Data Series 233
U.S. GEOLOGICAL SURVEY
Data Series 233
Some data tables show more than one laboratory reporting level (LRL) for a compound or element in different samples. This occurs, in part, because reporting levels are updated annually, as necessary, as a component of the NWQL’s yearly assessment of long-term method detection levels and LRLs (Childress and others, 1999). Reporting levels also sometimes vary based on differences in sample volumes or the presence of interferences. Some concentrations are reported as estimated (E). In this case, the compound was determined to be present in the sample on the basis of mass spectral information, but the concentration is less certain because the determined concentration is below the lowest calibration standard or the LRL, whichever is greater, or because of recognized method limitations for certain compounds.
Water samples were collected at three sites in SWR (sites 1, 3, and 6, fig 2), two sites at the Perdue Treatment Plant (sites 8 and 9, fig.2), one site on the Sweetwater River above SWR (site 10, fig.2), and one site at LLR (LLR01, fig. 3). The results for water samples are entered into the USGS National Water Information System database. All sites within SWR, with the exception of site 6, were within the reservoir’s minimum pool boundary to ensure that water would be available for sampling throughout the year. Site 6 was located in the eastern third of the reservoir in very shallow water (fig. 2). As the water level fell, the water depth at this site decreased and the bed sediments became exposed. When this happened, the sampling site was moved to a location where the water depth was about 1 m deep. Sampling sites at both SWR and LLR were marked with stationary buoys anchored to the bottom of the reservoir.
Three water-sampling sites (sites 8, 9, and 10, fig. 2) were established outside the reservoir boundaries. Site 8 monitors the quality of the finished (treated) water as it leaves the treatment plant for distribution to customers. Site 9 monitors the quality of the imported raw water before it enters the treatment plant or resevoir. Site 10, Sweetwater River at the Low-Flow Diversion Dam (LFDD), monitors the quality of the watershed drainage water entering SWR. During low flows, the water from LFDD is diverted into the Urban Runoff Diversion System (URDS) ponds. Local urban runoff and the first flush (initial flow after a dry period, when pollutants might occur in higher concentrations) in the Sweetwater River are diverted into the URDS ponds to prevent unwanted water from entering the SWR. All site identification numbers, sampling site names, and other identifiers are listed in table 1.
In most cases, imported water is pumped by pipeline directly into the treatment plant. Occasionally, this water is pumped directly into SWR to augment the local supply. When imported water is pumped directly into the reservoir, it significantly increases the water level with volume increases on the order of tens of thousands of acre-feet.
Baseline water sampling at both SWR and LLR began in September 1998 and continued at 2-month intervals through September 1999. This bimonthly sampling allowed monitoring of various operational modes of the reservoirs, such as replenishment or withdrawal events that significantly change the water level in the reservoirs. Baseline water sampling also showed the spatial variability in chemical occurrence and concentration in each reservoir. Beginning in October 1999, the sampling frequency was reduced to once every third month (quarterly). The number of sampling sites at SWR was reduced from seven to three, and the two sampling sites at LLR were reduced to one. The reduction in the number of sampling sites was done to focus the sampling efforts on “indicator” sites—those sites that are believed to provide the most relevant information without compromising the scientific integrity of the project. These sites are
Before any reservoir water was sampled, depth profiles of dissolved oxygen, pH, specific conductance, and temperature were measured at 1-m intervals from the surface to the reservoir bottom at each sampling location using a multiparameter water-quality monitor (table 2). At LLR, the depth-profile measurements below 10 m were taken every 2 m because the depth of LLR is much greater than the depth of SWR. If the temperature profile indicated a thermocline, two sets of water samples were collected at the site: one at midepilimnion and one at midhypolimnion. The epilimnion can be defined as the layer in a lake extending from the surface to a depth where photosynthesis no longer occurs. The hypolimnion can be defined as the poorly illuminated lower region of a stratified lake where denser, colder water currents are minimal. The temperature of the hypolimnion is nearly uniform and oxygen is depleted. This stratum of water is characterized by decay rather than by the production of organic matter. If no thermocline was evident, only one sample set was collected at a point midway between the water surface and the reservoir bottom.
