Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

Issue link:

Contents of this Issue


Page 30 of 100

treatment plant began treating water from the Flint River on a full-time basis and dis- tributing the treated water to residents and other customers. When the plant went into full-time operation, the Michigan Depart- ment of Environmental Quality (MDEQ) did not implement corrosion control, as mandated by the LCR. Instead, the Flint water treatment plant was allowed to com- plete two six-month monitoring periods without corrosion control and then the MDEQ would decide if corrosion control treatment was necessary. Not too long after the city began dis- tributing treated river water from its own water treatment plant, problems were noted concerning the water's odor, taste, and appearance. According to the Virginia Tech researchers, discolored water can be caused by metallic rust that is released into the water from unlined cast iron pipes or iron service lines that have corrosion occurring along their lengths. Additionally, microorganisms may be living in the cor- roded pipes, such as sulfate-reducing bac- teria (SRB) that produce hydrogen sulfide (H 2 S) and its characteristic rotten-egg smell, which contribute to the acidity of the water and increase its corrosivity. 2 To prevent the growth of microorgan- isms, chlorine is added to the water as a disinfectant, and maintaining a residual amount of chlorine in the water protects public health against the presence of opportunistic pathogens (OPs)—microbes capable of causing disease when a host has lowered resistance. Since chlorine is con- sumed by iron corrosion, chlorine added to the water going through corroding pipes will quickly disappear, making it even more likely that harmful bacteria are growing in the water pipes. When the first round of Flint's water quality monitoring ended in December 2014, the Flint water treatment plant's ex- emption from corrosion control treatment was rescinded due to the high lead levels found in tap water, and it was required to implement corrosion control treatment. Several months later, in February 2015, the EPA was contacted by a Flint resident about the high levels of lead found in the home's drinking water (the EPA lead action level is 15 ppb and the home's water tested at 104 ppb in February and 397 ppb when tested again the next month). The Flint water treatment plant had not implemented the (40.1%) had first draw lead levels >5 ppb and 42 samples (16.7%) exceeded the 15 ppb lead action level. According to the researchers, Flint's 90th percentile lead value was 25 ppb in their survey. Several samples exceeded 100 ppb, and one sample collected after 45 seconds of water flushing exceeded 1,000 ppb. 3 The chemistry of Flint River water was known to be highly corrosive to lead plumb- ing as well as iron pipe due to its high chlo- ride content, which was about eight times higher than the chloride content in the DWSD water. During their visit in Flint, the researchers tested copper pipe pieces joined with lead solder that was 50% lead by weight to test the relative corrosivity of Flint's treated river water vs. the DWSD water. (Although lead solder was banned in 1986 for use in drinking water systems, almost all the homes in Flint were built before then and plumbing pipes contained lead solder.) For the test, they put the a cop- per piece with lead solder in a container filled with either DWSD water, Flint city- treated water, or Flint city-treated water with orthophosphate added to determine whether the corrosion inhibitor would stop lead corrosion. During the experiment, the Flint city- treated waters (with and without ortho- phosphate) started turning white due to rapid corrosion of the lead, while the DWSD water remained clear. The researchers then took water from each container after one, two, and three weeks and measured the lead levels in the water. After three weeks, the test results showed lead levels in Flint city- treated water without the corrosion inhibi- tor were slightly above hazardous waste levels (5,000 ppb), and 19 times higher than the lead levels detected in the DWSD water. The lead levels in the Flint city-treated water with a corrosion inhibitor eventually dropped to low levels. The researchers con- cluded that the corrosivity of the Flint city- treated water caused more lead from plumbing to leach into the water compared to the DWSD water, and that the water cor- rosivity of Flint River would have been coun- tered by the addition of orthophosphate. Edwards notes that iron corrosion is also a major concern and could poten- tially be the most expensive problem fac- ing Flint and other water utilities. The researchers decided to establish the rate of iron corrosion when exposed to the Samples of lead solder connected to copper pipe in Flint River water with orthophosphate (left) and Detroit water (right). The white suspended particles visible in the Flint River water are tiny lead particles. Photo credit: required optimized corrosion control treatment. Virginia Tech Researchers Study the Water In August 2015, the Virginia Tech researchers, led by Marc Edwards, the Charles Lunsford Professor in the univers- ity's Department of Civil and Environmen- tal Engineering, traveled to Flint to sample and test the water and evaluate the water quality. They sampled water at sites used by the city for its water distribution system monitoring, and analyzed the samples for OPs, water temperature, dissolved oxygen, and chlorine residual. The researchers also sampled tap water at four businesses that were still using water from the DWSD, four homes that used the city's treated water from the Flint River, and two homes where residents had reported health issues. Chlo- rine levels were also monitored at one site that used the DWSD water and another site that used the city's treated water. Testing results did not indicate the presence of OPs in the Flint city-treated water ; however, chlorine residuals were low throughout the system. At their Virginia Tech lab, the team con- ducted lead testing on 252 water samples provided by Flint residents. Out of 252 water samples taken from Flint homes, 101 28 JUNE 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 6 FEATURE ARTICLE

Articles in this issue

Links on this page

Archives of this issue

view archives of Materials Performance - JUN 2016