The Wilmington Water Department serves over 100,000 people in New Castle County with surface water. According to EPA monitoring from 2013 to 2015, chromium-6 was detected in all samples taken from this system, with levels ranging from just above the reporting threshold of 0.03 micrograms per liter (ppb) to 1.5 ppb. While there is no federal maximum contaminant level (MCL) specifically for hexavalent chromium (chromium(VI)), total chromium is regulated with an MCL of 100 micrograms per liter.
Why California Set Its Own 10 Micrograms per Liter Limit and Its Implications
California has established a public health goal for chromium-6 at 10 micrograms per liter (ppb), which reflects their assessment of potential long-term health risks. This state-level precaution differs from federal regulations, which currently do not have a separate enforceable limit for chromium-6, relying instead on the total chromium MCL. For residents in Wilmington and the broader New Castle County area, this means that while federal standards are met, some consumers might consider California's advisory as a more conservative benchmark when evaluating their water quality.
Trivalent Versus Hexavalent Chromium: Why Total Chromium Levels Aren't Enough
Chromium appears in water mainly in two forms: trivalent chromium (chromium(III)) and hexavalent chromium (chromium-6 or chromium(VI)). These have very different chemical behaviors and health considerations. Total chromium measurements combine both forms without distinguishing them, so knowing the total chromium level alone does not clarify the presence or concentration of chromium-6 specifically. Since Wilmington's monitoring detected chromium-6 separately, this provides more targeted information for making treatment decisions than total chromium results alone.
Distinguishing Aesthetic Secondary Standards from Health-Based Limits
Aesthetic secondary standards address factors such as taste, staining, and corrosion potential, whereas health-based limits regulate substances that may pose health risks. In the case of chromium-6, there is no federal aesthetic standard. The total chromium MCL primarily focuses on health impact but does not specify an aesthetic threshold. It's important to note that a detection of chromium-6 above a reporting level indicates measurement presence, not a violation or necessarily a concern for taste or appearance.
How Chromium-6 Enters the Wilmington Water Supply
Chromium-6 in surface water sources can originate from natural mineral deposits and certain industrial activities. In Wilmington, the surface water supply is monitored regularly, and the presence of chromium-6 is documented but remains below any federal enforceable limits. The state of Delaware and the Wilmington Water Department continue to track these levels to maintain compliance with regulations and protect the water supply.
Seasonal and Multi-Year Variation in Chromium-6 Levels
The EPA's Unregulated Contaminant Monitoring Rule (UCMR3) data from July 2014 through July 2015 shows that chromium-6 was consistently detected across 16 samples, with some variation in concentration but no readings exceeding 1.5 micrograms per liter (ppb). This one-year snapshot suggests relative stability in chromium-6 levels over that period; however, concentrations can vary seasonally or over multiple years due to environmental factors and water source changes.
To determine the chromium-6 level specific to your residence, independent water testing is necessary since system-wide data cannot guarantee individual household water quality. Testing will reveal the concentration relevant for your home, informing which class of treatment you may require.
For those seeking a water treatment solution designed to address chromium-6 presence at these demand levels, the Pentek Chromium-6 Filter ships ready to configure and is developed to manage hexavalent chromium in residential water supplies.
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
- ✓ 90-Day Money-BackNo restocking fees — return within 90 days.
- ✓ Manufacturer WarrantyGenuine Fleck · Pentair · VIQUA equipment.
- ✓ Free Expert SizingTalk to a specialist and buy the right system the first time.