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Plastic casing or screen shall not be driven or otherwise subjected to impact forces during installation. The effects of heat generated by curing cement on plastic casing are discussed in Section 9, Part B, paragraph 8. Section 13. Sealing-off Strata. In areas where a well penetrates more than one aquifer, and one 'or more of the aquifers contains water that, if allowed-to mix in sufficient quantity, will result in a significant deterioration of the quality of water in the other aquifer(s) or the quality of water produced, the strata producing such poor-quality water shall be sealed off to prevent entrance of the water into the well or its migration ': to other aqu A. Strata producing the undesirable quality water shall be sealed off by placing impervious material opposite CASING CONDUCTOR CASING SEAL the strata and opposite the confining formation(s). (See Figure 8.) The seal shall extend above and below the strata POOR no less than 10 feet (3 metres) even should the confining QUALITY formation be less than 10 feet (3 metres) in thickness. In WATER ,; SEAL the case of; "bottom" waters, the seal shall extend 10 feet PRODUCTION CASING (3 metres) in the upward direction. The sealing material shall fill the annular space between the casing and the wall of the drilled hole in the interval to be sealed, and the surrounding void spaces which might absorb the sealing `' SHOE material. The sealing material shall be placed from the IMPERVIOUS !MATERIAL bottom to the top of the interval to be sealed.. IO'Min. i In areas where deepsubsidence m occur IMPERVIOUS f; example, (as, for MATERIAL IOC Min. p , portions of the San Joaquin Valley provision shall be made for maintaining the integrity of the annular seal in the event of subsidence. Such preventive measures may POOR QUALITY include the installation of a "sleeve" or "slip joint" in the WATER SEAL casing, which will allow vertical movement in the casing _ GOOD without its collapse. QUALITY GRAVEL WATER PACK IMPERVIOUS 104n. B. Sealing material shall consist of neat cement, MATERIAL cement grout, or bentonite clay (see Section 9, Part D for description of the various materials). GOOD GRAVEL QUALITY PACK C. Sealing shall be accomplished by a method WATER approved by the enforcing agency. IMPERVIOUS MATERIAL Section 14. Well Development. GOOD Developing, redeveloping, or conditioning of a well QUALITY WATER shall be done with care and by methods which will not cause damage to the well or cause adverse subsurface conditions that may destroy barriers to the vertical movement of water between aquifers. The following methods used in developing, redevel- oping, or conditioning a well when done with care are acceptable: (a) overpumping, (b) surging by use of a Suggested methods for sealing-off strata are presented in Figure 8. SEALING-OFF STRATA Appendix B.