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' California Department of Transportation p p November 4, 1999 <br /> Shop 10 Maintenance Station, Stockton, California Project No 103872-02 <br /> 4 GROUNDWATER MONffTORING ACTIVITIES <br />' 4.1. Groundwater elevation and hydraulic gradient <br /> On September 23, 1999, a representative from Ninyo & Moore measured depth to static <br />' groundwater in eight of the twelve on-site groundwater monitoring wells Four of the wells, <br /> MW-9, MW-11, MW-16, and MW- 20, were not measured this round due to construction <br />' work occurring in the southern section of the site Static groundwater levels were measured <br /> using a Solrnst water level probe The probe was decontaminated prior to each use A sum- <br /> mary of the current and previous depth-to-groundwater measurements is presented in Table <br /> I Groundwater elevation has decreased in the on-site wells since the last monitoring event <br />' in June 1999 Based on groundwater data collected during this round of monitoring, the in- <br /> ferred direction of groundwater flow beneath the site is to the southeast with a hydraulic <br />' gradient of 0 002 feet per foot <br /> M4.2. Groundwater Sampling and Observations <br /> Using a 2-inch submersible pump, which was decontaminated between wells, a rrunimum of <br /> three well casing volumes of water were purged from eight 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 Four of the wells, MW-9, MW-11, MW- <br />' 16, and MW- 20, were not sampled this round due to construction work occurring in the <br /> southern section of the site <br /> 1 <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 /> 03972 shop 10 3 q,?M /®&(��%�®®U M <br />