Hexavalent and Total Chromium at Low Reporting Concentrations

Overview

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Key numbers

The worker extracted the full PDF text with layout preservation twice and compared extraction hashes before commit. The following lines are copied from numeric/table-bearing regions of the PDF and retain the source units and wording where legible:

By Patrick C. Mills1 and Richard P. Cobb2 public health goal of 0.02 of µg/L. Cr(VI) was undetected in
of 0.06 µg/L when detected. All but two (94 percent) of
Abstract surface water, the median concentration was 0.09 µg/L,
On the basis of their recent review of the human health 0.20 µg/L. Surface waters treated with lime for softening
water, the U.S. Environmental Protection Agency is consider- 2.4 µg/L; median, 1.2 µg/L).
total chromium is regulated, at a Maximum Contaminant was 1.8 µg/L. Maximum concentrations in untreated and
Level (MCL) of 100 micrograms per liter (µg/L). The occur- treated surface water were 1.8 µg/L and 2.5 µg/L, respectively.
California’s recently established MCL for Cr(VI) of 10 µg/L ter samples, with a median of 0.40 µg/L, when detected. All
specific standard that approximates the California level on the tion was 0.40 µg/L, whereas in treated (tap and distributed)
management of Illinois’ public drinking water, the U.S. Geo- water the median was 0.30 µg/L. As with Cr(VI), surface
water-supply wells and 32 surface-water intakes; also, 32 frequencies of occurrence and range of concentrations indicate
of collection at reporting limits of 0.02 µg/L for Cr(VI) and aquifers, particularly the Cambrian-Ordovician aquifer system,
0.1 µg/L for Cr(T). The occurrence of Cr(VI) was compared are possibly most commonly affected by geologic sources of
was 2.1 µg/L. Maximum concentrations in untreated and concentrations of Cr(VI) and Cr(T) in untreated water sam-
of 0.02 μg/L. transformation process has important implications regarding
micrograms per liter (µg/L) (U.S. Environmental Protection 1. the occurrence of Cr(VI) in Illinois’ waters used for
µg/L for Cr(VI) (National Ground Water Association, 2014) 2. selected factors that affect its occurrence, and
of 0.02 µg/L (California Department of Public Health, 2014). 3. the impact of a specific regulatory standard for Cr(VI)
about 0.07 µg/L (New Jersey Drinking Water Quality Institute, public drinking waters.
guideline of 10 µg/L and an adult water health guideline of also, 32 treated surface-water samples were collected near
40 µg/L (Illinois Environmental Protection Agency, 2011a). the point of treatment and 32 near the endpoint of distribu-
concerns associated with Cr(VI) and suggest that, if estab- residence time). A reporting limit at the lower end (0.02 µg/L)
fall within the range of 0.02–40 µg/L and possibly close to Cr(VI) was applied in the assessment; a similarly low report-
10 µg/L. ing limit (0.1 µg/L) was applied for assessment of Cr(T).
occurrence of Cr(VI) with respect to aqueous geochemistry , µg/L, respectively (Ball and Izbicki, 2004). The samples were
potentials, were either not available or of insufficient accuracy of 0.1 µg/L. The concentration of 25 percent of the samples
in this study. Also, other redox-sensitive chemical constitu- was greater than 10 µg/L. A statewide assessment of Cr(VI) in
of redox conditions on the basis of those constituent data that in California found detectable concentrations above 1 µg/L
were sufficiently available was beyond the scope of the study. in about 55 percent of well-water samples and above 10 µg/L
(Sutton, 2010) found Cr(VI) at concentrations above 0.06 µg/L
tion was 12.9 µg/L. More than 26 million people are served
method detection3 or reporting limit of 0.2 µg/L in 42 percent
µg/L. The study included almost 20 supply facilities and about
population was 1.1 µg/L, and the median was less than the
and analysis at the reporting limits of 0.02 µg/L for Cr(VI) and
0.1 µg/L for Cr(T). Results are summarized statistically and
water or groundwater at concentrations above the 100 µg/L results for Cr(T) from the State’s 1,750 or so public-supply
on Environmental Quality (2013); in large part those elevated centrations exceeding the MCL of 100 µg/L for Cr(T). The
waters used as sources for public supply. In samples from by USEPA (1986), is the lowest concentration of an analyte reportable with
detected in the range of 0.2–0.3 µg/L (Central Lake County or minimum reporting level (MRL), is the minimum concentration that can be
surface-water sources was 7 µg/L. The median detectable as groundwater or surface-water source deposits for the State’s
concentration in treated drinking water was 11 µg/L, with a public water supply. Limestones are prevalent throughout the

Methods (brief)

Front cover and other images: Front cover shows collection of groundwater samples, Union-York Water District (intake 00251). This and
Well, Intake, and Treated-Sample Site Selection. …7
Sample Collection and Laboratory Analyses…12
Effects of Treatment and Distribution on Sample Concentrations…37
Sample Temperature and Holding Time…39
Sample Tap Composition…40
samples from selected source-water aquifers and surface waters used for public
Appendix 2. Protocols for collecting representative samples of untreated source water
1. Photos showing typical quality-assurance measures and collection of samples
samples, 2013…20
1. Graphs showing hexavalent chromium and total chromium in samples from
chromium in intake, tap , and distribution samples from public-supply surface-
1. Graph showing concentrations of hexavalent chromium in intake and tap samples
1. Graph showing relation of concentration of hexavalent chromium in tap samples
in public-supply source waters in Illinois, by sample-tap material, 2013. …40
in Illinois, by chrome-plated and brass sample-tap material, 2013. …41
in samples from source-water aquifers and surface waters used for public
1. Summary statistics for detections of hexavalent chromium in samples from

Implications

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised