In response to recent reports of unpalatable water regarding both taste and odor, the Montpelier water treatment facility staff has conducted various investigations for verification purposes and to ascertain the cause. Our findings indicate that the Montpelier water system poses no health or safety issue and meets or exceeds all potable water quality standards.
To assist with this effort, Ray Solomon, Environmental Scientist, Drinking Water and Groundwater Protection Division, VT Dept. of Environmental Conservation was consulted and provided guidance on possible causes and what tests should be conducted. Mr. Solomon stated that taste and odor in drinking water is not well understood and “finding out the cause may be very difficult “. The sensory ability to detect taste and odor varies widely among individuals.
Typically, the cause of detectable odor and taste issues is found in the water source. Routine flushing of the filters at the water treatment facility can release biological growth resulting in the formation of compounds that produce earthly and musty smells at very low levels. Therefore, determination of the cause began at the treatment facility. The source water (untreated raw water) was sampled and tested with nothing unusual discovered. Next, flushing was performed with no detectable odors produced. The finished water reservoir was also tested and no undesirable taste or odor was detected by several people.
Testing for iron levels was conducted and while some was detected it was not considered to be a high level. Results indicate that the levels are far less than considered to be a water quality problem. The fact that some iron is present within the system could explain the odor and subtle bitter and metallic taste some people have experienced. Testing for a variety of other compounds within the raw water source was also conducted revealing no unusual levels that might be contributing to taste or odor issues.
The team also visited seven locations at representative locations around town where palatability concerns were raised. Interviews were conducted and samples collected at each site which were tested for chlorine residual and the presence of iron. Some sites did have detectable levels of earthly or musty smelling water but taste issues were not fully verified.
The test results at both the plant and sample sites were inconclusive revealing no certain cause for the less than palatable odor and taste. Therefore, some theories were considered and a course of action was discussed for implementation. We found nothing that points to the raw water as the cause, but we also can’t completely rule it out. We also don’t believe it’s a treatment process issue. At this time we believe a possible cause to be the city’s very old water distribution system much of which consists of cast iron pipes. Mapping of all of the known locations where complaints have been voiced was performed but no pattern was found although reports are widespread.
The treatment plant has utilized the same process since it first went on line which can therefore be ruled out as a cause. However, there have been more frequent back flushing of the filters related to the presence of occasional high organic loads originating from the source but there is no known correlation between this maintenance activity and the odors and taste issues being experienced.
Chlorine, used as a disinfectant, is known to react with natural biological compounds in the source and may be reacting with the old cast iron water mains to produce a metallic like taste and odor. Biological growth can accumulate inside old water mains over time. Mr Solomon indicated that our chlorination level is normal but chlorine residuals in the distribution system were found to be at “robust” levels meaning there is little loss or degradation occurring. It was also noted that the amount of powder activated carbon being used in the treatment process for odor and smell control is considered to be on the low side of the scale for our system.
Again, we want to emphasize that the Montpelier water system poses no health or safety issue and meets or exceeds all potable water quality standards. Moving forward, we decided to try a couple of measures to address the concerns people have raised. The chlorine will be reduced by about 10% which will lower the residual in the distribution system and old cast iron pipes. Second, the amount of powder activated carbon will be increased to help further address the odor and musty taste from the organic load in the water source. Last, consideration is being given to another round of system flushing which is normally done once per year.
We’d like to take this opportunity to express our appreciation to folks who graciously let us into their homes to collect water samples and who were willing to answer questions and offer ideas. We also sincerely appreciate the posted comments on Front Porch Forum which guided our tactical approach to this issue. As a community water system, customer input and collaboration help us meet our objective of delivering the best possible water quality.
Tom McArdle, Director of Public Works, (802) 223-9508