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.,d TRACY WWiP-TASK 10 TDS MONTORING WELL INSTALIAnON WORK Po N This configuration is proposed because the three facilities to be monitored are located in close proximity to each other. In addition,data from other W WTP and Spreckels(Holly Sugar)monitoring wells occur in the vicinity and can be considered when assessing data from the TSD monitoring wellst. Monitoring wells at Sites A and B will be installed on the south side of the fence surrounding the W WTP(inside the facility). Site A will monitor groundwater conditions downgradient of the sludge drying beds and the biosolids storage area. Site B will be downgradient of the lined pretreatment lagoons. The upgradient,or background,well(Site C),will be installed at the northeast comer of the intersection of Larch Road and Holly Drive. This is along the southern boundary of the Tracy W WTP property,but is outside the facility fence. Water quality data from the well and existing well HP-5 will be considered background data for the W WTP. In addition, water quality data from existing Leaking Underground Storage Tank(LUST)sites (discussed further below)will be added to the background water quality data base for the WWTP. Photographs of the proposed well sites are included in Figure 6. Historical Water Level Information Water level measurement and water quality samples have routinely been obtained from the existing monitoring wells at the W WTP since they were installed. Assessment of the water level measurements was conducted to assess potential well screen lengths and intervals for the new monitoring wells. Figure 7 shows the historical groundwater elevations measured at the existing W WTP monitoring wells. Water level measured between 1990 and 2006 Fluctuated no more than 6 feet at any single well,except for during the construction dewatering at the W WTP between 2004 and 2007. Water level data for WP-12 (the Spreckels Sugar monitoring well just north of Arbor Avenue)between 1985 and 2005 Fluctuated in a slightly larger range of approximately 8 feet,excluding the construction dewatering. Pertinent Offsite Information To the west of the W WTP,there are several LUST and Spills,Leaks,Investigations,and Cleanups(SLIC)sites(Figure 8,Table 2). Four of these sites have active groundwater investigations and include background monitoring wells. As appropriate and applicable, groundwater elevation and water quality data from these investigations will be incorporated into the ongoing review of groundwater monitoring data from the W WTP. I It was decided to install a City-evened monitoring well downgradient of the Sludge Drying Beds and the Biosolids Storage Area versus incorporating Spreckels Sugar WP.I into the City monitoring well network because WP-1 is currently sampled semi-annually and the analyses do not completely overlap. Additionally,documentation of the well construction is not available 2 Wall level elevations for this well are not shown on Figure 6 because they are referenced to a different datum than the City VWVTP monill wells. Odcber J I,2007 4