Dredged Material

ERDC TN-DOER-C22

September 2001

The dredged material at these three sites has the following characteristics in common that set them

apart from most terrestrial soils (Table 1): (1) low organic matter contents (8-15 percent dry weight)

compared to most terrestrial soils (this level is high for sediments with organic matter levels on the

order of 1 percent), (2) low bulk density (~1 g dry weight (DW) mL-l) typical for structureless soils,

(3) relatively high plant-available phosphorus concentration (1.7-2.8 mg kg-1), and (4) relatively

low nitrate-nitrogen concentration (0.001-0.012 mg kg-1) and generally high NH4+ concentration

(not measured in this case). The low nitrate-nitrogen concentration, however, may have been due

to the high moisture content of the dredged material and/or relatively long period of 1 week between

sample collection and nutrient analyses.

Comparison of the chemical characteristics of dredged materials before and after dredging (Table 1)

indicated that differences can be considerable. At Monroe, the concentrations of several metals

(cadmium, chromium, nickel, zinc, and copper) were considerably lower at the wettest site (i.e.,

recently deposited) of the CDF than in the predredged sediment. However, the concentration of

mercury was unchanged. Levels of total polychlorinated biphenyls (PCBs) had also decreased, but

total polycylic aromatic hydrocarbons (PAHs) were low but unchanged. At Manitowoc, the

concentrations of a few metals (cadmium, chromium, and zinc) were considerably lower in the CDF

than in the predredged sediment, those of nickel and copper were unchanged, but the levels of

arsenic, mercury, iron, and manganese were higher. Levels of total PCBs, PAHs, and pentachlo-

rophenol (PCP) were low and no change was detected. At Bayport, the concentrations of arsenic,

cadmium, and chromium were considerably lower in the CDF than in the predredged sediment,

nickel was unchanged, but levels of lead, zinc, mercury, copper, iron, and manganese were higher

in the CDF. Levels of total PCBs had decreased in the CDF, and those of PAHs and PCP were low

and unchanged. Comparison of the chemical characteristics of dredged materials located at different

distances from point of entry of the CDF (data not shown) confirmed the assumption that

contaminant concentrations increased with distance from the point of entry in the CDF.

No environmental quality benchmarks for dredged material placed in CDFs currently exist. Recent

data collected for USEPA's hazardous waste identification rule suggest protective levels for receptor

taxa of concern, including terrestrial plants and soil biota (USEPA 1999). Dredged materials in

CDFs can be considered as special cases of terrestrial soils, and, therefore, the concentrations listed

as protective for terrestrial soil-based communities are likely to be similar to those for CDF dredged

materials. Protective levels for terrestrial soils, Chemical Stressor Concentration Levels (CSCL,

expressed in mg total element per kg dry soil), vary with the receptor taxa. It was concluded from

a comparison of the recent chemical data with the published CSCLs for terrestrial plants and

invertebrates (Table 2) that dredged material of the Monroe CDF would be the most suitable

substrate to test for effects of metals, since only a few CSCLs for metals and none for organics were

exceeded. CSCLs for plants were greatly exceeded for vanadium and zinc; and CSCLs for

invertebrates were exceeded by nickel, selenium, and zinc. It was concluded also that none of the

dredged material evaluated would be particularly suitable to test for effects of organic contaminants,

since the only published CSCL for organics, PCP, was not exceeded for test organisms, and several

CSCLs for metals were exceeded.