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a August b, 1991 ARCO Station No. 548 r^ Gradient Evaluation r� The local groundwater gradient will be evaluated to provide an indication of the direction of ground-water flow at the site. The elevation of the top of each well casing will be measured relative to mean sea level by a licensed land surveyor. Water-depth nearest 0.01 foot in each well with an electric water-level measurements will be made to the indicator. The well will be vented t the atmosphere for a minimum of 1 hour before obtaining depth-to-water measureme-ts. Venting is conducted to ally_ •lie ground water to equilibrate to barometric pressure. This data will be combined to evaluate the elevation of the groundwater surface in each well and the slope of the ground-water surface across the site. r Lab orata Anai ses We will submit the soil sample showing the highest reading on the PID and the cssa Epee collected from directly above ground water to a laboratory approved by ARCO a - by the State of California. These soil samples will be analyzed for TFHg by EPA Method 8015 and for BTEX by EPA Method 8020. The four samples collected from the drill the cuttings will be composited into one sample by the laboratotted ry and will be analyzed for constituents listed above using the same laboratory methods. One soil sample sub VOC, from the boring drilled near the waste-oil tank will also be analyzed for TPHd,TOG, and total cadmium, chromium, nickel, lead, and zinc. The water samples will be analyzed for TPHg by EPA Method 8015 and for EPA Method 602. In addition,the water sample collected from the monitto jnZ.g w�e11 downowngradient of the waste-oil tank will be analyzed for TPHd,TOG, and VOC. Detection limits for the _. Laboratory tests and concentrations present will be stated on the laboratory reports. t. i3 AGS 30000.-4 e. l