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• • • SECTION 6.0 EVALUATION OF REMEDY PERFORMANCE • • 6.1.6 Stormwater Pond —Annual Review • Approximately 31 poplars and 14 willows died or were removed between August 2010 and • August 2011 (Figure 6-4).An additional 18 poplars show signs of severe infestation and may • die in the next few years. • Approximately 30 trees were replaced between 2008 and 2010. The tree species were • intermixed (sycamore and fruitless mulberry) to increase localized species diversity.The new plantings were observed to be performing well.In addition,approximately 25 sour • gum trees were planted in the 2008 to 2009 dormant season and 10 water gum trees were • planted in November 2010 in the southern stormwater pond planting location(seasonal ponding location).Both tree species appear to be growing and performing well. • The approximately 30 mature poplars planted on the south bank of the seasonal ponding • area continue to appear healthy and show no signs of infestation.These trees are not • currently irrigated.Volunteer poplar trees are sprouting from roots of adjacent trees on the • south bank and,as trees fill in open areas,will increase the capacity for phytoremediation in • this area over time. 6.2 Contaminant Reduction • • In general,analytical data collected over the past 10 years indicate a reduction in nitrogen • concentrations in groundwater across most of the site.With exception to KP-3,nitrate and • ammonia concentrations in groundwater have either stabilized or are decreasing,suggest- ing that the selected remedy,phytoremediation,is effective.Nitrate concentrations have • decreased significantly in monitoring well KP-1R and in piezometers TG-1 and TG-2, • located near the original test grove,which was planted during 1998. Nitrate concentrations • have also decreased at KP-4,which is located downgradient from the original test grove. Nitrate concentrations recorded at KP-3 since 2002 have increased over historical • concentrations recorded at this well. Downward trends in ammonia concentrations have • been observed in well KP-2 and piezometers TG-2,and TG-4. Additional discussion regarding groundwater results at KP-3 and the former bagging plant area is provided • below. • In general, dissolved oxygen concentrations slightly above zero,positive redox,and the • predominately higher nitrate-to-ammonia ratios recorded in most areas of the site indicate • that conditions are not reducing,and there is no clear evidence that attenuation(denitrifica- tion) is occurring. Low nitrate-to-ammonia ratios were recorded in some areas of the site, • such as the north of warehouse planting location(monitoring well KP-2) and the storm- • water pond planting location(monitoring well pair KP-4/KP-4D) suggests that denitrifica- tion may be occurring to some extent in those areas. During denitrification,it is anticipated • that dissolved oxygen concentrations will decrease to zero and redox will become negative; • however,this does not generally appear to be occurring.In general,oxygen is the preferred • electron acceptor for the types of bacteria that perform denitrification. If the bacteria are using all of the available electron donor in the system and never deplete the available • oxygen, they are unable to reduce nitrate.Therefore,it appears that denitrification at the • Koppel Stockton Terminal may be limited by the amount of electron donor that is available • to denitrifying bacteria. • • 6-4 RDD/112370001(CAH5003.DOCX) • E9001511ME1ULUl0 • • •