Understanding Chromium-6 Water Results for Silver Bow Households in Butte
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1. How oxidation state changes between the well, the distribution main and the tap
Chromium exists in multiple oxidation states, with hexavalent chromium (chromium-6 or Cr(VI)) being one distinct form that can occur in water. The Butte Silverbow Water Department primarily sources water from surface supplies, where chromium species may shift chemically during treatment and distribution. Alterations in water chemistry between the source, distribution mains, and household taps can change chromium-6 concentrations and its chemical form. This shift means that monitoring chromium-6 at the tap presents a different profile than source water or distribution samples alone.
Understanding these changes is essential because chromium's oxidation state affects both its behavior in water and how it might be addressed by water treatment technology in homes.
2. Trivalent versus hexavalent chromium: why a total-chromium result cannot answer the question
The water system’s record shows that total chromium levels, which include all chromium oxidation states, were below the reporting threshold in tests. However, total chromium measurements do not distinguish chromium-6 from other chromium forms such as trivalent chromium (chromium-3), which behaves differently chemically and biologically. Therefore, relying solely on total chromium figures cannot determine the presence or extent of hexavalent chromium specifically.
For residents concerned about chromium-6, results that focus exclusively on this form are more relevant. The Butte system recorded several chromium-6 detections, all below federal reporting levels but above detection thresholds, indicating its presence in trace amounts.
3. What the measured range means against the relevant federal standard, and what it does not mean
Federal regulations do not establish a maximum contaminant level (MCL) for hexavalent chromium. The EPA’s MCL for total chromium is 100 micrograms per liter (µg/L or parts per billion), and the Butte Silverbow Water Department’s chromium-6 measurements—from 0.034 to 0.0413 µg/L—are far below this total chromium threshold.
Detection of chromium-6 in these ranges is not a violation or a statement of water safety concerns by federal regulators. The detections reflect the presence of chromium-6 above lab reporting limits in a monitoring survey, not a health-based limit exceedance. No samples exceeded the total chromium MCL.
4. What a certified laboratory test for this constituent reports and how to read it
A certified laboratory test that measures chromium-6 in a private household water sample will report the concentration in micrograms per liter (µg/L). To understand these figures, it is important to compare them carefully against local, state, and federal guidelines where available. Since federal standards do not set an MCL specifically for chromium-6, homeowners should interpret results with caution and consider professional consultation for a full assessment.
Testing your own tap water is the only way to know the actual chromium-6 level in your home’s supply, as public system data represents an average across many connections. The laboratory report may also provide detection limits, i.e., the smallest concentration reliably measured, clarifying what 'detected' means versus levels below which chromium-6 is not measurable.
5. Why California set its own 10 µg/L limit and what that history means for a reader elsewhere
California has established a public health goal and a maximum contaminant level for chromium-6 at 10 µg/L, motivated by state-specific risk assessments. This limit is considerably higher than the chromium-6 concentrations detected in Silver Bow's water system. While these California standards do not apply in Montana, they illustrate how different jurisdictions respond variably to chromium-6 presence based on local priorities and scientific review.
For Silver Bow households, this history highlights that regulatory responses are not uniform nationwide. It also underscores that chromium-6 presence at the detected levels in Butte Silverbow's water system is below some state-level action thresholds and well below the EPA total chromium MCL.
Closing
The Butte Silverbow Water Department's chromium-6 data covers its public water system serving approximately 33,000 residents via 12,958 connections and reflects surface water sourcing from 2013 to 2015. This record describes occurrence in the public system broadly, not individual household tap water levels. For specific knowledge about your own household water, testing from a certified laboratory is necessary. The United States Environmental Protection Agency provides public access to these data and resources for further information on chromium-6 and water quality.
When considering options to address chromium-6 on a household scale, the Pentek Chromium-6 Filter, which ships ready to configure, is a documented option designed to reduce chromium(VI) and improve water quality at the tap.
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