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Caitfornia Department or Transportation 1Ia,, f: i', 2,jj i I Stockton Maintenance Station, Stockton, California Project No 400296-01 • 4 GROUNDWATER MONITORING ACTIVITIES 4.1. Groundwater elevation and hydraulic gradient I On September 13, 2000 a representative from Ninyo & Moore measured depth to static Igroundwater in the twelve on-site groundwater monitoring wells and two vapor extraction wells Static groundwater levels were measured using a Solinst water level probe The probe was decontaminated prior to each use A summary of the current and previous depth-to- groundwater measurements is presented to Table 1 The general groundwater elevation has decreased in the on-site wells since the last monitoring event in June 2000 Based on groundwater data collected during this round of monitoring, the inferred direction of groundwater flow beneath the site is to the east with a hydraulic gradient of 0 002 feet per foot i • 4.2 Groundwater Sampling and Observations 421. Standard Groundwater Sampling Procedures Using a 2-inch submersible pump, which was decontaminated between wells, a mini- mum of three well casing volumes of water were purged from each of the fourteen on- site wells prior to the collection of groundwater samples The wells were allowed to re- cover to at least SO percent of their original static groundwater levels prior to sampling During well purging, temperature, acidity, and conductivity were measured using a Fly- dac instrument Additionally, characteristics of the water (color, turbidity, odor, sheen) were noted on the field data sheets and are included in Appendix A Subsequent to purging, samples were collected using disposable PVC bottom- discharging bailers The samples were transferred from the bailer to the appropriate sample containers, labeled, and placed in a cooler containing ice at 4 degrees Celsius under chain-of-custody protocol The samples were secured to a cooler and transferred to Associated Laboratories (AL) in Orange, California via United Parcel Service (UPS) Purged and decontamination water generated during sampling activities were trans- �4 f C 240 01 r Stockton Fnl 7Q2000 doc 3