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Geofo ' af%,chnks Inc. . . Page 2 { Sinclair Trucking-QMR Project No. 320.2 November 8, 1999 4. MW-1 contains low concentrations of contamination that has migrated downgradient to ' MW-4, which only has trace concentrations of BTEX compounds. 5. MTBE and the other oxygenated fuel compounds were not detected for a second time. It is recommended that: ' 1. That testing for MTBE and the other OFCs should be discontinued. 2. Future investigation of the extent of contamination should consider the following site- specific conditions: ' • The lateral and vertical extent of the clay encountered in MW-4, which could act as a barrier to vertical contaminant migration. • The apparent thin zone of contaminant migration through the sandy unit between 12 and 16 feet below ground surface (bgs). • Predominant direction of groundwater flow. 3. Future monitoring should include a complete natural attenuation parameter analysis. 4. Several more rounds of quarterly monitoring should take place prior to any additional ' investigative work in order to determine if the concentrations in MW-4 continue to decrease and to determine if the gradient direction is stable to the north-northeast. ' 1.0 GROUNDWATER MONITORING 1.1 Hydrology of Site On September 22, 1999, Del-Tech Geotechnical Support personnel measured the four monitoring wells for depth to groundwater. The average depth to water was measured to be approximately 11.5 feet from the top of casing measuring point. The groundwater gradient and bearing of flow were calculated to be 0.0041 ft/ft, flowing N25°E, respectively. This hydrologic behavior is consistent with previous groundwater gradients measured at this site, ' however is a little more to the north. This may be a result of having the wells Iaser surveyed which changed the spatial relationship of the wells on the map. Figure 2 is a map showing both the water table and intermediate groundwater gradients. ' 1.2 Groundwater Sampling Procedure On September 22, 1999, Del-Tech Geotechnical Support personnel arrived on-site, opened the wells, and measured the depth to water with an electrically actuated sounding tape. The water level reading was recorded to an accuracy of 0.01 foot. In wells where free floating product was suspected, a clear disposable bailer was used to gauge the interface. ' Stagnant water in the well casing was purged using a Centrifugal pump as recorded in the field logs (Appendix Q. The rate of well purging was monitored. The wells were purged of at least three casing volumes or until the groundwater parameters (temperature, conductivity, and pH) had stabilized (Appendix C) indicating that water, representative of actual aquifer conditions, was entering the well. Groundwater parameter stabilization was characterized by ' three successive readings within 10%. Before a sample was collected, the well's water level was allowed to recharge to at least 80% of its initial level. All water removed from the monitoring wells and not used as a sample, ' was placed in a 55 gallon DOT (Department of Transportation 17-H) approved container that is properly labeled and temporally stored on-site.