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L v L4.0 Discussion and Request for Site Closure ure During the January 2010 monitoring event,low levels of TPHD were detected in groundwater samples collected from monitoring wells MW-1,MW-2,and MW-6 prior to silica gel cleanup. NCL reviewed the laboratory chromatograms and indicated in their analytical report(Appendix C)that Lthe samples contained material in the diesel range of molecular weights;however,the material did not exhibit the peak pattern typical of diesel. Upon processing the samples through a silica gel cleanup procedure and re-analyzing the samples,TPHMO and TPHD were nondetectable in the L groundwater samples collected from wells MW-1,MW-2,and MW-6. The purpose of performing a silica gel cleanup is to remove polar and semi-polar compounds that Lmay interfere with analytical results. Natural Organic Matter(NOM) may be present in site soils, due to natural or anthropogenic sources. NOM often consists of polar and semi-polar compounds that have similar molecular weights as diesel or motor oil range hydrocarbons. Biogenic Linterference is the term used to describe the NOM that is quantified and reported in the diesel or motor oil range of molecular weights. Generally,most fresh,non-biodegraded petroleum hydrocarbons are considered non-polar compounds (ADEC,May 2006). Therefore,the analytical L results obtained during the January 2010 monitoring event indicate that the low levels of material detected in groundwater samples collected from monitoring wells MW-1,MW-2,and MW-6 may be NOM. LSHN requests that the site be considered for closure based on the information provided in the following sections. 4.1 Site History LThe site is located in a mixed residential,light industrial,and agricultural area of Acampo, California. The historic operations at the site have been chronicled since 1955 and have consisted predominantly of asphalt related operations. The site was purchased by John and Mike Telfer in 1985,at which time WOS began operation. WOS has used the site for storage,dispensing,and mixing of asphalt and lignin-based road oil,which included the operation of several Aboveground Storage Tanks (ASTs). The site is currently being used as a transfer and storage facility of asphalt L and lignin-based road oil,which is transferred from a mobile AST into 55-gallon drums,and then stored on site prior to transportation. The site has historically been used to store liquid asphalt cutback,which is a petroleum product composed of diesel range hydrocarbons and heavy end V hydrocarbons. Five Underground Storage Tanks (USTs)were historically used to store liquid cutback asphalt,diesel,and gasoline. Eight ASTs are located within a bermed area on the central portion of the site;however,the ASTs are not currently in use. Four small ASTs were recently removed in the northeastern corner of the site(Figure 2). Prior to dismantling the ASTs,the underground distribution piping,which connected the two AST areas,was drained,flushed,and abandoned in place. On October 22,1987,WOS,at the request of the California Regional Water Quality Control Board, L Central Valley Region(RWQCB),removed five USTs from the site,consisting of two 20,000-gallon USTs that were used to store liquid cutback asphalt,one 2,000-gallon UST used to store diesel,one I \\Eureka\projects\2007\007152-WOS\PUBS\rpt\20100324-1stHalf2(T10GWMR&RFC.doc � 4 I