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Section 1 • Introduction and Background 1.2 SITE GEOLOGY AND HYDROGEOLOGY 1.2.1 GEOLOGY AND SOILS The Ripon wastewater facility is located within the recent fluvial deposits of the Stanislaus River (Wagner et.al.). The United States Department of Agriculture's(USDA) soil survey for San Joaquin County indicates that the WWTF occurs on primarily three soil series. The majority of the site is on a Columbia fine sandy loam subdivided into three map units based on flooding potential and drainage. Relatively small areas of Merritt silty clay loam occur in the southwestern portion of the municipal disposal ponds and in the southwestern area of the industrial disposal ponds. A small area in the northern portion of the industrial disposal ponds is underlain by Honcut sandy loam. The soils are characterized by limited soil development associated with relatively recent deposition. Permeability of the surface soils is moderately rapid, except for the Meritt which has moderately slow permeability based on USDA data. Recent soils investigations at the Ripon WWTF were conducted during the construction of MW- 4, MW-5, and MW-6 in 1995, and in 1999 for design of the 2001 plant improvements. Borings from these investigations suggest the soils under the treatment and percolation/evaporation ponds are primarily medium to coarse sand with lenses of soil/sediment mixtures containing fine sand, silt and clay. 1.2.2 SHALLOW GROUNDWATER OCCURRENCE Depth to groundwater, as measured during the quarterly groundwater monitoring and reporting program, has varied seasonally from approximately 5 to 33 feet below ground surface (bgs),with an average depth of about 17 ft. bgs. Groundwater flow direction is generally to the south and southwest toward the San Joaquin River, except during high river stages, as exhibited in the first and second quarters of 2006 where flow was toward the north and northwest, contrary to most other historically monitored quarters. Additionally, the combined monitoring of WWTF, Fox River Paper Company, and Nestle Products shallow wells indicates that a large mound exists beneath the Fox River Paper Company facility located adjacent to and east of the WWTF. This mound affects shallow groundwater flow direction and gradient, as well as possibly influencing groundwater quality, in the vicinity of the WWTF. 1.2.3 WATER QUALITY REGULATORY FRAMEWORK In order to comply with State Board Resolution 68-16, otherwise known as the "Antidegradation Policy",the City of Ripon must evaluate potential impacts associated with the disposal of wastewater and determine if the discharge is maintaining the "highest water quality consistent with the maximum benefit to the people of the State." In practice, this has meant that groundwater quality down gradient of wastewater disposal is evaluated with regards to conservative water quality goals (WQGs) and background groundwater quality. The background values are typically determined through statistical analysis of parameters measured in monitoring wells outside the influence of wastewater treatment and disposal, accounting for potential spatial variability at the site. In the event that background values are of higher quality than the conservative WQGs, the WQGs become groundwater limitations. In this case, groundwater April 2007 City of Ripon Wastewater Treatment Facility 1-2 Groundwater Monitoring Well Installation Workplan