(1) Driven wells - An upper hole at least four inches greater in diameter than the permanent casing shall extend a minimum of six feet below land surface. The annular space between the upper oversized drill hole and the permanent casing must be kept at least one-half full with bentonite or bentonite slurry throughout all driving of the pipe. The remaining annular space to land surface shall be filled with neat cement grout, neat cement, or bentonite. See Figure 4.

(2) Jetted wells - The surface seal in jetted wells shall be constructed to seal the annular space between the permanent casing and undisturbed native soil. An upper hole at least four inches greater in diameter than the permanent casing shall extend a minimum of six feet below land surface.

(3) Dewatering wells:

(a) Permanent dewatering wells shall be sealed in one of the following manners:

(i) For wells in which the top of the screen interval is greater than twenty-one feet below land surface, the minimum sealing depth shall be eighteen feet.

(ii) If the top of the screen interval is twenty-one feet or less below the land surface, the seal shall be within three feet of the top of the screen. In no instance shall the seal be less than ten feet in depth.

(iii) All permanent dewatering wells shall be constructed to prevent interconnection of separate aquifers penetrated by the well, and provide casing stability.

(b) Temporary dewatering wells are wells that are in place less than twelve months.

(i) Temporary dewatering wells shall have a minimum of a three-foot surface seal.

(ii) Temporary dewatering wells that connect different aquifers, allowing waters to commingle, must have a dewatering plan that addresses and mitigates potential inter-aquifer transfer and cross-contamination.

(iii) All temporary dewatering wells must be decommissioned or reconstructed to meet standards for permanent dewatering wells within twelve months from the date of installation.

(c) The minimum annular space requirements, sealing material, and decommissioning procedures of this chapter apply to all dewatering wells. This includes wells that have been cut down, altered or damaged during the dewatering process. Temporary dewatering wells located within an area to be excavated for construction are exempt from these sealing requirements but are required to be decommissioned in accordance with this chapter.