WSP06416

• File Number: 8027
• Description: Section D General Correspondence - Federal Agencies - USDA - Agricultural Research-Service
• State: CO
• Basin: Statewide
• Date: 8/1/1975
• Author: USDA
• Title: Field Observations of Transient Ground Water Mounds Produced by Artificial Recharge into an Unconfined Aquifer
• Water Supply Pro - Doc Type: Report/Study

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well and other profile observations indicated that a layer of heavier textured
material existed in the profile at the center of the pond between 17 and 18 feet
below ground surface. This layer and the initial and maximum position of the
mound are indicated relative to one another in figure 5. Apparently, the true
ground water mound has a perched mound. supel:imposed over it but only just
beneath the plot. Had recharge continued, the real mound would, no doubt, have
overridden it. For theoretical comparisons, the mound was considered to be that
measured by the deeper wells, and the storage in the perched mound was consid-
ered to be just part of that present in the vadose zone.

Determination of Aquifer Properties

The saturated depth (D) was first estimated by determining if zones of high
vertical head loss were present in the profile beneath the static water table.
The watel: table was 25 feet below ground surface at pond No. 1 and 20 feet, at
pond No.2. Piezometers showed a true perching layer existing at an approximate
depth below ground surface of 100 feet in both locations. Subsequent drilling
and coring in the area of the ponds (13) revealed a depth of 100 feet (D = 75
feet) for pond No. 1 and 101 feet(D = 80 feet) for No.2. However, at pond
No. 1 the actual horizontal hydraulic restriction or impeding layer (see fig. 6)
only became evident when development of the large central well was being carl:ied
out prior to the well test experiments. Because the vertical movement was prac-
tically nonexistent through the deeper layer, no head loss was measurable across
the shallower 41-foot layer (Dr = 16 feet) until significant vertical flow was
caused by pumping the well.

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ORIGINAL
WATER TABLE

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IMPEDING LA YERf

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LAYER

Figure 6.--Assumed and measured geometric values necessary for the theoretical
descl:iption of. the rechal:ge mound.

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