OCCURRENCE, DISTRIBUTION, AND EVALUATION OF REGIONAL SOURCES OF PERCHLORATE IN THE LOWER UMATILLA BASIN OREGON GROUNDWATER MANAGEMENT AREA

2005 Salt Lake City Annual Meeting (October 16–19, 2005)
Paper No. 141-13

Presentation Time: 11:35 AM-11:50 AM

OCCURRENCE, DISTRIBUTION, AND EVALUATION OF REGIONAL SOURCES OF PERCHLORATE IN THE LOWER UMATILLA BASIN OREGON GROUNDWATER MANAGEMENT AREA
RICHERSON, P.¹, CRAIG, H.², DADOLY, J.¹, ANDERSON, D.¹, MONROE, S.¹, MARCY, K.², KELLY, C.², BLACK, C.², and PARKER, K.², (1) Oregon Department of Environmental Quality, Eastern Region, 700 SE Emingrant, Suite 330, Pendleton, OR 97801, richerson.phil@deq.state.or.us, (2) U.S. Environmental Protection Agency, Region 10, 1200 Sixth Avenue, Seattle, WA 98101, craig.harry@epa.gov The Lower Umatilla Basin (LUB) Groundwater Management Area (GWMA) is a 550 square mile area of eastern Oregon that is currently under investigation for the occurrence and distribution of perchlorate on a regional scale. The LUB GWMA, primarily a semi-arid climate agricultural area, has been previously managed for regional elevated nitrate levels in groundwater related to commercial irrigation, farming, and food processing industries. Perchlorate was originally detected in regional groundwater resources in 2003 as part of the concurrent groundwater nitrate investigations. A number of well types were tested including monitoring, domestic, irrigation, industrial, community, and stock watering wells, with perchlorate concentrations ranging from 1 ug/l to 24.8 ug/l in groundwater. The frequency of occurrence based on major well types for monitoring, domestic, and irrigation wells were 59%, 46%, and 75%, respectively from a total of 135 wells tested. A number different land uses within the LUB GWMA may potentially contribute to perchlorate occurrence, including two Department of Defense munitions sites, a formerly used defense site (FUDS), a commercial aerospace rocket motor engine test facility, and agricultural application of Chilean nitrate fertilizers. Collectively, however, these potential sources do not account for the complete range of occurrence of perchlorate in the LUB GWMA, and a naturally occurring component may exist. The current hypothesized Conceptual Site Model (CSM) for regional groundwater perchlorate occurrence is facilitated transport of irrigation recharge in areas that may exhibit salt build-up due to evapotransporation in excess of precipitation. This is supported by a general correlation of total dissolved ions concentrations to perchlorate concentrations in groundwater. Due to the use of groundwater resources for crop irrigation, stock watering for dairy cattle, and food processing industries, further investigations of other exposure pathways are also planned.
2005 Salt Lake City Annual Meeting (October 16–19, 2005) General Information for this Meeting

Session No. 141 Naturally Occurring Perchlorate (and Other Oxyanions) in the Hydrologic Cycle—Origins, Accumulation, Transformations, and Transport Salt Palace Convention Center: 251 C 8:00 AM-12:00 PM, Tuesday, 18 October 2005 Geological Society of America Abstracts with Programs, Vol. 37, No. 7, p. 322
© Copyright 2005 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.