H.3.3 Sediment collection and preparation

H.3.3 Sediment collection and preparation

Freshwater. A minimum of 20 kg of sediment is required to conduct each

segment (wetland and terrestrial) of the plant bioaccumulation procedure. More

may be necessary if analyses requiring considerable biomass are necessary and

poor plant growth in the dredged material is expected. Sediment collected for

testing should be consolidated and thoroughly mixed with a high shear mixer to

ensure homogeneity. Samples are collected after mixing for the determination of

sediment physical and chemical characteristics and placed in new glass bottles

with Teflon lined lids. The mixed sediment should be stored at 4 EC until

needed. Half the mixed sediment is left saturated and anaerobic for use wetland

tests. For terrestrial tests, the other half of the mixed sediment should be placed

in an aluminum drying pan of appropriate size to allow for no greater than a 1-in.

depth of sediment in the bottom of the pan. The sediment is turned twice daily

with a polyethylene shovel to facilitate drying and any debris is removed. After

the material is air-dried to less than 5 percent moisture on a dry weight basis, or

at least 3 weeks, it is ground to pass a 2-mm screen and then remixed. The

mixed material is then ready for use in the terrestrial testing portions in the

following sections.

Saltwater. Saltwater sediment is prepared as above and in addition requires

the leaching of salts from the sediment to support terrestrial plants on the air-

dried sediment. One part air-dried sediment (5 kg ODW) and three parts of

reverse osmosis (RO) purified water (15 kg) (weight to weight basis) are placed

in 19.0-L buckets. Ten buckets are needed for each sediment. The sediment/

water in each bucket is then mixed for 5 min every hour for 5 hr using an electric

mixer. The suspension is allowed to settle until all visible suspended particles

have settled out and then the water is carefully siphoned off. A sample of the

water is collected from each bucket and a composite of all 10 buckets is

collected for pH and electrical conductivity determinations. The sediment from

each bucket is placed back into the drying flats and the drying, grinding, and

washing process is repeated until the sediment had been washed three times, and

dried and ground four times or until salinity of the sediment is 10 parts per

thousand or below.

Reference soil. A reference soil or sediment should be provided for a

comparison in the terrestrial and wetland tests, respectively. The reference soil

or sediment should be prepared as described above for the terrestrial or wetland

dredged material.

H.3.4 Sediment characterization

Electrical conductivity and salinity. Electrical conductivity is determined

on saturated extracts of each air-dried (AD) and air-dried + washed (ADW)

sediment using the method of Rhoades (1982). The extracts are measured on a

conductance meter to determine electrical conductivity (EC) in mmhos/cm.

Salinity is also measured on the extracts using a hand refractometer. EC and

salinity are also determined on original wet test sediment, reference sediment,

and wash water samples.

Appendix H Plant Bioaccumulation Procedures