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09) <br /> CONESTOGA-ROVERS <br /> &ASSOCIATES . <br /> November 30, 2009 -2- Reference No. 060223 <br /> 1 September 2009 SCM, prior to sampling the water supply wells, groundwater monitoring <br /> wells would be installed to provide better definition of deeper groundwater impacts between <br /> the groundwater surface and 150 feet below ground surface (ft bgs) and assist with evaluating <br /> potential impact to the water supply wells. <br /> Based on these responses and periodic discussions with CVWB staff, Shell was under the <br /> impression that appropriate justification was provided in the 15 June 2009 letter and the 1 <br /> September 2009 SCM for not sampling the water supply wells. The strategy being to assess <br /> groundwater flow direction and impacts between the site and the water supply wells as the first <br /> step considering the site is approximately 1,000 feet southeast of the wells, and the presumed <br /> groundwater flow direction is northeast or crossgradient of the wells. The assessment data <br /> would then be used to determine if the site impacts could potentially reach the water supply <br /> wells. <br /> Based on the CVWB's 30 September 2009 letter to Shell, and subsequent discussions with <br /> CVWB staff,however,we recently learned that CVWB staff agrees with Shell's strategy outlined <br /> above, but regardless of this strategy there is a need to sample the water supply wells because <br /> they are possibly in close proximity to the former pipelines. Shell understands the CVWB's <br /> concern and will plan to sample the wells based on the proposed scope of work presented after <br /> Item 2 below. <br /> ESTABLISHING A VERTICAL ASSEMENT LIMIT <br /> CVWB Item 2 <br /> "Based on a review of the data, it appears that the recommendation to limit future investigation to depths <br /> shallower than 150 feet is based on the comparison of a single deeper sample collected from 171.5 feet to <br /> samples collected from 30 and 132 feet. Given this limited dataset, Central Valley Water Board staff does <br /> not concur that investigation should be limited to 150 feet below ground surface." <br /> Response <br /> The vertical investigation limit of 150 ft bgs is actually based on two separate forensics <br /> investigations. The first investigation was reported by Clayton Group Services (Clayton) with <br /> Worldwide Engineering, Environmental, Construction, and IT Services <br />