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Clayton <br /> � CQ'i ti%lEtiTnL <br /> C7��,L���15 <br /> (S',C/EHD) noted that the SJC/EHD had determined that all appropriate response <br /> - action, or monitoring required vAth regard to the underground storage tank formerly <br /> located at this site had been performed She recommended site certification and <br /> requested that the RWQCB concur This letter is presented in Appendix B <br /> In a letter to the SJC/EHD, dated August 19, 1991, Ms Thayer raised the following <br /> -� concern about the soil excavation: <br /> n" "Contaminants in five soil samples ranged from 60 ppm to 1100 ppm oil and grease <br /> 3 hydrocarbons. Apparently, additional lateral excavation (over-excavation) occurred <br /> towards the northeast However, it is unclear from either the report of the <br /> r, addendum whether the excavation was extended vertically below 10.5 feet." <br /> She raised the following concern about soil samples from the installation of well MW- <br /> 3B: <br /> V '"The soil samples from MW-3B indicated soil contamination of 770 ppb total <br /> r recoverable hydrocarbons at 4 feet and 20 ppb at 9 feet. The fractions of <br /> sr xn hydrocarbons were not identified" <br /> Based on these concerns, the RWQCB did not concur with site closure Ms. Thayer <br /> �}ti A stated that, <br /> W iv4 <br /> "Orchard Supply Hardware must present a precise description of the over- <br /> ty r4 <br /> excavation activities before closure may be considei ed, including the following <br /> information: <br /> 1. Total depth of excavation below samples MW-1, NW-1, MN-1, NE-1, and ME-1, <br /> 2. The depth to water below grade and below the excavation; <br />�V ''� ��i 3. If theexcavation was deeper than 10,5 feet, the reasons for not collecting <br /> corifirniatory,sdd-samples=from the baseof the excavation." <br /> Y F Wd prepared:this summary report to consolidate and clarify reports, addendums, and <br /> letters,fand personal communication that transpired between Clayton and the <br />' ' A SJ+C/EHD.. <br /> 4hMR6GE0LADGY <br /> r Soils,underVmg the site generally consist of clayey sands, sandy clays, and gravelly <br /> sands with gravel being more abundant near the surface. <br /> Depth,to groundwater ranges from approximately 8 to 12 feet bgs m the three onsite <br /> t wells (Figure 2). In the vicinity as the excavation (southwest corner of property) the <br /> depth to groundwater is approximately 10.5 to 12 feet bgs. Well elevations were <br /> surveyed to datum sea level by Mr. Bruce Tronoff, a licensed surveyor, and were <br /> ,r <br /> plotted on a scaled map (Appendix C). From the well elevation data, groundwater <br />�3 f' flow direction was calculated to be to the north. The groundwater gradient is 0.3 foot <br /> elevation drop per 100 feet of horizontal distance. <br /> Y 2 <br /> °-� 34500AL�ep <br /> c = <br /> z F <br /> 1 <br />�1 <br />�3 r <br /> 1��11 Y <br />