Trivalent versus Hexavalent Chromium: Why a Total-Chromium Result Cannot Answer the Question
When looking at chromium levels in local drinking water, it is essential to distinguish between chromium(III) and chromium(VI), also known as hexavalent chromium or chromium-6. Government monitoring by the EPA for the Butte Silverbow Water Department reports no detections above reporting levels for total chromium, which includes all oxidation states combined and has a federal maximum contaminant level (MCL) of 100 micrograms per liter (µg/L). However, hexavalent chromium alone was detected in some samples, but at levels much lower than health-based guidelines set by certain states.
This difference matters because total chromium measurements do not reflect the proportion of chromium-6 present, and chromium(III) has different chemical behavior and risk profiles. Only speciated testing that separately quantifies chromium-6 can inform effective treatment choices for households concerned about this particular form of chromium.
What Happens When This Problem Is Left Untreated for Years, Stated Without Exaggeration
Hexavalent chromium can occur naturally or through industrial sources. While the EPA record for the Butte Silverbow Water Department reflects detections of chromium-6 up to approximately 0.0413 µg/L (parts per billion), these levels remain well below any federal MCL and present no EPA-acknowledged health-based violation for the public water system. Nevertheless, without tailored water treatment, even low-level chromium-6 present in tap water will persist unchanged.
Over time, if a household relies on water with detectable chromium(VI), general household uses such as drinking and cooking will continue to be exposed to this constituent at the reported concentrations. Because domestic water demand varies, some homes may experience more cumulative exposure, but the water system's reported data alone cannot specify individual well or tap levels.
How the Treated Water Differs at the Tap Once the Documented Technology Is in Place
The Autotrol Chromium-6 Filter employs ion exchange technology designed specifically to address hexavalent chromium in residential water supplies. When configured for a household's daily water use, it reduces chromium-6 to levels generally below the detection limits reported by the EPA in this region.
Unlike general total chromium treatment methods, this technology targets Cr(VI) at the molecular level, improving water clarity and taste without relying on broad filtration that may affect other water qualities. The treated water at the tap shows lower chromium-6 concentrations, providing peace of mind for households attentive to this contaminant.
How Many Samples and Wells Stand Behind the Figures, and What a Small Sample Means
The chromium-6 data for Butte, Silver Bow County derive from 24 samples collected between July 2013 and April 2014 from the public water system serving over 33,000 people through nearly 13,000 connections. Of these, 6 samples showed chromium-6 at or above the reporting threshold of 0.03 µg/L but below any federal health-based limits.
This sample size provides a snapshot of the public water system quality during that period but does not represent testing of private wells or individual household taps. A small number of detections indicates the contaminant's presence in the system but cannot predict exact levels in any single home. Individual water testing remains essential for households wanting specific data on chromium-6 concentrations in their tap water.
How Oxidation State Changes Between the Well, the Distribution Main and the Tap
Hexavalent chromium's chemical form can change due to water chemistry factors, including pH, oxidation-reduction potential, and interactions with disinfectants and pipes. In Butte’s surface water source, chromium may exist predominantly as chromium(VI) when entering the treatment plant but can transform during treatment processes or within the distribution network.
Because the EPA data show only limited detections of chromium-6 and none for total chromium above reporting limits, the distribution system appears to maintain low levels throughout. However, changes in oxidation state after leaving the main and within home plumbing could result in slightly different chromium speciation at the tap. Only specific speciation tests on household water can clarify these variations.
Choosing effective treatment equipment involves considering these chemical behaviors. Technologies designed for chromium-6 specifically address the hexavalent form regardless of such changes, ensuring consistent treatment performance.
For households in Butte, Silver Bow County weighing treatment options for chromium-6, the Autotrol Chromium-6 Filter ships ready to configure according to measured household water demand, providing a targeted solution to reduce hexavalent chromium at the tap based on documented EPA monitoring data for the local system.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2014-04-28. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Butte Silverbow Water Department (MT0000170), MT: 48 results across 2 listed contaminants, 6 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L