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