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Ms. Wendy Arano Project No.: 791291 June 7, 2001 Page 5 • Because the Corcoran Clay horizon does not exist hydraulically upgradient of the landfill, all of the shallow monitoring wells are along the downgradient point of compliance of the landfill. However, because the EMP has not shown the presence of any contamination at shallow well MW-4, and Title 27 Section 20415(b)(2) allows for alternate background locations. We, therefore, propose that the shallow monitoring well MW-4 be recognized as the background well for the landfill. • The initiation of groundwater monitoring in a secondary series of deeper wells is not necessary with the depressed state of the deep groundwater zone. This is because of the following: • VOC contamination was not detected when the water level in the deep zone was higher. • The greatest threat to deep zone contamination was present when the landfill was operational and the existing deep zone wells were operational. • The existing secondary series of deep wells are currently monitored for the presence of groundwater. If the deep groundwater zone ever rebounds to where the existing secondary series of deep wells are saturated, water quality monitoring will be initiated at that time. • The mechanism for the landfill to be a stable source of VOC contamination to both the deep and shallow zones has been greatly diminished with the commencement of operation of the LFG extraction system. • The cost of the installation of a new secondary series of deeper wells is not a good use of public funds for the following reasons: • Because of ongoing overdraft that is occurring in the deep regional groundwater it is not possible to predict how deep into the zone of saturation the new wells will need to be installed before they also go dry. • Public funds are better allocated in shallow zone groundwater and vadose zone gas monitoring if the overall purpose of monitoring program is to provide the best assurance of the earliest possible detection of a release, and the shallow zone will be used to monitor progress of remediation. \\SACRFPI\COMMON\sacDP\2001\PRJ\PJ7\791291.1 aa.doc (00006000)