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1 <br /> California Department of Transportation June 9, 1999 <br /> Stockton Maintenance Station, Stockton, California Project No 103872-02 <br /> • <br /> 4. GROUNDWATER MONITORING ACTIVITIES <br />' 4.1. Groundwater elevation and hydraulic gradient <br /> On March 31, April 1 and 2, 1999, two representatives from Ninyo & Moore measured <br /> 1 depth to static groundwater in the twelve on-site groundwater monitoring wells and two va- <br /> por extraction wells Static groundwater levels were measured using a Heron air/water <br /> interface probe The probe was decontaminated prior to each use A summary of the current <br /> and previous depth-to-groundwater measurements is presented in Table 1 The depth to <br />' groundwater has risen in the on-site wells since the last monitoring event in December 1998 <br /> Based on groundwater data collected, the inferred direction of groundwater flow beneath the <br /> Isite is to the south ith a hydraulic gradient of 0 009 feet per foot <br /> 4.2. Groundwater Sampling and Observations <br /> Using 2-inch and 3-inch submersible pumps, a minimum of three well casing volumes of <br /> Mgroundwater were purged from each of the fourteen on-site wells prior to the collection of <br /> water samples The wells were allowed to recover to at least 80 percent of their original <br /> static groundwater levels prior to sampling During well purging, temperature, pH, and con- <br /> ductivity were measured using a factory calibrated Hydac instrument Additionally, <br /> characteristics of the water (color, turbidity, odor, sheen) were noted on the field data sheets <br />' 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 secured in a cooler and transferred to the Ninyo & Moore office <br /> in Oakland, California and temporarily stored in refrigeration California Overnight Service <br /> transported the samples to Applied Analytical Laboratory (AAL) in Orange, California <br /> Purged and decontamination water generated during sampling activities were transferred <br /> into labeled, reconditioned 55-gallon drums The drums were left on-site to be maintained <br /> by Caltrans <br /> 1101k= 3 <br />