D.3 Sequential Batch Leach Test (SBLT) for Freshwater Sedments

volume, test results will show little difference in sequential leach test cycles. So,

results of an SBLT test on freshwater sediments will result in a "clustered"

desorption isotherm for these compounds, with the data reduced essentially to a

dot when plotted on the isotherm graph. For such clustered isotherms, Kd is the

single point distribution coefficient. Therefore, if the only contaminants of

concern are hydrophobic organics and these COCs are or are assumed to be

reversibly sorbed with no subfraction resistant to leaching, a single-point

isotherm, based on one SBLT test cycle, is sufficient.

Challenge water. Both the SBLT and PCLT involve "challenging" a

sediment sample with water to produce a leachate sample for testing. The site

conditions expected at the CDF should be considered in selecting the water used

in the tests. Most leachate tests should be performed using deoxygenated,

distilled-deionized (DDI) water, which is the appropriate challenge water to

simulate leachate generated by freshwater infiltration via precipitation. Tests

conducted with challenge water simulating acid rain conditions have shown no

effects on results as compared to DDI water because of the buffering capacity of

the sediments. Therefore, DDI water should be used for testing freshwater

sediments and for saltwater dredged materials placed in upland CDFs. For

saltwater dredged material placed in nearshore or island CDFs, the anticipated

site conditions should be considered to determine if fresh or saline challenge

water is appropriate. For example, some portions of sediments placed in

nearshore or island CDFs constructed in brackish or saltwater may remain below

the mean low water level and would never be exposed to freshwater infiltration.

For these conditions, dredging site water would be the appropriate challenge

water for leachate tests. In this case, salinity washout is not expected, and the

SBLT is appropriate.

Oxidation status of sediments. Most leachate tests should be conducted

using anerobic sediment (no drying or oxidation prior to testing). Anerobic

sediments are appropriate for testing related to all nearshore or island CDFs in

which the sediments will remain below the mean low water elevation. For

upland CDFs, anerobic conditions are also appropriate in most cases, since lower

horizons of the dredged material will remain saturated and anerobic, even if an

aerobic surface crust develops. An aerobic leaching procedure (in which the

sediments are dried and oxidized prior to testing) may be necessary if anticipated

site management would result in dewatering the full lift thickness prior to

disposal of all subsequent lifts.

D.3 Sequential Batch Leach Test (SBLT) for

Freshwater Sediments

The sequential batch leach test (SBLT), used to evaluate potential leachate

quality in freshwater dredged material, involves exposing anaerobic dredged

material to successive aliquots of anaerobic distilled-deionized water

(http://www.wes.army.mil/el/dots/pdfs/mpd941.pdf). Sediment is prepared and

loaded into centrifuge tubes under anaerobic conditions at a 4:1 water to

sediment ratio, then sequentially leached for 24 hr with distilled-deionized (DDI)

Appendix D Leachate Testing Procedures