There is a growing body of evidence to suggest that small domestic discharges, such as septic tanks, pose an environmental risk to freshwater habitats in certain situations; however, our ability to systematically and accurately assess this risk on a site by site basis is currently limited by a number of key knowledge gaps. These need to be addressed to enable decisions to be made on how best to protect sensitive SSSIs from phosphorus enrichment. Knowledge gaps include the need to better understand how the lifestyle of a household, and the way that they manage their septic tank affect effluent quality; the distance over which phosphorus from these systems travels through the soil, both laterally and vertically; and how local environmental conditions affect the likelihood of phosphorus from these sources reaching a nearby water body.
To help address this issue, Natural England, with a contribution from the Broads Authority, commissioned the Centre for Ecology & Hydrology (CEH) in 2013 to investigate the movement of phosphorus in septic tank effluent plumes through the aerated zone of the drainage field, ie within the soil that is above the water table.