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CASE STUDY: SITE CONCEPTUAL MODEL FOR ENHANCED MNA OF ARSENIC
Citation:
FORD, R. G. CASE STUDY: SITE CONCEPTUAL MODEL FOR ENHANCED MNA OF ARSENIC. Presented at EPA Regional Site Managers Meeting on DOE Issues, Richland, WA, October 25, 2005.
Impact/Purpose:
To inform the public.
Description:
Field investigations have been conducted to understand the fate of arsenic in contaminated ground water during discharge into the Halls Brook Holding Area (HBHA) Pond at the Industri-Plex Superfund Site in Massachusetts. The ground water plume contains elevated levels of arsenic and hydrocarbon contaminants, along with ferrous iron and sulfate, that are derived from historical disposal of process wastes from upgradient industrial activities. The chemical speciation of arsenic and iron in ground/surface water, suspended solids, and sediments has been assessed using macroscopic and spectroscopic techniques in order to determine the fate of arsenic derived from ground-water discharge. Patterns in the chemistry of redox-sensitive elements point to both the direct and indirect influence of microbial processes on arsenic speciation and transport. Iron (hydr)oxides and iron sulfides are produced in oxic and suboxic/anoxic zones, respectively, within the HBHA Pond. The precipitation-dissolution of these precipitates exert a dominant control on the fate of arsenic discharged from ground water. Dramatic changes in chemical speciation were observed over spatial distances of meters or less and highlight the need to tailor monitoring efforts in order to address site-specific characteristics. Data collected from this study supported the use of the natural processes occurring within the HBHA Pond as a partial remedy for control of the ground-water plume. Proposed enhancements to the HBHA Pond include the installation of flow control structures to mitigate impacts from storm flows along with air-sparging within a portion of the HBHA Pond to enhance iron and arsenic oxidation-precipitation prior to discharge of surface water into a wetland. Notice: This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.