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Environmental Mr.Harlin Knoll Resources 23 April 1998 Management Page 3 g To address the occurrence of TPH-g and BTEX compounds in ground water at each location, ERM will install a monitoring well downgradient of each UST location. Ground water flow direction will be ascertained from ground water investigations that have occurred on-site (BJJ Trucking, 757111h Street) or at an adjacent site (UP Tracy Rail Yard). By using ground water flow information from these sites, the need for three monitoring wells, usually required by LUFT protocol to define the ground water flow direction, is eliminated and a single downgradient well is suitable to monitor the occurrence and migration of TPH-g and BTEX in ground water. The two monitoring wells will be sampled and analyzed for TPH-g and BTEX for two quarters to evaluate changes in concentrations of TPH-g and BTEX downgradient of the former UST areas; if the monitoring indicates static or declining contaminant concentrations over this sampling period, ERM believes that the site could be closed based on demonstrated low risk. ERM discussed this proposed scope of work with the County in phone conversations on 13 April 1998 and 21 April 1998. The County has indicated that the proposed scope of work will sufficiently address the TPH-g in soil issue and provide the information necessary to determine if site closure can be attained based on demonstrated low risk. PROPOSED SCOPE OF ADDITIONAL WORK Based on the conversations with the County, ERM will install one monitoring well at a location downgradient of each of the two former UST locations. The location of the monitoring well for UST #1 will be situated approximately 30 feet north of hydropunch location HB-6, as shown on Figure 1. The UST #2 monitoring well will be installed between the tank excavation and hydropunch location HB-4, as shown on Figure 2. Each of the proposed monitoring wells will be installed using a truck- mounted hollow-stem auger drill rig. The wells will be constructed of 2- inch Schedule 40 PVC and screened from a depth of approximately five to fifteen feet bgs with 0.010-inch machine slotted PVC screen. A filter pack of Lonestar #1C sand will be emplaced from the total depth of the well (approximately 15' bgs) to approximately 1 foot above the top of the screened interval. The wells will be swabbed prior to the installation of the annular seal to facilitate filter pack settlement. An annular seal consisting of approximately 1 foot of bentonite and 3 feet of neat cement will be installed following placement of the filter pack. A locking