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ARSENIC SORUCE IDENTIFICATION AT THE GROUND WATER-SURFACE WATER INTERACTION ZONE AT A CONTAMINATED SITE
Citation:
Ford*, R G., F P. Beck*, P J. Clark*, R T. Wilkin*, C J. Paul*, AND J. LeMay. ARSENIC SORUCE IDENTIFICATION AT THE GROUND WATER-SURFACE WATER INTERACTION ZONE AT A CONTAMINATED SITE. 2003 RCRA Nat'l. Mtg, Washington, DC, 08/12-15/2003.
Description:
One of the challenges in assessing the current impact of the discharge of arsenic contaminated ground water into a surface water body is differentiating the arsenic ground-water flux versus dissolution of in-place contaminated sediments. A field investigation has been carried out to assess the source of dissolved arsenic in the surface water of a wetland down gradient from a Superfund site in Massachusetts. Water and sediment chemistry was assessed periodically for two years within a monitoring network designed to capture the dynamics of water chemistry within the ground water-surface water interaction zone. The dynamics of dissolved arsenic concentrations and aqueous geochemistry in the surface water following a storm event indicated that surface water contamination is derived both from ground-water discharge and sediment re-dissolution. The increased flow resulting from storm water runoff significantly depleted dissolved constituents within the surface water column. Parallel monitoring of ground-water discharge and surface water chemistry during recovery to pre-storm conditions confirmed that a significant amount of dissolved arsenic within the water column is derived from sediment dissolution. This observation indicates that treatment of the ground-water plume will not completely eliminate arsenic contamination within the down gradient wetland. These results illustrate the importance of source delineation for development of appropriate remedial strategies to achieve site cleanup. This study also highlights the importance of a comprehensive site assessment strategy for identifying all sources of risk at sites with complex hydrology.