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Revised Workplan-Additional Site Investigation for PFAS BSK Project E20-016-01F Stockton Metropolitan Airport(SCK) March 1, 2023 Stockton, California Page 19 6.1.2.3 Groundwater Sampling from Monitoring Wells Once the monitoring wells have been installed by BSK's licensed C-57 drilling sub-contractor(e.g., MR Drill Co.) they will be allowed to sit for at least 48 hours prior to development. After development, the monitoring well will be allowed to sit for at least another 48 hours prior to purging, and subsequent collection of groundwater for chemical analysis. Following the installation and development of each of the four(4) monitoring wells, each monitoring well would be purged and sampled. Before purging and sampling each well would be opened and be allowed to equilibrate to atmospheric conditions for approximately 30 minutes. Once the wells have been allowed to equilibrate, static depth-to-water measurements would be collected with a water level meter to the nearest 0.01-inch and noted on the sampler's field log. A decontaminated submersible pump would be lowered into the well with disposable, or dedicated tubing approved for PFAS sampling. The well would be purged of at least three (3) casing volumes, or until parameters have stabilized, up to five (5) well casings.The following water quality parameters will be considered as stabilization criteria measured after each well casing volume is removed while purging. • ±3%for temperature, • ±0.1 for pH, • ±3%for conductivity, • ±10 millivolts (mV) oxidation reduction potential (ORP), • ±10%for dissolved oxygen (DO) and, • ±10%for turbidity. If three (3) of the six (6) parameters bulleted above are within the tolerances specified, (i.e., ±3% for temperature, ±0.1 for pH, ±3 %for conductivity, ±10 millivolts (mV) oxidation reduction potential (ORP), ±10%for dissolved oxygen (DO) and, ±10%for turbidity)for three (3) casing volumes, the groundwater in the well casing will be considered stabilized, and groundwater samples will be collected for chemical analysis. If groundwater does not stabilize after five (5) well casing volumes have been removed, the groundwater in the well casing will be considered stabilized, and groundwater samples will be collected for chemical analysis. Once the well has been purged at least three (3) well casing volumes and water quality parameters have stabilized, the submersible pump and associated tubing is removed, and a disposable bailer is lowered into the well with a non-PFAS cable. A new disposable bailer would be used at each monitoring well when collecting samples for chemical analysis. All purged groundwater and associated rinsate from decontamination would be containerized in 55-gallon Department of Transportation (DOT) approved drums awaiting characterization and disposal.