Section 920.70  Drilled Well Construction in Consolidated Formations

a)         Creviced Formations - Drift or Earth Cover Less Than 30 Feet.  A creviced or cracked formation, which is the upper bedrock formation and is overlain by a mantle of earth having a thickness less than 30 feet, shall be used as a source of groundwater supply when constructed by one of the following methods:

1)         Where the drift or earth cover is less than 30 feet in thickness, the well casing shall extend to a depth of at least 40 feet below ground level.  The diameter of the drill hole shall be a minimum of 3 inches greater than the outer diameter of the casing or coupling, whichever is greater.  The annular space shall be pressure grouted as provided for in Section 920.90(h).  If plastic casing is installed, it shall be installed in accordance with Section 920.90(g).

2)         Where the well is drilled to obtain water from a lower formation the casing shall extend at least through the creviced formation and be seated in firm rock.  The diameter of the drill hole through the creviced formation shall be a minimum of 3 inches greater than the outer diameter of the casing or coupling, whichever is greater.  The annular space shall be pressure grouted as provided in Section 920.90(h).  When an outer casing is left in place, the annular space between the casings shall be pressure grouted and the annular opening around the outer casing shall be grouted in accordance with Section 920.90(h).  If plastic casing is installed, it shall be installed in accordance with Section 920.90(g). (See Illustration D.)

b)         Drift or Earth Cover Over 30 Feet in Thickness.

1)         When an oversized drill hole is constructed for the installation of the casing, the diameter of the drill hole shall be a minimum of 3 inches greater than the outer diameter of the casing or coupling, whichever is greater.  The tremie pipe shall be installed when the casing is installed and casing grouted to a minimum depth of 60 feet.  When the casing is less than 60 feet, the entire length of casing shall be grouted.  When grout is pumped into the annular space through the inside of the casing, the diameter of the drill hole shall be a minimum of 2 inches greater than the outer diameter of the casing or coupling, whichever is greater.  If plastic well casing is installed, it shall be installed as required in Section 920.90(g).  After the casing is installed, the annular space shall be grouted as provided for in Section 920.90(h).  (See Illustration E.)

2)         When the casing is installed by mechanically driving the casing, an oversized hole shall be constructed to a depth of at least 10 but not more than 20 feet to allow the removal of the drive nipple and installation of a joint of casing.  While the casing is being driven, the bottom of the oversized hole shall be filled with granulated bentonite or natural clay mixture.  After the casing is installed, the annular space that exists around the well casing shall be either grouted as required in Section 920.90(h) or, when the diameter of the oversized hole is a minimum of 3 inches greater than the outer diameter of the casing or coupling, whichever is greater, the annular space that exists around the well casing can be filled with natural clay. (See Illustration F.)

c)         Flowing Artesian Well.  Initial drilling operations shall extend into but not through the formation confining the water.  The casing shall be installed and the annular opening between drill hole and casing shall be pressure grouted in accordance with Section 920.90(h).  If plastic casing is installed, it shall be installed in accordance with Section 920.90(g).  The hole shall then be extended into the artesian formation.  Flow control from the well shall be provided by valved pipe connections, watertight pump connections, or receiving reservoirs set at an altitude corresponding to the artesian head.

(Source:  Amended at 24 Ill. Reg. 11934, effective August 1, 2000)