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Continued from font page have come from maintenance and (TPH) (found near the sites of Earlier this year, 163 wells were sampled. waste management activities that took former underground fuel storage TCE was detected above the MCL in 53 place before 1976. Current activities tanks) of these wells. Only 7 wells contained at Sharpe do not pollute the • Arsenic and selenium (naturally- TCE at concentrations exceeding 100 environment. occurring elements) in very small ppb. The highest concentration of TCE amounts, and was found at 370 ppb in monitoring well Area residents who receive their • Bromacil (an herbicide) in very 437B, located in the central area of the drinking water from the city of small amounts depot near the western boundary. Lathrop's municipal water supply are not exposed to contaminants TCE is the chemical of greatest Groundwater Treatment. DDJC has from Sharpe. Municipal wells draw concern at Sharpe because it is installed three "air stripping" groundwater from a deep, uncontaminated water present in the greatest amounts. treatment systems to remove TCE and source, and they are not located in TCE and, to a lesser extent, PCE are PCE from the groundwater. These the direction of groundwater flow found in groundwater that is moving systems are called the South Balloon from Sharpe. The city will continue from the depot in a northwesterly Treatment Plant (constructed in 1988), to regularly monitor the municipal direction. The groundwater "plumes" the North Balloon Treatment Plant (1990) water supply to ensure that the (the term "plume" refers to defined and the Central Area Treatment Plant water continues to meet California areas of contamination) containing (1995). drinking water standards. most of the TCE and PCE are located between 40 feet and 120 feet below After the air strippers have removed the Since the early 1980s, DDJC has the ground surface. chemicals from the groundwater, DDJC conducted a number of additional returns some of the clean water to the studies to learn more about where the TCE and PCE have also been aquifer (groundwater zone) through chemicals of concern can be found detected to a lesser extent in the and how best to remove these groundwater zones located Ro n Rana' chemicals from the environment. nearer to the ground surface and * — AP Cleanup actions are now underway. between 90 and 170 feet below N Many cleanup actions are long-term the ground surface. In a few and will continue into the future. cases,TCE has been detected Figure 2 1 \ more than 200 feet below the WE - 1988 i' Past Environmental Activities ground surface. . V Groundwater—To determine if -'i- chemicals are present in groundwater, Figure 1 shows where PCE was DDJC installed 199 groundwater found in groundwater beneath 4 Sharpe monitoring wells. These groundwater Sharpe in 1995, and where it was , monitoringwells, located both on the detected in 2000. Figure 2 Groundwater 1 :1.� Flow Direction depot and outside its boundaries, •• •�. �; I "- shows where TCE was found in provide DDJC with the ability to groundwater in 1988. The .• analyze the groundwater for colored plume outlines show the contamination.The wells are sampled groundwater areas where the �. . on a regular basis. chemicals were present at concentrations higher than the Studies have found the following Maximum Contaminant Levels •` !_ chemicals in the groundwater (MCL) established by the State of beneath Sharpe: California Department of Health Services. MCLs are the maximum • Trichloroethylene (TCE) (a cleaning level at which a particular solvent) chemical is allowed to exist in /"..•.\ public drinking water supplies. • Tetrachloroethylene (PCE) (a I J cleaning solvent) The State MCL for both TCE and 1 �,,� • Total petroleum hydrocarbons PCE is 5 parts per billion. L Legend: Trichloroethylene (TCE) Plume Groundwater Zone -- •�•., Ill Detected in Groundwater at 1/ "A Zone"-40 feet BGS Concentrations Above the °B Zone"-40 to 90 feet BGS Ill '� •' Maximum Contaminant Level MCL "C Zone"-90 to 170 feet BGS (MCL) Lathrop Roatl BGS =below ground surface