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up-gradient well will be monitored for potential groundwater contamination. The three proposed <br />B-Groove wells nearest the experimental volume are expected to provide the earliest detection of <br />groundwater contamination. <br />(vii) a time-schedule for implementation; and Monitoring of water will begin as soon as wells are <br />completed. <br />(viii) ambient groundwater quality data sufficient to characterize potentially impacted <br />groundwater quality. Ambient data have been collected monthly at the existing locations since <br />June 2007. The analyses demonstrate stable groundwater quality at all locations. <br />4. Proposed abandonment for non-cased drain holes is stated to be "as-is." <br />Response : As per Rule 16.2.1, ExxonMobil will plug the non-cased drain holes, when they are <br />no longer needed, by filling the hole(s) with drill cuttings, clean native clays, cement or high <br />solid bentonite grout to within five (5) feet of the ground surface and capping at the tunnel wall. <br />NOTE: these drain holes are NOT water wells. <br />5. Please describe how the drilling water quality will be affected after it has been used for <br />drilling. Will the discharge of drilling water cause degradation to the existing discharge water <br />quality ? <br />Response : No degradation to the existing surface water quality is anticipated due to drilling the <br />non-cased drain holes. It is anticipated that no additives to the water will be required, so the drill <br />return water would be exposed only to oil shale rock, and it would be returned to the surface <br />water system as part of the mine outflow. If additives are used, the drill return water will be <br />retained in temporary tanks on the mine bench and evaporated or disposed of off-site. No <br />discharges of water beyond the existing water and storm runoff are anticipated. <br />We appreciate your assistance with this matter. Should you have general questions about this <br />response, please contact me at 281-654-6246. Technical questions may be addressed to Mark <br />Del Pico at 713-431-7581 or mark.delpico(a)exxonmobil.com. <br />Respectfully submitted, <br />V ? V <br />Tom L. Adams <br />Colony Supervisor <br />ExxonMobil Global Services Co. <br />Acting for and on behalf of <br />Exxon Mobil Corporation