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Revised Additional Vapor and Groundwater Monitoring Well Work Plan Raymond Investment Corporation October 30,2009 Page 3 Condor proposed the installation of one monitoring well 10 to 20 feet from SB-3 and SB-4 (in the location of the center of the suspected contaminant source area), four soil borings, and three down- gradient hydropunch borings located in the sidewalk or street on the other side of the above-mentioned building. The rationale for installing only one additional monitoring well at that time was the uncertainty of the distribution of contamination in the down-gradient area. Results of the samples collected from the proposed well and other proposed borings would assist in effectively locating additional wells, if necessary. If other additional wells were installed during the previous work phase, prior to evaluating the results from the new borings, they might have been ineffectively located. MW-4 was installed on August 29, 2006. Soil borings were installed on September 7, 8, and 28, 2006. The installation and investigation activities were documented in the report titled Additional Soil.and Groundwater Investigation Report and Third Quarter 1006 Monitoring Report, dated January 2, 2007. Groundwater monitoring continued with some modifications. The report titled Site Conceptual Model 2008, dated October 31, 2008, summarized data that had been collected regarding the Site to date and clarified existing data gaps. The letter from the SJCEHD dated May 12, 2009,authorized the reduction of sampling frequency and analyte list for the existing monitoring wells. The May 12, 2009 letter indicated that the SJCEHD "believes that additional investigation is needed to delineate the vertical and lateral extent of groundwater contamination at the identified source of the contamination and down-gradient northeast of the source area. This includes investigating soil and groundwater beneath the building located northeast of the source and may possibly warrant collecting soil gas samples near the building." A Condor representative met with Ms. Victoria McCartney and Mr. Nuel Henderson of the SJCEHD at the Site on May 28, 2009. The SJCEHD observed he conditions and placement of the building and basement of the building,and agreed.that the interior of the building w sa practically inaccessible.and, dawn-gradient wells would need to be placed along the exterior'of the building. .-T The Additional Vapor and Groundwater Monitoring Work Plan, dated August 4, 2009, was prepared by Condor and submitted to the SJCEHD for approval. Modifications to the work plan were recommended by SJCEHD in their letter dated October 8, 2009 Condor concurs with those recommendations and has included them in the revised work plan. L 3.0 PROPOSED MONITORING WELL LOCATIONS AND SAMPLE INTERVALS A total of six additional groundwater monitoring wells, three soil borings, and three soil vapor monitoring wells are proposed.,The wells will be installed in two phases. The first phase will include theme 'installation of-one well`f r icaI deflnition,.two �onitonng.wells,for.horizontal.;definition,Fthree'soil borings, and three.soil vapor wells.F.If laboratory analytical results,or field,4observations indicate that L hydrocarbons are present in the monitoring wells installed during the first phase, then three.additional. monitoring wells-will,be,installed-northeast_of,the building along Grant Streeter nd in line with'he average groundwater gradient direction from MW-4. - LOne monitoring well, MW-4D, will be placed adjacent to MW-4. The purpose of MW-4D will be to provide data on the vertical distribution of aqueous phase hydrocarbons. There will be a 15-foot vertical separation between the screen interval of MW4 and MW-4D. Specifically, the data will support or j L discount the analytical data from the-groundwater grab sample collected in September 2006 from SB-7 at b' 68 to 72 feet bgs. Monitoring well MW-41) will be advanced to a,-depth of approximately 70 feet bgs and gl.},D U- - --� .�- �.. constructed with a j 0-foot screen interval. The monitoring well will be constructed with 2-inch-diameter � �� Lcasing.No soil_samplesywill be collected_from the soilLboring made-for the installation of monitoring well a��"`�` MW4D due its proximity to so>T sample analytical data collected from SB-7. i +.� CONDOR I .wIC: