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In areas where freezing is a potential problem, the top of the seal may be below Sround surface but in no case more than 4 feet (1.2 metres) below ground surface. ANwU4Ar� �� ANNULAR spa:- Sealing Conditions. Following are -equire- -- _ meats to bi observed in sealing the annular space: S OIL ' SOIL }1. Wells situated in unconsolidated, caving " TEMPORJ�RY LASIHUGROUT SEAL SAwo B GRA' EL material. An oversized hole, at least 4 inches (100 milli- flriIh0+gPn as aafl9 :4metres) greater in diameter than the production casing, shall Ps *re0CLAT be drilled and a conductor casing installed to the depth of s seal specified in Part A of this section. The space between r the conductor casing and the production casing shall be CASING SAND filled with sealing material. The conductor may be withdrawn as the sealing material is placed (see Fig%we 4A). — - - -� 2. Wells situated in unconsolidated material CLAY __ stratified with significant clay layers. If a clay formation is encountered within 5 feet (1.5 metres) of the bottom of �, SAND 5 c.r r the seal described in Part A of this section, the seal should 111 be extended 5 feet (1.5 metres) into the clay formation (thus III the depth of seal could be as much as another 10 feet or PERFORATIONS 3 metres). An oversized hole at least 4 inches (100 milli- OR SCREENIII metres) greater in diameter than the production casing, shall III be drilled and the annular space filled with sealing material (see Figure 4B). A. WELL DRILLED IN UNCONSOLIDATED B. WELL IN UNCONSOLIDATED STRATIFIED If caving material is present, a conductor casing CAVING MATERIAL FORMATIONS shall be installed and the annular space sealed as described in 1, above. 3. Wells situated in soft consolidated forma- tions (extensive clays, sandstones etc.). An oversized hole, ANNULAR 5FA4E at least 4 inches (100 millimetres] greater in diameter than the production casing, shall be drilled to the depth of seal SOIL specified in Part A of this section and the space between the production casing and the drilled hole shall be filled with OKUTsealing material (see Figure 4C). CEky SEAL If a conductor casing is to be installed (to establish a foundation for the construction of the remainder of the well) the oversized hole shall be at least 4 inches IOLE (100 millimetres) greater in diameter than the conductor BOREN SAlIDSFOwE CASINGO Defined here as those areas in which the mean length of freeze-free period as described by the National Weather I Service s le8s than 100 days, i.e., temperatures at or below 32 (0 C) are likely to occur on any day during a III period of 265 or more days each year. In general I I1 PERFORATIONS geographic terms, these areas are the northeastern part of III the State (parts of Modoc, Lassen, and Siski-you Counties), the north Lahontan area (essentially the eastern slopes of C. WELL IN SOFT CONSOLIDATED FORMATIONS the Sierra Nevada and subsidiary valleys north of Mount Whitney and Mono Lake) and at Lake Arrowhead in the San Bernardino Mountains. 1 Methods of sealing are described in Appendix B. Figure 4. SEALING CONDITIONS FOR UPPER ANNULAR SPACE- UNCONSOLIDATED AND SOFT,CONSOLIDATED FORMATIONS