Chromium-6 in Drinking Water: Sampling Results
Last Update: September 28, 2007
In 2001 the California Department of Health Services (DHS, now CDPH) adopted a regulation that added chromium-6 to the list of unregulated chemicals for which requiring monitoring is required (UCMR). The monitoring data that are collected 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 drinking water standard.
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 the UCMR regulations Systems with fewer than 150 service connections may be exempted from the monitoring requirement.
Recent Monitoring Results
Monitoring for chromium-6 under the UCMR was to have been completed by December 31, 2002.
Results of monitoring over 7,000 drinking water sources showed chromium-6 detection (Excel)
at or above the 1-µg/L detection limit for purposes of reporting (DLR) in about one-third of them. Occurrence is mostly at low levels: 86% had peak detections at or below 10 µg/L.
| Chromium-6 in drinking water (See notes 1,2 and 3) |
| Peak level (µg/L) |
No. of Sources |
% of Detections |
| > 50 |
6 |
- |
| 41 - 50 |
6 |
- |
| 31 - 40 |
13 |
1 |
| 21 - 30 |
52 |
2 |
| 11 - 20 |
237 |
10 |
| 6 - 10 |
487 |
21 |
| 1 - 5 |
1,516 |
65 |
| TOTAL |
2,317 |
- |
1. "Sources" are those reporting more than a single detection of chromium-6 and may include both raw and treated sources, distribution systems, blending reservoirs, and other sampled entities. This table does not include 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). Data should be considered draft.
2. A number of sources may have been screened using a 1-µg/L reporting limit for total chromium (PDF). If below that level, specific analysis for chromium-6 was not required.
3. As of January 24, 2006 |
Prior 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.
Ground Water Samples
- 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).
- Also 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).
Surface Water Samples
- In 2000, DHS took four samples from a source in Solano County. Total chromium was 0.5-8.9 µg/L, and chromium-6 was ND.