The concentrations of VOC analytes detected in water ranged from 0.01 µg/L to 66.6 µg/L, and the results are given in table 3. The concentrations of pesticide analytes detected in filtered water ranged from 0.002 µg/L to 0.02 µg/L, and the results are given in table 4. Any additional analyses that were added to the sampling regime were performed on samples collected from selected sites. That is, these analyses were done to show occurrence and possible source of new analytes of interest, not necessarily their distribution within the watershed.
The purpose of the air data collected at the air sample site (fig. 2) is to establish the occurrence, temporal patterns, and ambient levels of selected airborne organic compounds (VOCs, PAHs, and pesticides). This site was installed downwind of the proposed SR 125 routes and upwind of SWR (fig. 2), along a transect of the predominant wind direction. The site includes a fully instrumented meteorological station that records hourly averages of wind speed and direction, ambient air temperature and relative humidity at two heights, rainfall, barometric pressure, and atmospheric stability. Establishment of this air sampling station followed the guidelines outlined by the National Atmospheric Deposition Program (Bigelow, 1984), with the help of the South Coast Air Pollution Control Board (William Brick, oral commun., 1999).
The first VOC air sample was collected on March 23, 1999. Each sample was a 24-hour composite collected every 12th day. The timing of the VOC sample collection was coordinated with the CARB Air Toxics Program. The LRL for these analytes ranged from 0.02 to 0.06 part per billion by volume. The results for the VOC air samples collected during the time frame of this report are given in table 5A for the 7 compounds with low breakthrough volumes. Table 5B gives the results for the remaining 79 VOCs.
The first PAH and pesticide air sample was collected during the week of May 11, 1999. Each sample was a 24-hour/7-day weekly composite collected every third week. Air samples were not collected at LLR because its foothill location (30 km east of SWR) is considered sufficiently downwind of SR 125 to be minimally impacted by any airborne contaminants originating from it. Analytical results for PAHs in air samples collected during the time frame of this report are given in table 6. PAHs with molecular weights less than 178 Daltons are not reported because of incomplete collection on PUF at the sampled volumes (You and Bidleman, 1984). Compounds analyzed for pesticides in air samples using a modification of NWQL water Schedules 2001 and 2002 are given in table 7A. Results for these pesticides analyzed using a modification of NWQL water sample Schedules 2001 and 2002 are given in tables 7B and 7C, respectively. Not all of the compounds that were determined by the corresponding water methods are reported for the air samples because certain analytes were known to have incomplete collection on the PUF plugs based on a previous study (Foreman and others, 2000) or inadequate analytical performance in the air method.
The first special study, which began in January 2000, focused on moderate-use pesticides in filtered water analyzed using NWQL Schedule 2002 (table 8). Between January 27 and February 12, 2000, water was transferred (11.2 hm3) from LLR to SWR via the Sweetwater River. Because there are several golf courses along the Sweetwater River between LLR and SWR, this water transfer was an opportunity to examine whether pesticides used on the golf courses would accumulate in the river channel during extended dry periods and be carried downstream with the initial flow of the river after a dry period (first flush). This first-flush sampling occurred on the 29th and 30th of January 2000 at two sites along the Sweetwater River. One sample was collected at the Steele Canyon Bridge at Cottonwood Golf Course site (fig. 1) as the released water was passing through the area. Four additional samples were collected at the LFDD (site 10, fig. 2) at approximately 12-hour intervals. One sample was collected in early January at the LFDD for comparison with the first-flush data. In addition, several samples from SWR (sites 1 and 3, fig. 2), the LFDD, and the imported raw water (site 9, fig. 2) were taken in June and September 2000 and analyzed using this method (table 8).
The second special study investigated concentrations of dissolved-phase organochlorine compounds (legacy persistent organic pollutants), PAHs, and other semivolatile organic compounds using semipermeable membrane devices (SPMD). The organochlorine compounds and PAHs, especially, have low water solubility and are of concern with regard to human health. This study was conducted during a period of extended dry weather when the water level in SWR was low. Three SPMDs were deployed in January 2001 near the pump tower (site 1, fig. 2); one was implaced for one month and two for two months. The results are presented in tables 9A and 9B.
