ARCHIVED REPORTS_MONITORING WELL M-10 INVESTIGATION REPORT 2010

Home Browse Search

M-10A Investigation Report November 30, 2010 Nestle USA, Inc., Ripon, California 2.2 HISTORY OF TCE CONCENTRATIONS IN WELL M-10A Nestle installed monitoring well M-10A in June of 1988 and monitored M-10A semi- annually in 1989. Quarterly monitoring of well M-10A began in 1990. The TCE concentration in well M-1 OA (Figure 3) has varied over time as follows: • 1990 to April 1993: TCE concentrations ranged from non-detect to approximately 5 pg/L with the exception of 14 pg/L in July 1991 and 22 pg/L in June 1992; • April 1993 through April 1996: TCE concentrations ranged between 5 pg/L to 10 pg/L; • July 1996 through July 2004: TCE concentrations remained below 5 pg/L; • July 2004 through April 2005: TCE concentrations remained above 5 pg/L, but below 10 pg/L; • April 2005 through August 2005: TCE concentrations increased from 8.4 pg/L to 29 pg/L; • 2005 through 2007: TCE concentrations slowly increased from 29 pg/L to 160 pg/L; • 2007 through April 2009: TCE concentrations decreased to approximately 85 pg/L; • July 2009: TCE concentrations increased to 250 pg/L; and • July 2010 (the most recent sampling event): TCE concentrations increased to 310 pg/L. ECM reviewed data trends and the pumping history for nearby wells, including the City of Ripon municipal wells, and extraction wells at the Site. Historical groundwater elevation data indicates that the groundwater flow direction has varied between northeasterly and northwesterly in the general area north of the Site. Monitoring well M-10A is screened from 92 feet bgs to 112 feet bgs in the lower A zone of the Upper Aquifer. Well M-10A is located approximately 450 feet to the southeast of former municipal supply well MW-4(screened in the Upper Aquifer' and Lower Aquifer b), approximately 1,800 feet to the northeast of former municipal supply well MW-6 (screened through all three aquifers°), and approximately 500 feet to the north/northwest of former municipal pumping well MW-1 (screen unknown; total depth of 156 feet bgs). All three of these municipal wells are located west of the Site and M-10A (Figure 2). Well MW-1 was installed in 1928, was active until 1985, and was idle until it was decommissioned in 1994. Well MW-6 was installed in 1972 and was active until January of 1990. Well MW-4 was installed in 1957 and was active until October of 2002, after which it was idle prior to being decommissioned in July of 2009. In addition, an industrial supply well serviced the former Regal Almond facility (Figure 2), located to the west of a Screened from 55 feet below bgs to 63 feet bgs, and 92 feet bgs to 108 feet bgs. b Screened from 200 feet bgs to 252 feet bgs. ° Screened from 84 feet bgs to 338 feet bgs. d Formerly located at 239 Industrial Avenue, across from the former Nestle facility to the west. 2