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STANDARD PROCEDURE FOR GROUNDWATER SAMPLING Depth to Groundwater/LPH Thickness Measurements Prior to purging each well, the depth to groundwater and thickness of liquid phase hydrocarbons (LPH), if present, within each well casing are measured to the nearest 0.01 foot using either an electronic Solinst water level indicator, or an electronic oil-water interface probe. Measurements are taken from a point of known elevation on the top of each well casing as determined in accordance with previous surveys. Groundwater Monitoring Well Purging Groundwater wells will be purged prior to sampling with a bailer or groundwater pump. Purge water may be contained on-site in 55-gallon, DOT-approved drums. To help assure that the collected samples were representative of fresh formation water, the conductivity, temperature, and pH of the delivered effluent are monitored and recorded using a Cambridge Hydac meter or another meter similar in nature during purge operations. Purge operations are deemed sufficient once successive measurements of pH, conductivity, and temperature stabilize to within +1- 10 percent. I During purging, a minimum of three well casing volumes are removed from each well. However, in the case of very slow recharging wells, purging is deemed sufficient if the well contents are completely evacuated during purge operations. Unless recharge takes more Ff than a couple of hours, wells are sampled after groundwater levels are recharged to within 80 E percent of pre-purge groundwater elevation. For very slow recharging wells (wells pumped E dry during purging), samples may be collected'after two hours of recharge. Groundwater Sample Acquisition and Handling Following purging operations, groundwater samples are collected from each well using pre- cleaned, single-sample polypropylene, disposable bailers. The groundwater sample is 4 discharged from the bailer to the sample container through a bottom emptying flow control valve to minimize volatilization. 4 t Collected water samples are discharged directly into laboratory provided, pre-cleaned, 40 milliliter (ml) glass vials and sealed with Teflon-lined septum, screw-on lids. Labels documenting sample number, well identification, collection date and time, type of sample and G type of preservative (if applicable) are affixed to each sample. The samples are then placed into an ice-filled cooler for delivery under chain-of-custody to a laboratory certified to perform the specified tests by the State of California Department of Health Services Environmental Laboratory Accreditation Program. Trip Blanks E To help assure the quality of the collected samples, and to evaluate the potential for cross contamination during transport to the laboratory, a distilled-water trip blank accompanies the samples in the cooler. The trip blank is analyzed for the presence of volatile organic 3 f F X k r