Page 101 - Water Engineering Hydraulics, Distribution and Treatment

in US federal and state sanitary codes. In some cases, it
are surprisingly short when reasonable precautions are taken
will be easier to replace the source with a properly designed
in disposal.
and constructed well or spring or possibly to modify the
The principal determinant of the distance traveled seems
to be the size of the media. Romero (1970) provides diagrams
source to eliminate the direct influence of surface water. Pub-
lic water systems with groundwater sources under the direct
that may be used to evaluate the feasibility of disposing of
influence of surface water are also subject to more stringent
biologically contaminated wastes in saturated and unsatu-
monitoring requirements for total coliform, turbidity, and
rated granular media. The danger of bacterial pollution is
entry point disinfection residual. The types of groundwater
greater in fractured rocks, cavernous limestones, and gravel
sources potentially regulated under the SWTR include dug
deposits where the granular materials have no filtering capac-
wells, springs, infiltration galleries, shallow or improperly
ity. The distances traveled will be higher in areas of influence
constructed wells, or other collectors in subsurface aquifers
of discharging or recharging wells because higher velocities
are present. The higher rates of artificial recharge and greater 3.20 Groundwater Under the Direct Influence of Surface Water 79
near surface waters.
permeability of artificial recharge basins enable bacteria to Each local health department (LHD) throughout the
be carried to a greater depth. United States is responsible for identifying which public
water sources are subject to the SWTR. However, it is the
responsibility of the water supplier to provide the informa-
3.19.2 Subsurface Disposal of Liquid Wastes
tion needed to make this determination to the LHD. The
Subsurface space may be used to an increasing degree for the LHD is also responsible for recording and reporting the cri-
disposal of wastes. The oil industry pumps nearly 20 million teria used and the results of determinations. All groundwater
barrels of salt water per day into subsurface formations from sources used to supply public water systems must be evalu-
which oil has been extracted. Some highly toxic chemical ated for evidence of groundwater under the direct influence
wastes are disposed of underground. The use of an aquifer of surface-water GWUDI. This evaluation will focus on the
as a receptacle for toxic waste materials is justified only if likelihood that the groundwater source could be contami-
it has little or no value as a present, or potential, source of nated with large-diameter pathogens, such as Giardia lamblia
water supply. Further, there should not be any significant and Cryptosporidium, through a hydraulic connection with
risk of contaminating other aquifers or of inducing fractures surface water. If a drinking water source has been identified
in the confining formations. Recharging of groundwater by as GWUDI, the source must meet the criteria established
injection or spreading of reclaimed municipal wastewaters under the SWTR.
is an accepted practice that will undoubtedly be increasingly
used in the future.
3.20.1 GWUDI Determination: Source Screening
Phase
3.20 GROUNDWATER UNDER THE DIRECT
INFLUENCE OF SURFACE WATER Information gathered during sanitary surveys is important
when making GWUDI determinations. In addition, informa-
The US Federal Surface Water Treatment Rule (SWTR) gives tion such as compliance monitoring data, topographic maps,
the following definition for groundwater directly under the geologic reports, well logs, and data on potential contaminant
influence of surface water (GWUDI): “any water beneath source(s) is useful.
the surface of the ground which exhibits significant and A two-phase methodology is being used in the United
rapid shifts in water characteristics such as turbidity, tem- States to determine whether or not a groundwater source
perature/conductivity or pH which closely correlates to cli- is under the direct influence of surface water: the source
matological or surface water conditions and/or which con- screening phase is used first to separate those sources that
tains macroorganisms, algae, large diameter (three microns are clearly not subject to surface-water influences from those
or greater) pathogens or insect parts of a surface water ori- sources in need of further evaluation. Then the second phase,
gin.” In the United States, true groundwater, which is not the detailed evaluation phase, is applied to sources identified
directly influenced by surface water, will be monitored and/or for testing to evaluate their degree of hydraulic connection
treated under the Groundwater Rule, whereas GWUDI will with surface water.
be monitored and treated in accordance with the SWTR and The source screening phase should be used to separate
the Long-Term 2 Enhanced Surface Water Treatment Rule those sources that are clearly not subject to surface-water
(LT2-ESWTR). influences from those sources in need of further evaluation.
The purpose of regulating groundwater sources under A schematic of the screening procedure is shown in Fig. 3.17,
the direct influence of surface water in the SWTR is to pro- and the overall methodology for the detailed evaluation phase
tect against contamination from large-diameter pathogens is presented as a flowchart in Fig. 3.18.
associated with surface waters. Groundwater sources deter- Box 1 in Fig. 3.17 includes criteria that will immedi-
mined to be under the direct influence of surface water must ately select a groundwater source for further review. These
be filtered or meet filtration avoidance criteria as contained source screening water criteria include the following: (a) a