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7 Logging of each boring will be performed utilizing the Unified Soil Classification System. A California Professional Geologist (PG) will provide office and field direction for the drilling and logging operations. Boring logs depicting the soil conditions encountered will be included in the report. The soil samples will also be field screened with a photo-ionization detector (PID) to assess possible qualitative indicators of volatile organic compounds (VOCs) in the soil samples collected. The PID readings will be recorded on the field boring logs. Each monitoring well will be constructed using 2-inch-diameter Schedule 40 PVC casing. The lower portion of each well will be constructed with a 20-foot section of 0.020-inch slotted PVC well screen casing. A filter pack consisting of Monterey #2/12 silica sand or equivalent will be placed around the screen from the bottom of the boring to approximately 1 foot above the screen zone. Following introduction of the filter pack material,the wells will be pre-developed by swabbing with a surge block to assist in settlement of the filter pack and to minimize the potential for bridging. A 2-foot-thick transition seal consisting of hydrated bentonite chips will be placed above the filter pack. Above the seal, a mixture of bentonite powder and cement will be placed to within 1 .foot of grade level. A 12-inch-diameter traffic-rated well box set in concrete will be used to complete construction. A typical monitoring well construction detail is presented as Figure 3. Quality assurance/quality control (QA/QC) procedures will be provided during the field exploration activities. These procedures will include cleansing/rinsing of the sampling equipment between sampling intervals, hot water pressure-washing downhole drilling equipment prior to and between borings, and providing chain-of-custody documentation for each sample transferred to the laboratory. Cleansing/rinsing of the sampling equipment will be performed prior to the collection of each soil sample by washing the equipment with an Alconox'm solution followed by subsequent tap water and deionized water rinses. Soil cuttings and rinseate generated during the drilling activities will be temporarily stored onsite in labeled, Department of Transportation-approved, 55-gallon drums pending the results of the laboratory analyses and subsequent disposal following regulatory protocol. A permanent reference mark will be made on the top of each well casing, and a California-licensed land surveyor will survey the top of casing elevation at the reference mark. No sooner than 48 hours after completing the grout sealing of the new wells, each new well will be developed to remove sediment that may have infiltrated the wells during construction. The well development will be performed using a combination of bailing and pumping with a portable electric submersible pump. Measurements of pH, conductivity, temperature and turbidity will be periodically recorded during the development activities and noted on a field log. Development will continue until turbidity measurements are less than 5 nephelometric turbidity units or 10 casing volumes have been removed from the well, whichever is sooner. The purged water generated from well development will be retained in 55-gallon drums and disposed of as previously described. Groundwater samples will be collected from the three new groundwater monitoring wells during the Third Quarter—2008 groundwater monitoring event scheduled for August 2008. Stockton Yard Maintenance Station,Task Order No.45 Caltrans Contract 06A1141,EA 10-ON8300 Project No.59200-06-45 -3 - June 26,2008