Water analysis

an effective cap thickness has been achieved, there will be no significant dif-

ference in oxygen-depletion rates between the contaminated sediment with cap

material and the cap material alone.

A similar rationale is applicable for using ammonium-nitrogen and

orthophosphate-phosphorus as tracers. These constituents are released only

under anaerobic conditions. However, if the layer of cap material is thick enough

to prevent the diffusing materials in the underlying contaminated dredged

material from reaching the water column, the release rates from the capped

contaminated sediment will be the same as from the cap material alone.

Because of the potential variation of chemical and biochemical properties in

sediments, more than one tracer (ammonium-nitrogen, orthophosphate-

phosphorus, and DO depletion) must be considered for each application

(Brannon et al. 1985, 1986; Gunnison et al. 1987; Environmental Laboratory

1987). Frequently, the contaminated sediment and the proposed capping mate-

rial are so different that a chemical property of the contaminated sediment is

easily distinguishable from that same property of the cap material. However,

when the cap material has chemical properties similar to the contaminated

sediment, chemical differences are harder to distinguish. In such a case, if only

one tracer is measured and negative results are obtained, a second series of tests

is necessary.

Water analysis

The release rates of ammonium-nitrogen and orthophosphate-phosphorus

must be determined in accordance with procedures recommended by Ballinger

(1979). The depletion rate of DO is determined using either the azide modi-

fication of the Winkler method, as described in Standard Methods (American

Public Health Association 1986), or a DO meter.

Sediment collection

Samples of contaminated sediment must be collected that are representative

of sediment to be dredged. Samples of the proposed capping material must also

be taken. To ensure that sediment samples are not diluted with large volumes of

water, a clamshell dredge or similar device is used to sample both contaminated

sediment and capping material. Representative subsamples of both materials are

taken for initial bulk analysis and characterization. All sediments are to be

placed into polyethylene-lined steel barrels, sealed, and stored at 4 oC until

tested.

Sediment sampling and preparation

The capping effectiveness test is run using representative samples of the

contaminated and capping sediments (see Chapter 3 of the main text). Sediment

Appendix C Capping Effectiveness Tests