Monitoring Cyclic Fluctuations in Ground‐Water Qualitya

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Abstract
The chemical quality of water in many shallow and surficial aquifers exhibits cyclic fluctuations. These fluctuations are caused by the intermittent flushing of contaminants into the ground during recharge events. The contaminants may be natural or reflect man's activities, particularly waste disposal schemes.Over the past 12 years an oil‐field brine contaminated aquifer in central Ohio has been monitored. Data from three closely‐spaced wells tapping selected parts of the aquifer indicate that brine is flushed into the ground during recharge events and that each contaminated mass maintains much of its integrity as it sinks to the bottom of the aquifer and then migrates laterally to the adjacent river. The most concentrated mass that covers the largest area infiltrates during the spring recharge period, but less concentrated and smaller masses may occur any time rainfall is sufficient to overcome the soil‐moisture deficiency.Because of the cyclic nature of recontamination events, care and common sense must be exercised in the extrapolation of quality data, particularly in regard to estimation of contaminant flushing rates.