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2024 ANNUAL GROUNDWATER MONITORING REPORT TEICHERT AGGREGATES AND GRANITE CONSTRUCTION VERNALIS AREA 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 have mainly resided between 20 and 30 mg/L with the highest value occurring in 2009 (33.8 mg/L) and a declining trend since then. 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 mostly within that range or lower. 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. Metal concentrations (i.e., copper, iron, and zinc) in shallow groundwater samples (i.e., from the Hall and Faulkner wells) are typically low and frequently below their respective reporting limits. Iron and zinc detections are more frequent at the Faulkner well than at the Hall well. In the deep wells Tracy#1 and#3, metal concentrations are typically low and frequently below their respective reporting limits. Metal concentrations (i.e., particularly iron and manganese) are more frequently detected and more variable in the other deep wells (i.e., Brown's New, Brown's#1, Granite #3, Granite#4, and Granite#5). Total coliform bacteria have been nondetect from the Hall and Faulkner domestic wells with few exceptions. Most recently,total coliform bacteria were detected at the reporting limit of 1.1 MPN/100 mL in the August 2008 sample retrieved from the Hall well. Fecal coliform organisms were nondetect. The sporadic presence of coliform bacteria can be due to sample contamination at the time of collection,the introduction of coliform bacteria to the well structure during well and pump maintenance work, or the detachment of bacterial biofilm from the well structure in combination with naturally occurring coliform organisms. 5 SUMMARY Quarterly groundwater level and quality monitoring of two identified aquifer zones (a shallow and a deep zone) commenced in 1994 and mining of the Vernalis Central area commenced in 1998. Water LUHDORFF&SCALMANINI CONSULTING ENGINEERS 9