B.2.2 Effluent elutriate test procedure (Cont.)

Step 3 - Aeration. The prepared slurry must be aerated to ensure that

oxidizing conditions will be present in the supernatant water during the subsequent

settling phase. Bubble aeration is therefore used as a method of sample agitation.

Pour the mixed slurry into a 4-L graduated cylinder. Attach glass tubing to the

aeration source and insert the tubing to the bottom of the cylinder. The tubing can

be held in place by insertion through a predrilled No. 4 stopper placed in the top of

the cylinder. Compressed air should be passed through a deionized water trap,

through the tubing, and bubbled through the slurry. The flow rate should be

adjusted to agitate the mixture vigorously for 1 hr.

Step 4 - Settling. Remove the tubing, and allow the aerated slurry to undergo

quiescent settling for a time equal to the anticipated field mean retention time, up

to a maximum of 24 hr. If the field mean retention time is not known, allow

settling for 24 hr.

Field mean retention time Td can be estimated for a given flow rate and

ponding conditions by applying a hydraulic efficiency correction factor (HECF) to

the theoretical detention time as follows:

Td =

(B-3)

(HECF)

where

Td = mean detention time, hr

T = theoretical detention time, hr

HECF = hydraulic efficiency correction factor (HECF > 1.0) defined as the

inverse of the hydraulic efficiency

The theoretical detention time is calculated as follows:

A D

(12.1) = p p (12.1)

(B-4)

where

Vp = volume ponded, acre-ft

Qi = average inflow rate, cfs

Ap = area ponded, acres

Dp = average depth of ponding, ft

12.1 = conversion factor, acre-ft/cfs to hr

The hydraulic efficiency correction factor HECF can be estimated by several

methods. The most accurate estimate is that made from dye tracer studies to

Appendix B Column Settling Test and Effluent Elutriate Procedures