SITE INFORMATION AND CORRESPONDENCE_PRE 2019

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Stantec April 30, 2010 Page 1 of 3 Reference: First Quarter 2010 Site Status, Groundwater Monitoring and Remedial Summary Report- Stockton Terminals Technical Committee Facilities Appendix C -Stantec Standard Procedures STANDARD PROCEDURE FOR GROUNDWATER SAMPLING Depth to Groundwater/SPH Thickness Measurements Prior to purging each of the wells, the depth to groundwater and thickness of SPH, if present, within each well casing is measured to the nearest 0.01 foot using either an electronic 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 may or may not be purged depending on the requirements of the project. Where purging is conducted prior to sampling wells that do not contain SPH, a dedicated 1-inch diameter PVC "stinger," bailer or groundwater pump may be used to purge the wells. Purge water may be discharged directly to a vacuum truck via the "stinger", or contained onsite in holding tanks or 55-gallon DOT-approved drums. To help assure that the collected samples are representative of fresh formation water, the conductivity, temperature, and pH of the groundwater are monitored and recorded using a Cambridge Hydac meter or equivalent during purge operations. Purge operations are determined to be sufficient once successive measurements of pH, conductivity, and temperature stabilize to within +/- 10 percent. During purging a minimum of three (3) 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 than two hours, wells are sampled once the well is recharged to within 80 percent of pre-purge groundwater elevation. For very slow recharging wells (wells pumped 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 of the wells using pre-cleaned, single-sample polypropylene, disposable bailers. The groundwater sample is discharged from the bailer to the sample container through a bottom emptying flow control valve to minimize volatilization. Collected water samples are discharged directly into laboratory provided, pre-cleaned, 40 milliliter (ml) glass vials and sealed with Teflon-lined septum and screw-on lids. Labels documenting sample number, well identification, collection date and time, type of sample and 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 by the State of California Department of Health Services Environmental Laboratory Accreditation Program to perform the specified tests.