(1) Unconsolidated formation sealing - Without significant clay beds or other confining formations - Drilled wells that penetrate an aquifer overlain by unconsolidated formations such as sand and gravel without significant clay beds (at least six feet thick) or other confining formations shall be sealed in accordance with the surface sealing requirements of WAC 173-160-231. See Figure 1.

(2) Unconsolidated formation sealing - With significant clay beds or other significant confining formations - Drilled wells that penetrate an aquifer overlain by clay or other confining formations that are at least six feet thick, shall be sealed to prevent movement of water or contamination in the annular space between the permanent casing and the clay or other confining formation(s). One of the following methods shall be used to seal the annular space:

(a) A drill hole at least four inches greater in diameter than the nominal size of the permanent well casing shall extend from the land surface into the clay bed or other confining formation located directly above the aquifer to be developed. The annular space shall be filled with bentonite (slurry or unhydrated), neat cement grout, or neat cement to form a watertight seal between the permanent casing and all significant confining formations encountered during drilling. If bentonite slurry, neat cement grout, or neat cement is used to seal the annular space it must be placed by either pumping or tremying the seal material from the lowest clay bed or other confining formation of significance encountered, to land surface. The drill hole shall be kept open through the use of a temporary casing or any other drilling method that stabilizes the bore hole wall. See Figure 1.

(b) An upper drill hole at least four inches greater in diameter than the nominal size of the permanent well casing shall extend to a minimum of eighteen feet from land surface. A temporary casing or other means of maintaining an open bore hole shall be utilized. All temporary casing will have an outside diameter of a minimum of four inches larger than the permanent casing (for example, a ten-inch temporary casing for a six-inch permanent casing). The upper drill hole shall always contain a minimum of nine feet of sealant throughout the advancement of the permanent casing. Except, if the temporary casing is removed or not utilized, the upper drill hole shall be kept full of sealant. See Figure 1.

(3) Consolidated formations - In drilled wells that penetrate an aquifer, either within or overlain by a consolidated formation, sealing of the casing shall conform with one of the following procedures.

(a) Procedure one - An upper drill hole at least four inches greater in diameter than the nominal size of the permanent well casing shall extend from land surface into a sound, unfractured, consolidated formation. An unperforated permanent casing shall be installed to extend to this same depth, and the lower part of the casing shall be driven into the consolidated formation and sealed in a manner that establishes a watertight seal between the formation and the casing. The remainder of the annular space to land surface shall be filled with neat cement grout, neat cement, or bentonite.

(i) If the consolidated formation is encountered at a depth less than eighteen feet from land surface, the upper drill hole and permanent casing shall extend to a minimum of eighteen feet from land surface. See Figure 2.

(ii) If neat cement grout, neat cement, or bentonite slurry is placed by pumping to seal the entire annulus from the bottom up to land surface, the upper drill hole may be a minimum of two inches larger than the outside diameter of the permanent casing.

(b) Procedure two - An upper drill hole at least four inches greater in diameter than the nominal size of the permanent casing extends from land surface to a depth of at least eighteen feet. An unperforated permanent casing shall be driven into the consolidated formation and sealed in a manner that establishes a watertight seal between the formation and the casing. Throughout the driving of the well casing to the consolidated formation, the annular space between the upper drill hole and the permanent casing shall be kept at least one-half full with unhydrated bentonite, or bentonite slurry. The remainder of the annular space to land surface shall be filled with cement grout, neat cement, or bentonite. See Figure 2.

(c) If temporary surface casing is used in either procedure (a) or (b) of this subsection, the casing must be a minimum of eighteen feet long and at least four inches larger in diameter than the permanent casing. If a consolidated formation is encountered within the first eighteen feet, the temporary casing may terminate at the interface of the consolidated formation. Withdrawal of the temporary casing must take place simultaneously with proper sealing of the annular space to land surface.