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SECTION 1 INTRODUCTION AND BACKGROUND 1 .2 Summary of Former Bagging Plant Investigations 1.2.1 2011 Investigation In the former bagging plant area, nitrate concentrations in groundwater samples from Monitoring Well KP-3 have been increasing since 2002(CH2M HILL, 2010).To determine if a nitrate source area is present around Monitoring Well KP-3 and to define its extent,an additional investigation in the former bagging plant area was conducted in July 2011.The results of that investigation were presented in the 2011 Annual Report(CH2M HILL, 2011). Conclusions could not be drawn about sources of nitrate in groundwater from the 2011 soil concentrations of nitrate as nitrogen (nitrate-N). However,the greatest soluble and exchangeable ammonium concentrations were detected in soil collected from soil Sampling Area 3K(Figure 2), suggesting that this area could be a source of nitrogen to groundwater.The pH of soil in soil Sampling Area 3K has decreased since 2000,as would,be expected with microbial nitrification (ammonium oxidation to nitrate)or plant uptake of ammonium. In addition,decreases in soil pH could be associated with aluminum hydrolysis. Low pH can reduce availability of certain required plant nutrients,such as phosphorus, and increase availability of micronutrients and other elements,such as atun+inum, to levels that can become toxic to plants.As discussed in the 2011 Annual Report, levels of free aiuniinum increase as pH values decrease below 5.5,which can be detrimental to plant growth. 1.2.2 2012 Investigation In April 2012,four trenches were excavated in the former bagging plant area to observe tree root Osslwaili within the soil profile and to collect soil samples.The results from this investigation were pres~a tine 2012 Annual Groundwater Monitoring Report(2012 Annual Report;CH2M HILL, 2012).The re$u t t.M%d samples collected during the 2012 investigation confirm that a source area likely exists in the vspw +w awl of Ow former bagging plant area.As expected, low pH and elevated concentrations of nitrate and excNo4ppo r ammonium were detected in the soil samples from this investigation.According to historical aerrs 0%WAVa PI the western side of the former bagging plant area appears to be in the general location where aretsmew travelled (for example, skid loaders),and fertilizer could have spilled there during routine operomme In addition to the low pH of the soil,the agronomic soil testing performed during the 2012 invent✓~rwaAd several soil deficiencies, including calcium, potassium,and boron.The agronomic soil results also v6swed etemeted concentrations (that is,excesses) of soluble salts and extractable aluminum.The combination of 00 tww wW gtt and high extractable aluminum levels suggests that aluminum toxicity is likely occurring at the sant er VI soil deficiencies and excesses were found in all the soil samples tested; however,they were generalIt more pro nounced in the samples from deeper soil (that is, 2-to 4-foot and 4-to 6-foot samples)at each Int-aeion Stmt deficiencies and excesses can result in a number of symptoms, including limited plant growth,stud^not growth,and poor plant health.The soil deficiencies and excesses likely contributed to the suscept6 tity of poplar trees to moth infestation, and could explain why the observed extent and depth of tree roots duswq the 2012 investigation were generally limited. Leaf tissue samples also were collected from trees in the former bagging plant area in 2012;the results were presented in the 2012 Annual Report.The leaf tissue sample results indicate adequate plant nutrition Although levels of many nutrient elements in the leaf samples were higher than expected,they are not likely to cause adverse plant symptoms. High concentrations of aluminum and manganese in the leaf samples likely are due to high concentrations in soil resulting from acidity. High aluminum concentrations in soil do not appear to inhibit plant uptake of other nutrient elements,such as calcium. Finally,observations made during the 2012 former bagging plant soil and root zone investigation indicate the presence of a clay layer(varied between 2.5 and 4.3 feet bgs),which may be a barrier to deep rooting. 1 .3 Proposed Activities This work plan proposes the following activities,which were recommended in the 2012 Annual Report: • Implement an interim remedy in the former bagging plant area that involves amending the soil and replanting approximately 300 trees in the eastern part of the former bagging plant area.The interim remedy is intended RDD/131490001(CAH5152.DOCX) 1-2 ES052913233837