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_Mr. Mike Huggins - Fetii-uary 9, 2009 Groundwater Monitoring Plan Page 2 of 8 Granite Construction Company,Vernalis Plant The report is organized as follows:,:--, of water bearing sediments in the Vernalis area and 1. Hydrogeologic Conditions: Description discussion of historical groundwater levels and quality. 2. Potential Impacts to Groundwater Resources_Assessment of mining operations as to their potential to affect groundwater levels and quality.- 3. Groundwater Monitorin Plan: Based on the review of historical data and the potential for groundwater impacts,a well network and monitoring plan is proposed that is suitable for long- ater conditions in the Granite Vernalis Plant area. term monitoring of groundw 1. Hydrogeologic Conditions Granite's Plant site overlies the western edge of the northernmost portion of the San Joaquin Valley Groundwater Basin in the area south of the city of Tracy. Within San Joaquin county, this basin is subdivided into the Cosumnes Basin(north of Stockton and extending into Sacramento and Amador counties),the Eastern San Joaquin County Basin(essentially the remainder of the county east of the San Joaquin River), and the Tracy Basin(the remainder of the county west of the San Joaquin River, except of the Coastal Range,and extending into Contra Costa and Alameda counties). Therefore,the Granite Plant overlies the Tracy Basin. The following briefly describes the main water bearing sediments,the occurrence of groundwater,and the groundwater quality in that portion of the basin. Additional information regarding the Tracy Basin is provided in an excerpt from Bulletin 118 (DWR,2003) in Attachment 1. � I Main Water Bearing Sediments , The Plant site is underlain by the Quaternary Alluvium,which generally comprises the alluvial fans and plains along the western side of the northernmost San Joaquin Valley(Hotchkiss and Balding, 1971). The results from drilling programs conducted by Teichert in 1992, 1997,and 2005 to the northwest, north,and east of the Plant indicate that the Quaternary Alluvium is comprised of loosely compacted clayey to sandy gravel with thin and discontinuous layers of silt and clay. The thickness of the r Quaternary Alluvium is difficult to determine because it is underlain by older alluvial deposits of similar character. These latter deposits are comprised of the Tulare Formation(Fm.),which consists of unconsolidated to consolidated lenses of silt, sand, and gravel with interbedded thick;continuous layers k, of clay. The Tulare Fm. is of continental origin and is Plio-Pleistocene in age,and it includes in its upper portion a distinctive clay bed known as the Corcoran Clay(Hotchkiss and Balding, 1971)that informally divides the formation into upper and lower sections and acts as a confining bed for groundwater in the lower section. Both the Quaternary Alluvium and the Tulare Fm. dip to the northeast beneath the project site. The Quaternary Alluvium is reported to range in thickness in the Plant vicinity from approximately a feather edge to 100 feet(from west to east), and the Tulare Fm. thickness is approximately 100 to 600 feet,with the Corcoran Clay.thickness ranging from 10 to 80 feet(Hotchkiss and Balding, 1971). Hotchkiss and Balding(197 1)refer to the base of the Tulare Fm as the base of the "presently usable groundwater reservoir". Deeper materials of consolidated sedimentary and partially-metamorphosed sedimentary rocks of Cretaceous to Tertiary(Miocene)age,and the basement complex comprised of the Franciscan Fm. and granitic and ultramafic intrusive rocks of Cretaceous to Jurassic age are of no relevance to this GMP. Groundwater Levels Groundwater levels have been monitored in the Plant area by Granite's neighbor, Teichert Aggregates, for their Vernalis mining site since 1994. The groundwater level record shows different conditions in the water bearing sediments overlying the Corcoran Clay and water bearing sediments below the © LUHOOFRFF 6 SCAL-MANINI