Chromium-6 in Nassau Water: Understanding Hexavalent Chromium Levels in Hempstead and Lynbrook

Government sampling by the EPA’s Unregulated Contaminant Monitoring Rule 3 (UCMR3) reports chromium-6 (hexavalent chromium, Cr(VI)) detected at varying levels in the Long Island American Water Corporation system serving Hempstead (T), Lynbrook (V), and surrounding Nassau County. This system provides groundwater-sourced water to about 220,000 people across more than 74,000 connections.

1. Trivalent Versus Hexavalent Chromium: Why Total Chromium Data Is Not Enough

The EPA’s public water system records show measured concentrations for both total chromium and chromium-6. Total chromium includes all oxidation states, primarily trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)). Cr(III) often occurs naturally and is considered less mobile and less toxic, while Cr(VI) is more soluble, mobile, and associated with greater health concerns. Because total chromium results combine these forms, they cannot precisely indicate the level of hexavalent chromium present. For households wishing to understand their specific water quality relative to chromium-6, a test targeting Cr(VI) specifically is necessary.

2. Sources of Hexavalent Chromium in Groundwater: Geogenic Versus Industrial Origins

Hexavalent chromium in Nassau County’s groundwater primarily stems from natural geogenic sources, particularly in aquifers that are more alkaline and may be influenced by regional geology. This contrasts with hexavalent chromium contamination linked to industrial activities such as metal plating, which typically presents different spatial patterns and concentration ranges. Recognizing the likely origin helps in understanding variability in chromium-6 levels and the potential need for household-level water treatment options.

3. Aesthetic Secondary Standards Compared to Health-Based Limits for Chromium-6

While aesthetic secondary standards govern water characteristics such as taste, color, staining, and corrosiveness, hexavalent chromium does not have an established federal maximum contaminant level (MCL) for health under current regulations. The total chromium MCL is set at 100 micrograms per liter (µg/L or parts per billion, ppb), but this applies to all chromium forms combined and does not specifically address hexavalent chromium. Detections below or near these values do not imply safety breaches but can influence water aesthetics or guide consumer interest in treatment technologies.

4. The Purpose and Limits of UCMR3 Monitoring for Household Water Quality

The UCMR3 data collected from 2013 to 2015 was designed to assess the occurrence of unregulated contaminants like hexavalent chromium across public water systems nationwide. It informs regulatory and public health research but is not intended as a compliance test or a direct indicator of any individual home's water quality. For a homeowner, these findings highlight regional presence and trends but do not substitute for private water testing to determine exact household chromium-6 levels.

5. How Water Source Characteristics Affect Chromium-6 Levels in Your Home

Factors such as the depth of the municipal well, aquifer characteristics, and water treatment protocols influence chromium-6 levels delivered to residences within the water system. Homes closer to deeper or geologically distinct wells may observe varying chromium-6 concentrations. Therefore, understanding the system’s source type and conducting specific private water testing can help identify if additional treatment is desirable for chromium-6 management.

Addressing Household Chromium-6 Concerns

For households seeking to manage hexavalent chromium, technology like the Pentair Chromium-6 Filter is documented to reduce chromium-6 concentrations effectively. This equipment ships ready to configure for home water treatment and can be considered once a household’s chromium-6 concentration is established through appropriate testing.

In summary, the Long Island American Water Corporation system, serving Hempstead, Lynbrook, and Nassau County, has documented hexavalent chromium presence through federal monitoring at levels below federal total chromium limits. These results provide a regional snapshot but require household-level testing to assess individual water conditions. For detailed information, consult the EPA’s public water system data for Long Island American Water Corporation (NY2902835).

Where this information comes from

Source: EPA SDWIS public water system record. Sampled 2015-12-14. These figures describe the public water system's record, not the plumbing inside any individual building.

On record: EPA UCMR3 monitoring (2013-2015) for Long Island American Water Corporation (NY2902835), NY: 100 results across 2 listed contaminants, 63 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L