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Site Investigation Work Plan-Second Revision Raymond Investment Corporation Former Helena Chemical Facility Page 10 the depth intervals of the screen, sand pack, and seals. A generalized shallow monitoring well construction diagram is included as Figure 4,Appendix A. Table 3-Monitoring Well Construction and Sample Interval Details Well ID MW-1 MW-2 MW-3 Location Near former East from Southeast from ASTs MW-1 MW-1 Sample Interval 15 feet 15 feet 15 feet Neat Cement Interval 0-1 feet 0-1 feet 0-1 feet Bentonite Interval,Pellets or Chis 1-3 feet 1-3 feet 1-3 feet Sand Interval, 2/12 Washed Monterey 3-25 feet 3-25 feet 3-25 feet Screen Interval,0.010"Slotted PVC 5-25 feet 5-25 feet 5-25 feet Total Depth 25 feet 25 feet 25 feet 8.2 MONITORING WELL SURVEYING,DEVELOPMENT,AND SAMPLING Following installation of the monitoring wells, the wells will be surveyed to determine the location and elevation of the well collar in order to comply with AB2886 (Water Code sections 13195 — 13198). The well collars will be surveyed with a vertical accuracy of 0.01 foot to a NAVD 88 or NGVD 29 datum,and with a horizontal accuracy of 0.03 foot to a NAD 83 datum. The measuring point for water-level measurements will be marked on the well collar. Well survey data will be submitted in the required electronic deliverable format to GeoTracker. 8.3 GROUNDWATER MONITORING WELL DEVELOPMENT AND SAMPLING At least 48 hours following construction, the monitoring wells will be developed by surging and bailing the groundwater in the well until the discharge water is relatively free of sediment (clear to the unaided eye). The monitoring well will be purged until the temperature, electrical conductivity, and pH of the water have stabilized. All well-development equipment will be cleaned prior to use by washing in a solution of laboratory-grade, non-phosphate detergent and deionized water, and by double rinsing with deionized water. The purge water discharged from the well during development will be containerized in 55-gallon drums,sealed,labeled,and left on Site to await disposal pending results of laboratory analyses. A groundwater sample will be collected at least 48 hours following development of each monitoring well. Prior to sample collection, the static water level in the well will be measured to the nearest 0.01-foot with a battery-operated water level meter. A disposable bailer will be lowered into the well to check for floating product, petroleum odor, and/or sheen. If floating product is encountered, the thickness of the product will be measured,but no laboratory sample will be collected.The monitoring well will be purged using a clean, disposable bailer until the temperature, electrical conductivity, and pH of the water have stabilized. At least three casing volumes of water will be purged from the monitoring well. The water purged from the well will be containerized in 55-gallon drums and left on Site pending analytical results of the groundwater samples. The groundwater samples will be collected with a clean, disposable baiter and transferred to laboratory-supplied containers. Each container will be labeled for sample identification and placed in a cooler chilled with ice. Upon completion of the fieldwork, the groundwater samples will be delivered under chain-of-custody procedures to a California-certified laboratory for analyses. ob ILA CONDOR