Field evaluation of fluorescent whitening agents and sodium tripolyphosphate as indicators of septic tank contamination in domestic wells

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Abstract
Two indicators of septic tank effluent were measured in a groundwater quality survey of an unsewered, semi‐rural community. The selected indicators were fluorescent whitening agents and sodium tripolyphosphate (STP). Other water quality determinands indicated that the groundwater was of good chemical quality for drinking purposes but, in about half of the wells, levels of total coliform bacteria exceeded New Zealand Board of Health recommended guidelines for drinking water. Fluorescent whitening agents and/or STP were detected in 17% of the samples and concentrations of STP correlated significantly (P<0.001) with levels of faecal coliform bacteria. The study showed that the selected indicators could be detected in groundwater used for domestic purposes, and could be used for assessing whether septic tanks were implicated in contaminated domestic wells.