Abstract

Sediment porewater, or interstitial water as used in this discussion, is defined as the water occupying the spaces between sediment particles. Interstitial water might occupy about 50% (or more) of the volume of a depositional (silt–clay) sediment. The interstitial water is in contact with sediment surfaces for relatively long periods of time and therefore might become contaminated due to partitioning of the contaminants from the surrounding sediments. In addition, interstitial waters might reflect groundwater–surface water transition zones in upwelling or downwelling areas. In these areas, their chemistry might be more reflective of ground or surface waters at the site. Therefore, flow, residence time, and other physicochemical factors (e.g., pH, temperature, redox potential, organic carbon, sulfides, carbonates, mineralogy) might have varying roles in determining whether interstitial waters are contaminated. Because many interstitial waters are relatively static in many depositional sediments, the contaminants in the interstitial water and in the solid phase are considered to be at thermodynamic equilibrium. This makes interstitial waters useful for assessing contaminant levels and associated toxicity. Interstitial water is often isolated to provide either a matrix for toxicity testing or an indication of the concentration or partitioning of contaminants within the sediment matrix (USEPA, 2001).