Understanding the UCMR3 Survey and Its Limits for Homeowners
The goal of UCMR3 sampling
The EPA’s third Unregulated Contaminant Monitoring Rule (UCMR3) collected data nationwide from 2013 through 2015 to better understand the occurrence of unregulated contaminants, including chromium-6 (hexavalent chromium) in public water systems. This was not a compliance test but a survey to gather baseline data representative of the public water system as a whole. It does not provide a direct measurement of chromium-6 levels at any individual household tap.
Detection versus health limits
Detecting chromium-6 means the instrument found measurable amounts above the reporting threshold, but this is not a violation or an indication of unsafe water. The Butte Silverbow Water Department showed chromium-6 detections ranging up to 0.0413 micrograms per liter (µg/L) or parts per billion (ppb), well below the federal total chromium maximum contaminant level of 100 µg/L. No federal MCL exists specifically for chromium-6.
Comparing Butte’s Records with Neighboring Areas
System size and water sources matter
Butte’s public water system serves about 33,000 people from surface water sources through nearly 13,000 connections. Variability in sources or system size among neighboring counties can affect chromium-6 occurrence levels. Comparing Butte’s data to Silver Bow’s neighbors requires noting these operational differences rather than assuming similar chromium-6 concentrations at home.
CA’s chromium-6 guideline versus federal data
Some states like California have set their own guidelines (e.g., 10 µg/L) for chromium-6 based on health risk assessments, but Butte’s recorded values are much lower. This regional difference in standards underscores that detections in Butte’s system tend to be below levels used for state-based precautionary measures.
Differentiating Chromium-6 from Other Common Water Concerns
Hexavalent chromium versus total chromium
Government data reported no total chromium detections above the reporting limit in Butte, even though some chromium-6 was detected. Total chromium includes all chromium forms; chromium-6 is a specific, more reactive form. Measuring total chromium alone does not reveal chromium-6’s presence or concentration.
Chromium-6 separate from other metals or contaminants
Chromium-6 is chemically distinct from other metals or common water quality issues like iron or manganese that cause aesthetic or taste problems. Addressing chromium-6 concerns should focus specifically on technologies documented to interact with hexavalent chromium.
Seasonal and Multi-Year Variation in Chromium-6 Levels
Monitoring occurred from mid-2013 to early 2014
The sampling window for Butte’s data spanned from July 2013 to April 2014, capturing different seasons and operational conditions. Observed chromium-6 levels ranged from non-detects to a highest recorded 0.0413 µg/L, with a median of detected samples at 0.034 µg/L. This shows relatively stable low-level presence without spikes recorded during that time.
Understanding variability in public water data
These figures represent an approximate range but do not predict exact future tap water chromium-6 concentrations. Seasonal source water changes, treatment adjustments, or infrastructure modifications can influence levels over time.
Effects of Sample Depth, Well Depth, and Source Type
Surface water source considerations
Butte relies on surface water sources, which can differ in chromium-6 dynamics compared to groundwater or wells. Surface water chromium-6 levels can fluctuate with runoff and environmental inputs. This differs from deeper wells that might show geogenic chromium-6 contributions.
Sampling location vs household water
Samples were taken at system-level monitoring points, not individual taps. A household’s own supply may vary based on plumbing, pipes, or point-of-entry conditions. Testing your own water is required to determine your home's chromium-6 status accurately.
Steps to Clarify Your Chromium-6 Situation at Home
Start with a general water quality test
Begin by testing your water with a certified laboratory for basic parameters to identify any obvious concerns or anomalies that could suggest chromium presence or other treatment needs.
Obtain a specific chromium-6 test
Only a targeted chromium-6 analysis can confirm your household’s chromium(VI) levels. This test is necessary because general chromium measurements may not discern chromium-6 specifically.
Consider documented equipment for chromium-6 control
After confirming presence and concentration, equipment designed to reduce hexavalent chromium like the Fleck Chromium-6 Filter, which ships ready to configure for household use, can be considered as a specialized solution.
What Not to Conclude from Butte Area Chromium-6 Data
Area-wide data provide valuable context but do not reveal the chromium-6 concentration or safety status of your water at home. Detections in the public system are measurements, not violations or indicators of unsafe water. The absence of a federal health-based limit for chromium-6 means regulatory benchmarks specific to chromium-6 are not established nationally. To understand your risk or need for treatment, personal water testing is essential rather than inferring from public system averages.
By following this checklist, homeowners in Butte, Silver Bow County can better grasp the available chromium-6 data, its limitations, and the appropriate steps to address their concerns effectively.
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