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Quik Stop Station No 039 February 28,2000 Stockton California Subsurface Site Assessment 4.0 GROUNDWATER DEPTH EVALUATION Depth to groundwater will be measured to the nearest 0 01-foot using an electronic hand held water level indicator The tip of the probe will be examined to evaluate whether a product sheen is present 6.0 MONITORING WELL DEVELOPMENT/ PURGING AND SAMPLING Following installation, the wells will be surged with a surge block to remove fines from the sand pack After surging, ten casing volumes of groundwater will be purged from each well using a bailer or centrifugal pump to remove sediment and enhance representative sample quality Groundwater sampling events conducted after the initial well development will be preceded by purging a minimum of three well casing volumes as described above Purge water will be monitored for the parameters temperature, pH, and conductivity until stabilized Wells will recharge to 80% before sampling If wells dewater, they will be allowed to recharge for a minimum of one hour prior to sampling After the water levels within the wells stabilize, a sample will be collected with a clean disposable bailer Samples will be contained in air-tight vials and then packed on ice and sent to the laboratory for analysis Groundwater samples will be transported to the laboratory and analyzed within the EPA-specified holding time for requested analysis Each sample container submitted for analysis will have a label affixed to identify the job number, sample date, time of sample collection, and a sample number unique to that sample Samples will be analyzed by a California-certified laboratory A Chain-of-Custody form will be used to record possession of the sample from time of collection to its arrival at the laboratory When the samples will be shipped, the person in custody of them relinquishes the samples by signing the Cham-of-Custody form and noting the time The Sample Control Officer at the laboratory will verify sample integrity and confirm that the sample was collected in the proper container, preserved correctly, and that there is an adequate volume for analysis 6.0 WELLHEAD TOP OF CASING MEASUREMENT The top of each new well riser will be measured to allow correlation of the groundwater levels at the site The measured point on each well riser will be marked to help insure future groundwater level measurements are taken from the same location All measurements will be measured relative to an arbitrary datum or benchmark to the nearest 0 01-foot using a surveyor level and graduated stadia rod If using an arbitrary datum, one well riser will be assigned the arbitrary datum and the other well riser will be measured higher or lower relative to the arbitrary datum 7039-12 rpt B-2 HORIZON ENVIRONMENTAL INC