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Cation exchange capacity (CEC), megl100g of soil: Cation-exchange capacity (CEC) is an index of the soil's capacity to exchange cations with the soil solution. It affects the ability of the soil to adsorb and retain cations and heavy metals. Cations are held to the soil particles by adsorption and can be returned to the soil solution for plant use by the exchange process. Soils that have high CEC and organic soils can ex-change and retain large amounts of cations released by agricultural waste mineralization processes. Conversely, soils in which the CEC is low have low potential for exchanging and retaining these t agricultural waste materials. The potential for agricultural waste contamination of underlying ground water and aquifers is highest for soils that have low CEC and lowest for those with high CEC. f �,. The limitations for solid and liquid waste applications are slight for soils that have a cation- yexchange capacity of more than 15, moderate for those with a capacity of 5 to 15, and severe for those for which it is less than 5. Underlying ground water supplies and aquifers can become contaminated when agricultural wastes are applied at high rates to soils that have moderate or severe limitations because of their CEC. Reducing agricultural waste application rates can reduce the hazard for ground water contamination. Twenty one (21) soil samples were collected from.the subject site and analyzed for CEC. The laboratory results (see Appendix D) show that most of the site soils have CECs between 9.6 and 33.2 meg1100 g of soil; therefore, it can be concluded that the limitations for solid and liquid waste applications are slight. Values between 5 and 15 meq/100 g of soil were detected in only two (2) soil samples and in these cases the limitations are "moderate". t In general, soil monitoring of element concentrations through the soil profile is recommended t evaluate farming practices and application rates of manure solids and nutrient laden water. - Depth to bedrock or cemented pan The depth to bedrock or a cemented pan is the depth from the soil surface to soft or hard consolidated rock or a continuous indurated or strongly cemented pan. A shallow depth to bedrock or cemented pan often does not allow for sufficient filtration or retention of agricultural wastes or agricultural waste mineralization by-products. Bedrock or a cemented pan at a shallow depth, less than 40 inches, limits plant growth and root penetration and reduces soil agricultural waste adsorptive capacity. Limitations for application of agricultural wastes are slight if bedrock or a cemented pan is at a depth of more than 40 inches, moderate if it is at a depth of 20 to 40 inches, and severe at a depth of less than 20 inches. Based upon the NRCS soil data, the Jacktone, Madera, and Manteca soils have moderate . limitations because have a cemented pan between approximately 20"40" and the Stockton soils have slight limitations because the cemented pan is between 40"-60". s ! Refer to page 22 for Endnotes and Reference Sources 4 °Western Dairy Design Associates, Inc.2003 f Page 12 I