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Mr. Todd Del Frate 0 -2- <br />UPDATED ENGINEERING FEASIBILTY STUDY AND AMENDED REPORT OF WASTE <br />DISCHARGE CORRAL HOLLOW SANITARY LANDFILL <br />Unfortunately, our options available to us on site are limited due to the limited space between the <br />edge of refuse and property boundary. We can, however, install two additional LFG wells to again <br />increase the collection of LFG from the area between MW -5 and -8 (Figure 2). <br />VOCs May Be from Off -Site Source <br />Additional shallow aquifer flow direction information available since the installation of monitoring <br />well MW -8 in December 2007 indicates that the flow direction in the vicinity of well MW -5 and -8 <br />includes a south-westerly component, with flow from the refuse in the CalTrans property to the <br />Corral Hollow Landfill. It is possible that the VOCs detected at MW -5 originate from that refuse, <br />and not from our landfill. <br />It is also possible that the groundwater is "contained" by the groundwater gradient, regardless of <br />the source of the VOCs. <br />Evaluating the groundwater flow direction requires additional shallow aquifer elevation data which <br />can only be collected from locations off-site. In an effort to gather that data, we will contact <br />CalTrans to request permission to install a shallow aquifer monitoring well north and east of <br />Interstate 580 adjacent to our site. This location will provide "triangulation" with wells MW -5 and <br />SB -1, allowing a more accurate estimate of flow direction beneath the surface between those two <br />wells. <br />In addition, we will contact the owner of the property northwest of our site, on the other side of <br />Corral Hollow Road, with a similar request to install a well on their property. That well would be <br />installed to "triangulate" with wells MW -5 and -8, allowing a more accurate estimate of flow <br />direction beneath the surface between those two wells also. <br />If we are allowed to install these wells, and if it is determined that the shallow aquifer gradients <br />bring water into our property, then we will ask that Regional Water Board staff consider that the <br />VOCs are from an off-site source, and that further corrective action on our property would not be <br />appropriate. <br />If you have any questions, please call me at (209) 468-8504. <br />Sincerely, <br />W. MICHAEL CARROLL, PE <br />Senior Civil Engineer <br />WMC:KB <br />NA1Corral Hollow\Groundwater Monitoring\TDelFrateN-Update EFS.doc <br />Enclosure <br />c: Robert McClellon, Environmental Health Department (letter only) <br />LA 21850 <br />