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16 <br /> 1.0 ENTRODUCTION <br /> This report documents the results of quarterly groundwater monitoring conducted on April 23, <br /> 1996, sod boring verification sampling, and no further action request for the subject site (Figure <br /> ' 1) The monitoring included collection of depth-to-groundwater measurements and groundwater <br /> sample collection from monitoring wells MW-1B, and MW-2 through MW-6 located on site <br /> (Figure 2) This report also contains results of verification soil borings and soil sample collection <br /> ' from the vicinity of the former underground storage tank(UST)location Lastly, this report <br /> contains a request for site closure and all supporting documentation <br /> Thus report is based, in part, on information obtamed from Moore Petroleum, and is subject to <br /> modification as newly acquired mformation may warrant <br /> 1 1.1 Purpose <br /> ' The purpose of this report is to <br /> summarize the history of the subject site in regards to environmental investigations, <br /> ' 9 report the results of the fourth consecutive quarter of groundwater sampling which <br /> resulted in below laboratory detection limits for total petroleum hydrocarbons(TPH), as <br /> gasoline, and benzene,toluene, ethylbenzene and xylenes, <br /> • perform a mass balance comparison of TPK as gasoline,initially estimated m soil at the <br /> subject site to the estimated quantity of TPH, as gasoline, extracted through vapor <br /> extraction, <br /> ' document the results of two soil borings drilled to the north and south of the former tank <br /> locations on April 5, 1996, and, <br /> ' - request closure for the subject site based on a summary of site specific data <br /> ' 1.2 Background <br /> A summary of the site's history is as follows <br /> ' In August of 1988, Earth Treatment Systems(ETS) of Merced, California, drilled four soil <br /> bonngs (SB-1 through SB-4)on site One boring, SB-4,was completed as a 2-inch <br /> ' diameter monitoring well, MW-1, to approximately 36 5 feet below surface (bs) <br /> • In April 1989, Delta Environmental Consultants, Inc , of Rancho Cordova, California, <br /> drilled and installed 2-mch diameter wells MW-2 and MW-3,to an approximate depth of <br /> 36 5 feet each <br /> • On September 26, 1989, three underground storage tanks(USTs) and associated product <br />