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Description
The Riverside Sanitary Landfill is a waste disposal facility located in the City of Riverside, California. The landfill is situated on the bank of the Santa Ana River in an area where the water table is within a few feet of the ground surface. Groundwater flow is upward from the aquifer beneath the landfill to the river. The potential for groundwater contamination due to leaching of contaminants from the waste products is high. Concentrations of major ions were determined for samples collected from the 13 PVC wells and from three deep metal-cased wells located on the landfill. In addition, concentrations of six trace metals (zinc, copper, nickel, cadmium, lead and silver) were measured to determine how the landfill is affecting these metal concentrations in the area's groundwater. Concentrations of chloride, hardness, calcium, magnesium, sodium, potassium, alkalinity, and reactive phosphate were determined and specific conductance, temperature and pH were measured in the field. These analyses clearly demonstrate t hat a plume of contamination is moving away from the landfill. Values of specific conductance approximately double as water passes under the landfill. Chloride concentrations increase from less than 100 mg/l up-gradient to 270 mg/l immediately down-gradient. In general, the highest values observed down-gradient occur near the center of the landfill. However, the maximum concentrations for total hardness and calcium have shifted slightly to the north to an area which is down-gradient from a concrete disposal site. Dissolution of the concrete adds large amounts of calcium to the groundwater. Indirect evidence indicates that a large amount of organic matter is moving out of the landfill into the groundwater and decomposing as it travels in the down-gradient direction. An increase in alkalinity of about 200 percent over up-gradient values is noted immediately down-gradient from the landfill. An increase in temperature occurs at the down-gradient edge of the landfill. The decay of organic matter is an exothermic reaction and may be a major source of heat in the groundwater near the edge of the landfill. A decrease in pH is observed immediately down-gradient of the landfill because of the increase in carbon dioxide, one of the by-products of the decomposition of organic matter. The pattern of reactive phosphate concentrations is qualitatively reciprocal to that of the other major ions. That is, it is lower near the landfill and increases as water moves away from the landfill. It is hypothesized that the phosphate coming out of the landfill is being bound up by cations such as calcium and aluminum and by organics. As water moves away from the landfill hydrolysis of phosphate attached to the strongly binding cations and organics occurs and the reactive dissolved phosphate concentration increases. Concentrations of copper and, to a lesser extent, cadmium and lead show a decrease down-gradient over up-gradient background values. This decrease may be due to a combination of adsorption of metals onto clay particles and to complexation of metals by the abundant organic matter produced by this municipal landfill. Copper, in particular, has a strong tendency to complex with organic matter. Additionally, the rate at which trace metals can be expected to move out of a landfill is considerably less rapid than the rate at which soluble major ions move out.
