Indicators of Chemical Pollution from Septic Systems

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Abstract
The median‐polish statistical method was used to test and quantify chloride (Cl‐), electrical conductivity (EC), pH, and fluorescence of laundry detergent optical brighteners as indicators of ground‐water pollution from septic systems. The septic systems were located in coarse‐textured soils over a high water table close to discharge areas in south‐central Wisconsin. Parameters were measured monthly for two years in septic tank effluent samples and in water samples collected downgradient from 17 septic systems and from upgradient background samples. The median‐polish technique was excellent for comparing hydrochemical data: Cl‐was a conservative tracer and the most suitable indicator of contaminant plumes; EC was semiconservative and EC and pH were only acceptable; and fluorescence was unacceptable. Fluorescence as an optical brightener in septic tank effluents ranged between 0.14 and 0.98 mg/1 with an average value of 0.40 ± 0.16 mg/l. In ground water downgradient from the septic systems, fluorescence levels were within the background levels. Natural substances such as humic and fulvic acids were probably the sources of fluorescence in ground water, not optical brighteners, because optical brighteners did not pass through septic systems drainfields. Fluorescence of naturally occurring compounds in ground water was between >0.01 and 260 μ/1 with a mean of ≤51± 14 μ/1 expressed as optical brightener. Nitrification in the soil below the drainfields caused ground‐water pH values to decrease within a few meters of the drainfields.