The majority of urban receiving
Where detailed site surveys have been undertaken, for example on the River Roding in NE London where 15 surface water outfalls over a 10 km stretch were determined to be polluted primarily as a result of surveyed misconnections, rectification work has been able to substantially remediate the receiving water quality. Average in-stream phosphate levels have been reduced from 1.28 mg/l to below 0.4 mg/l, with improvement of the ecological categorisation of the watercourse from grade C (poor status) to B (good status) over a 7 year BRL 37344 to 2012. Detailed MST backtracking tracer surveys of PSWO discharges to the receiving watercourse of a 1 km2 residential catchment containing 2068 properties in the Chingford area to the north east of Greater London, detected some 347 misconnections (17%) discharging to the River Ching recording BOD5 and E. coli levels as high as 275 mg/l and 2.42 × 104 MPN/100 ml respectively. The rectification of the identified household misconnections has upgraded the receiving water body to good status (Grade B) confirming the prejudicial impact of such illicit sources on ecological potential. A survey of the 1.5 km2 catchment of the Moston Brook, a small urbanised tributary of the River Irwell in the NE Manchester metropolitan area, similarly identified a total of 400 properties having misconnections ( Hulme and Rukin, 2013). Scaled up to the 9950 km2 catchment area of Thames Water divergent plate boundary would yield a misconnection rate some 28 times higher than the recent UKWIR (2013) national estimate of 140,000. It is only through such detailed multiple-method site investigations that the distribution and extent of pollution sources and contributions within an urban catchment can be established and rectification works appropriately prioritised.