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EPA recommendations for enhanced monitoring for Hexavalent Chromium in Drinking Water

Recent news articles are generating concern over the possible presence of hexavalent chromium in drinking water. EPA has provided the following guidance to water systems on how they may monitor for chromium-6 in addition to the monitoring they are required to perform for total chromium. The national primary drinking water regulations established in 1991 set the maximum contaminant level (MCL) of 0.1 mg/L for total chromium, which includes hexavalent chromium. California is considering a level of 0.06 ug/L for hexavalent chromium in drinking water. This level is over 1000 time lower than the current drinking water standard for total chromium.

In September, 2010, EPA released a draft of the scientific assessment (Toxicological Review of Hexavalent Chromium) for public comment and external peer review. When this human health assessment is finalized in 2011, EPA will carefully review the conclusions and determine if a new standard needs to be set.

* EPA Press Release

Should my water system conduct enhanced monitoring for Chromium-6?
Given the emerging public health information, EPA is providing this guidance to all public water systems to show how a system could enhance chromium monitoring through additional sampling and analysis specifically for chromium-6. The Agency strongly encourages water systems to consider the following recommendations and to determine how your system might enhance drinking water monitoring for chromium-6.

Where should water systems collect samples?
Chromium is complex in its behavior in drinking water systems as it may occur in water systems in both the chromium-3 (trivalent chromium) and chromium-6 forms. Under distribution system conditions, e.g., in the presence of an oxidant such as chlorine, chromium-3 can be transformed into the more toxic chromium-6 form. Existing treatment processes such as conventional treatment may be effective in removing chromium-3, but not chromium -6. To understand the fate of incoming chromium-6 in raw water supplies or transformed chromium-6 from chromium-3 following conventional treatment and disinfection, EPA recommends that systems collect samples at the locations listed below.

  1. Intake/well locations: EPA recommends that water systems collect samples of untreated water at the intake/well. Systems with multiple intakes/wells should identify sampling points that result in a representative sample of the utilized source waters to account for the multiple sources, seasonal variation in sources and historical measured total chromium concentrations at entry points to the distribution system. Chromium data at entry points can serve as a guide for identifying the corresponding source water intakes/wells, which should preferably be targeted for monitoring.
  2. Entry points to the distribution system: EPA recommends that systems with drinking water treatment processes also collect samples at the point that treated water enters the distribution system. Systems with multiple entry points should collect samples from representative entry points to the distribution system.
  3. Distribution System: EPA recommends that systems collect representative samples from locations within the distribution systems. Since chromium-3 can transform into chromium-6 in the distribution system due to the presence of an oxidant such as chlorine, it is desirable that systems monitor for chromium-6 at locations considered to represent the maximum residence time, which is consistent with the monitoring goals for disinfection byproducts. The number of locations to consider for sampling within the distribution system will depend on the number of entry points, the relational proximity of entry points and the overall size of the distribution system. EPA also recommends that systems collect samples at a subset of 10 or fewer distribution system locations where they currently sample under the Disinfection By-products Rule (DBP) Stage 1 and 2, and that systems not disinfecting consider collecting samples from a subset of 10 or fewer locations where they typically sample under the Total Coliform Rule (TCR).

How frequently should samples be collected?
EPA recommends that water systems with surface water sources collect samples quarterly to capture the variation that may occur in the levels of chromium-6 in source waters. EPA recommends that ground water systems be sampled semi-annually. EPA recommends that systems collect samples from each of the locations listed above on the same day.

How can I find a laboratory to measure chromium-6?
EPA recommends the following steps for monitoring specifically for chromium-6. Public water systems should contact a drinking water laboratory they typically use for compliance monitoring and request sample analysis using a modified version of EPA Method 218.6. These modifications allow for improved low concentration measurement and are outlined in Dionex Corp. Application Update 144 “Determination of Hexavalent Chromium in Drinking Water by Ion Chromatography” found at www.dionex.com/en-us/webdocs/4242-AU144_V18.pdf. With these modifications, laboratories are capable of attaining a detection limit as low as 0.02 µg/L (ppb) and can support a reporting limit of 0.06 µg/L (ppb).

Laboratories that have the necessary equipment and are certified by an accrediting authority to conduct an approved ion chromatography method (e.g., EPA Method 300.0, SM 4110B, ASTM D4327) should be given preferential consideration to provide this analytical support. EPA is in the process of contacting drinking water laboratories across the country in an effort to further establish national drinking water laboratory capacity. SVL is working to develop its capability to perform the modified EPA 218.6.

To address concerns regarding the sample holding time of 24 hours specified in EPA Method 218.6, EPA reviewed published literature and recent laboratory sample holding time studies for drinking waters.The holding time of 24 hours prescribed in Method 218.6 was based upon the most conservative holding times for wastewater and sludge extracts, also covered by the method, and not the stability of chromium-6 in drinking water matrices. Consequently, EPA is temporarily recommending an extension of the maximum holding time for properly collected and buffered drinking water samples from 24 hours to 5 days following sample collection.

Who should I call if I have questions about EPA’s recommended enhanced monitoring for chromium-6?
Contact EPA via email at the Safe Drinking Water Hotline website or call the Safe Drinking Water Hotline at 1-800-426-4791 (Monday through Friday, 10:00 am to 4:00 pm eastern time)

Adapted from http://water.epa.gov/drink/info/chromium/guidance.cfm

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