In order to measure the presence of MTBE in California drinking water supplies the DHS in February 1997 required public water utilities to begin testing their sources of drinking water for MTBE. Although this paper focuses only on surface public drinking water sources monitored by the DHS, it is worth noting that the problem of ground water MTBE contamination appears to pose a greater threat than surface water contamination, and is also monitored by the DHS. For example, the City of Santa Monica in 1996 had to shut down the majority of the City's drinking water wells due to MTBE contamination. South Tahoe Public Utility District has been forced to close at least 13 of its 34 drinking water wells due to MTBE contamination or the threat of contamination. As a result of MTBE contamination, public drinking water wells have been closed down in Santa Clara County, the City of Sacramento, and the towns of Glennville, Riverview, and Cambria. Some water districts have imposed restrictions on motorized recreation at surface water reservoirs to reduce the release of MTBE from two-stroke marine engines, but two-stroke marine engines are not the only source of MTBE surface source contamination. Lakes and reservoirs where no gasoline-powered boats are allowed have been found to contain MTBE. In addition to two-stroke marine engines as a source of contamination, MTBE-laden fuel spilled at gasoline stations is eventually washed into storm drains, and then on to creeks, streams, rivers, lakes and reservoirs.  Due to its extremely high water solubility,  MTBE, whether from engine exhaust or evaporation, combines with water vapor and rises up into the atmosphere, eventually falling back to earth with precipitation, often many miles distant from where it originated, even upon isolated pristine mountain lakes and ponds.

Methods

After doing a search on the internet for information on MTBE contamination, the best source of data within the scope of this project was found to be California Department of Health Services' (DHS) website. DHS provides summary tables of ground and surface drinking water sources in which MTBE has been detected in two or more samples taken from the same source. Because the exact locations (latitude/longitude) of water wells is not provided by the DHS website, it was decided to focus only on surface sources. It was hoped that these sources (in most cases lakes or reservoirs) could be easily located by name and mapped using Arc View GIS. A problem became immediately apparent. Some of the source names used in the DHS table either could not be found in the Arc View dbf table of names, or multiple candidates with similar names were found. To clarify the situation, an internet search was done to find the websites for each public water agency listed in the DHS table. Each agency's site was then visited to search for information to determine the name and location of the most likely source name matching the one cited in the DHS table. If available, service area maps and photographs of these were downloaded. In the beginning stages of the project the author found the software program Street Atlas 7.0 helpful in finding where some of the more obscure sources were located. Once a likely geographic location and its proximity to other water bodies nearby was determined, that area was zoomed-in-to on the ArcView map, and, if a water body was found that matched, Arc View's "Identify" tool was used to determine the Arc View .dbf name.

Results

The DHS currently reports that out of 455 surface public drinking water sources sampled in California for MTBE, 21 (4.6%) have had two or more positive test samples.  The author was able to show locations for all except three surface sources listed in the DHS table.  Given more time, these would have been located.   The table below was downloaded from the DHS website and source location information was added by the author using a combination of author-created Arc View GIS maps and material downloaded from other online sources.