Water-Quality Monitoring of Sweetwater Reservoir he Sweetwater Reservoir has Sweetwater Reservoir Study Authority to evaluate the environmental been supplying water to local res- Objectives health of the watershed by monitoring T idents since 1888 and is presently changes that may degrade the quality of • Assess the chemical impact on water operated by Sweetwater Author- the water supply and by applying addi- quality in the reservoir resulting from ity (Authority) under the guidance of its tional water treatment if necessary. This board of directors. The Authority is the land-use changes and development in report describes a cooperative moni- third largest water retailer in San Diego the watershed. toring study by the Authority and the County and serves residential and com- • Compare chemical concentrations of U.S. Geological Survey (USGS) mercial customers in Chula Vista, samples from air, water, and bed sedi- designed to assess the impact of increas- ment, and determine if any changes in National City, and Bonita, California. ing urbanization on the water quality of The water is supplied from a combina- reservoir water quality are the result of atmospheric deposition of organic Sweetwater Reservoir. tion of sources, including local surface chemicals and metals originating runoff, ground water, and imported One urban project that has the poten- from the construction and operation tial to affect the water quality of Sweet- water from the San Diego County Water of SR-125. Authority. The surface runoff—and water Reservoir is the construction and when needed, imported water—are operation of State Route 125 (SR-125). stored in Sweetwater Reservoir, which Forest; agricultural land; rural, urban, In 1984, the San Diego Association of is located about 9 miles southeast of San and suburban residential developments; Governments added SR-125 to the Diego, California. Runoff from the mining and industrial land use; and Regional Transportation Plan as part of upper watershed is stored in Loveland commercial recreation and business San Diego’s future freeway system. The Reservoir, which is located about 19 developments. The watershed also SR-125 alignment connects SR-125 to miles east of Sweetwater Reservoir, includes four golf courses. The Author- SR-905 (fig. 1). The initial project will near Alpine, California. The Sweetwater ity, very concerned with identifying all be a four-lane tollway that will be River watershed contains these two res- factors that can degrade water quality, is expanded to eight lanes (Caltrans, ervoirs and covers an area of 180 square implementing ways to protect the water- 1996). More than 200,000 vehicles per miles (fig. 1). shed. These efforts include education of day, including a high percentage (more The Sweetwater River watershed is watershed stakeholders, studies to eluci- than 10 percent) of heavy diesel trucks undergoing a rapid change in land-use date the relation between water quality from both the United States and Mexico, patterns as urbanization increases. The and watershed characteristics, and the are expected to travel the SR-125 align- watershed includes two Indian reserva- construction of an urban runoff diver- ment when it is completed. The align- tions; part of the Cleveland National sion system. These programs help the ment will be upwind of the reservoir, elevated about 100 feet at its highest 117° 00' 116° 30' point, and within 500 feet of the reser- voir at its nearest point. Because of these Road factors, the Authority is concerned that Stream vehicle emissions, as well as road dusts, SR-125 alignment might enter the reservoir by atmospheric Watershed boundary deposition in concentrations that exceed Reservoir governmental health standards and thus, increase the cost of treating the reservoir 79 water. 32° 52' 30'' Alpine USGS Monitoring Program 8 er Riv ater In 1998, the USGS began a study to Sweetw 8 monitor the effects of the construction and operation of the SR-125 alignment CALIFORNIA 8 Loveland on the water quality in Sweetwater Res- Reservoir ervoir and to assess the overall health of San Francisco 32° 45' 94 the watershed with respect to chemical contamination. Three environmental S17 125 Study compartments—air, water, and bed sedi- Area 94 Los ments—in the Sweetwater watershed are Sweetwater Angeles 0 2 4 Miles Reservoir San regularly sampled for chemical contami- to SR-905 0 2 4 Kilometers Diego nants:
Figure 1. Sweetwater and Loveland Reservoirs, the surrounding watershed, and the proximity • Air—sampled for volatile organic of SR-125 to Sweetwater Reservoir. compounds (VOCs), polynuclear
