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Journal of Environmental Quality Abstract -

Nitrogen Leaching from Unlined Cull-Onion Landfills


This article in JEQ

  1. Vol. 27 No. 5, p. 1254-1260
    Received: Sept 16, 1997

    * Corresponding author(s): jhammel@uidaho.edu
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  1. J. J. Hutchings,
  2. J. E. Hammel * and
  3. J. L. Osiensky
  1. Dep. of Geology, Univ. of Idaho, Moscow, ID, 83844.



Disposal of cull onions (Allium cepa L.) in unlined landfills in the Treasure Valley region of eastern Oregon and southwestern Idaho is a historic management practice that has been identified as potentially causing NO3-N contamination of regional groundwater. To investigate NO3-N generation and transport during a 6-yr period, monitoring wells were placed in the cull onion waste inside two landfills. The soil below each landfill was instrumented with soil-solution samplers and matric-potential sensors. Four to 6 Mg of organic N were loaded into each landfill in the form of onion waste. Little leaching of NO3-N was observed during the study. With the exception of a NO3-N pulse during loading, solution NO3-N concentrations within and beneath both landfills remained <1 mg L−1. Concurrently, NH4-N increased to 500 mg L−1 at 0.5 m and to 7 mg L−1 at 3 m below the landfill bases. Build-up of NH4-N and lack of NO3-N in the landfills are hypothesized to result from nitrification inhibition in an anaerobic environment. Hydraulic heads showed that saturated waste resided over unsaturated soil. Formation of a hydraulically restrictive layer at the interface between the landfill contents and the underlying soil probably caused these conditions. Saturated cull-onion landfills do not appear to be a source of NO3-N contamination. Potential groundwater contamination from nitrification upon drying of landfill contents can be mitigated by removing and land-applying residual waste after sufficient degradation.

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