Purpose and Limits of the UCMR3 Nationwide Survey
The Unregulated Contaminant Monitoring Rule (UCMR3) survey by the EPA aimed to gather nationwide data on emerging contaminants, including chromium-6 (hexavalent chromium), in public water systems. For Portsmouth Waterworks, which serves about 33,000 people over 7,200 connections with surface water, this meant collecting periodic water samples between July 2014 and April 2015. It is important to understand this dataset was not designed to determine water quality at individual homes; rather, it offers a system-level snapshot. Therefore, the presence of chromium-6 at certain levels in this survey does not reveal the exact concentration at any one household tap in Portsmouth.
Comparing Ion Exchange and Reverse Osmosis for Chromium(VI)
When considering treatment for chromium-6, two common technologies are ion exchange and reverse osmosis. Ion exchange involves exchanging chromium(VI) ions in water for less harmful ions attached to resin beads, effectively reducing chromium-6 concentrations. Reverse osmosis forces water through a semipermeable membrane, filtering out chromium(VI) along with many other dissolved substances. Both technologies can be effective, but each treats chromium-6 differently; ion exchange specifically targets chromium(VI) ions, while reverse osmosis reduces a broader range of dissolved solids, including chromium(VI).
How to Interpret Portsmouth's Data Compared to Neighboring Counties
Portsmouth's public water system reported 18 samples for chromium-6, with 16 detections above the 0.03 micrograms per liter (µg/L or parts per billion) reporting level. The highest recorded measurement was 0.46 µg/L and the median among detections was 0.165 µg/L. While neighboring counties or systems might have different concentrations, it is crucial not to infer individual household water quality or safety from these system-wide findings. These detection figures serve as regional indicators but do not establish specific household conditions.
Sample Size and Its Influence on Data Reliability
With 18 samples taken from Portsmouth Waterworks during the monitoring period, these results offer a limited but useful view of chromium-6 presence in the system's surface water source. A small sample size can mean greater variability and less certainty about long-term averages or extremes. Residents evaluating their own water should consider testing their private well or household water directly to obtain precise chromium(VI) concentrations applicable to their water supply.
Seasonal and Multi-Year Variation in Chromium(VI) Concentrations
The monitoring window for Portsmouth's chromium-6 data spanned from mid-2014 to early 2015, capturing some seasonal variation. However, no data beyond this period was reported in the UCMR3 records. Environmental factors such as rainfall, source water quality changes, and treatment adjustments can influence chromium(VI) levels over time. Without ongoing monitoring, it is difficult to predict current water quality trends for chromium-6 based on this dataset alone.
Conclusions on Household Decision-Making
Portsmouth's water system record shows no violations of federal health-based standards for total chromium or chromium-6. The presence of chromium(VI) measured in the EPA survey reflects system-wide sampling, not the condition of any individual home's water. Homeowners seeking to understand their personal water quality should conduct specific in-home testing. For those wanting a targeted approach to address chromium-6, equipment based on the Pentair chromium(VI) filter technology ships ready to configure and offers a documented method to reduce hexavalent chromium in residential water supplies. Importantly, the area's data should not be taken as a health warning or evidence of unsafe water but as informational context in water treatment considerations.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-04-07. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Portsmouth Waterworks (NH1951010), NH: 36 results across 2 listed contaminants, 31 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L
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