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ETIC Engineering,Inc. Mr. Paul Anderson May 24,2007 Page 2 and California Department of Water Resources (DWR) requirements. An inspector from the SJCEHD observed and approved the grouting procedures. Soil encountered in soil borings C1 through C11 consisted mainly of clay, silt, and sand. Groundwater was typically encountered in saturated flowing sand at depths ranging from approximately 42 to 47 feet below ground surface (BGS). In the borings where groundwater levels recovered after sampling, the depth to water was subsequently measured at depths ranging from approximately 18 to 29 feet BGS. Limited groundwater monitoring data are available for the Site; however, data from nearby sites indicate that the direction of groundwater flow in the shallowest aquifer is generally to the southeast. The depth to water in groundwater monitoring wells MW-1, MW-7S, MW-7D, and VE-1 was measured during the January 16, 2007 groundwater monitoring event and ranged between 20 and 21 feet BGS. The analytical data indicate that elevated levels of TPH-g and related compounds are present in soil and groundwater in the vicinity of the former UST excavation. Lower levels of these compounds were detected in groundwater samples collected from the downgradient and cross-gradient borings. Soil boring logs, geologic cross-sections, and a detailed evaluation of the hydrogeologic and analytical data will be presented in the report to be submitted upon completion of this investigation. Based on the analytical and hydrogeological data obtained during this phase of the investigation, ETIC proposes to install four 2-inch diameter groundwater monitoring wells (MW-IA through MW-4A)downgradient and cross-gradient of the former UST excavation at the Site. The locations of the proposed wells are shown on Figure 2. The four groundwater monitoring wells will aid in determining the hydraulic gradient and extent of contamination in the shallow aquifer. Future investigations will be performed,as necessary,to fiuther define the extent of impact. Details concerning drilling, soil sampling, groundwater monitoring well installation, and post- installation procedures are described in the March 1, 2007 Soil and Groundwater Investigation Work Plan. Each groundwater monitoring well will be constructed using 2-inch diameter Schedule 40 PVC casing. The monitoring wells are expected to be installed no more than 55 feet deep and constructed with screened intervals having lengths between approximately 10 and 20 feet. Final well construction details, including the screened intervals and the slot-size used in the screened portion of each well will be deternrined based upon hydrogeologic data obtained during drilling. An inspector from the SJCEHD will observe and approve the grouting procedures. Following installation activities, a DWR 188 Well Completion Report will be prepared for each monitoring well and submitted to the SJCEHD and the DWR. Upon receiving approval of this work plan addendum, ETIC will schedule and conduct the installation of the groundwater monitoring wells. The written report summarizing the results of both the soil and groundwater investigation and the well installations will be completed within eight weeks following the receipt of analytical data for soil and groundwater samples collected during well installation.