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108 Chapter 3 Water Sources: Groundwater
bacteria and viruses may survive and the distances they may travel through specific
rock materials in different subsurface environmental conditions are uncertain. They
seem to behave in a manner similar to the degradable and adsorbable contaminants.
Under favorable conditions some bacteria and viruses may survive up to at least 5 years
in the underground environment. However, the distances traveled in both the saturated
and unsaturated media are surprisingly short when reasonable precautions are taken in
disposal.
The principal determinant of the distance traveled seems to be the size of the media.
Romero (1970) provides diagrams that may be used to evaluate the feasibility of disposing
of biologically contaminated wastes in saturated and unsaturated granular media. The dan-
ger of bacterial pollution is greater in fractured rocks, cavernous limestones, and gravel de-
posits where the granular materials have no filtering capacity. The distances traveled will
be higher in areas of influence of discharging or recharging wells because higher velocities
are present. The higher rates of artificial recharge and greater permeability of artificial
recharge basins enable bacteria to be carried to a greater depth.

3.19.2 Subsurface Disposal of Liquid Wastes
Subsurface space may be used to an increasing degree for the disposal of wastes. The oil
industry pumps nearly 20 million barrels of salt water per day into subsurface formations
from which oil has been extracted. Some highly toxic chemical wastes are disposed of un-
derground. The use of an aquifer as a receptacle for toxic waste materials is justified only
if it has little or no value as a present, or potential, source of water supply. Further, there
should not be any significant risk of contaminating other aquifers or of inducing fractures
in the confining formations. Recharging of groundwater by injection or spreading of
reclaimed municipal wastewaters is an accepted practice that will undoubtedly be increas-
ingly used in the future.

3.20 GROUNDWATER UNDER THE DIRECT INFLUENCE OF SURFACE WATER
The U.S. Federal Surface Water Treatment Rule (SWTR) gives the following definition for
groundwater directly under the influence of surface water (GWUDI): “any water beneath
the surface of the ground which exhibits significant and rapid shifts in water characteristics
such as turbidity, temperature/conductivity or pH which closely correlates to climatological
or surface water conditions and/or which contains macroorganisms, algae, large diameter
(three microns or greater) pathogens or insect parts of a surface water origin.” In the United
States, true groundwater, which is not directly influenced by surface water, will be moni-
tored and/or treated under the Groundwater Rule, whereas GWUDI will be monitored and
treated in accordance with the Surface Water Treatment Rule (SWTR) and the Long-Term
2 Enhanced Surface Water Treatment Rule (LT2-ESWTR).
The purpose of regulating groundwater sources under the direct influence of surface
water in the SWTR is to protect against contamination from large-diameter pathogens as-
sociated with surface waters. Groundwater sources determined to be under the direct influ-
ence of surface water must be filtered or meet filtration avoidance criteria as contained in
U.S. federal and state sanitary codes. In some cases, it will be easier to replace the source
with a properly designed and constructed well or spring, or possibly to modify the source
to eliminate the direct influence of surface water. Public water systems with groundwater
sources under the direct influence of surface water are also subject to more stringent mon-
itoring requirements for total coliform, turbidity, and entry point disinfection residual. The