HR: 09:00h
AN: H41I-05    [Abstracts]
TI: Determining Sources and Transport of Nuclear Contamination in Hudson River Sediments with Plutonium, Neptunium, and Cesium isotope ratios
AU: * Kenna, T C
EM: tkenna@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, P.O. Box 1000, Palisades, NY 10964 United States
AU: Chillrud, S N
AF: Lamont-Doherty Earth Observatory, P.O. Box 1000, Palisades, NY 10964 United States
AU: Chaky, D A
AF: Lamont-Doherty Earth Observatory, P.O. Box 1000, Palisades, NY 10964 United States
AU: Simpson, H J
AF: Lamont-Doherty Earth Observatory, P.O. Box 1000, Palisades, NY 10964 United States
AU: McHugh, C M
AF: Lamont-Doherty Earth Observatory, P.O. Box 1000, Palisades, NY 10964 United States
AU: Shuster, E L
AF: Rensselear Polytechnic Inst., 110 8th St., Troy, NY 12180 United States
AU: Bopp, R F
AF: Rensselear Polytechnic Inst., 110 8th St., Troy, NY 12180 United States
AB: Different sources of radioactive contamination contain characteristic and identifiable isotopic signatures, which can be used to study sediment transport. We focus on Pu-239, Pu-240, Np-237 and Cs-137, which are strongly bound to fine grained sediments. The Hudson River drainage basin has received contamination from at least three separate sources: 1) global fallout from atmospheric testing of nuclear weapons, which contributed Pu, Np and Cs; 2) contamination resulting from reactor releases at the Indian Point Nuclear Power Plant (IPNPP) located on the Hudson River Estuary $\sim$70km north of New York Harbor, where records document releases of Cs-137; 3) contamination resulting from activities at the Knolls Atomic Power Laboratory (KAPL) located on the Mohawk River, where incomplete records document releases of Cs-137 but no mention is made of Pu or Np. Here we report measurements of Pu isotopes, Np-237 and Cs-137 for a series of sediment cores collected from various locations within the drainage basin: 1) Mohawk River downstream of KAPL, 2) Hudson River upstream of its confluence with the Mohawk River, and 3) lower Hudson River at a location in close proximity to IPNPP. In addition, we present data from selected samples from two other lower Hudson River locations: One site located $\sim$30km downstream of IPNPP and another $\sim$30km upstream of IPNPP. By comparing the isotopic ratios Pu-240/Pu-239, Np-237/Pu-239, and Cs-137/Pu-239, measured in fluvial sediments to mean global fallout values, it is possible to identify and resolve different sources of non-fallout contamination. To date, isotopic data for sediments indicate non-fallout sources of Pu-239, Pu-240, and Cs-137; Np-237, however, appears to originate from global fallout only. Mohawk River sediments downstream of KAPL exhibit enrichments in Pu-239, Pu-240, and Cs-137 that are 7 to 20 times higher than levels expected from global fallout as indicated from Np-237. The elevated levels, non-fallout isotopic signatures, and core location are all consistent with KAPL being a source of Pu and Cs isotopes. Sediments from upper Hudson River and a section of the lower Hudson Estuary both contain Cs-137 levels that are more than twice that expected from global fallout. While elevated Cs-137 in selected lower Hudson samples is consistent with reported reactor releases from IPNPP, there is no known source of non-fallout Cs in the upper Hudson. We have been able to estimate end-member isotopic compositions of radionuclides originating from KAPL as well as detect its presence and estimate its contribution to contaminant inventories far downstream in tidal Hudson sediments. By comparing KAPL-derived Pu-239 inventories measured in the Mohawk and Lower Hudson Rivers, we estimate a dilution factor of $\sim$140. While there is isotopic evidence of KAPL derived radionuclides in all the lower Hudson sediments that we have analyzed, elevated levels of Cs-137 (not attributable to KAPL)were only observed in sediments collected in the vicinity of IPNPP and those collected 30km downstream of the plant's location. We attribute the elevated Cs-137 levels in these Lower Hudson sediments to contamination originating from IPNPP. The lack of elevated levels of Cs-137 in sediments collected 30km upstream of the plant's location plus a dilution factor for Upper Hudson sediments that is larger than that estimated for Mohawk River sediments alone, allows us to conclude that Cs-137 enrichment observed in the Upper Hudson is not likely to be a significant source of Cs-137 contamination to lower Hudson River sediments.
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting