How Chromium Oxidation State Changes From Source to Tap
Hexavalent Chromium is primarily detected in surface water sources supplying Wilmington.
Chromium can exist as chromium(III) or chromium(VI), with chromium-6 being the more oxidized, and chemically distinct, form.
Changes in water treatment and distribution can alter chromium's oxidation state but the public record focuses on chromium-6 presence in finished water.
Understanding Geogenic versus Industrial Origins of Chromium-6
Chromium-6 in Wilmington’s water supply predominantly reflects data from surface water, which may carry chromium from natural and human-made sources.
Geogenic sources of chromium-6 are more common in arid, alkaline aquifers, which does not characterize Wilmington's surface water supply.
Industrial activities, such as plating and manufacturing, can contribute chromium-6 presence even at low levels in surface water.
What Wilmington Public Water Records Establish Versus Private Well Testing
Wilmington Water Department data represent aggregate sampling across approximately 37,915 service connections, not individual home water quality.
All sixteen chromium-6 samples detected hexavalent chromium above the reporting level of 0.03 micrograms per liter, with a median of 0.25 micrograms per liter.
Municipal water records do not specify individual household concentrations; testing at your own tap is required for precise chromium-6 levels.
Seasonal and Multi-Year Variations Seen in Chromium-6 Records
The 2013-2015 EPA Unregulated Contaminant Monitoring Rule data reflect monitoring over 16 months, capturing short-term variations.
The highest recorded chromium-6 concentration was 1.5 micrograms per liter, illustrating fluctuation without constituting a violation.
Such data sets do not predict future fluctuations in chromium-6 levels at a specific residence.
Distinguishing Chromium-6 From Frequently Confused Water Issues
Chromium-6 is chemically distinct from total chromium; the federal MCL applies only to total chromium at 100 micrograms per liter, a far higher threshold than detected levels.
Chromium-6 detections reported are below any federal maximum contaminant level and should not be interpreted as unsafe.
Chromium-6 concerns differ substantially from common aesthetic water problems like iron staining or hardness.
Understanding the Terms "Detected," "Median," and "Range" in Wilmington's Sampling Record
"Detected" means chromium-6 was measured at or above the instrument's reporting level, not that it is present at harmful levels.
"Median" shows the middle value of detected chromium-6 measurements, providing a typical concentration among detections.
"Range" shows the spread from the lowest to the highest chromium-6 sample; Wilmington's range was 0.03 to 1.5 micrograms per liter.
For households in Wilmington whose existing water equipment is challenged to keep pace with chromium-6 concerns, the Pentek Chromium-6 Filter ships ready to configure and directly addresses the need to manage hexavalent chromium effectively at point of use. Accurate measurement of your own water demand helps select the appropriate capacity.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-07-07. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Wilmington Water Department (DE0000663), DE: 32 results across 2 listed contaminants, 32 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L
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