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r Z- 03 em, Mr. Kyle Christie December 9, 1988 .� Page 4 h .� To track the dissolved hydrocarbon trends systematically ARCO authorized quarterly groundwater sampling and analysis for benzene, toluene, and xylene (BTX). Groundwater samples were collected for analysis on September 29 and 30 and October 3 and 4, 1988. Monitoring well W-8 was not sampled as dissolved hydrocarbons have never been identified hydrocarbon occurrence. in groundwater from 1•:'-8, and it is located some distance from any identified dissolved Field Methods Groundwater was purged from each monitoring well prior to sample collection using a bladder pump and stainless steel bailer. Throughout the purging process, pH and specific conductance of the discharged water were monitorP.4. These parameters had stabilized (three consecutive measurements within 10 percent of each other taken 5 minutes apart) before groundwater samples were collected. Three well volumes of groundwater (one well volume being the volume of water inside the well casing- g plus 35 percent of the gravel packed annular space) were evacuated from monitoring wells W-2, W-213, W-3, W-5, W-6, and W-7. The low groundwater level in September/October 1988 (see Figure 2) made purging difficult in t` monitoring wells W-1, W-2A, and W-4. Due to slow recharge of g groundwater into monitoring wells W-2A and W-4, 0.7 and 1.3 well volumes, respectively, were evacuated from these wells. Monitoring well W-i contained only muddy water. Therefore, no groundwater sample !, J was collected from monitoring well W-1. Each well was sampled with a Teflon bailer equipped with a bottom-eml,tying valve. The t:3 sample was drained directly from the bottom valve into two 40-milliliter glass bottles with Teflon-lined septums. The samples were stored on ice from the time of collection through delivery to Eureka Laboratories Inc., in Sacramento. All purging and sampling equipment was washed with laboratory-grade detergent and tap water then rinsed with deionized water before each use. All groundwater produced during purging and sampling was contained in 55-gallon Fri drums and temporarily stored on site pending results of the laboratory analysts. ARCO f- contracted with Armour Petroleum, Inc.,of Fairfield,California, to dispose of the contaminated groundwater. a September/October 1988 Field and Analytical Results €>$ Groundwater levels were measured at approximately 49 feet below ground surface in April 1987 when the first three monitoring wells were installed. Water level measurements show that groundwater dropped to approximately 55 feet below ground surface in October 1987 and E rose to approximateiy 52 feet below ground surface in March I988. Groundwater levels were measured at approximately 59 feet below ground surface in late September 1988. In late September 1988, Groundwater flow direction was to the southwest under a hydr4UGc_ _t _.-. _._of_about.-Il-feet.per-mile 0.2- ------ - -- - -- P ( percent)- ---- - ---._..- __.—.-.------------ 1} Dissolved BTX concentrations in groundwater samples collected from April 1987 through t j September/October 1988 are summarized in. Table 1. September/October 1988 benzen; concentrations are shown on Figure 1. Complete laboratory reports of the September/October i a BLOWN AND CALDWILL 723 S STREET sACRAPAEN -- TOL CALIFCANLA M141M.glel 441.0127 .