A water quality test report for chromium-6 (hexavalent chromium or Cr(VI)) typically lists the detected concentration in micrograms per liter (µg/L), also known as parts per billion (ppb). For residents served by the Middleborough Water Supply system in Plymouth County, Massachusetts, federal sampling data reveals multiple detections of chromium-6 ranging up to 0.22 µg/L, with a median near 0.145 µg/L. These measurements reflect groundwater conditions feeding the public distribution network across over 6,000 residential connections.
Geogenic Hexavalent Chromium in Arid and Alkaline Aquifers Versus Industrial Plating Sources
Hexavalent chromium can originate from natural (geogenic) sources, especially in certain rock formations where oxidation processes in aquifers raise chromium to the hexavalent state. These sources often relate to arid or alkaline groundwater environments, unlike chromium contributions from industrial plating waste or other manufacturing discharges. In the Middleborough system, chromium-6 detections are consistent with geogenic background levels rather than industrial contamination, as the water supply is groundwater sourced and maintains zero EPA health-based violation records.
How Oxidation State Changes Between the Well, the Distribution Main and the Tap
The form of chromium in water can change as water moves from its source to consumer taps. Hexavalent chromium is more soluble and mobile, but treatment plant processes and distribution conditions can alter its oxidation state. Chlorination, pH variations, and residence time in the mains can partially reduce hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)), which behaves differently in the water system and generally presents lower mobility and toxicity. Thus, the chromium-6 concentration measured near the source may not directly reflect what a household tap water test would find, highlighting the importance of a home-specific water test.
Trivalent Versus Hexavalent Chromium: Why a Total-Chromium Result Cannot Answer the Question
Total chromium tests combine concentrations of chromium in all oxidation states but do not distinguish hexavalent chromium from trivalent chromium. Because hexavalent chromium is typically the more concerning form regarding water quality, a total chromium value alone cannot determine if chromium-6 is present or if treatment is needed. In Middleborough, total chromium levels measured up to 0.5 µg/L, well below the federal maximum contaminant level of 100 µg/L, but this does not specify the hexavalent portion. Therefore, specific chromium-6 testing is essential for an accurate assessment.
Maintenance Rhythm of the Documented Technology in Plain Terms
The documented Pentek Chromium-6 Filter offers a direct-purchase option for residential water treatment targeting chromium-6 concerns. This equipment ships ready to configure and relies on filtration media designed to address hexavalent chromium captured from household water. Maintenance for such a filter typically involves periodic replacement of the filter cartridge according to usage levels and water quality but does not include complex servicing. Homeowners can monitor performance by testing water before and after the filter to ensure chromium-6 concentrations remain at acceptable levels.
How Sample Depth, Well Depth or Source Type Changes What a Reader Should Expect
The depth of a water source and its geological context affect chromium speciation and concentration. Deeper wells may access water with different chemical characteristics than shallow ones. In Middleborough’s groundwater system, chromium-6 presence relates to the natural rock matrix and aquifer chemistry rather than surface contamination. Residents relying on private wells should test their specific water source separately since public system data may not reflect individual well conditions. Sample depth influences the likelihood of detecting chromium(VI) versus the less mobile forms.
In summary, Middleborough’s public water records indicate detectable but low levels of chromium-6 consistent with geogenic sources, with no EPA health-based violations on record. Deciding on a treatment approach requires understanding hexavalent chromium’s chemistry, differentiating it from total chromium, and considering household water testing results. The Pentek Chromium-6 Filter presents a documented option for residential users seeking to address detected chromium-6 in their water supply.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2014-09-25. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Middleborough Water Supply (MA4182000), MA: 69 results across 2 listed contaminants, 52 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L
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