Inorganic Contaminant Accumulation in Potable Water Distribution Systems
As part of the revision of the Total Coliform Rule, USEPA published a series of issue papers to present available information on topics relevant to possible TCR revisions. The objectives of the issue papers were to review the available data, information and research regarding the potential public health risks associated with the distribution system issues, and where relevant identify areas in which additional research may be warranted. The issue papers serve as background material for EPA, expert and stakeholder discussions. The papers only present available information and do not represent Agency policy. Some of the papers were prepared by parties outside of EPA; EPA does not endorse those papers, but is providing them for information and review.
Inorganic Contaminant Accumulation in Potable Water Distribution Systems
This paper discusses factors that may lead to contaminant accumulation and subsequent release back into drinking water, and methods for detecting and controlling contaminant release. Inorganic contaminants entering the distribution system either through the treatment process or through other mechanisms can adhere to pipe scales and accumulate within the scales or pipe and storage tank sediments. Biofilms are discussed also. Under some circumstances these inorganic contaminants may be released during times of water chemistry change (e.g. initiation of residual disinfection), or during hydraulic disturbances (e.g., pressure fluctuations). There are documented instances of inorganic contaminants being released from scales or sediments at levels above the Maximum Contaminant Level (MCL), where levels below the MCL existed at entry to the distribution system. By and large, these events likely go undetected due to a lack of sampling in the distribution system.