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California Department of Transportation P p February 24, 2000 <br /> Shop 10 Maintenance Station, Stockton, California Pro3ect No 103872-02 <br /> 4. GROUNDWATER MONITORING ACTIVITIES <br /> 4.1. Groundwater elevation and hydraulic gradient <br /> On January 4, 2000, a representative from Ninyo & Moore measured depth to static <br /> groundwater in eleven of the twelve on-site groundwater monitoring wells Well VM-2 was <br /> not measured or sampled this round since it had been paved over Static groundwater levels <br /> were measured using a Solinst water Ievel probe The probe was decontaminated prior to <br /> each use A summary of the current and previous depth-to-groundwater measurements is <br /> presented in Table 1 Groundwater elevation has increased in the on-site wells since the last <br /> monitoring event in September 1999 Based on groundwater data collected during this round <br /> of monitoring, the inferred direction of groundwater flow beneath the site is to the northeast <br /> with a hydraulic gradient of 0 003 feet per foot <br /> 4.2. Groundwater Sampling and Observations <br /> Using a 2-inch submersible pump, which was decontaminated between wells, a minimum of <br /> three well casing volumes of water were purged from eleven of the twelve on-site wells on <br /> site prior to the collection of groundwater samples The wells were allowed to recover to at <br /> least 80 percent of their original static groundwater levels prior to sampling During well <br /> purging, temperature, pH, and conductivity were measured using a Hydac instrument Addi- <br /> tionally, characteristics of the water (color, turbidity, odor, and sheen) were noted on the <br /> field data sheets and are included in Appendix A <br /> Subsequent to purging, samples were collected using disposable PVC bottom-discharging <br /> bailers The samples were transferred from the bailer to the appropriate sample containers, <br /> labeled, and placed in a cooler containing ice at 4 degrees Celsius under chain-of-custody <br /> protocol The samples were transferred to Associated Laboratories (AL) in Orange, Califor- <br /> nia via United Parcel Service (UPS) Purged and decontamination water generated during <br /> sampling activities were transferred into labeled, reconditioned 55-gallon drums The drums <br /> were left on-site to be maintained by Caltrans <br /> shop l0doc 3 <br />