SITE INFORMATION AND CORRESPONDENCE

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MW-1 has historically contained low levels of nitrate relative to other wells, as has MW-7,which is screened in a deeper water bearing zone. Analysis of nitrate concentrations in wells MW-9 and MW- 4,the historically upgradient wells(Table 2,Figure 7),reveals that an off-site slug of nitrate migrated in groundwater through MW-9 in June 1998, and was observed on-site in MW-4 in September 1998. Since 1998 and through 2011, nitrate has generally decreased on the north side of the site(Table 2). Since well MW-4 was considered redundant with MW-9, the RWQCB agreed that MW-9 could be removed from the MRP(RWQCB,2003). In October 2011, concentrations of nitrate in wells MW-3 and MW-4 remained above the California maximum contaminant level (MCL) of 45,000 ug/l, whereas nitrate fell below the MCL in well MW-2. Nitrate remained at relatively low concentrations in wells MW-1 and MW-5 where petroleum hydrocarbons have been historically present. Deeper well MW-7 continues to exhibit low to non-detectable concentrations of nitrate(Table 2 and Figures 4 and 7). Ammonia Ammonia has been sporadically detected above reporting limits in all wells since groundwater monitoring began in December 1997 (Table 2). The most consistent detections above reporting limits have historically been observed in MW-1, which also contains petroleum hydrocarbons. Ammonia has not been analyzed since March of 2004 based on the acceptance by the RWQCB of recommendations to remove ammonium because of historic low to non-detect concentrations site wide. Petroleum Hydrocarbons- TPH-g, BTEX, and oxygenates Historically, petroleum hydrocarbons were monitored in six wells (MW-I, MW-2, MW-4, MW-5, MW-7,and MW-8), and with the exception of MTBE, all but MW-1 lacked reportable concentrations for at least six quarters(Table 2). Oxygenates are discussed separately below. TPH-d had not been reported in MW-2 and MW-4 since June, 1998, and in MW-5, MW-7, and MW-8, since December 1997. MW-1,located near the former UST,was the only well exhibiting consistent reportable TPH-d,TPH- g, and BTEX through March 2004- General trends observed at MW-1 (Table 2) show a steady decline in these constituents since September 1998. In October 2004 and 2005, neither TPH nor BTEX were detected above RLs in MW-1. In October 2011, TPH and benzene were once again detected but at relatively low levels. In October 2005, MtBE was reported at concentrations of 15 and 1.7 ug/1 in wells MW-1 and MW- 5, respectively. In October 2011, only MW-5 contained MtBE at a low concentration of 0.55 ug/1. Both wells MW-1 and MW-5 display a decreasing trend in MtBE concentrations (Table 2), and exhibit levels less than the both the California primary and secondary MCLs (13 and 5 ug/l, respectively). Pesticides and Herbicides Historically, organochlorine(OCP)and triazine pesticides were not detected in samples from eight of the nine monitoring wells since the fourth quarter 1997 (Table 2). Based on six quarters of non- detects, triazine pesticides were removed from the MRP after the April 2002 event. MW-3 was the only well to exhibit detectable levels of OCPs since 1997. cmc ayo-ii 6 Io Sm C�We�Iv7no11