Chromium-6 in Drinking Water Sources: Sampling Results

Last Update: July 11, 2014

Recent Monitoring and Analytical Information

Sampling Results

Unregulated Chemical Monitoring for Chromium-6

In 2001, the California Department of Public Health CDPH (then the California Department of Health Services, DHS) adopted a regulation that added chromium-6 to the list of unregulated chemicals for which monitoring is required (UCMR). The analytical methods associated with the UCMR are here.

Of the ~4,400 community systems and non-transient non-community systems that have ~12,000 drinking water sources, those that are vulnerable to contamination are subject to UCMR regulations. Systems with fewer than 150 service connections may be exempted from the monitoring requirement. Results of UCMR monitoring from over 7,000 drinking water sources showed chromium-6 at or above the 1-μg/L DLR in about one-third of them.

The monitoring data that were collected as a result of the UCMR regulation will enable us to determine the extent to which chromium-6 exists within drinking water supplies, and at what concentrations it exists. This information is needed in order to evaluate the costs of treatment of drinking water containing chromium-6 when developing a chromium-6 maximum contaminant level (i.e., drinking water standard).

The monitoring for chromium-6 under the UCMR regulations was to have been completed by December 31, 2002, and the regulations were repealed in October 2007. However, some water systems continued to monitor their sources and submit their findings.


The Division of Drinking Water's water quality database's reported findings of chromium-6 from 2000 to November 2012 are presented here (Excel, 4.1MB); sources with no detections are excluded. A summary of the peak concentrations is presented in Table 1. Detections included in the accompanying spreadsheet should not be considered to reflect chromium-6 in drinking water served to customers, since water from the listed sources may be blended, treated, or not used to provide drinking water. For more information about the quality of specific drinking water supplies, see public water systems' annual Consumer Confidence Reports.

The water quality monitoring database is available here.

Table 1. Chromium-6 peak detections in drinking water sources (2000 - 2012).

Peak level (μg/L)
No. of Sources
% of Detections
1 - 5
6 - 10
11 - 20
21 - 30
31 - 40
< 1
41 - 50
< 1
> 50
< 1
1. Data are extracted from monitoring results from 2000 through November 13, 2012 (Excel, 4.1MB). They will change with subsequent updates and should be considered draft.
2. "Sources" are active, standby, and pending sources reporting more than a single detection of chromium-6. Data may include both raw and treated sources, distribution systems, blending reservoirs, and other sampled entities. This table does not include inactive sources, abandoned or destroyed wells, agricultural wells, monitoring wells, or more than one representation of the same source (e.g., a source with both raw and treated entries is counted a single source). 
3. For UCMR sampling, a number of sources may have been screened using a 1-μg/L reporting limit for total chromium (PDF). If total chromium was below the screening level, specific analysis for chromium-6 was not required.

Peak concentrations of chromium-6 were reported in the greatest numbers in the following counties (see Notes in Table 1):

  • 1 - 5 μg/L: 1,596 sources in 39 counties, including San Bernardino (228 sources), Los Angeles (218), Fresno (164), Sacramento (131), Riverside (126), Kern (123), and San Joaquin (84)
  • 6 - 10 μg/L: 496 sources in 31 counties, including Los Angeles (98), Sacramento (78), San Bernardino (66), Riverside (49), San Joaquin (31), Stanislaus (26), and Kern (25)
  • 11 - 20 μg/L: 247 sources in 27 counties, including Riverside (48), Los Angeles (41), San Bernardino (32), Yolo (19), Sacramento (18), and Solano (16)
  • 21 - 30 μg/L: 66 sources in 14 counties, including Yolo (16), Los Angeles (9), San Bernardino (11), Merced (6), Solano (6), Riverside (6), and Santa Barbara (4)
  • 31 - 40 μg/L: 17 sources in 6 counties: Merced (6), Los Angeles (4), Yolo (4), Santa Barbara (1), San Bernardino (1), and Santa Cruz (1)
  • 41 - 50 μg/L: 5 sources in 3 counties: Los Angeles (2), Yolo (2), and San Bernardino (1)
  • 50 μg/L: 4 sources in 2 counties: Los Angeles (3) and Santa Barbara (1)

Early Sampling

Drinking water sources have monitored total chromium since the 1970s, and the results of monitoring have been maintained in the Drinking Water database since 1984. Of 11,785 sources sampled for total chromium through 2001 (prior to the UCMR monitoring for chromium-6 and the "screening level" for total chromium of 1 μg/L mentioned above and in Note 3 of Table 1), detections were reported for 1,311 sources (1,227 ground water and 84 surface water sources). The DLR for total chromium is 10 μg/L.

Until the required monitoring for chromium-6 under the UCMR, little information was available about the presence of chromium-6 in drinking water supplies. DHS performed limited analyses from 1997-2000 to determine the fraction of total chromium that is chromium-6, with the following results. For these samples, not detected (ND) indicates chromium-6 at <0.5 μg/L.

  • In 1997-98, DHS sampled 10 wells in Merced County. Total chromium was 18.8-33.5 μg/L, and chromium-6, 16.8-33.0 μg/L (68-100% of total chromium).
  • In 1998, DHS sampled three wells in Los Angeles County. Total chromium was 3.4-10.3 μg/L, was chromium-6, ND-5.1 μg/L (<14-54% of total chromium).
  • Also in 1998, DHS sampled one well in Contra Costa County. Total chromium was 18.7 μg/L and chromium-6, 1.5 μg/L (8% of total chromium).
  • In 1999, a water agency's consultant sampled nine wells in Los Angeles County. Total chromium was 5.3-15 μg/L, and chromium-6, 3.6-11 μg/L (58-100% of total chromium).
  • In 2000, DHS sampled eight wells in San Mateo County. Total chromium was 11-28 μg/L, and chromium-6, 7.4-28 μg/L (64-100% of total chromium).
  • In 2000, DHS sampled three wells in Yolo County. Total chromium was 31-54 μg/L, and chromium-6, 24-35 μg/L (44-97% of total chromium).
  • In 2000, DHS took four samples from a surface water source in Solano County. Total chromium was 0.5-8.9 μg/L, and chromium-6 was ND.