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HYDROLOGY <br /> Ground water elevations at the site ranged between 5 and 6 feet <br /> below sea level from January 20, 1989 to April 18, 1989 From <br /> April 18 , 1989 through September 13 , 1991, ground water <br /> elevations decreased an average of eight feet, to approximately <br /> 13 ' to 14 ' below sea level This decrease may be attributed to <br /> both sampling time (summer vs winter) as well as an effect of <br /> the continuing drought period <br /> A period of recharge began in December, 1992 and reached a peak <br /> in March, 1993 During this period, ground water elevations rose <br /> approximately 2 5 feet throughout the site Ground water <br /> elevations have dropped approximately 1 5 feet since the last,. <br /> depth-to-water measurements on March 3-1—,--1-"3 The current <br /> ground water elevation gradient across the site is fairly flat <br /> with an average slope of 0 006 (0 006 feet per linear foot) <br /> downward from MW2 toward MW7 <br /> SITE INVESTIGATION <br /> Ground water sampling was conducted on July 7, 1993 in compliance <br /> with the quarterly monitoring requirements for this site The <br /> various ground water parameters were determined by. 1) recording <br /> depth to water (by use of a resistivity meter) at each monitor <br /> well, 2) purging and containment of ground water from the wells, <br /> . 3) collecting water samples from the wells, 4) submitting these <br /> water samples to a State Certified Analytical testing laboratory <br /> via established "chain of custody" procedures <br /> The water samples were analyzed for Total Fuel Hydrocarbons (TFH) <br /> as gasoline and Volatile Aromatic Hydrocarbons (BTEX) using EPA <br /> Methods 5030 and 602 , respectively Laboratory detection limits <br /> are as follows TFH is 0 05 mg/L and BTEX is 0 3 µg/L with <br /> xylenes being 0 9 Ag/L <br /> Methods and Procedures <br /> The ground water was sampled in four monitoring wells (MW3 , MW4, <br /> MW6, and MW8) by a Western Geo-Engineers (WEGE) <br /> geotechnician working directly under the supervision of <br /> California Registered Geologist 43037 Prior to sampling each <br /> well, the WEGE geotechnician measured the depth to ground water <br /> using a resistance probe A ground water contour surface was <br /> later plotted from these depth-to-water measurements, ground <br /> water flow directions at the site were then inferred from the <br /> contour gradients This information is presented in Figure 4C. <br /> 3 <br />