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• • • CITY OF RIVERBANK WASTEWATER TREATMENT PLANT • GROUNDWATER MONITORING WELL INSTALLATION WORKPLAN • • MARCH 2005 • This Groundwater Monitoring Well Installation Workplan (Workplan), submitted on • behalf of the City of Riverbank(City), describes the proposed location and design of two • monitoring wells to be installed at the City wastewater treatment plant (WWTP). The • Workplan was prepared based on requirements presented in the document Standard Requirements for Monitoring Well Installation Reports,provided by the California • Regional Water Quality Control Board(Regional Board). A. GENERAL INFORMATION • The City operates a WWTP located adjacent to the Stanislaus River. As depicted in • Figure 1, the City is located south of the river in Stanislaus County while the WWTP is • located north of the river in San Joaquin County. Wastewater treatment occurs in aerated lagoons (labeled T-1, T-2, and T-3 in Figure 2), and disposal occurs within percolation • basins (labeled P-1 through P-8). • • The City is currently proceeding with plans to remove accumulated sludge from pond • T-2. To provide continuous wastewater treatment, ponds P-1 and P-2 will be lined and used as treatment ponds. To ensure that groundwater quality in the vicinity of ponds P-1 • and P-2 is protected by the liner, the Regional Board has required that two monitoring • wells be installed. Specifically, in correspondence dated January 31, 2005, the Regional • Board requested a Workplan describing the installation of the two monitoring wells. This Workplan contains the following elements: • • • Proposed monitoring well locations and rationale • • Monitoring well installation and design • • Monitoring well development and survey instructions • Monitoring well installation schedule • • Groundwater sampling and analysis plan • • 1. Background Information • Currently,nine monitoring wells are used to observe groundwater conditions at the • WWTP. Groundwater contours for the last four quarters are presented in Figures 2 and 3. • As shown in Figures 2 and 3, the gradient is generally toward the south, towards the • Stanislaus River. During the winter and spring there is a slight easterly component to the gradient; a slight westerly component occurs in the fall (summer 2004 values may be • skewed by an erroneously low value at MW-1). Based on groundwater samples collected • during 2004, the depth to groundwater is about twenty feet in the vicinity of the • wastewater ponds. • • • Riverbank WWTP Workplan Nolte Associates,Inc. • March 2005 1 \\SasO\project\SA1542\mon_well\new\gwmwiwp\wp.doc •