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Page 1 of 2 <br /> Lori Duncan [EH] <br /> From : Lori Duncan [EH] <br /> Sent: Monday, February 23, 2009 2:26 PM <br /> To: 'Mike Siembieda' <br /> Cc: Nuel Henderson [EH] <br /> Subject: RE: well design Barnes Trucking <br /> Mike, <br /> I discussed this with our geologist; we consider the sand unit at approximately 22-25 feet bsg to be the most likely <br /> transport pathway and the best depth at which to identify the lateral extent of the impacted groundwater. We do <br /> not consider there to be justification for two shallow wells, so if you prefer to screen over the sand unit only then <br /> that is what we would agree with . <br /> If you have any question, please do not hesitate to contact us . <br /> Thank you , <br /> Lori Duncan, Senior REHS <br /> San Joaquin County <br /> Environmental Health Department <br /> Iduncan sjcehd .corn <br /> (209) 468-0337 phone <br /> (209) 468-3433 fax <br /> From: Mike Siembieda [mailto: MSiembieda@clearwatergroup.com] <br /> Sent: Thursday, February 19, 2009 5 : 17 PM <br /> To: Lori Duncan [EH] <br /> Subject: well design Barnes Trucking <br /> February 19, 2009 <br /> Dear Lori ; <br /> Thank you for your letter regarding the property at 1817 South Fresno Blvd. , in Stockton (Site Code 2506 ) . <br /> Our current interpretation of shallow groundwater conditions at the site identifies two discrete shallow <br /> groundwater bearing zones at this site. One , a surface clay occurring to approximated depths of 25 <br /> feet, followed by a lower sand unit below the clay . Clearwater generally believes that aquifers should <br /> not be cross-connected by a well , by means of screening across a confining strata . The proposed well is <br /> designed so as not to construct a well over two different hydrogeologic units . There is a potential <br /> that water chemistry and hydraulic heads may be different (between these two different hydrogeologic <br /> units) and interpretation data may be problematic. <br /> If the intent is to document the groundwater quality down gradient from the plume, and SJEHD <br /> staff suspects that the sand layer between 22 and 25 feet bgs is likely the contaminated zone, then <br /> Clearwater proposes that the MW-9 be screened two feet below the aquitard, in a similar fashion as <br /> well AS-1 . If SJCEHD is interested in the downgradient water quality in both zones, then two wells at that <br /> location , with different screen locations, would be more appropriate. <br /> In summary, Clearwater believes that one well should be constructed in the upper clay (no connection <br /> with the lower sand ) and a second, deeper well should be constructed with screen sections exclusively in <br /> the lower sand with the upper clay sealed off. Again we will likely see different chemistry in the two wells <br /> as well as different hydraulic heads . <br /> 994 /moo <br />