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Administrative Draft Environmental Impact Report
<br /> Gill Medical Center Project
<br /> Table 4.12-1.Historical Water Demand and Supplies Based on Hydrological Water Year Type
<br /> Water Year T e San Joaquin River Index
<br /> Component Wet Above Below Dry Critical 50-Year
<br /> Normal Normal
<br /> Number of Years' 17 7 4 8 14 50
<br /> Precipitation,AF/Year 1,376,000 987,000 866,000 790,000 652,000 984,000(15.4)
<br /> Precipitation,inches 21.6 15.5 13.6 12.4 10.2
<br /> Notes:
<br /> 1 List of projected water budget water years by water year type:
<br /> Wet:1969, 1974,1975, 1978,1980, 1982,1983, 1986,1993, 1995,1996, 1997,1998,2005,2006,2011,2017
<br /> Above Normal:1970, 1973,1979, 1984,1999,2000,2010
<br /> Below Normal:1971,2003,2009,2018
<br /> Dry:1972, 1981,1985,2001,2002,2004,2012,2016
<br /> Critical:1976,1977,1987, 1988,1989,1990, 1991, 1992, 1994,2007,2008,2013,2014,2015
<br /> 2 Summations in table may not match the numbers in the table.This is due to rounding of model results.
<br /> Prior to 1995, the site was primarily used for cattle grazing. In 1995, the land was converted to a vineyard.
<br /> The vineyard currently occupies approximately 32 acres of the 42-acre Project site. Vineyard water
<br /> demand in the Central Valley is reported to be in the range of 2.5 acre-feet per acre (Sumner 2016). Thus,
<br /> the average current water demand for the vineyard area on the Project site is in the range of 80 acre-feet
<br /> per year.
<br /> The existing irrigation well was installed in 1961 (State Water Well Drillers Report No. 67139-see
<br /> Appendix A of the Water Supply Assessment (ECORP 2021) contained in draft EIR Appendix G). The well
<br /> encountered alternating layers of sand and clay to a total depth of 208 ft bgs. Water production occurs
<br /> from perforated intervals extending from 116 ft bgs to 165 ft bgs. At the time the well was installed, the
<br /> depth to groundwater was reported to be 42 ft bgs.
<br /> In March 2021, Terracon Consultants, Inc. installed a test well at the Project site (Terracon 2021 A). The
<br /> test well was drilled to a total depth of 450 ft bgs, encountering alternating layers of sand and clay within
<br /> the Principal Aquifer. The well was completed with 8.625-inch diameter PVC casing and screened from
<br /> 270 ft bgs to 450 ft bgs.The depth to groundwater was 58 ft bgs. The ground surface elevation at the
<br /> location of the two wells on the Project site is approximately 25 feet above mean sea level (ft msl, NAVD
<br /> 88). Thus, the groundwater surface elevation beneath the site has decreased from about -17 ft msl (i.e., 17
<br /> feet below sea level) in 1961, when the existing onsite irrigation well was installed, to -33 ft msl in 2021.
<br /> After well development, a series of pumping tests were conducted in the new test boring. An initial test
<br /> was conducted for approximately five hours at a rate of 467 gpm. The drawdown in the pumping well
<br /> was 28 feet at the end of the test, resulting in a specific capacity of 17 gpm per foot of drawdown.
<br /> A 24-hour hour aquifer pumping test was subsequently conducted at an average rate of approximately
<br /> 430 gpm. Drawdown and recovery were measured in the test well and at several other locations ranging
<br /> from 186 feet to 2,000 feet from the test well. The test well and other monitored locations are shown on
<br /> Figure 4.12-5.The maximum drawdown observed in the test well during the 24-hour aquifer pumping test
<br /> was 28 feet, consistent with that observed during the initial five-hour test. The data from the test well
<br /> indicate that the aquifer transmissivity is between 88,000 gpd/ft and 158,000 gpd/ft.
<br /> Hydrology and Water Quality 4.12-9 October 2021
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