The effects of acid precipitation runoff episodes on reservoir and tapwater quality in an Appalachian Mountain water supply

Our plain-English summary of The effects of acid precipitation runoff episodes on reservoir and tapwater quality in an Appalachian Mountain water supply, by W.E. Sharpe, D.R. DeWalle (Environmental Health Perspectives, 1990).

The study

• Authors: W.E. Sharpe, D.R. DeWalle
• Journal: Environmental Health Perspectives
• Published: 1990;89:153-8
• Read it: PubMed · Publisher · Free full text

Abstract

The aluminum concentration and Ryznar Index increased and the pH decreased in a small Appalachian water supply reservoir following acid precipitation runoff episodes. Concomitant increases in tapwater aluminum and decreases in tapwater pH were also observed at two homes in the water distribution system. Lead concentrations in the tapwater of one home frequently exceeded recommended levels, although spatial and temporal variation in tapwater copper and lead concentrations was considerable. Since source water and reservoir water copper and lead concentrations were much lower, the increased copper and lead concentrations in tapwater were attributed to corrosion of household plumbing. Tapwater copper concentration correlated well with tapwater pH and tapwater temperature. Asbestos fibers were not detected in tapwater. The asbestos-cement pipe in the water distribution system was protected by a spontaneous metallic coating that inhibited fiber release from the pipe. Several simultaneous reactions were hypothesized to be taking place in the distribution system that involved corrosion of metallic components and coating of asbestos-cement pipe components in part with corrosion products and in part by cations of watershed origin. Greater water quality changes might be expected in areas of higher atmospheric deposition.

In plain English

This study examined a small central Pennsylvania water system serving several thousand people, fed by a forested mountain stream. The authors sampled the stream, reservoir and household taps around rain and snowmelt runoff episodes in 1983 (4 homes) and 1984 (2 homes), and on several occasions in 1985 and 1986 (6 homes). After acid runoff, reservoir pH fell and aluminum rose, and tapwater pH and aluminum changed in step. Copper and lead were higher at taps than in the reservoir, probably from household plumbing, the authors judged. Lead routinely exceeded the EPA recommended level of 20 micrograms per liter at one home. The system contained asbestos-cement (Transite) pipe. The source water's aggressiveness index averaged 7.8, below the 10.0 under which such pipe is not recommended. Even so, no asbestos fibers were positively identified in tapwater from six homes tested on two occasions. A pipe section in service about 40 years had an inner coating mainly of silica, calcium, iron and manganese, which the authors thought prevented fiber release. The authors noted that the small number of homes precluded definitive conclusions.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Field water-quality study of one water supply system, summarizing several studies. It combined repeated sampling of the source stream, reservoir and household taps with electron-microscope testing of tapwater for asbestos fibers and examination of a removed asbestos-cement pipe section.
• Who was studied: A small surface water system in central Pennsylvania serving several thousand people, supplied by Galbraith Gap Run (a 1053 ha forested watershed). Sampling covered the source stream, the reservoir and taps at 4 homes (March 3 to April 1, 1983), 2 homes (March 20 to April 12, 1984) and 6 homes (several occasions in 1985 and 1986). Sampling in 1983 and 1984 was timed around runoff events. Tapwater from six homes was tested for asbestos.
• Exposure: Acid precipitation runoff episodes (rainstorms and spring snowmelt) affecting source water chemistry, and asbestos-cement water pipe (Transite) in the distribution system. The article does not name the asbestos fiber type. Tapwater asbestos was measured by transmission electron microscopy using a modified U.S. EPA interim method.
• Main results:
  • In the reservoir, aluminum concentrations correlated positively with streamflow rates (R2 = 95%).
  • Tapwater pH tended to fall as reservoir pH fell. Reservoir total recoverable aluminum correlated with tapwater total recoverable aluminum (R2 = 98.2%).
  • Lead and especially copper were higher at household taps than in source or reservoir water. The authors judged the household plumbing to be the probable source.
  • Tapwater copper and lead concentrations were variable, with no clear-cut relationship to acid runoff.
  • At home 3, lead routinely exceeded the U.S. EPA Recommended Maximum Contaminant Level of 20 micrograms per liter.
  • Tapwater copper was predicted by reservoir pH, tapwater temperature and inside versus outside tap (R2 = 66%). Reservoir pH, tapwater pH and tapwater temperature explained at most 37% of the variation in lead, for home 3.
  • The source water's mean aggressiveness index was 7.8, never exceeding 8.2. This is below the 10.0 value under which Transite pipe is not recommended.
  • No asbestos fibers were positively identified in tapwater from six homes examined on two separate occasions.
  • A pipe section in service about 40 years had a brown inner coating containing scattered asbestos fibers and crystals. The coating's principal components were silica, calcium, iron and manganese.
• The authors' conclusion: The authors concluded that acid runoff episodes lowered pH and raised aluminum in water entering the distribution system, and that tapwater appeared to change in concert. They concluded that asbestos fibers were apparently not released from the asbestos-cement pipe despite aggressiveness index values indicating a problem. They thought a protective metallic coating, at least partly resulting from cation export during acid runoff, prevented fiber release.
• Limitations the authors state:
  • The small number of homes studied precluded definitive conclusions.
  • Inside taps showed weaker relationships with stream chemistry, possibly because their use during the study was not controlled.
  • Source water was analyzed for potassium, manganese and titanium only to a limited extent, and more extensive sampling might show different amounts.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement Pipe, Fiber Release, Cation, Deposition.

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