Roger W. Lee

Effects of carbon dioxide variations in the unsaturated zone on water chemistry in a glacial-outwash aquifer

Abstract The research site at Otis Air Base, Cape Cod, Massachusetts, has been developed for hydrogeological and geochemical studies of sewage-effluent contaminated ground water since 1982. Research of hydrologic properties, transport, and chemical and biological processes is ongoing, but the origin of background water chemistry has not been determined. The principal geochemical process giving rise to the observed background water chemistry is CO 2 -controlled hydrolysis of Na feldspar. Geochemical modeling demonstrated that CO 2 sources could vary over the project area. Analyses of unsaturated zone gases showed variations in CO 2 which were dependent on land use and vegetative cover in the area of groundwater recharge. Measurements of CO 2 in unsaturated-zone gases showed that concentrations of total inorganic C in recharge water should range from about 0.035 to 1.0 mmoles/L in the vicinity of Otis Air Base. Flux of CO 2 from the unsaturated zone varied for 4 principal land uses, ranging from 86 gC/m 2 /yr for low vegetated areas to 1630 gC/m 2 /yr for a golf course. Carbon dioxide flux from woodlands was 220 gC/m 2 /yr, lower than reported fluxes of 500 to 600 gC/m 2 /yr for woodlands in a similar climate. Carbon dioxide flux from grassy areas was 540 gC/m 2 /yr, higher than reported fluxes of 230 to 490 gC/m 2 /yr for grasslands in a similar climate.

Phreatophyte influence on reductive dechlorination in a shallow aquifer contaminated with trichloroethene (TCE)

Abstract Phytoremediation uses the natural ability of plants to degrade contaminants in groundwater. A field demonstration designed to remediate aerobic shallow ground‐water contaminated with trichloroethene began in April 1996 with the planting of cottonwood trees, a short‐rotation woody crop, over an approximately 0.2‐ha area at the Naval Air Station, Fort Worth, Texas. The project was developed to demonstrate capture of contaminated groundwater and degradation of contaminants by phreatophytes. Analyses from samples of groundwater collected from July 1997 to June 1998 indicate that tree roots have the potential to create anaerobic conditions in the groundwater that will facilitate degradation of trichloroethene by microbially mediated reductive dechlorination. Organic matter from root exudates and decay of tree roots probably stimulate microbial activity, consuming dissolved oxygen. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about 20 years of age and 60 meters southwest of the cottonwood plantings) where degradation products of trichloroethene were measured. Oxidation