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tD SECOR www secor com <br /> N <br /> ITERNATIONAL j, <br /> E C O R INCORPORATED 3017 Kilgore Road,Suite 100 <br /> Rancho Cordova,CA 85670 , <br /> . 916-861-0400 FAx <br /> a916-861-0430 FAx <br /> September 23, 2005 <br /> Victoria L McCartney L� �Il 1"J E r"i-I kL <br /> San Joaquin County <br /> Environmental Health Department SEP 'I'd 7 2005 <br /> 304 East Weber Avenue, Third Floor ` , <br /> Stockton, CA 95202 ENVIRONMENT HEALTH ` <br /> PERMIT/SERVICES `' <br /> RE Groundwater Mounding Study Report W� <br /> 7-Eleven Store#19976 <br /> 1399 North Main Street �^ <br /> Manteca, California 95336 ;a <br /> SECOR Project No 77EL 19976 05 0104 <br /> Dear Ms McCartney (�y � <br /> This report is prepared by SECOR International Incorporated (SECOR) on behalf of 7- I� <br /> Eleven, Inc to document the results of a groundwater mounding study conducted at 7- <br /> Eleven site #19976 located at 1399 North Main Street, Manteca, California (Figures 1 and <br /> . 2) The report has been prepared in response to San Joaquin County Environmental <br /> Health Department (SJCEHD) letters dated May 3, 2005 and May 24, 2005 which <br /> requested documentation that groundwater mounding is not occurring during oxygen <br /> injection at the site (Attachment A) rn'° <br /> Groundwater Mounding Study k <br /> i <br /> In order to determine whether or not groundwater mounding occurs at the site during <br /> oxygen infection activities, SECOR proposed monitoring the depth to water (DTVI) below t <br /> the top of the casing (TOC) in select wells before, during and after the oxygen injection �4 <br /> events The SJCEHD approved the proposal in the May 24, 2005 letter and requested that t13 <br /> groundwater monitoring wells MW-2, MW-51MW-5A, and MW-4 be used for the study <br /> 4 � ; <br /> On September 2, 2005, SECOR field personnel conducted the scheduled oxygen injection <br /> event into dual-nested oxygen sparge wells SP-1 and SP-1A Between 8 45 a m and 9 15 <br /> AM, 150 ft3 oxygen was injected into each well simultaneously Before, during and onerj <br /> hour after the injection event, DTW was monitored in wells MW-1, MW-1A, MW-2, MW-4, , <br /> MW-5, MW-5A, and MW-6 Field notes documenting the oxygen injection event and N <br /> groundwater mounding study are in Attachment B <br /> As summarized in Table 1, the water table elevation (WTE) in groundwater monitoring well 1 <br /> MW-2, located immediatelycent to oxygen sparge wells SP-1 and SP-1A, rose from ; { <br /> 20 98 feet below TOC to , feet below TOC This represents a 3 05 feet rise in WTE <br /> However, the WTE in MW-2 dropped back down to 21 12 feet below TOC one hour after <br /> • completion of the injection The WTE in the remaining groundwater monitoring wells rose <br /> approximately one foot, but also returned to pre-injection levels after one hour <br /> "'n-1i <br /> 19976 Groundwater Mounding Study 19976 Grounwater Mounding Study Report 09-23-05 doc <br />