Geogenic Hexavalent Chromium in Aquifers vs. Industrial Sources
A common misconception is that chromium-6 in drinking water always comes from industrial contamination, such as plating or manufacturing wastes. In Hamilton County, including Carmel, chromium-6—or hexavalent chromium—is found at very low levels stemming mainly from natural geologic sources. Aquifers in this region, generally sourced from surface water supplies, have alkalinity and mineral content that can influence chromium speciation. This means the chromium detected in the community water supply largely originates from the surrounding geology rather than industrial pollution.
Trivalent vs. Hexavalent Chromium: Why Total Chromium Results Are Not Enough
Water testing often reports total chromium, the combined measurement of chromium(III) and chromium(VI). These two forms differ chemically and in their behavior. Chromium-6 (hexavalent chromium) has different health and aesthetic considerations compared to chromium(III). For example, total chromium data from Carmel’s water system show detections at or below 0.6 micrograms per litre (ppb), but these figures cannot be assumed to reflect chromium-6 levels specifically. Understanding the presence of chromium-6 requires targeted testing rather than relying on total chromium screening.
The Purpose and Limitations of the UCMR3 Survey for Household Water
The U.S. EPA’s Unregulated Contaminant Monitoring Rule 3 (UCMR3) survey conducted between 2013 and 2015 measured chromium-6 in Carmel’s public water system to gather occurrence data for regulatory consideration. This data includes 24 samples, with one detection above the reporting level at 0.04 micrograms per litre. It is important to note that these results are for the public water system as a whole, not individual household taps. They are not compliance tests nor safety limits but provide a snapshot to inform future monitoring and research.
Seasonal and Multi-Year Variation in the Monitoring Record
The chromium-6 measurements recorded by the EPA cover approximately nine months in 2015, showing very limited variation within that timeframe. Because chromium-6 concentrations can fluctuate seasonally or across years due to factors like source water changes or treatment adjustments, a single survey period cannot predict long-term levels at a specific home. Ongoing testing and maintenance are important when existing water treatment equipment no longer functions properly.
The Order of Testing to Identify Chromium-6 Concerns
For homeowners experiencing issues with water quality after equipment failure, the first step is to confirm whether chromium-6 is present in their water. The least expensive approach starts with reviewing the public water system’s reported data for their area. Following that, a laboratory analysis of a representative tap water sample specifying hexavalent chromium is necessary to determine actual household levels. This step distinguishes chromium(III) from chromium(VI) and informs appropriate treatment choices.
How Source Type and Sample Depth Influence Expected Chromium-6 Levels
Since Carmel’s water system uses surface water sources rather than deep wells, chromium-6 concentrations tend to be lower and less variable than in some groundwater systems in arid or alkaline regions. Homes served by private wells or different source types may encounter different water chemistry, so well depth, source characteristics, and plumbing materials all can affect chromium-species presence and concentration.
In summary, the Carmel Water Department’s public water records present measured chromium-6 and total chromium occurrences from a 2013-2015 federal survey. These data apply to the water system serving nearly 100,000 people through over 36,000 connections, reflecting system-wide conditions rather than individual household levels. For homeowners dealing with water treatment equipment failure and concerned about chromium-6, targeted testing of their own tap water is essential. The C-Series Chromium-6 Filter ships ready to configure and offers a documented way to address hexavalent chromium where it is detected and confirmed at the household level.
For in-depth federal data on water system monitoring of chromium-6 in Carmel and Hamilton County, please refer to the EPA’s public water system records and UCMR3 reports.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-12-15. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Carmel Water Department (IN5229004), IN: 48 results across 2 listed contaminants, 2 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L