AWWA ACE91045

Severn Trent Water is one of the largest of the UK supply utilities; about 1.2m customers are still supplied by lead service lines. However, research and action has kept lead levels at the tap relatively low compared to water quality standards in force a few years ago. New regulations prompted a major revaluation of the lead reduction program. Based on experience, the water system evolved a systematic approach to the problem. The approach is based initially on a comprehensive survey and collation of all information connected with lead risks on a zonal basis. In this paper, the author describes the various types of lead that may be found in distribution systems: colloidal lead, particulate, plumbosolvency, flaking, and electrochemical lead. The author then describes the Severn Trent's sampling program. Confirmation of the causes of lead in water may be determined through sequential size fractionation studies, macro examination of the internal pipe surface, electron microscopic/X ray diffraction examination, and infra-red studies of pipe surface deposits. Understanding of the potential causative factors for high lead, in conjunction with water chemistry and operational data, often rapidly indicate the optimum solutions to reduce lead levels at the tap. The author discusses treatments and tests that may be used for each source of lead (colloidal, flaking, etc.).