5.3.2 Tier II - Runoff Water Quality Decision

An electronic spreadsheet program is available to apply the screens to include

all necessary calculations. The spreadsheet, along with documentation can be

downloaded as an ADDAMS module from the USACE DOTS website at

www.wes.army.mil/el/dots. If desired manual calculation procedures are available

(Schroeder, Lee, and Price in preparation).

5.3.2 Tier II - Runoff Water Quality Decision

After consideration of the Tier II runoff partitioning screen, one of the

following conclusions is reached for runoff (Figure 5-2).

1. Information is sufficient to reach a decision regarding runoff quality. In

this case either:

a. WQS exist for all COC and are met for all COC after consideration of

mixing. No further runoff evaluation is necessary.

b. WQS are exceeded for one or more COC after consideration of

mixing, and management actions should be considered. A decision to

implement management actions for runoff, such as placement of

surface covers or runoff treatment, may require more detailed

information for design of such actions. If management actions are

selected, no further runoff evaluation is necessary.

2. Information is not sufficient to reach a decision, which includes cases

where:

a. WQS are exceeded for one or more COC after consideration of

mixing, and more detailed information is desired for a decision

regarding WQS.

b. There are no applicable WQS, or there is concern about interactive

effects.

In either case, further evaluation in Tier III, or management actions as an

alternative to further evaluation, should be considered. A decision to implement

management actions for runoff may require more detailed information for design

of such actions. If management actions are selected, no further runoff evaluation

is necessary.

In determining the potential level of concern regarding interactive effects, the

number and classes of COCs that may be exceeded and the relative degree of

exceedences should be considered. Interactive effects may be purely additive,

synergistic (the resulting effect is greater that the sum of the effects resulting from

individual COCs), or antagonistic (the resulting effect is less that the sum of the

effects from individual COCs). WQS were developed for single contaminants.

Where several are present and are close to WQS, especially if they are the same

class of contaminants (metals, chlorinated organics, metal-organic complexes,

nonpolar organics, etc), interactive effects may be of concern.

5-8

Chapter 5

Surface Runoff After Disposal Operations