Long-Term Effects of Graywater Irrigation on Soil Quality in Arid Regions

As communities throughout the United States and abroad are becoming interested in innovative approaches to water resource sustainability, household graywater reuse for residential landscape irrigation is gaining popularity. However, the application of graywater for irrigation may result in increased levels of emerging contaminant and pathogens, negative impacts to soil quality, or potential groundwater contamination with chemical constituents present in graywater. A study is currently being conducted at Colorado State University to examine the long-term effects of graywater irrigation. The objective of this research project is to elucidate information on the fate and occurrence of graywater chemical constituents and pathogens and their long-term potential impacts on soil quality, as a result of its application for residential landscape irrigation. Sampling locations were selected to encompass a variety of soil types and climatic conditions. Soil samples were collected at four different households where graywater has been applied for irrigation for more than five years in Arizona, California, Colorado, and Texas. Soil cores were taken at depths of 0–15, 15–30, and 30–100 cm separately in both an area irrigated with graywater as well as a control area with analogous soil and landscaping that irrigated with fresh water in each site for quantification of soil physical and chemical properties, antimicrobials, surfactants, and pathogen indicator organisms. Soil samples were analyzed for pH, electrical conductivity, organic matter, total C, total N, extractable NH₄-N, NO₃-N, P, effectivecation exchange capacity, sodium adsorption ratio (SAR), surfactants, and antimicrobials. Widely used surfactants including linear alkyl benzene sulphonates, alcohol ethoxylates, and alcohol ether sulphates and two common antimicrobials in personal care products, triclosan and triclocarban have been quantified by liquid chromatography-mass spectrometery in soil samples. Soil samples also were analyzed for indictor organisms including total coliforms, E. coli, Enterococci, Clostridium perfringens. Results from this study will provide guidance to decision makers, water agencies, regulators, product manufactures and consumers so that safe graywater irrigation systems can be installed and operated for household landscape irrigation.