4.3 Tier II - Water Quality Screens for Effluent

4.3 Tier II - Water Quality Screens for Effluent

The Tier II effluent evaluations focus on the evaluation of water quality of the

effluent and include two procedures and evaluation of initial mixing as an integral

part of the effluent quality evaluations. The Tier II procedures rely on bulk

sediment data for the proposed dredged material. If adequate bulk sediment data

are not available, samples should be collected and the bulk sediment chemistry

should be determined. It is possible to skip Tier II and go directly to the Tier III

effluent elutriate test. However, this is not an efficient use of resources in most

cases, since bulk sediment data are also needed for Tier II evaluations for the

other pathways.

4.3.1 Tier II - Effluent Quality Screen - Assumed Total Dissolved

Release

A screening procedure based on the assumption of total dissolved release of

COC in effluent was developed for the ITM and is included here for the sake of

completeness and consistency. This screening procedure is highly conservative,

in that it grossly over-predicts the concentrations of COC in effluent.

The procedure involves a determination of whether the WQS, after consid-

eration of mixing, would be met if the bulk concentration of COC present in the

sediment were to be completely dissolved in the water flowing into the CDF and

discharged as effluent from the disposal site.

The COC that would require the greatest dilution is determined by calculating

the dilution that would be required to meet the applicable WQS. To determine the

dilution (D) the following equation is solved for each COC:

D = [(Cs SS/1000) -- Cwq] / (Cwq -- Cds)

where

Cs = concentration of the COC in the dredged material expressed as

micrograms per kilogram (g/Kg), on a dry weight basis;

SS = suspended solids concentration in the CDF inflow expressed as grams

per liter (g/L);

1000 = conversion factor, g to Kg;

Cwq = WQS in micrograms per liter (g/L); and

Cds = background concentration of the COC at the disposal site in micrograms

per liter (g/L).

The mixing zone evaluation is then made for the COC that would require the

greatest dilution.

After consideration of the Tier II total release screen, one of the following

conclusions is reached for effluent (Figure 4-2).

4-8

Chapter 4

Effluent During Disposal Operations