Page 103 - Water Engineering Hydraulics, Distribution and Treatment

3.20 Groundwater Under the Direct Influence of Surface Water
Option 4
From source screening
Option 1
GWUDI
Source selected
for further review
Hydrogeologic
Inconclusive/positive
Water quality
assessment
assessment
Negative
Not under
Significant
the direct
correlation?
influence
of surface No Option 2 Yes Potentially 81
water
Adequate seal No Reconstruct
and
construction?
Yes
Hydraulic
connection
Low risk
factor
MPAs High risk
Consult with factor
local dept. of Option 3
health Moderate
risk factor Figure 3.18 Identification of groundwater
Under the direct sources under the direct influence of
influence of surface water—detailed evaluation phase
surface water
methodology.
the source can be designated as not being under the direct (option 3) to complete the detailed evaluation phase, or sim-
influence of surface water, or not-GWUDI. ply accept the GWUDI determination (option 4).
Most project engineers would like to choose the straight-
forward option of water quality assessment instead of
3.20.2 GWUDI Determination: Detailed the complex option 1, hydrogeologic assessment, for their
Evaluation Phase clients. If the option 2 test fails, then option 3 follows.
The MPA option is usually chosen, conducted during
Once a groundwater source has been selected for further
times of worst-case GWUDI conditions, as indicated by the
review, as a result of the source screening phase, the proce-
water quality assessment or as predicted by historical infor-
dure described in Fig. 3.18 should be closely followed.
mation.
The detailed evaluation phase has three components, as
shown in Fig. 3.18: (a) hydrogeologic assessment, (b) water
quality assessment, and (c) microscopic particulate analysis
3.20.3 Hydrogeologic Assessment
(MPA). The water supplier makes the decision about whether
to begin with option 1 (hydrogeologic assessment), option As discussed and shown in Fig. 3.18, a water system has
2 (water quality assessment), or option 3 (MPAs). Either four evaluation options. Option 1 requires a detailed hydro-
the hydrogeologic assessment or water quality assessment geologic assessment that addresses the potential of surface
is capable of providing the information required to deter- water to move quickly to the subsurface collection device.
mine that no surface-water influence is present. Sometimes, However, at any time during the hydrogeologic assessment,
for example, when the project time is extremely important, the water system’s engineer can halt an ongoing evaluation
the project engineer may want to choose option 3 (MPAs) by accepting a GWUDI designation (option 4) and mak-
directly or even option 4 (accept GWUDI determination). ing the appropriate modifications to bring the system into
If the hydrogeologic assessment option was chosen, compliance with the SWTR, or changing it to option 2 or
but its results were inconclusive, the project engineer who option 3.
represents the groundwater source owner/developer may If the hydrogeologic assessment is selected, and results
request further water quality assessment (option 2) or MPAs of the assessment indicate that the aquifer supplying the