Laserfiche WebLink
The Leadville Mill <br />Environmental Sampling Procedures <br />Water Sample Collection <br />Page 2 -12 <br />chemistry of suspected pollutants and the geologic setting play a major role in <br />determining drilling techniques and materials used. <br />The type of material used for monitoring well casing may have a distinct effect on the <br />quality of the water samples collected. Galvanized casing will impart iron, <br />manganese, zinc and cadmium to many waters. Steel casing may impart iron and <br />manganese to the water samples. PVC has been shown to release and absorb trace <br />amounts of various organic constituents to water after prolonged exposure. <br />Stainless steel has been found to work satisfactorily under most monitoring <br />conditions. <br />Well screen length is an important consideration. The transmissivity of the aquifer <br />will be used to establish the length of screen. Low yield aquifers may require greater <br />screen lengths that permit the collection of adequate sample volumes in a timely <br />manner. Thick aquifers may require the completion of several wells at different <br />depth intervals. <br />A two -inch diameter casing is appropriate for most groundwater monitoring and the <br />smaller diameter borehole reduces drilling costs. <br />The primary filter pack will consist of a clean silica sand or sand and gravel mixture of <br />selected grain size and gradation that is installed in the annular space between the <br />borehole wall and the well screen, extending an appropriate distance above the <br />screen. The sand pack will extend a minimum of two feet above the top of the <br />screen. A seal will extend from the top of the sand pack to the ground surface. The <br />main goal of the sealants is to affect a seal between the surface or overlying <br />formations and the casing or screened intervals so that runoff or other sources of <br />water do not enter the wellbore. A bentonite seal shall be placed immediately <br />above the sand pack and will occupy at least two vertical feet in the borehole. A <br />cement /bentonite grout will fill the annulus from the top of the bentonite seal to the <br />ground surface. <br />2.5.2 COMPLETION OF SURFACE INSTALLATION <br />In areas subject to frost heave, place a soil or bentonite /sand layer adjacent to the <br />protective casing sloped to direct water drainage away from the well. Where <br />monitoring well protection must be flush with the ground, an internal cap should be <br />fitted on top of the riser within the vault. This cap should be leak -proof so that if the <br />April 2013 <br />