Figure 4-4. Photo of typical laboratory setup for the effluent elutriate test

in the CDF supernatant water during active disposal operations (Palermo 1985a-d;

Palermo and Thackston 1988a and b). EET results define the concentration of

COCs discharged from the CDF (i.e., over the weir structure), therefore an

evaluation of initial mixing should be conducted (Appendix E) prior to

comparisons with WQS.

Figure 4-4 is a photo of a typical laboratory setup for the EET. Sediment and

water from the dredging site are mixed into a slurry with a solids concentration

equivalent to that expected in the CDF inflow. The slurry is placed in 4-L

cylinders and aerated for 1 hour to ensure that oxidizing conditions will be present

during the subsequent settling phase. The aerated slurry is allowed to settle for a

time period equivalent to the expected field mean retention time in the CDF, up to

a maximum settling time of 24 hour. The supernatant water is extracted from the

cylinders and analysed as the effluent elutriate. The results may then be compared

with applicable water quality standards after consideration of initial mixing.

Figure 4-4. Photo of typical laboratory setup for the effluent elutriate test

Depending on the basis of applicable WQS (Section 2.3.2), the prediction of

the quality of effluent from CDFs accounts for the dissolved concentration of

contaminants and may also consider that fraction associated with the released total

suspended solids. If the WQS are applied to dissolved concentrations, the effluent

elutriate samples are analysed for dissolved contaminants only, and the results are

compared to WQS after consideration of initial mixing (this approach is identical

to that for effluent in the ITM).

If the WQS are applied to whole water concentrations, both the EET and

LTCST are required. For this evaluation, the EET determines the contaminant

partitioning between dissolved and particulate phases, while the LTCST

determines the total particulates (TSS) in the effluent. In this case, the EET

samples are analysed for TSS concentration and for both dissolved contaminants

and total concentrations of contaminants, allowing for determination of both

dissolved and particle-associated contaminant concentrations. Using results from

both the EET and an estimate of effluent TSS from the LTCST, a mass balance

4-12

Chapter 4

Effluent During Disposal Operations