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History of Perchlorate in California Drinking Water

Last Update: October 19, 2007

Sampling for perchlorate by CDHS (the Department of Health Services, now CDPH) began in February 1997, when perchlorate was first found in drinking water wells in eastern Sacramento County, near Aerojet General Corporation's facility, reflecting the use of ammonium perchlorate as a solid rocket propellant.  

These findings prompted the Sanitation and Radiation Laboratory (SRL) to develop an analytical method (PDF)Opens new browser window.that was substantially more sensitive than other methods, and able to detect perchlorate at levels as low as 4 µg/L.  Shortly thereafter, SRL established a process by which commercial laboratories could be approved for the more sensitive analysis. That process remained in use until US EPA's Method 314.0 — Determination of Perchlorate in Drinking Water by Ion Chromatography — became effective, and its list of approved laboratories became available.

In April 1997, we sampled wells in southern California and found perchlorate in drinking water wells in Los Angeles County, where several sites have been identified as potential sources of contamination, including an Aerojet facility (Azusa), the Whittaker-Bermite site (Santa Clarita), and the Jet Propulsion Laboratory (Pasadena). 

We also found perchlorate in drinking water wells in Riverside County and in San Bernardino County drinking water wells. The perchlorate contamination is in a trichloroethylene plume associated with past operations of the Lockheed Propulsion Company. Perchlorate at 270 µg/L was in an inactive well near a defunct fireworks site near Rialto. We also found perchlorate in 24 agricultural wells in San Bernardino County, in concentrations of 11 to 221 µg/L.

Sampling also showed perchlorate at low levels (5 - 9 µg/L) in Colorado River water, an important source of drinking water and water for agriculture (irrigation) in southern California. The Colorado River's perchlorate results from ammonium perchlorate manufacturing facilities in Nevada.

At about the same time, several Regional Water Quality Control Boards (RWQCBs) advised us of several other locations of perchlorate in groundwater not associated with contamination of public drinking water supplies.  RWQCB sites included: (1) an explosives facility in Placer County near Lincoln (1,200 and 67,000 µg/L), (2) In Santa Clara County, United Technologies in Santa Clara County ( up to 180,000 µg/L), and (3) the Whittaker Ordnance Facility in San Benito County near Hollister (up to 88 µg/L with an agricultural well in the vicinity at 34 µg/L, and a private well, 810 µg/L). 

Advisory Levels and Requirements for Monitoring

Notification Level:  In 1997, we established an "action level" (now called a "notification level") of 18 µg/L, based on the upper value of the 4- to 18-µg/L range calculated from US EPA's 1992-1995 "provisional" reference dose (RfD) for perchlorate. Later, in January 2002, following release of a revised US EPA external review draft perchlorate RfD that corresponded to 1 µg/L in drinking water, we concluded that the action level needed to be revised downward and reduced it to 4 µg/L, the lower end of US EPA's 1992/1995 range of values, and the same as the analytical detection limit for purposes of reporting.  The notification level was revised to the 6 µg/L in March 2004, when the Office of Environmental Health Hazard Assessment established perchlorate's public health goal.   Use of a notification level ended when we adopted an MCL for perchlorate, effective October 2007

Monitoring Requirement:  In 1999, we adopted a regulation that added perchlorate to the list of unregulated chemicals for which monitoring is required (UCMR).  Of the ~4,400 community systems and non-transient non-community systems (~12,000 drinking water sources), those that were considered vulnerable to perchlorate contamination were subject to UCMR requirements. Systems with fewer than 150 service connections could be exempted. The UCMR monitoring was to have been completed by December 31, 2003.  The regulation was repealed in October 2007.

Subsequent Analyses

Table 1 presents the number of drinking water sources of any type with detections of perchlorate at any level, by year first detected through 2005. Data are draft, and will change with subsequent updates.  They represent results from over 7,000 drinking water sources in the department's water quality monitoring database.  Sources with two or more reported perchlorate detections (Excel, 1.0MB)Opens new browser window.at any concentration are included.  "Sources" in the database are both raw and treated active sources, distribution systems, blending reservoirs, and other sampled entities, including standby, inactive, and abandoned or destroyed wells.  For the table we excluded agricultural sources, monitoring wells, or more than one representation of the same source (e.g., a source with both a raw and treated entry, or with a distribution system or blending reservoir is counted as a single source).  We use a 4-µg/L detection limit for purposes of reporting (DLR).  Detections at or above the DLR are required to be reported.  Some laboratories report findings at lower concentrations.   This table includes reported detections lower than the DLR.

Table 1. Drinking water sources with perchlorate detections.

County Year initially detected Total No. of Sources Peak level (µg/L)


1999 2000 2001 2002 2003 2004 2005
Los Angeles 54 31 21 13 8 24 7 12 7 177 159
San Bernardino 31 1 1 8 34 8 3 4 5 95 820
Riverside 14 5 5 11 16 19 10 3 1 84 73
Orange  - 20 - - 1 9 7 - - 37 11
Sacramento 10 2 - 1 - 1 - 1 9 24 400
Tulare - - - 2 11 1 - - - 14 24
Santa Clara - - 1 2 1 2 3 - 1 10 8.5
San Diego -  - - - 1 - - 4 - 5 7
Ventura - 1 1  - - - 2 - 4 20
Imperial - - - - 3 1 - - - 4 6
Sonoma - - - 1 - - - - - 1 5
Stanislaus - - - - - - 1  - - 1 3.3


 109 60 29 38 75 65 31 26 23 456 -


More recent data for active and standby wells with perchlorate at or above the DLR are presented here.

Last modified on: 3/23/2011 12:37 PM