CEMP-E
TI 814-01
3 August 1998
5-4. WATER QUALITY EVALUATION. Both well location and method of construction are of
major importance in protecting the quality of water derived from a well. Groundwater may
become contaminated as a result of leakage from sources as diverse as improperly sealed
wells, septic tanks, garbage dumps, industrial and animal wastes.
a. Selection of a Well Site. Prior to selecting the well location, a thorough survey of the
area should be undertaken. The following information should be obtained and analyzed:
(1) Local hydro geology such as terrain, soil type, depth, and thickness of water bearing
zone.
(2) Location, construction, and disposal practices of nearby sewage and industrial
facilities.
(3) Locations of sewers, septic tanks, cesspools, animal farms, pastures, and feed lots.
(4) Chemical and bacteriological quality of ground water, especially the quality of water
from nearby wells.
(5) Histories of water, oil, and gas well exploration and development in area.
(6) Location and operating practices of nearby industrial and municipal landfills and
dumps.
(7) Direction and rate of travel of ground water.
Recommended minimum distances for well sites from commonly encountered potential
sources of pollution are shown in table 5-2. It is emphasized that these are minimum distances
which can serve as rough guides for locating a well from a potential source of groundwater
contamination. The distance may be greater, depending on the geology of the area. In
general, very fine sand and silt filter contaminants in ground water better than limestone,
fractured rock, coarse sand and gravel. Chemical contaminants may persist indefinitely in
untreated groundwater. If at all possible, a well should be located up gradient of any known
nearby or potential sources of contamination. It is a good practice to consult local authorities
for aid in establishing safe distances consistent with the subsurface geology of the area. Dry
wells should be abandoned and plugged in conformance to local regulations.
Table 5-2. Minimum Distances from Pollution Sources.
________________________________________________________
Minimum
Source
Horizontal Distance
Building Sewer
15 m (50 ft)
Disposal Field/Septic Tank
30 m (100 ft)
Seepage Pit
30 m (100 ft)
Dry Well
15 m (50 ft)
Cesspool/leaching pits
45 m (150 ft)
Note: The above minimum horizontal distances apply to wells at all depths. Greater distances are recommended
when feasible.
5-5
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