SPMDs are flat polyethylene plastic tubes filled with triolein, a lipid-like material. The polyethylene membrane of the SPMD allows dissolved (bioavailable) contaminants to pass through the membrane while excluding water. The triolein inside the SPMD is similar in characteristics to a highly purified fish fat. The contaminants dissolve in the triolein just as they do in the fats of a fish. The SPMD was placed on a rack, which was inserted into a protective stainless steel container that was then submerged in the water at a depth of 1 m. SPMDs collect contaminants in the water that are often hard to detect through normal chemical sampling procedures because they are present at such low dissolved-phase concentrations. SPMDs measure the bioavailable form of a chemical that an organism can absorb and incorporate. Very low concentrations of certain contaminants (such as PAHs, organochlorine pesticides, and polychlorinated biphenyls) may still be important in the environment because of their ability to bioconcentrate in animals (by dietary uptake or uptake through fish gills with subsequent accumulation in the animal’s fat). The concentrations of these chemicals in rivers can change daily or even hourly, but their concentrations in reservoirs are expected to be more constant. The SPMD allows the calculation of an average concentration of each contaminant per kilogram of SPMD during the period that the sampling device is in the water.
The third special study analyzed additional water samples from various sources for copper concentration in April and July 2001 (table 10). In April, two water samples were taken at the Perdue Treatment Plant—finished and imported waters; and one taken at the Reynolds Desalination Facility—discharge water. The Reynolds Desalination Facility uses reverse-osmosis treatment to remove dissolved salts and microscopic particles that could be found in alluvial ground water. The facility, completed in 1999, can produce four million gallons of drinking water a day. The sample collected at the Desalination Facility was from the plant discharge, which is referred to as “sample point 45” because it is the compliance point for the facility’s National Pollutant Discharge Elimination System (NPDES) permit. The sample was collected just before the discharge went into a concrete channel that flows to the Sweetwater River. This sample was a composite sample taken over a 21-hour period.
In July, ten water samples were collected for dissolved copper determination (table 10): one at the Perdue Treatment Plant (finished water) (site 8, fig. 2), four at the Reynolds Desalination Facility (fig. 1), and five at selected San Diego Formation wells (SDF1 through 5, table 1, fig. 1). The Desalination Facility samples were collected from the inflow, feed, effluent, and discharge. The inflow sample point is raw water coming into the plant from ground-water wells. The feed sample point is the inflow water filtered through a cartridge with sulfuric acid with a scale inhibitor added. The effluent sample point is water that goes into the drinking-water system. The discharge sample point is water that goes back to the Sweetwater River. The five ground-water wells that were sampled supply water that feeds into the plant. Depending on the needs of the plant, all or a combination of these San Diego Formation wells make up their inflow.
The fourth special study analyzed VOCs in water from two National City wells that the SWA uses to supplement their drinking-water supply. These wells were sampled so that SWA would have a better understanding of measured VOCs in their supplemental drinking water. The results from sampling these two wells in April 2000 are listed in table 11.
The fifth special study analyzed dissolved trace metals in reservoir water samples collected in March 2001 (table 12). A variety of trace metals occur naturally, but are also emitted from auto exhaust, tire wear, and road dust. These analyses were added to help understand the role of atmospheric deposition of trace metals originating from the SR125 alignment and their affect on water quality.
The last special study analyzed contaminants typically associated with wastewater effluent in reservoir whole-water samples (sites 1, 8, 9, fig. 2, and LLR01, fig. 3) collected in December 2000 and March 2001 (table 13). Some compounds have a second LRL because the laboratory quality control required that the level be raised to decrease the possibility of false positives. The laboratory reporting levels for some compounds were higher in the March 2001 samples.
U.S.
Department of the Interior | U.S. Geological Survey
Persistent URL: https://pubs.water.usgs.gov/ds233
Page Contact Information: Publications
Team
Page Last Modified: March 8, 2007
