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Geological reckaacs mc. Page 5 ' Work Plan George's Service Project No.425.2 August 14,2002 and labeled with a unique designation, inserted into foam holders and placed in a chilled ice chest for transport to the laboratory. ' All non-disposable sampling equipment is decontaminated using a steam cleaner and/or an Alconox solution before and between uses. Disposable gloves will be used by the ' technician to collect all samples and will be changed with each sampling event. A chain of custody document, listing all samples collected, accompanies the samples from field to laboratory, thereby providing a means to track their movement and insure their ' integrity. All water purged from each monitoring well and not used as a sample, will be placed in a 55 gallon DOT approved container, properly labeled and stored on site. 2.2.1 Groundwater Sample Analyses ' Groundwater samples from each monitoring well will be submitted to Sherwood 4 �� Laboratories of Hilmar(State Certified Laboratory#1400) and analyzed for: Z➢cK 14�,r° • BTEX by EPA method 602 ' • TPH-G by EPA method 8015(m) �qdw • MTBE,TBA, DIPE, ETBE and TAME by EPA method 8260 (o. Note: MTBE has been detected and confirmed at the site. If the other oxygenates are non-detect after two monitoring events, the analysis by method 8260 will be dropped and regular monitoring will include MTBE analysis by method 602. 2.2.2 Natural Attenuation Concept Each site has geologic, geochemical, and hydrogeologic conditions that are unique. These ' conditions control the fate and transport of contaminants in the subsurface. It is also the case that as the contaminant plume spreads and migrates, it will alter the natural condition of the vadose zone and groundwater aquifers. With sufficient monitoring points, both ' inside the plume and out, the state of the plume with regards to its tendency to attenuate and actually reduce the mass of chemicals through biodegradation of the organic matter can be measured. The risk these chemicals pose to public health and the environment can than be evaluated. Combined with the hydrogeologic character of the groundwater and the chemistry of the plume are understood, the risk can be quantified by using the natural attenuation data to ' calculate the following: 1. contaminant flow paths, 2. chemical degradation rates, 3. plume expansion rates and chemical travel times, 4. point of compliance, w 5. potential receptors that could be impacted in a 2 to 5 year travel time -U ' The following table gives general characteristics of background conditions compared to conditions inside the plume at two stages of evolution.