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City of Ripon Well#12 May 31,2006 Nitrate Study Report Recent nitrate concentration data for the water supply well indicate a pronounced seasonal increase (Figure 2). Since 1998, concentrations have increased in the tate summer to fall from a baseline of less that 100 mg/I to concentrations in excess of 700 mgA. The timing of these increases appears to coincide with the peak period of groundwater system stress that results from pumping (The Source Group, 2005a). In October 2005, RFS installed and sampled four shallow monitoring wells (MW-101 through MW-104)at the site. The groundwater samples were analyzed for nitrate in addition to organic compounds as per a request from the CRWQCB. Samples were analyzed by Cal Tech Environmental Laboratory (CTEL) of Paramount, California. The analytical results from CTEL indicated that no nitrate was present in any samples collected from RFS wells (AGE, 2005). Subsequent to the AGE report, additional sampling of the RFS wells (MW-1 through MW-10, MW-103, MW-104, and Agricultural Well) was performed (Email communications with RFS and AGE, 2006a). These analyses confirmed the presence of nitrate at concentrations above the maximum contaminant level for drinking water (45 mgll as NO3). However, there were significant differences between results run on split samples at two different laboratories (McCampbell Analytical Laboratory and Cal Tech Environmental Laboratory). a,pd,wen 12 croon3-3 the ss'a@Qnp.mup,mr,