The substances in drinking water that the Portland Water Bureau tests for fall into two categories: regulated and unregulated. Regulated contaminants have national health-based or aesthetic-based regulations that are set by the Environmental Protection Agency (EPA). Unregulated substances do not have drinking water regulations, but the EPA may consider regulating them in the future.
One of the key pieces of information the EPA uses to determine if substances should be regulated is the occurrence of the substance in drinking water. Under the Unregulated Contaminant Rule (UCMR), every five years the EPA releases a new list of substances that public drinking water systems will test for. The Portland Water Bureau and 6,000 water utilities across the country participate in a year-long testing program to collect data about the occurrence of these substances in water supplies. The results of the testing along with the potential health risks of the listed substances are evaluated by the EPA to determine if rules to regulate the substances are needed.
The Portland Water Bureau has participated in all three rounds of UCMR monitoring: the first in 2001-2003; the second in 2008-2010; and the third in 2013-2015. All data collected from the testing is reported to the EPA and is available online. The Portland Water Bureau also provides results to customers in the Annual Drinking Water Quality Report when these substances are detected.
How does this affect Portland Water Bureau customers?
The presence of a substance in drinking water does not necessarily indicate a health risk. Detection methods are becoming more sensitive, leading to more detections of substance at lower levels. The concentration of a substance is a far more important factor in determining whether a health concern exists. The substances detected by the Portland Water Bureau are also being detected by other utilities as part of their UCMR monitoring.
The Portland Water Bureau will closely monitor both the concentrations of these substances and their potential impact on customers based on EPA’s health studies. Should the EPA ultimately determine that regulation is warranted, the Portland Water Bureau will take the necessary steps to protect the health of its customers.
UCMR1 Results: No substances detected in Portland’s drinking water.
UCMR2 Results: No substances detected in Portland’s drinking water.
Treated Drinking Water from Bull Run Watershed and Columbia South Shore Well Field Entry Points to the Distribution System
|Chlorate||<0.020 parts per million||0.60 parts per million||3.0 parts per million||Byproduct of drinking water disinfection|
|Chromium (total)||<0.2 parts per billion||<0.2 parts per billion||0.2 parts per billion||Found in natural deposits|
|Chromium-6||<0.03 parts per billion||0.031 parts per billion||0.048 parts per billion||Found in natural deposits|
|Strontium||0.010 parts per million||0.026 parts per million||0.074 parts per million||Found in natural deposits|
|Vanadium||0.27 parts per billion||0.84 parts per billion||2.9 parts per billion||Found in natural deposits|
Treated Drinking Water from Points throughout the Distribution System of Reservoirs, Tanks, and Mains
|Chlorate||<0.020 parts per million||<0.020 parts per million||0.029 parts per million||Byproduct of drinking water disinfection|
|Chromium (total)||<0.2 parts per billion||<0.2 parts per billion||0.24 parts per billion||Found in natural deposits|
|Chromium-6||<0.03 parts per billion||0.030 parts per billion||0.046 parts per billion||Found in natural deposits|
|Strontium||0.010 parts per billion||0.015 parts per billion||0.019 parts per million||Found in natural deposits|
|Vanadium||0.28 parts per billion||0.32 parts per billion||0.36 parts per billion||Found in natural deposits|
Chlorate, a byproduct of the drinking water disinfection process, can form when sodium hypochlorite is used as a disinfectant. The current EPA health reference concentration indicates that ongoing exposure to chlorate at levels of more than 0.21 parts per million per day may lead to negative health effects. In July 2014, the level of chlorate from the Columbia South Shore Well Field groundwater treatment plant exceeded this level. The Portland Water Bureau is investigating the cause of this unusually high level. Unlike the Bull Run treatment plant, which uses gaseous chlorine for a disinfectant, the groundwater facility uses liquid hypochlorite. As hypochlorite ages, it can contribute chlorate to drinking water. As a result of the detections at the groundwater treatment plant, the Portland Water Bureau is implementing several changes in how hypochlorite is managed to minimize the levels of chlorate in drinking water. Since only a small amount of groundwater was served for a limited time period, the presence of chlorate is unlikely to contribute to adverse health effects.
Chromium (total) and Chromium-6
Chromium is a naturally occurring element found in rocks, animals, plants, soil and in volcanic dust and gases. Chromium can exist in a variety of forms, but is typically found in the environment and drinking water in two main forms: trivalent chromium (chromium-3) and hexavalent chromium (chromium-6). Chromium can transform from one form to another in water and soil, depending on the conditions present. Chromium-3 occurs naturally in the environment and is an essential human dietary nutrient. Chromium-6 is the more toxic form and is generally associated with industrial processes. Recent studies have shown that ingestion of drinking water or food containing chromium-6 may cause cancer in laboratory mice and rats. Total chromium (combined chromium-3 and -6) is currently regulated by the EPA at a maximum contaminant level of 100 parts per billion. At the very low levels detected in Portland’s drinking water, chromium-6 is unlikely to contribute to adverse health effects.
Strontium is a naturally occurring metal and is commonly found throughout the environment including in drinking water. Consumption of small amounts of strontium is not harmful. However, high levels of strontium can occur in water drawn from aquifers that are rich in strontium minerals. The current EPA health reference concentration indicates that ongoing exposure to strontium at levels of more than 4,000 parts per billion per day may lead to negative health effects. At the very low levels detected in Portland’s drinking water, strontium is unlikely to contribute to adverse health effects.
Vanadium is a metal found in the earth’s crust which can dissolve into water that is in contact with natural deposits. The current EPA health reference concentration for vanadium indicates that ongoing exposure to vanadium at levels of more than 21 parts per billion per day may lead to negative health effects. At the levels found in Portland’s water, vanadium is unlikely to contribute to adverse health effects.