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Geo(oguaC?echnws Inc • • Page 3 Geo Corp-WP Addendum #2 Project 507 2 July 8, 1998 • portion of the contaminated zone Furthermore the SimulProbe's design reduces the possibility of cross contamination from shallower borehole waters After the SimulProbe groundwater sampling tool is advanced into the saturated zone the tool is retracted to expose the screen The sample collection chamber is allowed to fill with groundwater under ambient hydrostatic pressure Once full the chamber is sealed with a pneumatically actuated (NZ gas) solenoid valve and the apparatus is brought to the surface The sample chamber is carefully emptied using a bottom-emptying device thus reducing the possibility of sample agitation and volatilization Once the sample container (40-m1 VOA) is filled and capped, the bottle will be inverted, tapped, and checked for headspace bubbles ' The sample container is identified and labeled with a uruque designation, inserted into foam holders and placed in an ice chest cooled to 4°C for transport to the laboratory Soil boring permits will be secured as necessary and the local regulatory agency will be notified 48 hours prior to commencing work The subsurface will be cleared of underground utilities by notifying Underground Service Alert 2.4 Installation of Deep Monitoring Well Based on the data collected from the deep borehole and SimulProbe samples, a deep, discretely screened monitonng well (JM-109) will be installed in the borehole It is proposed to install the screened interval below the last detectable contamination The well will have a 2 5 or 5 foot screen, based on the geology encountered in the borehole The onsite geologist will confer with the representative from PHS/FHD on the final construction for the well 2.5 Revised Vapor Extraction Well Construction It was proposed in Addendum 91 that vapor extraction wells would be installed in three of the soil borings at the site if the geology and contamination levels were favorable It is now proposed that only one vapor extraction well will be installed if the conditions are favorable The vapor extraction well would be installed either in SB-2 or SB-4 The vapor extraction well would be constructed as follows • 2 inch casing, • screened from 5 to 15 feet, • 0 04 inch screen slot size, • pea gravel filter pack from 4 to 15 feet, • bentomte/cement grout from 4 to 2 feet, 6 dirt from 2 foot to ground surface, - - -- i the casing will be snubbed off and a water tight cap secured on it, O the surface will have a 2 inch concrete cap for security until the vapor extraction test are performed 2.6 Additional Groundwater Analysis ' In addition to the groundwater analysis proposed in the January 17, 1997 work plan, groundwater samples from two monitoring events will also be analyzed for the fuel oxygenate suite (MTBE, DIPE, TAME, ETBE, TBA, Ethanol and Methanol) I