HR: 15:10h
AN: H33H-07    [Abstracts]
TI: Fate of Arsenic at a Landfill Plume Discharge Point Into Surface Water, Central Massachusetts
AU: * Brandon, W C
EM: Brandon.Bill@epa.gov
AF: USEPA, Region 1 1 Congress Street, Boston, MA 02114 United States
AU: Hon, R
EM: hon@bc.edu
AF: Boston College, Dept. of Geology & Geophysics 140 Commonwealth Ave, Chestnut Hill, MA 02467 United States
AB: Fate of dissolved arsenic in ground water at the point of discharge into surface water raises a concern about the public health and the environment due to a potential of arsenic accumulation in the bottom sediments. Dissolved arsenic may become sorbed on amorphous precipitates of ferric hydroxides formed by a changing redox potential during the discharge and then locally deposited. Many landfill plumes and natural reducing ground waters in Central Massachusetts have dissolved arsenic well above the EPA 10 $\mu$g/L MCL level that could cause a local arsenic accumulation. The area of this study stretches along several man-made ponds in North Central Massachusetts located down gradient from (1) a landfill plume in which dissolved arsenic ranges between 50 and 700 $\mu$g/L occasionally up to 5,000 $\mu$g/L; (2) reduced natural ground water where dissolved arsenic can be as high as 200 $\mu$g/L; and (3) oxygenated natural ground water with dissolved arsenic levels below 10 $\mu$g/L. Bottom sediments were collected at 34 separate sites and additional samples were obtained from two to three foot cores at a subset of 9 sites. All samples were analyzed for extractable As, Fe, Ni, and other metals. Samples of bottom sediments near a discharge of the landfill plume form a layer highly enriched in Fe and As. Iron approaches the composition of 100% ferric hydroxides (390,000 and 420,000 mg/kg of Fe respectively). Corresponding arsenic values are 6,800 and 3,900 mg/kg which are nearly 100x the typical background values of arsenic in soils in this area. Arsenic concentrations in other sediments of the landfill plume area have a range from 220 to 2,000 mg/kg. Depth gradients from core sections indicate a decreasing As and Fe trend, yet significantly elevated arsenic levels are still detected at 2 ft depth (30 to 1,200 mg/kg of As). Sediments from the area where a reducing natural water mixes with the surface water have arsenic values that are 3 to 5 times the background soils (As range in the sediments: 66 to 140 mg/kg); no arsenic was detected at 2 ft depth (typical detection limit between 10 and 20 mg/kg). Sediments from the discharge area of oxygenated ground water have arsenic values indistinguishable from the background soils.
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
DE: 1030 Geochemical cycles (0330)
DE: 1065 Trace elements (3670)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting