2022-11-07_PERMIT FILE - M2022001 (13)

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The depth to groundwater maps were used to identify and confirm those areas within the Town where water levels need to be lowered and to quantify the amount the water levels need to be lowered beneath the Town to achieve target water level depths. Utilizing the depth to groundwater maps and the Town's input regarding required water levels within Town,target depths for lowering the groundwater table were established, as discussed in more detail below. HISTORICAL LOW GROUNDWATER CONDITIONS Historical (1950 to 1980)groundwater levels beneath Town are reported to be 13 to 35 feet below ground surface, based upon well construction reports. Regular water level measurements begin in August 2014 for the three wells located within the wastewater treatment plant. However, regular water level measurements were not recorded in a majority of the Town's wells until April 2015. Historical pre-2015 reported groundwater level measurements for Town wells are summarized above in Table 2.1. The nearest well with a long-term continuous water level record (LSP-102) does not indicate substantial long-term water level change (see Appendix A). However, a well located less than 1,000 feet north of the wastewater treatment plant(LSP-43)has continuous water level data from 1956 through 1976 and 2013. through present (see Appendix A). That well shows an approximately 10-foot water level rise, which is consistent with anecdotal reports from the Town. RECENT HIGH GROUNDWATER CONDITIONS A recent depth to groundwater map was prepared for the Town based upon April 2016 water level data from the Town, CSU, Tetra Tech, CDWR and BBA's field visit. April 2016 was chosen for depth to water mapping because the greatest number of water level measurements were available, including recent measurements toward the west of Town collected as part of this study. To prepare the April 2016 depth to water level map, groundwater elevations were contoured and subtracted from land surface elevations within Town. April 2016 water levels are approximately 3.5 feet deeper than the peak depth to water measured near the wastewater treatment plant during September 2014. The groundwater table was mapped at a 1-foot contour interval, as shown in Figure 2.2. The groundwater table beneath the Town shows groundwater flow direction from the southeast on the east side of the Town and from south-southwest through Town. The USGS 10-meter ground surface digital elevation model (DEM) was verified based upon surveyed elevation of the points within the Town, shown in Figure 2.3. The groundwater elevations from Figure 2.2 and ground surface elevations from Figure 2.3 were converted to a 15-meter grid spacing to determine April 2016 depth to groundwater, shown in Figure 2.4. April 2016 depth to groundwater mapping shows extremely shallow groundwater five to ten feet beneath ground surface generally isolated to areas east of Birch Street and immediately north of Liberty Park (baseball field). 6