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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 well 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 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 19). With the exception of the early monitoring record(1994-96),nitrate concentrations in the Faulkner well have typically been lower than in the Hall well,with a similar long-term trend. 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 fluctuations(its record extends from 2004 to the present). During its 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 concentrations in the Granite#3 well are similarly low. 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 since then increased to 48.5 mg/L(May 2004). Since nitrate concentrations began increasing in 1999, seasonal fluctuations also increased. 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. Copper, iron, and zinc concentrations in shallow groundwater samples are typically low and frequently below their respective reporting limits. For example,the record(59 monitoring events)for the Hall well shows one copper detection(100 gg/L in May 1999 sample),two iron detections(70 to 80 µg/L), and five zinc detections(30 to 130 µg2). To date,manganese has not been detected in the Hall well. In samples retrieved from the Faulkner well,copper-and manganese concentrations have always been nondetect; iron and zinc concentrations have ranged from<10 to 160 gg/L and from<20 to 220 µg/L,respectively. As in shallow groundwater samples, traces of copper concentrations in most deep groundwater samples are rarely detected. In contrast, iron,manganese and zinc are frequently detected in most deep wells; and variability is high. Most frequently,these metals were detected in samples retrieved from the Brown's New well and the Brown's#1 well. These metals are also present in well water more recently retrieved from the Granite#3 well. Metal detections in the South Tracy#1 well are few. In the South Tracy#3 well,copper, iron,manganese, and zinc concentrations have been nondetect to date(with the exception of one iron detection at the reporting limit of 50 µg/L). Lastly,total coliform bacteria have been absent from the domestic wells with few exceptions. Most recently,total coliform bacteria were reported at the reporting limit of 1.1 MPN/100 mL in the August 2008 sample retrieved from the Hall well. Fecal coliform organisms were absent. 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. ©LUHDORFF& 5CALMANINI 6 CONSULTING ENGINEERS