Laserfiche WebLink
3 <br /> Based o the aquifer thickness, the conductor casing will be founded approximately half way <br /> through t e aquitard. The conductor casing borehole is then drilled to the target depth into the <br /> aquitard. Drilling is slow as 15-inch augers are needed. Further_; it is critical that the boring be <br /> { advanced slowly and carefully so as to not pass through the aquitard.'' If this were to happen, <br /> a then the t orehole would have to be abandoned and re-drilled elsewhere. <br /> ii <br /> �L <br /> Once the target depth is reached, the conductor casing is placed downhole. The conductor <br /> casing is steel, approximately 9-inches in diameter, and generally comes in either 10 or 20-foot <br /> segments. It is lowered into the borehole one segment at a timer An on-site welder then welds" <br /> i each seg ent as it is lowered downhole. The welding is criticil in order to have a property <br /> sealed casing. Further, working with the heavy steel casing is awkward; a crane is oftentimes <br /> needed fdr lowering and placing the casing. <br /> i Once the proper length of conductor casing is placed, the conductor{casing. is there grouted. <br /> Given tht annulus size, the grout quantity and time required to place the grout is significantly <br /> more thar for a typical monitoring well. <br /> Following grouting, the grout must have sufficient time to set before we can come back and drill <br /> through t ie conductor casing. If.we do not wait long enough, the;impact of the augers banging' <br /> on the c ising during drilling might displace and crack the grout_ This would jeopardize the <br /> integrity the conductor casing seal. This downtime results in additional mob/demob costs. <br /> E. <br /> Additiona ly, what I have done in the past is hydrostatically test the conductor casing to test its <br /> integrity. Generally, this is accomplished by filling the casing' with ,water to near the top, <br /> measuring it accurately, and then checking one to two days later. A drop .in water level would <br /> generally suggest a breach in the casing somewhere. <br /> Once p perly placed and constructed, the deeper wells cane then be drilled through the <br /> conducto casings. The drill rig is brought back to the site and the two deeper wells drilled <br /> through a conductor casings. Once the target depths are reached, the wells are constructed <br /> per typi I standards. When grouted, the interior of the conductor casing serves as the well, <br /> 'annulus", The conductor casings are oftentimes completed as well monuments, with locking lids <br /> r casings. This provides excellent protection to the PVC well <br /> outfitted the top of the conduCto 9 p <br /> casing. <br /> As you n see, the installation of deeper wells requires a fairly rigid and time consuming <br /> i protocol. However, this is very important_ We must take proper measures to ensure that we <br /> have not nadvertently created a conduit between an uncontaminated aquifer and one of known <br /> high love contamination. 'I <br /> I hope thi it this information is helpful. Please feel free to call if you have any questions. <br /> E Dan <br /> E <br /> cc: M . Lori Duncan, Sart Joaquin County Environmental Health <br /> templatelfa�rans.doc <br /> I <br /> E <br /> c <br /> i <br />