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The exceedance curves indicate that variable, with occasional observed approximately 95% of all nitrate flow directions to the north and concentrations sampled are between 5 south. The groundwater gradient and 40 mg/L (with the exception of the ranges from approximately 0.001 abnormally high readings in well WSM- feet per foot to 0.003 feet per foot. 05 between 1992 and 1997 as discussed above). Concentrations in well WMS- 2) The existing data are not sufficient to 02, located near the center of the determine true background WSWPCF property, are consistently concentrations in groundwater given higher than the other wells (about 80% the apparent periodic change in of the time). Conversely, well WMS-03 groundwater flow direction and (located near well WMS-02) frequently uncertainty with respect to the has the lowest nitrate concentrations. potential sources of nitrates in groundwater. 4.2.1 Nitrate 47ontours We used the Surfer® grid-based 3) It is possible that observed graphics program to develop contour groundwater levels and nitrate maps of nitrate concentrations observed concentrations in some of the in the wells for selected quarterly existing monitoring wells are monitoring events (Figures 19 through influenced by their proximity to 22). Analysis of these maps indicates canals and ditches. If this were that monitoring well WSM-02 frequently occurring, the data from those contains the highest concentration of monitoring wells would not be nitrate, while well WSM-05 frequently representative of actual groundwater contains the lowest nitrate conditions beneath the study area. concentrations over the past three to four years. Otherwise, no significant trend or 4) Some of the monitoring data appear directional migration could be to be anomalous as discussed above. determined over different quarterly The cause of the anomalies is monitoring events. This lack of unclear, but could stem from local definitive migration pattern between interference from canals and ditches, monitoring events is consistent with the or from measurement error. observed shifts in groundwater flow direction. 5) Available data do not allow us to determine if the discharge of 5. Conclusions reclaimed water and biosolids has caused underlying groundwater to Based on our analyses of available contain waste constituents in groundwater data, we provide the concentrations greater than following conclusions: background water quality at or beyond the point of compliance. 1) Recent data indicate a local groundwater flow direction to the northeast and east. However, the 6. Recommendations data also suggest the groundwater flow direction near the study area is Based on the above conclusions,we believe the existing monitoring wells are Saracino-Kirby,Inc. 8 Lodi WSWPCF