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• • • • SECTION 5.0 RESULTS • • Nitrate(non-filtered)concentrations in grab groundwater samples collected in the former • bagging plant area are presented on Figure 5-5 and in Table 5-2.Grab groundwater samples collected in the former bagging plant area were analyzed for both field-filtered and non- filtered nitrate,but there is no significant difference between the results.Concentrations of • nitrate ranged from 324 to 1,080 mg/L in grab groundwater samples.The concentration of • nitrate in the grab groundwater sample from well KP-3 in July 2011 was 636 mg/L,but the concentration of the sample collected in August 2011 as part of the annual groundwater • monitoring event was 1,120 mg/L.The discrepancy in concentrations over a short time span • is likely a result of not purging the well prior to collecting a sample during the July 2011 • event.The sample from the annual groundwater monitoring event in August 2011 is likely more representative and is the sample presented on Figure 5-5. • Concentrations of nitrate recorded for shallow wells in the original poplar test grove area • were within or below the historical range of concentrations for these wells, as demonstrated • in Appendix B,Table B-1.The maximum nitrate concentrations recorded in the original test grove have generally decreased each year since 2000 (i.e.,from 791 mg/L in 2000 to • 388 mg/L in 2011). Nitrate concentrations in the deep monitoring well(KP-6D) in the • original test grove,which is screened from 45 to 55 feet logs,have fluctuated since this well • was installed in 1999,but concentrations decreased from the historical concentrations in the 2008 through 2011 groundwater samples.The nitrate concentration detected in the 2011 • annual groundwater sample(0.17 mg/L)is the lowest historically detected in this well • (previous range of 25.3 to 420 mg/L). • According to current and historical groundwater-level data and subsequent gradient • analysis,monitoring wells KP-9S,KP-10S-R,and KP-12S are hydraulically upgradient from the Koppel Stockton Terminal (see Figure 5-2).Nitrate concentrations detected at monitor- ing wells KP-10S-R(195 mg/L) and KP-12S(106J mg/L)in August 2011 groundwater • samples were consistent with previous concentrations. Monitoring well KP-10S-R replaced monitoring well KP-10S, and was sampled for the first time in October 2010.Both the • October 2010 and August 2011 groundwater sample results are within the range of historical • concentrations at monitoring well KP-10S.The data suggest that there is a source of nitrate • upgradient(north or northwest)from the Koppel Stockton Terminal,possibly associated with the former PM Ag,Cal-Farm Supply facilities,and/or the seasonal ponding area north • of the Koppel Stockton Terminal. A more detailed evaluation of groundwater elevations and • quality in the northern portion of the Koppel Stockton Terminal was presented in the • 2007 Annual Groundwater Monitoring Report(CH2M HILL,2007).Additional evaluation of a potential upgradient source of nitrate is provided in Section 6. • The nitrate results at shallow aquifer monitoring well KP-4 and piezometer TG-5 (2.6 and • 45J mg/L,respectively)were much lower than the nitrate results in the shallow aquifer • groundwater monitoring locations in the original poplar test grove area (205 to 388 mg/L) • and the former bagging plant area (282 to 1,120 mg/L).Previous groundwater elevation data have indicated that monitoring well KP4 is located downgradient from the original • poplar test grove,and a low nitrate-to-ammonia ratio for this well suggests that assimilatory • denitrification is occurring in this area at the Koppel Stockton Terminal. • A regression of nitrate concentrations recorded for each groundwater monitoring location in • the original test grove over time is shown on Figure 5-6.Regression and nitrate concentra- tion data are supplemented by groundwater elevation data.The nitrate trend is gradually • • RDDI112370001(CAH5003.DOU) 5-5 ES 51IN2708F • • •