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City of Lathrop 8617.000.000 Mossdale Landing Community Park, Monitoring Well Replacement May 5, 2009 SUMMARY OF MONITORING WELL INSTALLATION Page 2 expanding the City's Wastewater Recycling Plant (WRP) as regulated by the Wastewater Discharge Requirements and Master Reclamation Permit Order Number R5-2006-0094. The original location of MWM-10 was in the area of a future baseball field. The new well, identified as MWM-27 was installed in an area outside of the new field in a landscape area, as shown on Figure 2. The subject site consists of one approximately 20.2-acre parcel located in the Mossdale area of Lathrop, California (Figure 1). The parcel is identified as Assessor's Parcel Number (APN) 191- 350-04. The Address for the parcel is 17400 Golden Spike Trail. At the time of well installation, the site consisted of a large recreational field with small trees and lawn bordering the site. Two sports fields and a playground were located in the eastern portion of the parcel. Monitoring well MMW-27 is located at elevation 9.27 feet above mean sea level (msl)t in the northern portion of the site, approximately 15 feet south of the edge of pavement of Towne Centre Drive. Monitoring Well Installation Monitoring well MWM-27 was installed on April 21, 2009 near the northern edge of Community Park as shown on Figure 2. The well was installed by V&W drilling (a licensed drilling contractor) using a truck-mounted BK-81 drill rig equipped with 10-inch-diameter hollow stem augers. Soil samples were collected at frequent intervals during drilling and the soil conditions encountered were logged by an ENGEO geologist. The soils encountered within the borehole consisted primarily of sandy silt and clayey silt with interbedded silty clay to a depth of 13t/2-feet. Silty sand was encountered at 13t/x feet and was observed to a depth of 25 feet (the maximum depth drilled). A detailed description of the stratigraphy is summarized on the attached installation log. Groundwater was observed in the boring at a depth of approximately 101/2-feet below the existing ground surface (bgs) at the time of drilling. Following drilling, the stabilized groundwater in the monitoring well was measured at a depth of 7.2 feet bgs. The new monitoring well extends to a depth of approximately 24-feet below existing grade. The monitoring well was constructed of 4-inch-diameter PVC screen and blank casing and installed within a 10-inch-diameter borehole to allow for an annular seal of three inches between the well casing and the edge of the borehole. Well casings were installed with manufactured well screens that are positioned between 13 and 23 feet below the ground surface (bgs). A 1-foot solid casing sump was flush threaded to the bottom of the well screen and a four-inch bottom well cap fitted on the bottom of the well sump. The slot screen size was 0.010-inch with No. 2/12 sand used as filter pack material. Granular material was placed in the annular space beginning at the bottom of the borehole and extending to approximately 1-foot above the top of the well screen. During the well construction, the well driller consolidated the filter pack using a surge block. A two-foot-thick layer of bentonite pellets was placed over the filter pack. The filter pack pellets were hydrated The evaluation datum used in this report refers to NVGD 29.