D.2.5 Considerations in Test Selection and Test Conditions

waters in a CDF is properly represented. For these reasons, it is difficult to

couple results from sequential batch leaching with porous media fluid mechanics

(advection and dispersion) and from this coupling predict leachate quality.

D.2.5 Considerations in Test Selection and Test Conditions

This section presents recommendations for selecting the appropriate leach

test and testing conditions, accounting for both the theoretical considerations

described above and the practical aspects of testing. The selection of the

appropriate test (SBLT or PCLT) and testing options and procedures are a

function of the sediment salinity, the possible presence of Non-Aqueous Phase

Liquids (NAPLs), CDF site conditions, and the COC. The following tabulation

summarizes the recommended test for various sediment characteristics:

Recommended Leach

Sediment/ Site Characteristics

Test

Sediments containing NAPL

PCLT

Saltwater Sediments with freshwater infiltration

PCLT

Saltwater Sediments without freshwater infiltration

SBLT

Freshwater Sediments

SBLT

Freshwater Sediments with Hydrophobic Organics as the only

SBLT (single cycle)

COC

Presence of NAPL. If the sediments contain NAPLs, the PCLT is the

recommended leachate test. During the SBLT, the physical process of agitation

during the test has resulted in a release of trapped NAPL from the sediment

matrix that would not be expected under field leaching conditions. Since the

PCLT is conducted using a column, no agitation problems occur.

Ionic strength. Either the SBLT or PCLT may be used for freshwater

dredged materials. Since the SBLT test is a simpler procedure and is more cost

and time effective than the PCLT, the SBLT test would normally be preferred for

freshwater sediments. The PCLT is recommended for saltwater sediments

because of the influence of colloidal materials if the sediments are placed such

that they are subject to freshwater infiltration, e.g., in an upland CDF. As salt is

progressively leached from saline sediments during any leachate testing process,

the colloids become destabilized and are subsequently released. Since the SBLT

is a batch test, the aqueous phase concentrations of contaminants are obtained by

centrifugation or filtration of the test samples. These processes remove a portion

of the colloids, resulting in potentially erroneous results with saline sediments

for the SBLT. The PCLT is a column leach test in which samples are obtained

directly from the test column and analyzed without centrifugation or filtration,

and any potential colloidal release is properly accounted for. For this reason,

the PCLT test is required for saline sediments subject to freshwater infiltration.

Hydrophobic organics. Hydrophobic organics, such as PCBs or DDT and

its metabolites, have Kd values on the order of hundreds to thousands. Since

such a small portion of the contaminant mass is partitioned to a given pore water

Appendix D Leachate Testing Procedures