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r r 3.2 Groundwater Quality The electrical conductivity(EC)of samples retrieved from the shallow network wells(Hall and Faulkner domestic wells)mostly ranges between 900 and 1,000 µS/cm and has been stable during the period of record,with a trend to slightly lower values in recent years(Figure 13). The EC of samples retrieved from the deep network wells typically ranges between 800 and 950 pS/cm and has also been stable during the period of record. Samples retrieved from the Granite 43 well(sampling commenced in 2006 as a / replacement for the vandalized Brown's#1 well)and the Granite#4 well have EC of about 1,000 µS/cm4. Groundwater quality data for 2010 are summarized in Table 3 and the complete water quality record is provided in Table 4. Laboratory reports and field notes are provided in Attachment 3. r Time series plots of major cation concentrations(sodium, calcium, and magnesium)and anion concentrations (bicarbonate,chloride,and sulfate) prepared for the individual wells are in agreement with the EC measurements and reflect stable hydrochemical groundwater conditions(Figures 14 to 21). r Concentrations of major cations and anions were averaged over the period of record and plotted in milliequivalents per liter(meq/L)in a Schoeller Diagram (Figure 22). Calcium and sodium are the most prevalent cations in groundwater from both the shallow and deep zones. in the shallow zone(Hall and r Faulkner wells),bicarbonate is the most prevalent anion, followed by chloride; sulfate is proportionally the least represented. Bicarbonate is also the most prevalent anion in the deep zone(except at the Granite #3 and#4 wells), but it is closely followed by sulfate(and chloride is proportionally the least r represented). Shallow groundwater has greater chloride concentrations than deep groundwater and its hydrochemical facies is of Ca-Na/HCO3-CI type. Deep groundwater has greater sulfate concentrations than shallow groundwater and its hydrochemical facies is of Ca-Na/HCO3-SO4 type. Groundwater .r retrieved from the Granite 43 and Granite#4 wells have proportionally more sulfate and is of Ca-Na/504- HCO;type. Nitrate(as�nirate)concentrations in shallow groundwater samples retrieved from the Hall well increased .d from abo�t 15 to 30 mg/L between 1994 and 1996, decreased to about 20 mg/L in 1999, and have remained relatively stable since then with concentrations typically below 20 mg/L in the last few years (Figure 23). With the exception of the early monitoring record (1994-96),nitrate concentrations in the r Faulkner well have typically been lower than in the Hall well, decreased more in 2005,and have remained below 15 mg/L since then. r The highest nitrate concentrations have historically been observed at the South Tracy #1 well, ranging from up to 50 mg/L in 1994(i.e.. above the drinking water maximum contaminant level (MCL)of 45 mg/L)to approximately 35 mg/L in recent years. Nitrate concentrations observed in the South Tracy #3 well are approximately 10 mg/L lower than in the South Tracy #1 well,but show similar seasonal r fluctuations(its record extends from 2004 to the present). During its early period of record(1994-2001),nitrate concentrations in samples retrieved from the r Brown's New well were stable, fluctuating between 6 and 1 I mg/L; and its recent samples are within that range. Nitrate concentrations in the Granite#3 and Granite#4 wells are similarly low. The greatest long-tern variability and seasonal variability is exhibited by the Brown's#1 well. Nitrate r concentrations initially increased from 12 to 30 mg/L in 1994,decreased to 12-16 mg/L in 1997-98,and since then increased to 48.5 mg/L (May 2004). Since nitrate concentrations began increasing in 1999, seasonal fluctuations also increased. r 4 In August 2009,a sample was retrieved from Granite#4 in lieu of Granite#3,where a sample could not be r retrieved at the time. ©LW FF -- SCJlNAPIINI 6 CONSULTING ENGINEERS