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California of Transportation September 6, 2001 rf rma Dep artment p Shop 10 Maintenance Station, Stockton, California Project No 400296001 4. GROUNDWATER MONITORING ACTIVITIES 4.1.. Groundwater Elevation and Hydraulic Gradient On June 4, 2001, a representative from Ninyo & Moore measured depth to static groundwa- ter in ten of the twelve on-site groundwater monitoring wells Wells MW-14 and VM-2 have been lowered and paved over due to on-site construction in the area and were not sampled Static groundwater levels were measured using a Solmst water level probe The probe was decontaminated prior to each use with an Alconox wash and a distilled water rinse A sum- mary 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 March 2001 Based on groundwater data collected during this round of monitoring, the in- ferred direction of groundwater flow beneath the site is to the northeast with a hydraulic gradient of 0 21 feet per foot lie 4.2 Groundwater Sampling and Observations Using a 2-inch submersible pump, which was decontaminated between wells, a mini- mum of three well casing volumes of water were purged from the ten accessible on-site wells prior to the collection of groundwater samples The wells were allowed to recover to at least 80 percent of their original static groundwater levels prior to sampling Dur- ing well purging, temperature, acidity, and conductivity were measured using an Altrameter instrument Additionally, characteristics of the water (color, turbidity, odor, and 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 transferred to Associated Laborato- ries (AL) in Orange, California via United Parcel Service (UPS) Purged and decontamination water generated during sampling activities were transferred into la- 02%O lr shop 10 2Q01 doc 3