WORK PLANS - Laserfiche WebLink

Home Browse Search

Site Investigation Work Plan Raymond Investment Corporation ' Former Helena Chemical Facility Page 5 Monitoring well borings for MW-1 through MW-3 will be drilled to depths of approximately twenty-five ' feet bgs. It is anticipated that groundwater will be first encountered at approximately ten feet bgs. The groundwater monitoring wells will include a screened interval between five and twenty-five feet. The monitoring wells will be constructed with 20 feet of 2-inch O.D., Schedule 40, flush-threaded, machine- slotted PVC screen (0.010-inch slot size). The screen will extend from a depth of approximately fifteen feet below the water table to five feet above the water table. A flush-threaded PVC bottom cap will be placed at the bottom of the screen section in the well. Blank PVC casing will be installed above the ' screens to the ground surface. A filter pack of#2/12 Monterey sand will be placed in the annular space to approximately two feet above the screens while the augers are in place. The depth of the sand in the annulus of the well will be monitored with a weighted tape measure while the sand is being placed and ' the augers are being gradually retracted to avoid bridging. To form a protective seal, approximately two feet of bentonite chips will be installed above the sand in the well. The bentonite chips will be installed as the augers are retracted.The bentonite will be hydrated using potable water. A surface seal of neat cement will be poured from the surface into the annulus of the well and will extend from the bentonite to the t ground surface. The monitoring wells will be completed with locking caps and traffic boxes installed flush with the ground surface. Details of the well construction will be noted on the geologic log, including 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 1.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 i 25 feet 25 feet 25 feet 7.2 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. ' 7.3 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. 1 ' i� CONDOR