USACE Small-Scale Column Test

The U.S. Army Corps of Engineers (USACE) has also developed leach tests

to assess the quality of water moving through a contaminated sediment layer into

groundwater in a confined disposal facility environment (Myers and Brannon

1991). This test has been applied to similarly assess the quality of water poten-

tially moving upward into a cap due to advective forces.1

USACE Small-Scale Column Test

The USACE developed a first-generation capping effectiveness test in the

mid-1980s as part of the initial examination of capping as a dredged material

disposal alternative. The test was developed based on the work of Brannon et al.

(1985, 1986), Gunnison et al. (1987), Environmental Laboratory (1987), and

Sturgis and Gunnison (1988).

The tests basically involve layering contaminated and capping sediments in

columns (Figure C1) and experimentally determining the cap sediment thickness

necessary to chemically isolate a contaminated sediment by monitoring the

changes in dissolved oxygen, ammonium-nitrate, orthophosphate-phosphorous,

or other tracers in the overlying water column.

The thickness of granular cap material for chemical isolation determined

using this procedure is on the order of 1-ft for most sediments tested to date.

However, this column testing procedure does not account for potential advection

nor long-term flux of contaminants due to diffusion. The USACE Small-Scale

Column Test is therefore only applicable for evaluation of capping thicknesses

for isolation of nutrient-rich sediments.

The procedure for conducting the small-scale column test is presented below.

Chemical tracers

The test uses dissolved oxygen (DO) depletion, ammonium-nitrogen, and

orthophosphate phosphorus as tracers because they are easy and inexpensive to

measure. A cap thickness that is effective in preventing the movement of these

inorganic constituents will also be effective in preventing the movement of

organic contaminants that are more strongly bound to sediment (e.g., polynuclear

aromatic hydrocarbons (PAHs), petroleum hydrocarbons, and polychlorinated

biphenyls (PCBs)). The behavior of soluble-reduced inorganic species (e.g.,

arsenic) is also similar to the tracers.

Dissolved oxygen depletion in the water column is normally not a problem in

an open-water disposal environment, due to mixing and reaeration of the water

Personal Communication, 1995, Tommy E. Myers, U.S. Army Engineer Waterways Experiment

Station, Vicksburg, MS.

Appendix C Capping Effectiveness Tests