Laserfiche WebLink
TECHNICAL MEMORANDUM <br />To: Bill Lyle <br />Date: October 19, 2007 <br />Page 4 <br />3.0 FLUORIDE AND MANGANESE ATTENUATION BY SOILS <br />Due to the chemical and mineralogical characteristics of San Luis Valley soils, the <br />potential exists for attenuation of fluoride and manganese by Salazar Ranch soils. The <br />most important factors controlling fluoride solubility in soils are clay content, pH, and the <br />concentrations of calcium in soils (Kabata-Pendias and Pendias, 1984). Fluoride retention <br />in soils occurs by: (1) adsorption to clay mineral and/or mineral oxide surfaces and/or (2) <br />precipitation as fluorite (CaF2). In neutral to alkaline soils, adsorption to clays may be an <br />important retention mechanism for fluoride, especially when soil pH is between 6 and 7. <br />Precipitation of fluorite has also been proposed to control fluoride solubility in soils <br />(Lindsay, 1979; Reddy and Gloss, 1993). While the soil chemistry of manganese is more <br />complex, manganese attenuation can also occur either through ion exchange with clay <br />minerals, adsorption to iron or manganese oxide surfaces, or precipitation as manganese <br />oxide (Mn02) (McKenzie, 1989). <br />Attenuation tests for manganese were conducted using the surface (0-1 foot) and <br />subsurface (1-2 foot) soil samples that were collected for the baseline soil chemical <br />characterization (Section 2.0). Soil suspensions were prepared at a 2:1 water:soil ratio <br />using ground water from the West Pit (collected from Well BF-5R) (Table 3-1). The 2:1 <br />soil suspensions were extracted in a batch reaction vessel for 24 hours. The suspensions <br />were filtered through a 0.45µm pore-size filter and the extracts were analyzed for <br />manganese. The mass of manganese attenuated by the soil was calculated as the difference <br />between the initial manganese concentration in the West Pit ground water and the <br />manganese concentration measured in the soil extracts. <br />Attenuation tests for fluoride were also conducted using West Pit ground water and the <br />same baseline surface (0-1 foot) and subsurface (1-2 foot) soil samples used for the <br />baseline soil chemical characterization (Section 2.0) and manganese attenuation tests. <br />However, additional fluoride attenuation tests were performed with West Pit ground water <br />using soils collected from outside of the irrigated areas in July 2004. For comparative <br />P.-Wmjectsll/1 Newmont(SanLuis)S=LuisTa m-Shalom_RanchLSoilsWa/azar Cha=ter uon_firmldoc