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TECHNICAL MEMORANDUM <br />To: Bill Lyle <br />Date: October 19, 2007 <br />Page 5 <br />purposes, the fluoride attenuation tests were repeated for all soils (obtained from both <br />inside and outside of the irrigation circles) using Salazar Ranch ground water collected in <br />July 2004. The fluoride attenuation tests were conducted using the same procedures <br />described for the manganese attenuation tests previously described. The mass of fluoride <br />attenuated by the soil was calculated as the difference between the initial fluoride <br />concentration in the West Pit or Salazar Ranch ground water and the fluoride concentration <br />measured in the soil extracts. A complete analysis of the soil extracts was performed <br />(alkalinity, boron, calcium, chloride, manganese, pH, magnesium, nitrate, sodium, total <br />dissolved solids, potassium, sulfate, and phosphate) to calculate ion activities and <br />saturation index values for fluorite. <br />3.1 Manganese Chemistry <br />A summary of the manganese attenuation test results shows that manganese concentrations <br />in the soil extracts ranged from <0.001 to 0.012 mg/L when using the West Pit ground <br />water which contained an initial manganese concentration of 2.37 mg/L (Table 3-2). The <br />calculated mass of manganese attenuated by the soil was approximately 4.8 mg Mn/kg, or <br />19 lbs Mn/acre-ft. The rapid removal of manganese in the laboratory batch tests most <br />likely results from adsorption to mineral surfaces. Under natural conditions, manganese <br />that is initially adsorbed would eventually oxidize to form insoluble manganese oxides, <br />and therefore the calculated attenuation capacity represents a minimum value. <br />Soils contain a virtual unlimited capacity to retain manganese. In addition to formation of <br />stable manganese oxide minerals, manganese attenuation also occurs by adsorption to iron <br />oxide surfaces and complexation with soil organic matter (Smith, 1990). Soluble <br />manganese in ground water (Mn2+) is oxidized by oxygen in aerated soils to form insoluble <br />manganese oxides (McKenzie, 1989): <br />Mn2+ + H2O + 0.5 02 --> Mn02 + 2H+ [I] <br />P:(ProjectsU]2-Nmmon7(Sw&uis)LSm&uislFarm-S7zalom RanchL%ilsLSalawr_Cha ter hon_fimldoc