Sources of Information

The workgroup concluded that there are four categories of human receptors

who should be considered in the exposure assessment: (a) people drinking

groundwater; (b) subsistence populations; (c) recreational fishers; and

(d) consumers of commercial catches in the area of a dredged material

management site. Perhaps the single most important data need for calculating risk

to these potential receptors is a reliable fish ingestion rate based on local/regional

dietary habits.

Physical and chemical information needs. The exposure assessment will also

require information concerning the chemical and physical characteristics of the

dredged material, much if not all of which is available in conducting Tiers I and II

of the sediment evaluation procedures. The specific data needs include: sediment

type, geochemical properties, total organic carbon, grain size, density, porosity,

water content, and metal speciation. The group does not recommend the use of

Acid Volatile Sulfide/Simultaneously Extracted Metals (AVS/SEM), given the

uncertainties associated with extrapolating from measurements made on an in-

place sediment which will be dredged and placed in another location.

Terrestrial sites may require information on wind direction and transport,

groundwater table fluctuations, groundwater flow, and soil properties

(geochemistry, porosity, total organic carbon).

Hydrodynamic information needs. The exposure assessment must have

information on the hydrodynamic characteristics of aquatic dredged material

management sites. These include: current velocity, current depth profiles, net and

gross deposition, the occurrence of resuspension, wave exposure, wind fetch,

duration and direction, seasonal salinity and temperature profiles, occurrence of

hypoxia, and suspended solids. Freshwater river systems will require information

on high- and low-flow conditions, the occurrence of a spring freshet, and water

levels. Marine systems will require a knowledge of local tidal ranges and currents.

Sources of Information

The workgroup expressed concern that the user community understand that the

broad range of data needs does not suggest conducting a large-scale field data

collection effort. There are often data sources readily available to provide most of

the needed information in the exposure assessment. These data sources include the

information gathered during the Site Designation, subsequent monitoring

programs, and other databases. The Site Designation Process often requires the

development of an Environmental Impact Statement which is a ready source of

biological and physical characterizations of the dredged material management site.

Obviously, this information may be dated for some, if not most, sites.

Most monitoring programs include only elevation and navigational hazard

monitoring. Two exceptions are the Disposal Area Monitoring System (DAMOS)

in New England which employs a tiered approach in which successive tiers use

Chapter 2 Exposure Assessment Workgroup Summary