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SECTION 2 Former Bagging Plant Interim Remedial Action This section describes the rationale and field activities planned for the interim remedial action in the former bagging plant area.The proposed soil amendment and replanting area (also called the treatment area),which is approximately 3/4 of an acre in size and is restricted to the eastern portion of the former bagging plant area,is shown on Figure 2.The proposed treatment depth for slip plowing and soil amendment application is 6 feet. 2.1 Amendment Selection Amendments to enhance conditions for phytoremediation or create conditions conducive to denitrification were evaluated.Three primary amendments were considered: lime,gypsum, and a source of organic carbon.These amendments are discussed in the following subsections. 2.1.1 Lime Amending the soil with lime will raise soil pH and create conditions more conducive to phytoremediatwn However, over-applying lime could create additional problems,such as reducing the availability of same nutrientts, including magnesium, phosphorus,and micronutrient metals. Soil samples collected from trenches excavated in the western part of the former bagging plant area v 2012 (Figure 2)were analyzed for both pH and buffer pH. Buffer pH is a laboratory test performed to detwmm~"w mass of lime required to change soil pH.The average buffer pH was 5.6, based on the results for 12 a«a awwiaa Soil with a buffer pH of 5.6 requires approximately 4.6 tons of calcium carbonate(that is,calcitic lire w» atin aor every 6 inches of soil depth to achieve a target pH of 6(Hart, 1998).At a rate of approximately 55 tar am acm of calcitic lime for a 6-foot treatment depth,approximately 41 tons of calcitic lime would be needed for *rw w ac+w treatment area.This rate of lime application would require excellent mixing of the entire soil volun w awwo a impractical when considering the treatment depth (6 feet). Soil samples from the treatment area (eastern portion of former bagging plant area)were analyzed 4x am but not buffer pH.The pH values of soil samples collected within the treatment area were somewhat hip. m n me pH in soil samples collected from the western part of the former bagging plant area,where the sarrowt kv t pH were collected.The range of pH and average pH of soil samples collected from the western part co me tormer bagging plant were 3.19 to 6.61 and 4.54, respectively. However,the range of pH and average pH of ww"r"Pirs collected in the treatment area were 3.75 to 7.85 and 6.00, respectively. In general, soil is less acidic "* treatment area than in the western part of the former bagging plant area, and less pH adjustment is expected to be needed. Although there is uncertainty about the buffer pH of the treatment area,the rate of lime application requred in the treatment area, and the ability to evenly mix lime into soil in the treatment area, application of lane to the treatment area is expected to enhance conditions for phytoremediation in the treatment area.Consequently,a modest amount of calcitic lime (approximately 5 tons per acre,or 3.75 tons for the treatment area)wi8 be applied for the interim remedial action. 2.1.2 Gypsum Amending the soil with gypsum is expected to directly help reduce aluminum toxicity.The results presented in the 2012 Annual Report(CH2M HILL, 2012)suggest that aluminum toxicity is a problem in the former bagging plant area. Unlike lime (calcite),gypsum does not have a significant effect on soil pH.As gypsum dissolves in the soil, calcium is expected to improve base saturation,in which calcium replaces aluminum and hydrogen on the soil exchange sites. Gypsum also helps with soil aggregation;the calcium in gypsum promotes flocculation of clays, which in turn leads to aggregation.A clay layer was observed during the 2012 investigation that appeared to be restricting root growth,and soil aggregation,in addition to breaking up the clay layer by slip plowing, could help mitigate the effects of the clay layer on root growth. Because gypsum is approximately 200 times more soluble RDD/131490001 (D H5152.DMX) 1 ES052913233837