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California Department of Transportation March 13 2001 Shop 10 Maintenance Station, Stockton, California Project No 400296-01 TPH-G, TPH-D, and benzene, toluene, ethylbenzene, and total xylenes (BTEX) have been de- tected in the on-site monitoring wells 4 GROUNDWATER MONITORING ACTIVITIES 4 1 Groundwater elevation and hydraulic gradient On September 13, 2000, a representative from Ninyo & Moore measured depth to static groundwater in eleven of the twelve on-site groundwater monitoring wells Well VM-2 was not measured or sampled this round since it had been paved over 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 in Table 1 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 0 005 feet per foot 4.2. Groundwater Sampling and Observations 42.1. 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 eleven of the twelve on- site wells on site prior to the collection of groundwater samples The wells were al- lowed to recover to at least 80 percent of their original static groundwater levels prior to sampling During well purging, temperature, acidity, and conductivity were measured using a Hydac instrument Additionally, characteristics of the water (color, turbidity, odor, and sheen) were noted on the field data sheets and are included in Appendix A i 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 0290 Olt shuplO F\L 3Q2000 doc 3