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• • • • SECTION 6.0 EVALUATION OF REMEDY PERFORMANCE • • Nitrate concentrations for monitoring locations downgradient from the original test grove • (KP-4,KP-4D,and TG-5)continue to have lower concentrations than the monitoring loca- tions in the original test grove (KP-1R,TG-1,TG-2,and TG-3).The cause for the increase in nitrate concentrations at Monitoring Well KP-3 is unknown. Given the groundwater • gradient direction,it is possible that nitrate may be migrating offsite without being detected • at downgradient monitoring well pair KP-4/KP-4D.The groundwater elevations presented on Figure 5-2 suggest that groundwater flow is to the south-southeast and the nitrate- contaminated groundwater detected in monitoring well KP-3 may be migrating east of • monitoring well pair KP-4/KP4D. • The 2005 groundwater monitoring report for the former Cal Farm facility located north of, • and generally upgradient of,the Koppel Stockton Terminal site indicates that an"off-site slug of nitrate" was detected in groundwater monitoring wells on the upgradient side of the • site in 1998 (JD Smith Consulting,2005). Considering the distance from the upgradient side • of the former Cal-Farm site to monitoring well KP-3 in the former bagging plant area of the • Koppel Stockton Terminal site(approximately 1,500 feet) and the timeline (the slug of nitrate was observed in 1998 at the former Cal-Farm site and concentrations of nitrate in • monitoring well KP-3 started increasing in 2002),groundwater would need to be travelling • at approximately 750 feet per year for the slug of nitrate observed at the former Cal-Farm facility to reach monitoring well KP-3.The types of geologic materials (silts and sands) that • have been observed to compose the aquifer in the former bagging plant area generally do • not have groundwater velocities that high;therefore,it is unlikely that the slug of nitrate • observed at the farmer Cal-Farm facility is solely responsible for the increased nitrate concentrations being observed at monitoring well KP-3.However,nitrate concentrations in groundwater from the most southern well at the former Cal-Farm site (MW-6) had elevated • nitrate concentrations (974 mg/L)in the first sample collected from the well in 1997.The • maximum concentration of nitrate from well MW-6 was in a groundwater sample collected in 1998 (1,650 mg/L). The nitrate concentration in the most recent groundwater sample • collected from MW-6 in 1999(before the well was destroyed) was 1,220 mg/L. Even though • the nitrate concentrations previously detected at the former Cal Farm site may not be the sole source of the nitrate increase observed at monitoring well KP-3,it appears that the • nitrate slug may be contributing to the nitrate concentrations at the Koppel Stockton • Terminal site,as evidenced by the nitrate concentrations observed at upgradient monitoring • wells KP-10S/KP-10S-R and KP-125. • In general,TKN,nitrate,total soluble ammonia/ammonium-N,and exchangeable ammonium concentrations in soil have decreased or stabilized relative to concentrations detected in 2000 and 2006.These data indicate that phytoremediation is continuing to remove nitrogen from soil across the site.Sample 1K,collected from the stormwater pond planting location,continues to have the lowest concentrations of these constituents.These observations are consistent with low concentrations of nitrate and ammonia in groundwater .� downgradient from that area.However,increasing concentrations of nitrate in groundwater .' in the former bagging plant area suggest that a continuing source of nitrate in soil may be present in the former bagging plant area.The 2011 former bagging plant area investigation is discussed in the following section. .� RDD1112370001(CAH5003.DOU) 65 • • 41