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ATC Associates Inc. \v/ 1117 Lone Palm Avenue,Suite 201 Modesto,California 95351 209-579-2221 fax:209-579-2225 The proposed groundwater monitoring wells will be constructed of 2-inch inside diameter, Schedule 40 PVC casing-,with five-feet_of_O..01.O.inch..slotted.screen. A s nd=pack willbe`placed in the annulus of each well extending from 6-bottom of the well screen to approximately three feet-above the top of the screen. Approximately three feet of bentonite will beplaced,-ontop of the sand pack and hydrated with potable water. The remamrng annulus-will""be completed to surface with,cement grout. To protect theintegrity of the wells, locking, watertight well plugs will bei sn talled ori each well and a watertight wellhead labeled ':monitoring well" will be set in concrete over each well. The proposed monitoring well locations are shown on Figure 3. Well construction diagrams associated with the Zone B and C groundwater zones are provided as Attachment 1. Well Survey,Development, and Groundwater Monitoring Once the proposed monitoring wells are installed, the top of each well casing will be surveyed to sub-meter accuracy relative to a known benchmark. The surveying activities will include location and elevation of each well casing. The survey data will be used to tie in to the existing groundwater monitoring well network. At least 48 hours after installation, the new wells will be developed using surging and bailing techniques until the purged groundwater is relatively sediment free. The wells will be sampled at least 48 hours after they are developed. Prior to the collection of groundwater-samples,the depth to groundwater will be measured in each well and a minimum of three well volumes of groundwater will be purged from each well. Temperature, electric conductivity (eH), pH, dissolved oxygen (DO), and oxidation-reduction potential (ORP) will be monitored and allowed to stabilize. Groundwater samples will be collected using disposable bailers, one dedicated to each well. Sample Analyses Selected soil samples collected during installation of the proposed groundwater monitoring wells and subsequent groundwater samples collected from these wells will be submitted under chain- of-custody procedures to a California State-certified analytical laboratory. The groundwater samples will be analyzed for TPHg or gasoline range organics (GRO) utilizing EPA Method 801513; and BTEX, MTBE, tertiary butyl ether (TBA), ethyl tertiary butyl ether (ETBE) di- isopropyl ether (DIPE), tertiary amyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and 1,2- dibromoethane(EDB)utilizing EPA Method 8260B. �-- Report Preparation Upon completion of the field activities, a report will be prepared describing the field activities and laboratory analytical results. The report will include a detailed summary of the subsurface investigation and contaminant distribution, both in soil and groundwater. The report will be S:\Environmenta1\25847\37 Tracy\Repom\wkp-addendum 2009.doc 7