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R, 1 Mr. Mike Huggins February 9, 2009 Groundwater Monitoring Plan Page 5 of 8 Granite Construction Company,Vernalis Plant 2008 nitrate concentrations were lower than at the beginning of the record(Hall,Faulkner, and South Tracy#1 wells)or have remained unchanged(South Tracy#3 and Granite#3 wells). The observed fluctuations are attributed to historical regional agricultural land uses in the area. This includes the nitrate concentration increases in the Brown's#1 well in the early 2000s. Aggregate surface pit mining operations as conducted by Teichert, Granite,and other aggregate mining companies in the area are not i known to contribute nitrate loading (or more generally:nitrogen loading)to the subsurface. 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 µg/L in May 1999 sample),two iron detections(70 to 80 pg/L),and five zinc detections(30 to 130 pg/L). 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 frown<10 to 160 pg/L and from <20 to 220 pg/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 the variability is high. Most frequently,these metals were detected in samples retrieved from the Brown's New well and the Brown's#]'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 pg/L). 2./Potentidi Impacts Groundwater Resources �r Potential dwater Level Impacts t The consumptive use of water at the Plant was estimated to average 1,195 acre-feet per year between 2006 and 2035 (Granite,2006). The water will be obtained from two existing deep production wells (Granite#3 and Granite 94). For comparison,the consumptive use of groundwater at the adjacent Teichert Vernalis site has averaged approximately 2,200 acre-feet per year. Teichert processes mined J - aggregate in the same way as Granite and obtains its make-up water from its two deep production wells Y p (South Tracy#1 and South Tracy#3). The planned expansion of Teichert's mining operations in the r Vernalis area would increase its total consumptive use by approximately 1,100 acre-feet per year,and the increased pumping was estimated to result in less than 4 additional feet of deep-zone drawdown and about 2 feet of shallow-zone drawdown at the nearest off-site location(LSCE, 2005). Similar effects on groundwater levels would be expected due to Granite's mining operation. In comparison to both long-term historical groundwater level fluctuations and seasonal fluctuations (up to 40 to 60 feet)in the deep zone,a temporary(throughout the planned mining until 2035)incremental drawdown of less than 4 feet is considered small. 'Although overdraft conditions have been identified in the Cosumnes and Eastern San Joaquin Basins (NSJCGBA,2004; CDM,2001;DWR Bulletin.160-98,DWR Bulletin 118-05), such conditions do not appear to have been reported in the Tracy Basin,and are not indicated by the discussed groundwater level data record in the Vernalis area(see Figures 3 to 10). Potential Groundwater Quality Impacts Evaporative losses during aggregate washing and wash water storage in the settling pond could potentiall cause eva oconcentratioll and an associated increase of general mineral concentrations in the groundwater to the atmosphere can rec c ed-wasli water. Further, the exposure of bicarbonate-richg _ p i p _ — _ . sult in a changed natural buffering system; and the settling pond is expected to exhibit somewhat higher pH values than groundwater. 'Therefore, deep percolation of wasli water has the potential to © LLJHOORFF 6 SCALMANINI CONSULTING E N G I N E E.�5