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I 1 ' APPENDIX G ' GROUNDWATER MONITORING WELL CONSTRUCTION PROCEDURES tBOREHOLE DESIGN Casing Diameter: The minimum diameter of well casings will be 4 inches (nominal) . Borehole Diameter: The diameter of the borehole will be a minimum of 10 inches and a maximum of 12 inches greater than the ' diameter of the well casing. The minimum annular space will be 3 inches as measured from the outside diameter of the casing to the drill hole wall . ' Shallow Unconfined Zone Wells - When unconfined groundwater is encountered the borehole will be advanced through the aquifer to an underlying clay layer or aquitard The screened interval will ' begin a minimum of 5 feet above the saturated zone or above the anticipated seasonal high level of groundwater. The screen will extend the full thickness of the aquifer or no more than 15 feet into the sa'Zurated zone, whichever is reached first . The well ' screen will not extend into the aquitard, nor will the screened interval exceed 20 feet in length. Deep (Confined Zone) Wells : Any monitoring well to be screened below the upper aquifer will be installed as a double-cased well . A steel conductor casing will be placed through the upper water- bearing zone to prevent aquifer cross-contamination The conductor casing will be installed in the following manner: a large diameter borehole (typically 18 inches) will be drilled ' until it is determined that the first competent aquitard has been reached A low carbon steel conductor casing will be placed in the borehole to the depth drilled. Centralizers will be used to ' center the casing in the borehole . The annular space between the conductor casing and the formation will be cement-grouted prom bottom to top by tremae pipe method . The grout will be allowed to set for a minimum of 72 hours Drilling will continue inside the conductor casing, with a drill bit of smaller diameter than the conductor casing . If additional known aquifers are to be fully penetrated, the procedure will be repeated with successively smaller diameter conductor casings. The bottom of the well screen in a confined aquifer will be determined by presence or lack of a clay layer or aquitard as described above. The screened interval in a confined zone shall extend across the entire saturated zone of the aquifer or up to a length of 20 feet , which ever is less The screened zone and filter pack will not cross-connect to another aquifer .