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f✓ Page 4 <br /> 3.4 Evaluation of Exposure Risk <br /> !I, <br /> 3.4.1 Discussion of Historical Informatiorn <br /> i'. <br /> I� <br /> Historical data, (Beta Associates Report and Boring Logs, 1986), <br /> suggests that groundwater was encountered at 43 feet and that from 29 to 35 <br /> feet there is a very stiff clayey silt followed by a stiff silty clay from 35 to 43 <br /> feet. This would suggest that groundwater is separated from the contaminated <br /> i, <br /> soil by 6 feet of very stiff clayey silt and 8 feet of stiff silty clay. <br /> We have eliminated the source of the contamination and will remove <br /> the majority of contaminated soil. The remaining soil will have a lateral <br /> concrete barrier and a concrete cap. The remaining soil will be isolated from <br /> groundwater by clay and concrete. The remaining soil will be isolated from <br /> people at or near the site by the concrete {cap. <br /> 3.4.2 Modeling <br /> �{ Tri Valley Growers is proposing modeling of potential residual <br /> contamination. The modeling would be based on site specific samples secured <br /> during the bucket auger removal. (Note: See Attached Secor Proposal). <br /> 4. Site Housekeeping. +! <br /> 3� <br /> Tri Valley Growers is aware that the soil auger may tend to spin of soil <br /> when the auger is removed from the boring. To control potential for the spin- <br /> off soil from impacting the adjacent scl ool yard, plastic sheeting will be <br /> erected against the adjacent perimeter fence. <br /> Additional steps will be taken to prevent spin-off from affecting cleared <br /> borings and clean soil or pea gravel piles <br /> Sincerely, <br /> ' B b ennett AD�f <br /> Phone {209} 572-5564 <br /> Fax (209) 572-5298 <br /> Environmental Services Supervisor <br /> Tri Valley Growers <br /> it <br /> P.O.Box 7114,Battery St,San Francisco, California 94120-7114 Pbone:(415)404600 Telex:27.~ Fax (41.)445-1628 <br /> r <br /> i� <br /> 4 <br /> 7 -- <br />