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• • • SECTION 6.0 EVALUATION OF REMEDY PERFORMANCE • • grove.This rebounding is an indication that phytoremediation was contributing to the • overall reduction in nitrogen concentrations in shallow groundwater.As replacement trees • have become established,nitrate concentrations have generally decreased from the 2004 • levels in the original test grove(e.g.,at piezometer TG-2) and are expected to continue to decrease.Surviving hybrid poplars and new tree species will continue to be effective in • remediating elevated nitrogen at the Koppel Stockton Terminal through root uptake of • nitrogen from the soil and groundwater. In March 2007,there was a partial warehouse collapse,which caused fly ash to mound up • against the southern row of trees at the north of warehouse planting area.Fine layers of fly • ash also covered most of the tree foliage in that planting area.During the August 2008 site • visit,additional stress to the trees in this planting area was observed.In 2009,the warehouse • was reconstructed,but substantial interveinal and leaf margin necrosis was observed in trees at the north of warehouse planting area and in the original test grove during the 2009 • site visit.These symptoms were also observed during the August 2010 site visit; • symptomatic and control leaves from Paulownia and sycamore trees were obtained from the • original test grove and north of warehouse planting area during the 2010 site visit for analysis to determine,if possible,the cause of leaf symptoms on Paulownia and sycamore • trees.Leaf tissue concentrations of iron,aluminum,boron,copper,and zinc were above the • normal ranges of concentrations for both symptomatic and asymptomatic leaves of both tree species,but concentrations were often much higher in symptomatic leaves than in the • control leaves. It is possible that one or more of the elevated constituents in the leaf tissue is • causing toxicity and is contributing to the observed leaf necrosis. In particular,leaf • symptoms that were observed are consistent with those reported in scientific literature for boron toxicity. However,leaf test results were not conclusive,and the source of leaf necrosis • was not determined with certainty;no soil samples were obtained to assist with diagnosis. • Elevated iron,aluminum,and boron concentrations in the leaf samples may be associated with deposition of fly ash in both the planting area north of the warehouse and northwest • portion of the original test grove. • The following discussion presents a summary of tree health and specific observations made • in August 2011 for the individual planting areas. • 6.1.2 Original Test Grove—Annual Review • Approximately 168 Paulownia trees,25 sycamore trees,3 poplar trees,and 29 fruitless • mulberry trees are growing in this planting area,and only approximately three losses were • observed between August 2010 and August 2011. In the original test grove,the Paulownia • trees are generally performing better than other trees in other planting areas.The Paulownia trees appear healthy and there is a high percentage of canopy cover.These trees appear to • have responded well to the irrigation modifications done in March 2010 (i.e.,emitters placed • approximately 2 feet from either side of the trees). Additionally,the 2010 and 2011 winter rainfall was plentiful and continued into the spring,and 2010 and 2011 summer • temperatures were relatively mild;more rainfall and mild weather have likely contributed • to overall tree health. Leaf symptoms that were observed on sycamore and Paulownia trees in the original test grove in 2009 and 2010 site visit were also observed during the 2011 site visit,but the symptoms were not as severe as in 2009 and appeared to occur primarily on older leaves. • • 6.2 RDD/112370001(CAH5003.DOCX) • • • •