The IRWD site has an updated Q&A section re: the TCE/El Toro issue which seems to answer the most commonly asked questions and questions that have come up at IHB on this subject. It looks like it was last updated 4/5/09:
"1. Does IRWD?s drinking water contain TCE?
No. TCE has never been detected in the drinking water served to any IRWD customers. IRWD obtains drinking water from two sources: 1) water imported by the Metropolitan Water District of Southern California from the Colorado River or Northern California, and 2) locally-available groundwater. Most of IRWD?s groundwater supplies are obtained from its Dyer Road Wellfield, which consists of 18 drinking water wells located in Santa Ana. IRWD does not have any drinking water wells that are located in the TCE plume emanating from the former El Toro Marine Corps Air Station (ETMCAS). IRWD?s Dyer Road Wellfield is nearly 3.5 miles from the leading edge of the ETMCAS plume.
TCE has never been detected in the IRWD drinking water distribution system, which is routinely tested for TCE. In addition its standard testing protocol, IRWD has performed specific testing on five separate occasions since May 2006 at seven locations throughout the Woodbridge area; no TCE was detected in IRWD?s drinking water.
2. What about the IRWD 2008 Annual Water Quality Report shows trace levels of TCE in IRWD?s?
In 2007, TCE was detected at trace levels in one of IRWD?s 18 drinking water wells, Well No. 3, located in Santa Ana. At the time the TCE was detected in this well, it was removed from service. IRWD?s 2008 Annual Water Quality Report, which reflects the results of testing performed in 2007, reported water quality sampling data from all water sources to the IRWD drinking water system.
The concentration of TCE noted in the 2008 IRWD water quality report for Well No. 3 indicated a range of detections from non-detect to 0.8 parts per billion. The laboratory detection limit for TCE is 0.5 parts per billion. The allowable California Safe Drinking Water standard is 5.0 parts per billion ? more than six times the highest amount found in IRWD?s Well No. 3.
Note: The 2009 IRWD Annual Water Quality Report will show that no TCE was detected in any IRWD wells or drinking water in 2008.
...
6. Isn?t the TCE plume emanating from the former ETMCAS changing its shape?
Yes. The objective of the TCE plume clean-up program is to reduce the size and concentration of the plume. Because of the groundwater tends to move ?down-gradient? (toward lower pressures), the size, shape, depth and location of a plume will change over time. Since the clean-up of the TCE plume at the former ETMCAS began, moderate changes in the shape and location of the plume were expected and have been observed.
The shape and location of the TCE plume is based on data obtained from wells monitored by OCWD and the Navy. Water samples from these wells are tested on a quarterly basis and, from these tests, the lateral and vertical dimensions of the plume are calculated using proven scientific methods. The dimensions of the plume are included in updated maps of the TCE plume which are available for public viewing in groundwater monitoring reports at the Heritage Park Library.
The most current map shows the leading edge of the plume (where TCE has been detected) is located approximately three miles from the former ETMCAS, near Culver Drive in Irvine. The plume is not threatening San Diego Creek because gradient pressures in the aquifer pushes the water down and away from, not up and towards, San Diego Creek. At this time we estimate the depth of the TCE plume ranges from 150 to 500 feet beneath the Woodbridge area in Irvine.
7. Since TCE is ?volatile?, do IRWD customers risk exposure to TCE vapors while taking a shower?
No. IRWD?s drinking water has no detectable levels of TCE, so there is no risk of exposure to TCE ?vapors? while taking a shower. Furthermore, pink scum that may be present in shower stalls is not linked to TCE; it is a type of bacteria (Seratia marcescens) that can be removed with a common household cleaning product.
8. Is there an elevated frequency of cancer in the Woodbridge area of Irvine?
No. Inquiries with the California Department of Public Health?s California Cancer Registry show that this agency has not identified any elevated cancer frequencies in the Woodbridge area of Irvine. The mission of the California Department of Public Health?s California Cancer Registry is to collect statewide data, and conduct surveillance and research into the causes, controls, and cures of cancer and communicate the results to the public. Residents that concerned about cancer frequencies in the Irvine area should contact Dr. Thomas Mack of the California Cancer Registry at (323) 865-0445.
9. Is there a risk of TCE vapors rising out of the TCE plume from the former ETMCAS base and contaminating homes and businesses over the plume?
No. The United States Environmental Protection Agency (US EPA) has determined that there is no risk of TCE vapors emanating from the TCE plume and contaminating existing homes and businesses located above the plume. The US EPA will continue to evaluate the groundwater data from the Woodbridge area to ensure that the plume does not present a risk for residents in this area. Contact Rich Muza of the US EPA, at (415) 972-3349 or muza.richard@epa.gov for further information.
It is incorrect to conclude that TCE vapors could be present in homes overlying the plume simply because TCE vapors have been found in homes in other areas of the United States where TCE is present in groundwater. The following three existing conditions prevent TCE vapors from migrating from the plume to the ground surface: 1) layers of soil, rock and water, as confirmed by technical mapping of the groundwater basin, seal off and restrict the ability of TCE (in liquid or gaseous form) from moving though these layers to the surface; 2) TCE dissolved in water can only transform into a gaseous state under dry conditions, which is impossible in the Woodbridge area due to the observed presence of layers of shallow groundwater without TCE; and 3) the natural vertical flow of the groundwater is downward, thereby causing the plume to also trend downward, not upward toward the ground surface. Because of these conditions, it is impossible for TCE vapors to emanate from the plume and migrate through the soil to the surface. ..."