Comparison of Field Infiltration Testing Methods

Water Needs Time Required Equipment Technique per Test (gal) per Test (hr) Required

Comments

Flooding basin 600-3000

4-12

Backhoe or blade See this chapter for details.

AEP device See this chapter for details.

Air entry permeameter

(AEP) Cylinder

100-200

Standard device See Crites et al.

(2000) for details.

infiltrometer

Sprinkler 250-300

infiltrometer

Pump, pressure See Crites et al. tank, sprinkler, (2000) for details. collection cans approaches a "steady-state" condition. This steady-state rate can be taken as the limiting infiltration rate for the soil within the zone of influence of the test. A safety factor is then applied to that rate for system design, as described in Chapter 8.

Because it is the basic purpose of the test to define the hydraulic conductivity of the near-surface soil layers, the use of clean water (with about the same ionic composition as the expected wastewater) is acceptable in most cases. If, however, the wastewater is expected to have a high solids content that might clog the surface, then a similar liquid should be used for the field test.

The basin test is most critical for the SAT concept because large volumes of wastewater are applied to a relatively small surface area. Most SAT systems, as described in Chapter 8, are operated on an intermittent or cyclic pattern basis, alternating flooding and drying to maximize infiltration rates and allow alternating oxidation and reduction processes in the soil. If a particular project design calls for a continuously flooded seepage pond mode, then the initial field tests should be continued for a long enough period to simulate this condition.

If site conditions require construction of full-scale SAT basins on backfilled material (not recommended), a test fill should be constructed on the site with the equipment intended for full-scale use, and then the basin test described above should be conducted in that material. The test fill should be as deep as required by the site design or 5 ft (1.5 m), whichever is less. The top of the fill area should be at least 15 ft (5 m) wide and 15 ft (5 m) long to permit the installation of a flooding basin test near the center.

One flooding basin infiltration test should be conducted on each of the major soil types on the site. For large continuous areas, one test for up to 25 ac (10 ha) is typically sufficient. The test should be performed on the soil layer that will become the final infiltration surface in the constructed system.

10 ft

Sealed joint -

Aluminum flashing

FIGURE 2.5 Basin test for infiltration. Air Entry Permeameter

The air entry permeameter (AEP) was developed by the U.S. Department of Agriculture (USDA) to measure point hydraulic conductivity in the absence of a water table. The device is not commercially available, but specifications and fabrication details can be obtained from the USDA, Water Conservation Laboratory, 4332 East Broadway, Phoenix, AZ 85040. The unit defines conditions for a very small soil zone, but the small volume of water required and short time for a single test make it useful to verify site conditions between the larger scale flooding basin test locations. It can also be used in a test pit to define the in situ permeability with depth. The pit is excavated with one end inclined to the surface, benches are cut about 3 ft (1 m) wide by hand, and the AEP device is used on that surface.

Sealed joint -

6 in. below surface

Aluminum flashing

FIGURE 2.5 Basin test for infiltration. Air Entry Permeameter

The air entry permeameter (AEP) was developed by the U.S. Department of Agriculture (USDA) to measure point hydraulic conductivity in the absence of a water table. The device is not commercially available, but specifications and fabrication details can be obtained from the USDA, Water Conservation Laboratory, 4332 East Broadway, Phoenix, AZ 85040. The unit defines conditions for a very small soil zone, but the small volume of water required and short time for a single test make it useful to verify site conditions between the larger scale flooding basin test locations. It can also be used in a test pit to define the in situ permeability with depth. The pit is excavated with one end inclined to the surface, benches are cut about 3 ft (1 m) wide by hand, and the AEP device is used on that surface.

2.3.3 Subsurface Permeability and Groundwater Flow

The permeability of deeper soils is usually measured via laboratory tests on undisturbed soil samples obtained during the field boring program. Such data are usually required only for the design of SAT systems or to ensure that subsoils are adequate to contain undesirable leachates. In many situations, it is desirable for the design of SAT systems to determine the horizontal permeability of the subsurface layers. This can be accomplished with a field test known as the auger hole test, which, in essence, requires pumping a slug of water out of a bore hole and then observing the time for the water level to recover via lateral flow. The U.S. Bureau of Reclamation has developed a standard procedure for this test (details can be found in Crites et al., 2000; USDOI, 1978).

Defining the groundwater position and flow direction is essential for most of the treatment concepts discussed in this book. Overland flow and wetland systems

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