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Effects of Precipitation on Landfill Ground Water
Monitoring Data
By Arnie
Sugar
HWA GeoSciences Inc.
Presented at the 4th Symposium on the
Hydrogeology of Washington State, Tacoma, Washington, April
8-10, 2003
Abstract
Ground water monitoring data over a 12 year period was
evaluated at a landfill in Pierce County. The landfill was closed under the
Minimum Functional Standards for Solid Waste Handling (Chapter 173-304 WAC)
in 1991. Closure included a 60 mil membrane, drainage layers, topsoil, surface
water control, and passive gas venting. Ground water quality samples were
collected from four years before closure to eight years after closure, and were
analyzed for volatile organic compounds, four metals (arsenic, manganese, iron,
and zinc) chloride, sulfate, total organic carbon, total coliform bacteria, pH,
and specific conductivity.
Post-closure ground
water monitoring data indicated a general decrease in concentrations of most
indicator parameters after closure, then a marked increase four to five years
after closure. Long term (1-5 years) trends in analyte concentrations correlated
to precipitation trends, with soluble and mobile parameter concentrations
exhibiting the greatest apparent sensitivity to precipitation. This data
suggests that long term precipitation trends may strongly influence ground water
monitoring results, and therefore must be considered during performance and
regulatory compliance evaluation.
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