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112 Chapter 3 Water Sources: Groundwater
Most project engineers would like to choose the straightforward option of water qual-
ity assessment instead of the complex option 1, hydrogeologic assessment, for their clients.
If the option 2 test fails, then option 3 follows.
The MPA option is usually chosen, conducted during times of worst-case GWUDI
conditions, as indicated by the water quality assessment or as predicted by historical
information.

3.20.3 Hydrogeologic Assessment

As discussed and shown in Fig. 3.18, a water system has four evaluation options.
Option 1 requires a detailed hydrogeologic assessment that addresses the potential of
surface water to move quickly to the subsurface collection device. However, at any time
during the hydrogeologic assessment, the water system’s engineer can halt an ongoing
evaluation by accepting a GWUDI designation (option 4) and making the appropriate
modifications to bring the system into compliance with the SWTR, or changing it to op-
tion 2 or option 3.
If the hydrogeologic assessment is selected, and results of the assessment indicate that
the aquifer supplying the source is not in hydraulic connection with surface water, no fur-
ther analysis will be required. However, if the local health department determines that the
hydrogeologic assessment does not contain enough information to establish whether there
is a hydraulic connection between surface-water and the source-water collection device,
the water supplier should collect additional hydrogeologic information or proceed with a
water quality assessment or MPAs.
The hydrogeologic assessment should be designed to provide the following information:

1. Well construction details, which provide (a) a well log, well construction diagram,
and well description; and (b) its installation methods for comparison with current
well standards
2. Aquifer characteristics, data which include (a) aquifer geometry and texture, in-
cluding the unsaturated zone; (b) saturated thickness; (c) hydraulic conductivity;
and (d) transmissivity
3. Prepumping and pumping groundwater flow characteristics data, which include
(a) water table/potentiometric surface elevations; (b) groundwater flow direc-
tions; (c) groundwater flow velocity; and (d) zone of contribution/influence of
the well
4. Degree of hydraulic connection between surface-water source and aquifer, which
is indicated by (a) geology underlying surface-water body; (b) characterization of
bottom sediments in surface-water body; (c) determination of vertical hydraulic
gradient in surface-water body; (d) hydraulic relationship between the surface-water
body and the well; and (e) calculations of travel times between the surface-water
body and the well
5. Seasonal variations in hydrogeologic characteristics, such as the changes in flow
patterns during seasonal fluctuations or periods of drought
The hydrogeologic assessment should include, as a minimum, geologic logs and con-
struction details for the pumping well and any observation wells or piezometers; aquifer
pumping test(s); a survey of the elevations of water level monitoring measuring points;
water level monitoring of groundwater and surface sources; and preparation of detailed
maps of water table/potentiometric surface and geologic cross-sections. The owner/developer