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r CW&g&3I-r *X1akV_ Page 18 Revised Site Conceptual Model Report Project No.507.2 April 3,2008 • Although the groundwater plume is degrading at a very slow rate, it is unlikely to achieve levels for regulatory closure in an acceptable timeframe (a few years instead of many decades). 5.0 RECOMAMNDATIONS Our recommendations are based on our knowledge of site conditions, and on the state and limitations of subsurface investigative technology. Based on the conclusions outlined above, Geological Technics Inc. recommends the following: • We believe the clayey nature of the shallow soils at this site has been an asset in preventing off site migration of the contaminant. This same characteristic will pose a significant challenge in removing these contaminants, no matter what method is used. Given these factors, we believe that the remedial method selected for this site should include an evaluation of future property use and impacts of various remedial options. LM Excavation would be very intrusive and yet complete in a short time frame. A gradual approach would use time to achieve a cost reduction while allowing nature and the injection of oxidizing agents to degrade contaminants. • It is our understanding that the current business may be planning to move to a new facility. This may provide a unique opportunity for this site, in that there may be a period of time between cessation of the current business operation and resuming operation by another business. During this interim between business use of the property, the core of the contamination be could be excavated and the facility returned to its original condition. L., • Excavation may be implemented with additional treatment methods, such as introducing oxygen-releasing compounds at the base of the excavation to promote natural biodegradation of petroleum. ' 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 L. 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 i 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. w v