Data Series 233

Data Series 233

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The Sweetwater Authority (hereinafter referred to as the “Authority”), under the guidance of its Board of Directors, operates a public drinking-water supply system for over 175,000 residential and commercial customers in Chula Vista, National City, and Bonita, California. The Sweetwater Reservoir (SWR) (fig. 1), which has a storage capacity of 34.6 hm3, is located about 15 km southeast of San Diego, California. The Authority also stores water at Loveland Reservoir (LLR) (fig. 1), which has a storage capacity of 31.3 hm3 and is located about 30 km east of SWR near Alpine, California. In addition to the two reservoirs, the Authority operates two deep wells in National City and several alluvial wells near the Sweetwater River in Chula Vista. The Reynolds Desalination Facility, formerly known as the Demineralization Facility, in Chula Vista, treats brackish ground water from the wells along the Sweetwater River. Approximately 70 percent of the water the Authority provides comes from local supplies that include the Sweetwater River and ground water. The remaining water is imported from the Colorado River and northern California sources through pipelines and aqueducts. Both local reservoir and imported waters are treated at the Robert A. Perdue treatment plant located at the SWR.

The Sweetwater River watershed covers 466 km² (fig. 1). Although much of the land is undeveloped, the watershed includes the Sycuan and Viejas Indian Reservations, part of the Cleveland National Forest, agricultural land, rural residential acreage, urban and suburban residential development, mining and industrial land use, commercial recreation, and commercial business development. The watershed currently includes three 18-hole golf courses. During the data-collection period described (water years 2000 and 2001), no recreational activities were allowed at the SWR. Shore fishing is allowed at Loveland Reservoir in a restricted area at the east end of the reservoir. The Authority maintains a motorized boat at each reservoir for routine water-quality sampling and regular shore patrols.

The impact of local inputs of anthropogenic compounds, such as organic chemicals and pesticides, on the watershed and reservoir water quality is largely unknown. The Authority is concerned about the impact that increasing growth and development in the Sweetwater River watershed will have on the quality of their drinking-water supply and has initiated a variety of efforts to protect the watershed. These efforts include source assessments, total-organic-carbon assessments, watershed stakeholders’ outreach program to identify issues, and the construction and operation of an urban-runoff diversion system. These programs help the Authority evaluate and manage the overall environmental health of the watershed by monitoring changes that can degrade the quality of the water supply and necessitate additional water treatment as the population increases and land use intensifies. Responding to these concerns, in 1998, the Authority initiated a monitoring study in cooperation with the U.S. Geological Survey (USGS).

In addition to the increasing urbanization pressures within the watershed, another Authority concern and the primary reason for this study, is the construction and operation of State Route (SR) 125. In 1984, the San Diego Association of Governments added SR 125 to the Regional Transportation Plan as part of San Diego’s future highway system. The SR 125 project (fig. 1) consists of approximately 18 km of roadway construction and alignment that extends from SR 54 (northern terminus) to Interstate 905 (southern terminus). The project plans call for the initial construction of a four-lane toll way that may be expanded to include additional lanes for dedicated transit purposes such as high occupancy vehicles or light-rail (California Department of Transportation, 2001). More than 200,000 vehicles per day, including more than 10 percent of heavy diesel trucks from both the United States and Mexico, are expected to travel SR 125. The alignment will be elevated about 30 m above land surface at its highest point, and the most likely construction scenario will bring SR 125 within about 150 m of the reservoir at its nearest point. Construction of SR 125 was scheduled to begin in 2005 and is expected to be completed in 2007. Because the SWR is downwind of all proposed alignments, the Authority became concerned that toxic vehicle emissions and pesticides used on the roadside, as well as paved-road dusts, might enter the reservoir by atmospheric deposition in concentrations that could affect public health and have an impact on the cost of treating the drinking-water supply.

In 1996, the Authority commissioned a study (Ogden Environmental and Energy Services, 1997) to model the atmospheric depositional loading to the SWR. The model included a variety of toxic compounds from vehicular fuel combustion emissions and any attendant health risks associated with all SR 125 alignment scenarios. The predicted concentrations of selected contaminants were compared with the standards set by the California Safe Drinking Water Act (California Environmental Protection Agency, 1986) and with California and federal maximum contaminant levels (MCL). The model results indicated that drinking-water guidance levels for one or more contaminants would be exceeded in all three alternative freeway construction options. This study was repeated reaching similar conclusions (Byard and Giroux, 1999). Both the Authority and U.S. Environmental Protection Agency Region IX concluded that the findings in the Ogden and the Byard and Giroux reports warranted the implementation of a monitoring program to characterize the impact that atmospheric deposition of vehicular emissions from the operation of SR 125 may have on the quality of the drinking water stored in the SWR.

Purpose and Scope

The purpose of this report is to describe the data that were collected from October 1999 to September 2001 (water years 2000 and 2001), prior to the start of construction of SR 125. This report is the second in a series that describes the monitoring activities and presents the data that will be used to assess the potential impact on water quality in the Sweetwater Reservoir resulting from land-use changes and development in the watershed. Data collected during the first year of sampling (October 1998 to September 1999) were published in Majewski and others (2002). A full interpretation and assessment of the data will be completed at the end of the monitoring study.

The scope of the USGS study is to compare analytical results of samples from three environmental media—air, water, and bed sediment—to determine whether any measured changes in reservoir water quality are the result of atmospheric deposition from the construction and operation of SR 125. Because new chemical contaminants of concern are identified regularly, this project has worked closely with the Methods Research and Development Program (MRDP) group at USGS National Water Quality Laboratory (NWQL) to help bring online new analytical methods for chemicals of concern, such as endocrine disrupting compounds, pharmaceuticals, wastewater indicator compounds, and the ever increasing number of pesticides being used. The MRDP at NWQL continually develops new analytical methods for the various classes of emerging chemical contaminants.

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