ARCHIVED REPORTS 3RD QUARTER 2009 (1)

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City of Lathrop Third Quarter 2009 Groundwater Monitoring Report, Crossroads Wastewater Treatment Facility, Order No. 5-01 -251 1.0 INTRODUCTION As required by the City of Lathrop's Waste Discharge Requirements (WDRs) Order No. 5-01-251, this report summarizes quarterly data from wells monitoring groundwater located at the Crossroads Wastewater Treatment Facility (WWTF) (Figure 1). The facility consists of three wastewater storage ponds (Ponds A, B and C), three land application sites (LAS-1, -2 and -3), and nine monitoring wells (Figure 2). Also located within the facility are two wastewater storage ponds (Ponds S4 and S5) and four monitoring wells that are part of the Membrane Bioreactor Water Recycling Plant No. 1 (WRP-1). Groundwater is monitored for the WRP-1 facility under WDR Order No. R5-2006-0094. Sample collection and analyses were performed in accordance with Lathrop's Monitoring and Reporting Program No. 5-01-251 and this quarterly report summarizes Third Quarter 2009 data (July, August, and September). Consistent with Lathrop's WDRs, this groundwater monitoring report includes the following: • A narrative description of all preparatory, monitoring, sampling, and analytical testing activities for Third Quarter 2009 groundwater monitoring. Field logs for each well sampled are provided in Appendix A. The field logs document depth to groundwater; calculation of casing volume; parameters measured before, during, and after purging; method of purging; and total volume of water purged. • Calculation of groundwater elevations and contours, referenced to mean sea level (Figure 3), and an assessment of groundwater flow direction, gradient, and seasonality, including a comparison with previous conditions (Section 3.1). • A narrative discussion of the analytical results for all groundwater locations monitored including spatial and temporal trends (Figures 5 and 6) with reference to summary data tables (Table 6), graphs, and appended analytical reports. • A comparison of the analytical results of groundwater samples to the interim groundwater quality limitations cited in the WDRs and an explanation of any violation of those limitations (Section 3.2). - 5 -