrations of TPH were <br /> identified in soil samples collected from borehole B-1 and from a soil sample collected <br /> from the capillary fringe zone in borehole B-2 Table 1). BTX and TPH were again <br /> identified in groundwater samples collected from monitoring wells W-1, W-2, and W-3. <br /> Minor concentrations of BTX were identified in groundwater samples collected from <br /> monitoring wells W-4 and W-5. No hydrocarbon constituents, were identified in the <br /> groundwater samples collected from monitoring well W-6 (Table 2). Groundwater flow <br /> direction was to the west under an approximate gradient of 15 feet per mile. -Depth to <br /> groundwater was approximately 53 feet below ground surface. An Addendum to the <br /> Problem Assessment Report describing the results of the July 1987 work was ':,issued on <br /> September 16, 1987. <br /> Between July and November 1987, free product accumulated in on-site monitoring <br /> wells W-2 and W-3, particularly in monitoring well W-2. Armour Petroleum.Company <br /> (Armour) removed a total of 30 gallons of product from monitoring wells W-2 and W-3 <br /> during this time period. <br />