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INTAKE FACILITIES 4,9

FIGURE 4.6 Horizontal groundwater collection system. (Source: Hydro Group.)

ical diameters of 5 ft (1.5 m) or less with pipe casing. Collector wells are typically 13 to
20 ft (4.0 to 6.1 m) in diameter with a reinforced concrete caisson that has two or more
horizontal screens extending into the saturated zone.
Figure 4.6 shows a typical collector well. A collector well, similar to Figure 4.6, has
been installed in Lincoln, Nebraska, along the Platte River. A comparison between verti-
cal and horizontal wells determined that life-cycle costs would be similar for the devel-
opment of a 35 mgd (132 ML per day) well field. Two 17.5 mgd (66.2 ML per day) col-
lector wells were designed for this installation due to reduced maintenance requirements
and equivalent reliability compared with vertical wells. Extensive hydrogeologic testing
was performed to design the collector wells and to identify the most favorable sites. The
testing program included installation of test holes, observation wells, and test production
wells. Long-term pumping tests were conducted to determine the aquifer properties and
the amount of recharge available from the Platte River.
A 30 mgd (114 ML per day) well field along the Missouri River taps a ll0-ft-deep
(33.5-m) sand and gravel alluvial aquifer. This well field consists of seven gravel-packed
vertical wells and one collector well. The vertical wells include an elevated platform, lo-
cated above the flood of record, which houses the motor, controls, and valves. The col-
lector well house is located above the flood of record and includes two floors, a bridge
crane, and three 6 mgd (23 ML per day) pumps. One pump is outfitted with an adjustable-
frequency drive. Vertical well capacities are 2.9 mgd (10.9 ML per day), and the collec-
tor well capacity is 15 mgd (57 ML per day).
River Intake Locations. The preferred location for a shore intake system provides deep
water, a stable channel, and water of consistently high quality. In general, the outside bank
of an established river bend offers the best channel conditions. The inside bank is likely
to be troublesome because of reduced flow velocity, shallow water, and sandbar forma-
tions. The intake location should be upstream of local sources of pollution. Considerable