Permeation and Leaching
The distribution system infrastructure and piping, lining, fixtures, and solder can react with the water being distributed and the external environment. These interactions may create problems of water quality. Permeation is the movement of contaminants external to the pipe, especially contaminated soil, through the porous non-metallic joints of the pipe into the water. Leaching is the dissolving of metals, solids, and chemicals from the pipes into the drinking water.
Stagnation of water in the pipes intensifies permeation and leaching. Most permeation problems occur at the service connections because of the small diameter of the pipes and frequent stagnation there.
New or Repaired Water Mains (See endnote 33)
The construction and repair of water mains can create potential situations which will contribute to the contamination of the water by microorganisms, which cause disease. Other problems are turbidity and unusual colors, chemical contamination from the surrounding area, excess chlorine use, loss of residual of disinfectants, and pH instability. These problems can be the precursor to disease from microorganisms and chemicals as well as the beginning of problems in the pipes which will lead to leaching and poor water quality. The type and amount of contaminant entering the system plus its distribution will influence the potential for small or large outbreaks of disease or other health conditions, short-term or long-term. The disinfectant needed to be used after repair or construction may contribute to above-normal levels of disinfectant byproducts which may also be harmful to people.
The three times when contamination may occur for water main construction or repair activities are prior to the construction or repair; during construction or repair because of microbial and/or chemical contamination; and contamination after construction or repair from leaking pipe joints, stagnant water in the adjacent piping sections, cross-connections, or variations in pressure of the water. Prior to construction, the pipes may be exposed to soils, sediments, trash, stormwater runoff, harmful chemicals and chemically contaminated soil, and waste from animals and humans. This can create biological and/or chemical problems. During construction or repair which is usually done in open trenches or excavations, the interiors of the pipes and the fittings may come into contact with soil and water in the trench and the soil and water may be contaminated with microorganisms and/or chemicals. This is a substantial concern for contamination of the pipes and fittings. Crossconnections may also occur because of the construction. (See discussion on cross-connections below for more in-depth information.) Contamination of the pipes may occur from leaching during the in-place process which may be utilized for putting coatings inside the pipes and curing in place. Also, bacterial growth resulting in nitrification in reservoirs may occur during each of these phases because of the slowing down of processed water entering the distribution system.