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1 - - GevlogualT¢clutuslrtc Page 9 Monta Additional Site Characterization Report Project No 724 2 April 19,2004 Conclusions • This investigation was primarily undertaken to determine the lateral extent of the ' submerged plume that is sourcing the contamination recorded in off site well MW-106 The presence of contamination in deep well MW-202 (screened 70 — 80 feet bgs) confirms that a "core" of groundwater contamination is beneath the water table at the ' site • The fact that well MW-202 contains a higher level of TPH-G contamination, 381 ug/l, than well MW-2, 94—96 ug/1 in 2003, may be caused by several factors ' o the longer well screen in MW-2 is causing dilution of contaminant concentrations o the plume has migrated vertically and concentrations increase with depth o the contamination detected during the installation of MW-202 is a drilling artifact and may not be present in future monitonng events ' • The residual soil TPH-G contamination in the vadose zone and sorbed hydrocarbons below the water table continues to provide a source for dissolved hydrocarbon groundwater plume • The fluctuating groundwater table has contributed to a smear zone extending beyond the property boundaries ' a Figure 6 illustrates the wells' various screened intervals For future reporting purposes, the wells will be designated as shallow, intermediate or deep wells as follows (based on a depth to water of—38 feet bgs in December 2003) o Shallow MW- 4, 5, 6, 7 and 11 o Intermediate MW- 1, 2, 3, 106, 107, 108, 109, 110, and 111 o Deep MW- 104, 202, 208, 209 and 210 Recommendations The following recommendations are made 1 Incorporate the new wells in the quarterly monitoring schedule 2 Perform contaminant mass estimate calculations for groundwater contamination after ' the new wells are sampled These calculations will be included in the 1 ST Quarter 2004 Groundwater Monitoring Report for the sampling event scheduled for February 2004 3 Determine if the plume warrants an engineered clean up 6 0 LIMITATIONS This report was prepared in accordance with the generally accepted standard of care and practice in effect at the time Services were rendered It should be recognized that definition and evaluation of environmental conditions is an inexact science and that the state or ' practice of environmental geology/hydrology is changing and evolving and that standards existing at the present time may change as knowledge increases and the state of the practice continues to improve Further, that differing subsurface soil characteristics can be ' experienced within a small distance and therefore cannot be known in an absolute sense All conclusions and recommendations are based on the available data and information. The tasks proposed and completed during this project were reviewed and approved by the ' local regulatory agency for compliance with the law No warranty, expressed or implied, is made