SITE INFORMATION AND CORRESPONDENCE

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southeasterly direction of groundwater flow,whereas conditions in November 2014 indicate northwesterly direction of groundwater flow. The recent contours(including 2009-2014)represent conditions of the lowest water levels on record to date. 3.2 Groundwater Quality The electrical conductivity(EC)of samples retrieved from the shallow network wells (Hall and Faulkner — domestic wells)mostly ranged between 900 and 1,000 gS/cm between 1994 and the mid-2000's when EC values started to decrease until early 2014 when the lowest values were measured(853 and 757 gS/cm, respectively) (Figure 13). The November 2014 EC measurement in the Faulkner well was the highest on — record(1,130 gS/cm); Hall increased to 1,040 gS/cm. The EC of samples retrieved from the deep network wells South Tracy#l,#2, and Brown's New mainly range from 800 to 900 AS/cm and have been very stable over the period of record. The EC at Brown's#1 was more variable from 1994 until 2005 _ (when it was vandalized)—and the EC at its replacement well(Granite#3; sampling commenced in 2006) has been higher but similarly variable". Groundwater quality data for 2014 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. — 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). 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 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 represented). Shallow groundwater has greater chloride concentrations than deep groundwater and its hydrochemical facies is of Ca-Na/HCO3-Cl type. Deep groundwater has greater sulfate concentrations than shallow groundwater and its hydrochemical facies is of Ca-Na/HCO3-SO4 type. Groundwater retrieved from the Granite#3 and Granite#4 wells have proportionally more sulfate and is of Ca-Na/SO4- HCO3 type. _ Nitrate(as nitrate)concentrations in shallow groundwater samples retrieved from the Hall well increased from about 15 to 30 mg/L between 1994 and 1996,decreased to about 20 mg/L in 1999,and remained _ relatively stable around 20 mg/L until 2013 when concentrations further decreased to 11.1 mg/L(Figure 23). Nitrate concentrations in the Faulkner well exhibit similar trends with an overall decline from 36 to 7.1 mg/L(1994-2013). Both wells experienced large concentration increases since then to 34.2 and 28.1 mg/L,respectively, in November 2014. — 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 before sampling of this well was discontinued in 2009. Nitrate concentrations observed in the South Tracy#3 well were approximately 5-10 mg/L lower than in the South Tracy#1 well through 2008. Since then,concentrations increased and average about 30 mg/L. 4 In August 2009,a sample was retrieved from Granite#4 in lieu of Granite#3,where a sample could not be retrieved at the time. 6 ©WFOOFFF&SCALMANINI - CGN6VL�iNG EN61NEER9 J