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diameter shall be at least 4 inches greater than the outside diameter of <br /> the conductor casing. The inner diameter of the permanent conductor <br /> casing shall in turn be at least 4 inches greater than the outside diameter <br /> of the well casing. Appropriate sealing material shall be placed between <br /> the permanent conductor casing and the borehole wall and the well <br /> casing and the conductor casing. The seal shall extend at least to the <br /> depth specified in Section 13.12. <br /> 13.10. FILTER PACK MATERIAL <br /> 13.10.1. Filter pack material shall not degrade or consolidate after placement. <br /> 13.10.2. The grain-size of the filter pack shall be matched to the slot size of the <br /> well screen. <br /> 13.10.3. Filter pack material shall be non-reactive, and obtained from clean <br /> sources and properly packaged for handling, delivery and storage. <br /> 13.10.4. The storage of filter pack materials at a drilling site shall be done to <br /> ensure that material does not come into contact with chemical pollutants <br /> or contaminants. <br /> 13.10.5. Foreign substances shall not be introduced during placement of the filter <br /> pack. <br /> 13.10.6. Filter pack material shall be placed in the well boring by use of a tremie <br /> pipe or equivalent. <br /> 13.10.7. The depth of the top of the filter pack shall be carefully checked and the <br /> volume of the filter pack material installed shall be considered to verify <br /> that no bridging of filter pack materials occurred. <br /> 13.10.8. Surging the well prior to the installation of the transition seal and/or the <br /> annular seal is highly recommended. Refer to Section 13.15, "Well <br /> Development" for appropriate methods. <br /> 13.11. TRANSITION SEAL <br /> 13.11.1. A one (1)to five (5)foot long transition seal consisting of Bentonite or <br /> other approved material may be placed in the annular space between <br /> the filter pack and cement-based annular seals in monitoring wells. <br /> 13.11.2. Bentonite transition seals shall be installed by use of a tremie pipe or <br /> equivalent for depths greater than 30 feet and where water is present in <br /> the borehole. <br /> 13.11.3. Potable water shall be added to the Bentonite transition seal where it <br /> exists in the dry form in the borehole prior to the placement of neat <br /> cement-based sealing materials. <br /> 13.11.4. Sufficient time shall be allowed for Bentonite transition seals to properly <br /> hydrate before neat cement-based sealing materials are placed. <br /> EHD 43-03 Page 23 of 27 WELL STANDARDS <br /> 1019/07 <br />