In Spring 2020, the City of Craig switched disinfection treatment from free chlorine to chloramines to address frequently low free chlorine residuals in their distribution system. Low disinfectant residuals increase risk of pathogen presence in tap water, which can lead to waterborne disease outbreaks. Since this treatment change could potentially affect water corrosivity, the city and the department teamed-up to conduct a proactive coupon immersion study to simulate whether the chloramines would impact lead and copper levels in the distribution system. In our January 2020 article, we discussed the corrosion immersion study setup and in our August 2020 article, we discussed the immersion study results.
Figure 1: Jars with copper with lead solder and brass coupons.
For lead, the immersion study results predicted that switching from free chlorine to introducing chloramines would not meaningfully affect the existing lead concentrations at customer’s taps. Craig’s 90th percentile average lead concentration from 2018 and 2019 was 0.0026 mg/L which is considered quite low. The lead action level is 0.015 mg/L and the maximum contaminant level goal is 0.0 mg/L. The EPA and the Centers for Disease Control and Prevention (CDC) agree that there is no known safe level of lead in a child's blood. Lead is harmful to health, especially for children, therefore it is always advisable to minimize lead concentrations in water to the extent possible.
For copper, the immersion study results indicated some copper release may be expected with the disinfectant change but that would be a nominal change in copper concentrations. The immersion tests results indicate that introducing chloramines could increase copper concentrations by approximately 17% for the copper with lead solder coupons to 36% for the brass coupons.
The city has been operating the chloramines disinfection system for over 6 months. The city executed a chloramines conversion project despite significant challenges from the pandemic and state lockdown and should be applauded for the countless hours of hard work and diligence required.
Figures 2 and 3 below are graphs of the 90th lead and copper concentrations for the past 5 years. Again, based on immersion testing predictions - we did not expect to see the values for lead go up. The lead and copper 90th percentile results before and after the chloramines switch are roughly equivalent as predicted by the immersion testing.
Figure 2: Lead 90th percentile results over the past 4 years
Figure 3: Copper 90th percentile results over the past 4 years - note - a slight increase in copper concentrations was not seen full scale, which could be due to the nature of older pipes in distribution versus new coupons in the immersion study.
During the treatment transition period, the department also worked with the City to take sequential samples from two example homes in the city’s distribution system. For sequential sampling, also called a lead profile, consecutive samples (typically 1 liter bottles) are taken from a single home. Depending on the piping configuration, up to 20 liters need to be collected in order to capture the water from the home’s plumbing and service line (pipe underground to the water main in the street). Lead profile sampling may be helpful when trying to characterize household plumbing type and potentially identify lead service lines or other lead-containing plumbing like older solder or galvanized pipes.
In this instance, the profile testing was looking for potential lead release from older homes during the disinfection transition period. Two homes were sampled before and after the transition to chloramines. The profile sampling results did not indicate any notable change and for the most part indicated a low level of lead within the selected households. Figure 4 shows the results from one home prior to the transition to chloramines. The other home had all non-detects for lead for all samples.
Figure 4: Lead sequential profile sampling results from one home prior to chloramines.
Treatment and source changes can have impacts on distribution system lead release. The Lead and Copper Rule requires that these changes be approved by the Department prior to implementation. The corrosion immersion study helped the city predict the negligible corrosion impacts their treatment change would have on the distribution system, prior to making the change. The study helped build confidence in the treatment change and no notable corrosion impacts have been observed. While the sequential sampling in this case showed no effect, sequential sampling can be helpful if corrosion concerns occurred during the transition period or if the public needed reassurances that the new water chemistry was not causing a problem with public health. These modeling and sampling tools can help public water systems successfully plan and implement source and treatment changes in the future.
The department would like to thank the City of Craig for their constant communications and proactive approach to solving these water quality issues.
➽ Tyson Ingels and Melanie Criswell
