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casing and the borehole wall other than the depths specified in Subsection A, above, and Section 13, below (page 46 of Bulletin 74-81)." Items 4 through 7 (page 32 of Bulletin 74-81) are unchanged. Item 8 has been added, as follows: "8. Wells that enetrate zones containin oor- uali water ollutants or contaminants. If geologic units or fill known or suspected to contain poor-quality water, pollutants, or contaminants are penetrated during drilling, and, the possibility exists that poor- quality water, pollutants, or contaminants could move through the borehole during drilling and well construction operations and significantly degrade ground water quality in other units before sealing material can be installed, then precautions shall be taken to seal off or 'isolate' zones containing poor-quality water, pollutants, and contaminants during drilling and well construction operations. Special precautions could include the use of temporary or permanent conductor casing, borehole liners, and specialized drilling equipment. The use of conductor casing is described in Item 1, page 15, above." Subsection C (page 34 of Bulletin 74-81) is unchanged. Subsections 0, E, and F (page 34 of Bulletin 74-81) have been changed to read as follows: "D.Sealinl! Material. Sealing material shall consist of neat cement, sand cement, concrete, or bentonite. Cuttings from drilling, or drilling mud, shall not be used for any part of the sealing material. 1.~. Water used to prepare sealing mixtures should generally be of drinking water quality, shall be compatible with the type of sealing material used, be free of petroleum and petroleum products, and be free of suspended matter. In some cases water considered nonpotable, with a maximum of 2,000 milligrams per liter chloride and 1,500 mg/l sulfate, can be used for cement-based sealing mixtures. The quality of water to be used for sealing mixtures shall be determined where unknown. 2. Cement. Cement used in sealing mixtures shall meet the requirements of American Society for Testing and Materials C150, Standard Specification for Portland Cement, including the latest revisions thereof. Types of Portland cement available under ASTM C150 for general construction are: Type I -General purpose. Similar to American Petroleum Institute Class A Type II -Moderate resistance to sulfate. Lower heat of hydration than Type I. Similar to API Class B. Type III -High early strength. Reduced curing time but higher heat of hydration than Type I. Similar to API Class C. Type IV -Extended setting time. Lower heat of hydration than Types I and III. Type V -High sulfate resistance. Special cement setting accelerators and retardants and other additives may be used in some cases. Special field additives for Portland cement mixtures shall meet the requirements of ASTM C494, Standard Specification for Chemical Admixtures for Concrete, and latest revision thereof..-17-