Hydrologic controls on distribution of chlorinated volatile organic contaminants and biogeochemical constituents in a freshwater tidal wetland

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Authors:Lorah, Michelle M.; Fleck, William B.; Olsen, Lisa D.
Author Affiliations:Primary:
U. S. Geological Survey, Baltimore, MD, United States
Volume Title:Geological Society of America, 1997 annual meeting
Source:Abstracts with Programs - Geological Society of America, 29(6), p.383-384; Geological Society of America, 1997 annual meeting, Salt Lake City, UT, Oct. 20-23, 1997. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592
Publication Date:1997
Note:In English
Summary:Tidal fluctuations and temporal changes in recharge conditions are important hydrologic controls on the distribution of VOC's and biogeochemical constituents in a sand aquifer and overlying wetland sediments in a freshwater tidal wetland at Aberdeen Proving Ground, Maryland. Hydraulic head and groundwater quality were measured in 80 piezometers that are screened in both the 9-foot-thick wetland sediments and 45-foot-thick aquifer along two transects perpendicular to a creek. The contaminants entered the aquifer upgradient of the eastern wetland boundary. Along transect A-A', groundwater flows westward and upward in the aquifer, discharging on both sides of the creek at low and high tides. The upward decreasing VOC concentrations that were detected in pore water in the creek-bottom sediments and in the surrounding wetland sediments reflects these flow conditions. Increased precipitation during 1996 caused an increased groundwater flux westward into the wetland along A-A' and a concomitant VOC-concentration increase. Analysis of head distribution, along transect C-C', indicates that cyclic reversals in groundwater flow directions with tides result in no net discharge of groundwater to the creek and cause discharge to be concentrated about 40 feet east of the creek. The distribution of the VOC's along this transect mirrors this flow regime in that the contaminant plume does not reach the creek channel and the highest VOC concentrations in pore water from the wetland sediments were detected about 40 feet east of the channel. The higher amount of discharge of oxic water from the aquifer in this area along C-C' causes iron- and sulfate-reduction to be the predominant biogeochemical reactions near the base of the upper-peat wetland-sediments unit. In contrast, methanogenesis is the predominant reaction elsewhere in the upper-peat unit along both transects. Because anaerobic biodegradation rates are faster and more complete under methanogenic conditions than under less reducing conditions, an understanding of the controls on distribution of the biogeochemical constituents is crucial.
Subjects:Anaerobic environment; Biochemistry; Biodegradation; Chlorinated hydrocarbons; Controls; Fresh-water environment; Ground water; Halogenated hydrocarbons; Hydrology; Movement; Organic compounds; Pollutants; Pollution; Rainfall; Recharge; Sediments; Thickness; Volatile organic compounds; Volatiles; Water quality; Wetlands; Aberdeen Proving Ground; Atlantic Coastal Plain; Harford County Maryland; Maryland; United States
Coordinates:N391500 N393000 W0760500 W0762500
Record ID:1998057199
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
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