5.3 Tier II Water Quality Screen for Runoff

1. Information is sufficient to reach a decision without further evaluation.

2. Information is not sufficient to reach a decision regarding runoff quality.

Conduct Tier II and/or Tier III evaluations.

5.3 Tier II Water Quality Screen for Runoff

The Tier II screens rely on bulk sediment data of 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 the screens and go directly to the Tier III runoff tests. However, this is not an

efficient use of resources in most cases, since bulk sediment data are also needed

for screening evaluations for the other pathways.

5.3.1 Tier II - Runoff Water Quality Screen - Equilibrium Partitioning

The screen for runoff is based on equilibrium partitioning principles and

conservative (i.e., err on the side of environmental protection) application of

design and operating principles for CDFs (Schroeder, Lee, and Price in

preparation). The evaluation utilizes site-specific data and default values for

pertinent variables to calculate a predicted runoff concentration of contaminants.

The results are compared to water quality standards.

The surface runoff quality screening protocol, during the early stages of

drying, is similar to that for effluent quality for hydraulic disposal of dredged

material in a confined disposal facility and was likewise developed based on the

equilibrium and mixing boundary conditions. [The protocol produces two

estimates of the runoff concentration based on these boundary conditions. The

smaller of the two estimates (smaller calculated sediment contaminant

concentration meeting standards) is used as the screening criteria.] The

equilibrium partitioning calculations assume that only a fraction of the metals in

the sediment is soluble. The fraction varies from metal to metal.

After the dredged material dries out and becomes oxidized, the surface runoff

quality screening protocol was developed based on solubility/equilibrium and

mixing boundary conditions. During drying, the dredged material consolidates

and forms cracks in the surface of the CDF. Surfaces of the dredged material tend

to accumulate salt as the pore water moisture evaporates from the surface, leaving

any salt dissolved in the pore water on the surface of the cracks. Precipitation

dissolves the salt and removes it from the dredged material. During the drying

process many metals such as zinc, cadmium, copper, nickel, lead, and mercury are

converted from poorly soluble metal sulfides formed under reduced, anaerobic

conditions to more soluble metal salts. Organic contaminants become tightly

adsorbed onto soil and organic particulates and remain associated with suspended

solids in surface runoff water. As with effluent, dilution occurring within the

mixing zone at the point of discharge should be considered in evaluating runoff.

5-7

Chapter 5

Surface Runoff After Disposal Operations