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2020 ANNUAL GROUNDWATER MONITORING REPORT TEICHERT AGGREGATES AND GRANITE CONSTRUCTION VERNALIS AREA Faulkner wells), bicarbonate is the most prevalent anion, followed by chloride. Bicarbonate is also the most prevalent anion in the South Tracy#3 well, but it is closely followed by sulfate. Bicarbonate and sulfate are equally represented in the Brown's New well. Sulfate is the most prevalent anion at Granite #5 well,followed by bicarbonate. Shallow groundwater has greater chloride concentrations than deep groundwater and its hydrochemical facies is of Ca-Na/HCO3-CI (Faulkner) and Na-Ca/HCO3-Cl (Hall)type. Deep groundwater has greater sulfate concentrations than shallow groundwater. South Tracy#3 and Brown's New well hydrochemical facies is of Ca-Na/HCO3-SO4 type. Groundwater retrieved from the Granite#5 has 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 milligrams per liter(mg/L) between 1994 and 1996, decreased to about 20 mg/L in 1999, and remained relatively stable around 20 mg/L until between 2010 and 2013 when concentrations further decreased to 11.1 mg/L(Figure 24). Nitrate concentrations in the Faulkner well exhibit similar trends with an overall decline from 36 to 7.1 mg/L(1994-2013). Both the Hall and the Faulkner wells experienced concentration increases to 34.2 and 28.1 mg/L, respectively, in November 2014. From November 2014 to May 2017, concentrations fluctuated up to 16 mg/L.Since then, concentrations have declined to concentrations lower or similar to the mid-2000's(around 10 mg/L). 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. Between 2008 and 2014, concentrations increased and stabilized at an average of about 30 mg/L.Since November 2015, concentrations have stabilized at about 25 mg/L. During its early period of record (1994-2001), nitrate concentrations in samples retrieved from the Brown's New well were stable, fluctuating between 6 and 11 mg/L; and its recent samples are within that range or lower(with the exception of May 2019 when nitrate was 13.4 mg/L). Nitrate concentrations in the Granite#3, Granite#4, and Granite#5 range from 6.5 to 16.5 mg/L. The greatest long-term variability and seasonal variability is exhibited by the Brown's#1 well. Nitrate concentrations initially increased from 12 to 30 mg/L in 1994, decreased to 12-16 mg/L in 1997-98, and then increased to 48.5 mg/L(May 2004). Since nitrate concentrations began increasing in 1999, seasonal fluctuations also increased. Water quality data for this well are not available after 2004. The presence of the observed nitrate concentrations is likely related to both the historical agricultural land use in the area prior to the commencement of aggregate mining by Teichert Aggregates and also continuing farming practices.This includes the nitrate concentration increases in the Brown's#1 well. LUHDORFF He SCALMANINI CONSULTING ENGINEERS 7