Accumulation of Oil and Grease in Soils Irrigated with Greywater and Their Potential Role in Soil Water Repellency

The potential impact of oil and grease (O and G) to soils irrigated with greywater (GW) was investigated. O and G were found in domestic GW at concentrations ranging from less than 10 mg L super(-1) for most hold sources to around 200 mg L super(-1) for kitchen effluent. Higher concentrations and a greater depth of accumulation were observed for the more oil-rich kitchen GW-irrigated soil than bath GW-irrigated soil. Soil samples collected from GW-irrigated soil did not show a correlation between O and G concentrations and water repellency as measured by water drop penetration time (WDPT). Increase in soil water repellency could lead to water runoff and/or finger flow through the soil profile, both of which could exacerbate the migration of contaminants vertically or horizontally from the irrigated soil.