aromatic hydrocarbons (PAHs), and by 2.5 inches in diameter, were environment. DDT use began in 1939 pesticides. collected from the lower part of Sweet- and peaked in the 1960s (Majewski and • Water—sampled for VOCs and water Reservoir on September 24, 1998. Capel, 1995). Its widespread use contin- pesticides. The sampling site was located in an ued in the United States until it was • Bed sediments—sampled for PAHs, undisturbed area so that the core sample banned in 1972. DDT breaks down into polychlorinated biphenyls (PCBs), would reflect the undisturbed, natural two products, DDE and DDD, that pesticides, and major and trace sedimentation buildup in the reservoir. accumulate in sediment and both of One core was subsampled at discrete elements. which are also toxic and very resistant 1.6-inch intervals, and each segment to further chemical breakdown. DDE Study Design was analyzed for organochlorine insecti- and DDD were detected in the Sweet- cides, industrial compounds, the isotope water Reservoir sediments that were The study is divided into two phases. cesium-137, major and trace elements, deposited beginning in the late 1940s or During Phase I, the detection frequency grain size, diatoms, and pollens. The early 1950s (fig. 3). The concentration and concentration levels of select con- second was split lengthwise and of total DDT (sum of the DDT, DDE, taminants in the air, water, and bed sedi- inspected for color, texture, odor, ments are measured. These data will and DDD concentrations) in the sedi- organic detritus and benthic inverte- ment deposits peaks around 1964. establish baseline conditions for the brates, and original land-surface mate- target compounds of concern to the Together, cesium-137 and total DDT rial before the Sweetwater dam was concentrations allow for reliable dating Authority. During Phase II, sampling built. will continue at the established moni- of the sediment sections from 1940 to toring sites during and after the con- The age of the core sections can be the present. Once the core sections have struction of SR-125. The chemical estimated from the concentration of been dated, the chemical record of land- concentrations from Phase II moni- anthropogenic compounds, such as use activities in the watershed can be toring will be compared with those from cesium-137 and DDT, that were intro- examined. Phase I to assess the inputs of organic duced into the environment at known PAH compounds are another group of compounds resulting from changing chemicals that are long-lived in the land-use practices in the watershed and environment (National Research will determine what impact SR-125 has Council, 1983). They are produced on the water quality of Sweetwater during the combustion of organic sub- Reservoir. stances such as coal, oil, gas, and gar- Many of the sampling and analytical bage, and during brush and structure methods used in this study were devel- fires; they also are present in automo- oped for the USGS’s National Water- bile and diesel exhaust, as well as in Quality Assessment Program (Gilliom uncombusted petroleum products. PAHs and others, 1995). The results are are present in the air as gases and on entered into the USGS’s National Water Information System database so that DDT concentration water-quality data from Sweetwater (parts per billion) Reservoir can be compared with data 0 5 10 15 20 25 30 35 from other water supplies throughout 1998 the nation. 000–004 008–012 Total DDT 016–020 Cesium-137 Methods and Results 024–028 032–036 Bed Sediment 040–044 The bed sediments in the Sweetwater 048–052 056–060 Reservoir come from a variety of 064–068 sources. They wash off the surrounding 072–076 land surface and are transported by the 080–084 ~1970 Bed sediment coring at Sweetwater 088–092 Sweetwater River during rainstorms and Figure 2. 096–100 Reservoir. water transfers from Loveland Reser- 104–108 ~1964 voir. They also come from direct deposi- times. Cesium-137, a radioactive by- 112–116 tion of airborne dust and particles. Over 120–124 product of nuclear weapons testing, is 128–132 ~1952 time, these sediments accumulate and deposited into the watershed only from 136–140 form a thick layer on the bottom of the the atmosphere. Measurable concentra- 144–148 152–156 reservoir. The chemical composition of tions of this isotope first appeared in the deposited sediments changes over 160–164 the atmosphere around 1952 with the Core segment depth, in centimeters 168–172 time, thus reflecting the historical activ- advent of large-scale weapons testing, 176–180 ity in the watershed. An analysis of dis- then peaked around 1963 (Pennington crete slices of a sediment core provides and others, 1973). The top of the core 0 0.1 0.2 0.3 0.4 0.5 0.6 information on historical water-quality was assigned the sampling date (Sep- Cesium-137 conditions (Charles and Hites, 1987). tember 1998). (picocurie per gram) Sediment samples from the Sweetwater Reservoir were taken using a gravity Organochlorine insecticides like Figure 3. Total DDT and cesium-137 concentra- piston corer (fig. 2). Two sediment DDT are generally characterized by tions in bed sediment core segments from cores, approximately 75 inches in length their persistence and toxicity in the Sweetwater Reservoir. ~, approximately.
