ARCHIVED REPORTS_2010 YEAR 4 PHYTOREMEDIATION TREE MONITORING REPORT

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r r SECTION 5 L Summary and Recommendations LThis section provides a summary and recommendations from the Year 4 monitoring results. 5.1 Summary L The success criterion for the tree phytoremediation system is an average tree survivorship rate of 80 percent or greater (following the removal of irrigation for more than 1 year).Once r the 5-year success criterion has been attained,site monitoring and annual reporting of the plant system will cease. The average tree survivorship success criterion of 80 percent(for all six sub areas)was exceeded in all monitoring years. In Year 4 (2010), the average survivorship rate is 93 percent(Table 4-1 and Appendix A). This is slightly higher than the rate of survivorship Lrecorded in all previous monitoring years (Table 4-1 and Appendix A) and higher than the target survivorship rate of 80 percent.The average Year 3 survivorship rate was 91 percent. The average Year 2(2008) survivorship rate was 89.6 percent(rounded in Table 4-1 to 90 ` percent).This was essentially the same survivorship rate as observed in Year 1 (2007),which was 89.5 percent. A total of 17 trees (out of 239 planted) in the six sub areas were recorded as dead in Year 4 (2010) (Appendix A). Five fewer trees died in Year 4 (2010) than in Year 3 (CH2M HILL 2010). Tree mortality in Year 4 (2010) was also lower than Years 1 and 2(CH2M HILL 2008a,b). Limited replanting was performed in 2007 and 2008 based on results of Year 1 r. (2007) and Year 2 (2008) tree monitoring; therefore,the species composition of dead trees in 2009 differed slightly from that observed in 2007 and 2008. No additional replanting was conducted between Years 2009 and 2010. L Limited tree planting in Areas C and D was conducted in late-November 2008 subsequent to the annual Year 2 (2008) tree monitoring counts. No additional tree planting has been performed. Because health and vigor is relatively low in these two planting sub areas, additional planting in these two sub areas may be recommended in future years if mortality increases substantially. Irrigation in these two planting sub areas will be needed for an `, additional year. Site conditions are very challenging in Areas C and D. Soil texture (for example, compaction),soil fertility,and the amount of available water to the growing plant (supplemental irrigation or groundwater) are likely the most important factors contributing to tree mortality and tree heath and vigor in Areas C and D. Recommendations to increase Ltree survivorship and health and vigor,particularly in these sites,are presented below. 5.2 Recommendations LThe overall average site survivorship criterion of 80 percent was attained in all monitoring years.Tree irrigation ceased in 2009 in planting sub areas A,Addition to Area A,AA, and B. L . 1 L SAD166749/103500001(YEAR4-2010_HOLTTREE MONITORING_REPORT-FINALDOCX) 5-1