|
CHAPTER II. STANDARDS
Section 16. Special Provisions for Large Diameter Shallow Wells.
- Use as Community Water Supply Wells. Because shallow groundwaters are
often of poor quality and because they are easily contaminated, the use of
bored or dug wells, or wells less than 50 feet deep, to provide
community water supplies shall be avoided (unless there is no other feasible
means for obtaining water). When used for this purpose, these wells shall be
located at least 250 feet from any underground sewage disposal facility.
- Bored Wells. All bored wells shall be cased with concrete pipe or steel
casing whose joints are water-tight from 6 inches above the
ground surface to the depths specified in Section 9, Subsection A. Except where
corrugated steel pipe is used as casing, the minimum thickness of the
surrounding concrete seal shall be 3 inches. Where
corrugated steel pipe is employed, the joints are not watertight and a
thicker annular seal (no less than 6 inches) shall be installed.
- Dug Wells. All dug wells shall be "curbed" with a watertight curbing
extending from above the ground surface to the depths specified in Section 9, Subsection A.
The curbing shall be of concrete poured-in-place or of casing
(either precast concrete pipe or steel) surrounded on the outside by
concrete.
If the curbing is to be made of concrete, poured-in-place, it shall not be
less than 6 inches thick. If precast concrete pipe or
steel casing is used as part of the curbing, the space between the wall of
the hole and the casing shall be filled with concrete to the depths specified
in Section 9, Subsection A.
The minimum thickness of the surrounding concrete shall be 3 inches.
- Casing Material. Either steel (including corrugated steel pipe) or
concrete may be used for casing bored or dug wells. Corrugated aluminum pipe
is not recommended for use as casing.
Note 19
- 1. Steel used in the manufacture of casing for bored and dug wells should
conform to the specifications for casing material described in Section 12.
Minimum thickness of steel casing for bored and dug wells shall be:
|
Diameter (inches)
|
U.S. Standard Gage
or Plate Tickness
|
18
24
30
36
42
48
|
8 gage
1/4 inch
1/4 inch
1/4 inch
1/4 inch
1/4 inch
|
Corrugated steel pipe used as casing shall meet the specifications (including
the latest revision) of ASTMNote 20 A444, "Standard Specification for Steel Sheet,
Zinc Coated (Galvanized) by the HOT-DIP Process for Culverts and Under-
drains". The minimum thickness of sheet used shall be 0.109 inch.
- Concrete casing can consist of either poured-in-place concrete or precast
concrete pipe. Poured-in-place concrete should be sufficiently strong to
withstand the earth and water pressures imposed on it during, as well as
after, construction. It should be properly reinforced with steel to furnish
tensile strength and to resist cracking, and it should be free from
honeycombing or other defects likely to impair the ability of the concrete
structure to remain watertight. Aggregate small enough to place without
"bridging" should be used. Poured-in-place concrete shall be "Class A" (6
sacks of Portland cement per cubic yard) or "Class B" (5 sacks per cubic yard).
Precast concrete pipe is usually composed of concrete rings from 1 to 6 feet
in diameter and approximately 3 to 8 feet long. To serve satisfactorily as casing, these rings should be free
of blemishes that would impair their strength or serviceability. Concrete
pipe shall conform to the specifications listed in Section 12, Subsection A, Item
4.
- Covers. All bored and dug wells shall be provided with a structurally
sound, watertight, cover made of concrete or steel.
|
