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Chromium-6 in Drinking Water Sources:  Sampling Results

Last Update: February 17, 2009

CDPH (then the  California Department of Health Services, DHS) adopted a regulation in 2001 that added chromium-6 to the list of unregulated chemicals for which requiring monitoring is required (UCMR). 

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 detection limit for purposes of reporting (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, though more recent findings are included in the monitoring results (Excel, 1.4MB)Opens a new window..  An overview of findings is presented in Table 1.

 

Table 1. Chromium-6 in drinking water sources 1997 through 2008 (Active and Standby Sources)
(See notes 1, 2, and 3 )
Peak level (µg/L) No. of Sources % of Detections
> 50 7 0.3
41 - 50 5 0.2
31 - 40 14 0.6
21 - 30 61 2.8
11 - 20 231 10.5
6 - 10 456 20.7
1 - 5 1,434 64.9
TOTAL 2,208 100

1. Data are extracted from monitoring results (Excel, 1.4MB)Opens a new window.through January 2009.  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)Opens a new window..  If total chromium was below the screening level, specific analysis for chromium-6 was not required.

Early Sampling

Drinking water sources have monitored total chromium since the 1970s, and the results of monitoring have been maintained in the Drinking Water Program's database since 1984.  Of 11,785 sources sampled for total chromium through 2001, detections were reported for 1,311 sources (1,227 ground water and 84 surface water sources).  The detection level for purposes of reporting (DLR )for total chromium is 10 µg/L.  

Until DHS 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.