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1 <br /> E11��t® <br /> Mr James L Barton <br />' December 2, 2004 <br /> Page 11 <br /> mass of the plume Additionally, system performance was found to be protective of the public <br /> and the environment by not creating any exposure pathways Reductions of contaminant <br /> concentrations in groundwater have been observed and ENSR will continue to monitor plume <br />' distribution by performing quarterly groundwater sampling The following recommendations are <br /> provided to possibly improve system performance and provide data for future performance <br /> evaluations <br />' 1 A quarterly sparge and extraction well monitoring plan should be developed to more <br /> regularly collect data that benefits the performance of those wells in remediating the <br /> groundwater plume beneath the site ENSR should begin implementing this pian beginning <br /> with the first quarter of 2005, <br /> 2 If concentrations rebound or do not continue to decrease toward remediation goals and <br />' obtectives, ENSR should consider upgrading the spargmg system with ISCO to accelerate <br /> destruction and removal of the COCs, <br /> 3 ENSR should consider installing a catalyst or replacing the oxidizer with carbon to treat the <br /> off-gases of the SVE system and reduce fuel costs, <br /> 4 Evaluate the addition of sparge wells in the vicinity of MWA 1 and MW-3 to address the <br /> central portion of the plume not being treated by the current sparge well configuration The <br />' evaluation should consider if there are feasible options for reaching portions of the plume <br /> underlying Robinhood Drive <br />' If you have any questions or concerns please contact Ben Heningburg at (916) 362-7100 <br /> Sincerely, <br /> ENSR Corporation <br /> i7—min l Hen r <br /> John M Warren, P E <br /> Senior Protect Manager Senior Program Manager N;-t " 'X/ ue, <br /> RPLImr <br /> Ref 06940-293-100 <br /> Attachments ! <br /> Y <br /> cc Mr John Frary, Union Oil Company of California <br /> Ms Jill Tracy, Esq , Union Oil Company of California <br /> Mr Mike infurna, San Joaquin County, Environmental Health Division <br /> Mr Jay Allen, Stone Brothers Management Company <br /> Mr Gary Hall, GHH Engineering, Inc <br /> 41DcsacraMentolpro�ectskProjects10694OZO98 2937ina11Reports15098 RSE Results doc Re <br /> I p <br /> I <br />