Government sampling for chromium-6 in GU’s U.S. Navy public water system found all measurements above the detection threshold, ranging from 0.03 to 3.0 micrograms per liter (µg/L or parts per billion). No federal health-based violations were recorded.
Geogenic Hexavalent Chromium Sources in Arid and Alkaline Aquifers versus Industrial Plating
Chromium-6, also known as hexavalent chromium or chromium(VI), appears in groundwater from both natural geologic sources and industrial activities like metal plating. Arid and alkaline aquifers common in some GU areas can contribute naturally occurring chromium(VI), which differs from chromium introduced by industrial discharge. Understanding the source helps clarify whether chromium levels reflect local geology or potential contamination.
Why California Set a 10 µg/L Limit and What That History Means for GU Residents
California adopted a 10 micrograms per liter advisory threshold for chromium-6 based on research into potential health effects, though this is not a federal enforceable standard. GU’s system measurements fall below this figure, but keeping informed about such advisories helps residents contextualize their exposures and evaluate the need for further testing or treatment.
How Oxidation State Changes Between Well, Distribution Main, and Tap Affect Chromium Forms
Chromium can change oxidation state within the water system. Chromium(VI) in source water may be converted to less toxic chromium(III) as water moves through pipes depending on chemistry, microbial activity, and materials in the distribution network. This transformation means a tap sample may differ from source water measurements, emphasizing the importance of testing your household tap water to know your specific chromium-6 levels.
What 'Detected', 'Median', and 'Range' Mean in the Sampling Record on This Page
- Detected: Indicates the instrument measured chromium-6 at or above the reporting level of 0.03 µg/L, not a violation or a safety assessment.
- Median: The middle value among all detected concentration measurements, 1.1 µg/L here, representing a central tendency but not an individual household level.
- Range: The lowest to highest chromium-6 values observed, from 0.03 to 3.0 µg/L within this water system sampling period.
What Changes for a Large Household, a Second Home, or a Seasonal Property
Water usage patterns and stagnation in plumbing can influence chromium levels at the tap. Larger households or properties with intermittent use might experience variations in chromium(VI) concentration due to water age or pipe interactions. Testing tap water directly where you live or vacation provides the clearest picture for treatment decisions tailored to your situation.
For households concerned about chromium-6 levels, the Pentair Chromium-6 Filter provides a documented option that ships ready to configure. It is designed to address chromium(VI) in residential water based on measured demand, supporting informed management of your water quality.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-04-27. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for U.S. Navy Water System (GU0000010), GU: 58 results across 2 listed contaminants, 56 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L