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casing shall in I am bca at Icasi 4 incites gr ter than the outside diarn,eler of the well casing. Sealing material shall be.: placed between the permanent conductor casing and the. borehole wal1,and the i OrLductor casing and the well casing. 'the sealing material shall extend to at least the depINS specified in Subseclion A of this scedun. C. Radial Thickness of Scal_ A minimum of two inches of sealing material sliall be maintained between all casings-and the borchulc wall, within the intcMl to be sealed, except as noted in (CliOii 9 of the Wotcr Well Standards, At levsl two inches of sealing material MaH also be maintained between all casing" in a borehole,within the interval to be sealed unless otherwise approved by [be enforcing agency. Additional space shall be provided,where, n(;Oded, 10 allow casings tea be properly cr ntrali7md and spaced and allow the use of a tremic pipe during well construction (if required), especially for deeper wells. D. Sealing_Mil teriat. Sealing rna,teriA shatI cotlsM of neat Cement,sand-cernen1, nr bentonite clay. Cement-based sealing material shall be used oppositc fractured rock,unlessotherwise approved by the enrarcing agency. Concrete shall be used only witty the approval of the enforcing agency. Sealing material shall be selGCtCd based on regnirc rd ktructura1,handling, and sealing p roper tic,�, and the chemical environment into which it is placed. Used drilling mud or cuttings from drilling shall not be used for any Pat[ of siUlling material, 1. Water, Water used for scaling mixtures should generally bi� of drinking water quality, ' shall be compatible w1ih the type of scaling material used, shall be free of petroleum and petroleum products, and shall be free of suspended matter. uod-quality water • is necessary to ensure that sealing materials achieve proper consistency for phecraent and achieve adequate structural and sealing properties. Nonpo[able water can sometimes be used for iaruparing cement-lased Scaling trial6AB. En no case shall the con cc ntration a chlorije, in waiter used in cement-ha5ed scaling materiai exceed 2,M) miIIigrtirns per liter. Sulfate shall not exceed 1,500 nim. Water used for scaling material shall be chemically amalyzed if unknown. Only drinking-quality water of knowar compositiun should be used for preparing,scaling mixtures for znon ftoring wells to he used for sensitive water-quality detcrrninalions. 2_ Cement-rinsed Scaling Materials, Discussion and standards for cement-based scaling materials are contained in Section 9 of the: Water Well Standards, Spt:Oal consider- ations Mit apply to monitoring wells are- a, Add ii ive& Care shoijId be exercised in the use of special additives for cement- based soling materials,such as Ihose u5W for modifying Cement scatting times. Some additives could interfere with sensitive water. quality determinations, b, Cool in9 Water, lri the:case of water duality monitoring wells, cart±should be exercised in the ese of circulating cooling water to protect plastic r~Wng from heat build-up during setting of cenrent-based scaling materials. Water intro- ' duced and/or circulated in a wcli for cool Ing could inierf+aru with water quality determinations, 3. Beiitunite-Based Sealing Material. Discussion and srandards for bcntonite-based ! scaling materials are cuntaincd in Secilun 9 of the Water Wc11 Standards. -43- I