900 VOCs also are routinely detected in and Loveland Reservoirs, the most 800 the water at both reservoirs. Sources of likely sources of MTBE are from run- 700 these compounds include industrial sol- off and atmospheric deposition. The 600 vents, refrigerants, aerosol propellants, average concentrations of MTBE and 500 Trend line 400 petroleum production, dry cleaning the other VOCs detected at both res- 300 operations, plastic foam production, ervoirs are hundreds of times lower 200 and vehicle emissions. Common than the California primary and sec- (parts per billion) 100 ondary drinking water standards of otal PAH concentration otal PAH household products that contain VOCs T 0 1930 1940 1950 1960 1970 1980 1990 2000 include pesticides, painting supplies, 13 and 5 ppb, respectively (California Code of Regulations, 1998). The Estimated date of sediment deposition solvents, adhesives, cleaners and waxes, moth crystals, air fresheners, water quality in Sweetwater Reser- Figure 4. Total PAH concentrations in bed sedi- voir is very good with respect to the ment core segments from Sweetwater Reservoir. fabric protectors, chlorine bleach, and tobacco smoke. The gasoline additive monitored chemical contaminants, particulate matter, as well as on street methyl tert-butyl ether (MTBE) is clas- which are expected to increase dust. Although they are not very soluble sified as a VOC and is routinely because the dominant source of these in water, they can accumulate in fish and detected in both reservoirs at an aver- chemicals is urban activities. other wildlife that live in and around the age concentration of about 0.16 ppb Air reservoir. PAHs are ubiquitous in the (fig. 6). MTBE has been detected in environment and are good indicators of Many chemicals become airborne almost every reservoir in California during their manufacture or use and urban development. Figure 4 shows a (California Department of Health Ser- steady increase in PAH concentration can be present in gaseous and particle vices, accessed February 12, 2001). form. The atmosphere plays an over the past 70 years coincident with Table 1 shows that the MTBE concen- important role in moving these air- increasing urbanization over time. trations found in Sweetwater and borne chemicals from their point of Loveland Reservoirs are many times origin and depositing them into areas Water where their presence was 0.030 never intended. Dry deposi- The water in Sweetwater Simazine at Sweetwater tion of airborne gases and par- Reservoir also comes from a 0.025 Simazine at Loveland Prometon at Sweetwater ticulate matter is generally a variety of sources including Prometon at Loveland direct rainfall, local runoff, 0.020 Diazinon at Sweetwater continual and slow process. Precipitation cleans the and imported water. The 0.015 chemical composition in the atmosphere of airborne pol- local runoff reflects the 0.010 lutants and rinses the land sur- (parts per billion) urban, industrial, rural, and Concentration face of the accumulated dry
natural land-use activities in 0.005 deposition (Majewski and the watershed (Lopes and 0 Capel, 1995). The resulting Dionne, 1998). The water is runoff, including everything it 20 Apr. 14 Apr. 17 Oct. 22 Oct. 19 Feb. 14 Feb. 20 Jan. 15 Jan. 19 July 13 July 21 Dec. 16 Dec. 21 Nov. 16 Nov. 23 Aug. 20 May 14 May 18 Aug. 21 Mar. 15 Mar. has collected from the atmo- 19 June 13 June 22 Sept. sampled on a regular basis at 17 Sept. various locations within 1998 1999 2000 sphere and the land surfaces, Sweetwater and Loveland Sampling date replenishes the drinking- Reservoirs. These samples water reservoirs. It is critical are analyzed for various pes- Figure 5. Water concentrations of the herbicides simazine and in any assessment of water- ticides and VOCs used today. prometon and the insecticide diazinon in the Sweetwater and Loveland shed health to monitor the Two herbicides—simazine Reservoirs. atmosphere for the type, and prometon—are frequently detected at lower than the concen- both reservoirs. The insecticide diazinon trations found in other is also routinely detected, but only at southern California res- 1.5 Sweetwater. These pesticides are used for ervoirs. When water MTBE in water agricultural and urban purposes. Figure 5 from other reservoirs is MTBE in air shows that the concentrations in water for transferred into Sweet- 1.0 these pesticides are extremely low, with water Reservoir, how- average concentrations—0.015 parts per ever, the chemical contaminants also are billion (ppb) simazine, 0.006 ppb prome- 0.5 ton, and 0.007 ppb diazinon—many times transferred. (parts per billion) lower than maximum contaminant levels In other state reser- Concentation and health advisories set by State and voirs, MTBE water Federal governments (Majewski and concentrations are gen- 0 Capel, 1995). Sources for these pesticides erally associated with 20 Apr. 14 Apr. 14 Apr. 22 Oct. 17 Oct. 13 July 19 July 19 Feb. 14 Feb. 20 Jan. 15 Jan. 20 May 14 May 21 Dec. 16 Dec. 21 Nov. 21 Nov. 16 Nov. 16 Nov. 21 Mar. 21 Mar. 15 Mar. 15 Mar. 23 Aug. 18 Aug. 19 June 13 June 22 Sept. 17 Sept. include runoff from agriculture use, gasoline-powered 1998 1999 2000 water craft (Dale and maintenance of roadways and other Sampling date rights-of-way, home and garden use, and others, 2000). Because atmospheric drift during and after any there is no public boat- Figure 6. MTBE water concentrations at Sweetwater and Loveland application. ing in the Sweetwater Reservoirs, and MTBE air concentrations at Sweetwater Reservoir.
Table 1. MTBE concentrations in select southern California the SR-125 alignment. The site California Code of Regulations, 1998, Title 22, reservoirs includes a fully instrumented Division 4, Chapter 15, Article 4, Sections [Current California Primary Standard for drinking water is meteorological station (fig 7) 64444 and 64449. 13 ppb (parts per billion)] that records hourly averages of California Department of Health Services, Reservoir Concentration wind speed and direction, ambi- MTBE in drinking water; surface water range (ppb) ent air temperature and relative sources, accessed Feb. 12, 2001, at URL Lake Perris (Los Angeles County) 3.6–15.0 humidity at two heights, rain-