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LOL • � -' v�v� <br /> SER 09 '68 16: 13 HLA,CO(� 415 667-9673 P.z <br /> -? August 1988 <br /> Laurie Coh& <br /> San Joaquin Local Health District <br /> 7- 11 IN TRACT, 455 WEST GRANT LINE ROAD <br /> Harding Lawson Associates (HLA) submitted a workplan to drill a 60 foot well <br /> on the 7- 11 property to determine the vertid extent ofasoline <br /> contamination. Considering that first round water is abut five feet, it <br /> appears that 60 feet is excessive. HLA presumes that there is a confining layer <br /> MP-ears <br /> first aad second water. While this may be true, it would be <br /> better to drill into (not through) the confining layer to determine whether the <br /> gasoline has even reached the layer. If it has a deep well may be in order. <br /> However, that should be determined at that time. <br /> We a�gree that other wells are needed; especially in the area between MW- 2 <br /> and MW - 12 which could help determine whether the subsurface fill beneath <br /> the 7-11 convenience store (probably gravel) has acted as a conduit for <br /> gasoline. This would help explain the concentrations found in MW- 14, which <br /> HLA says '...appear to be anomalous...-. HLA should resample and analyze the <br /> ground water by GUID for TPH and method 8020 for BT%&E. <br /> There rt shows high levels of dissolved and gaseous phase Mline near and <br /> prol under the convenience store. Have any vapor stud es been <br /> conducted inside the building? With ound water so shallow and porous <br /> material beneath a buildingg,, our wMeence has shown that vapors can enter <br /> buildings via the sewer and other pipelines, - -- - -- - <br /> If <br /> --If you have any questions, please call me at (9 16) 361.5740. <br /> Gordon Lee Bo <br /> Underground I <br /> Program Coordinator <br />