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Mr Daniel K Barber, P E ' September 9, 2003 • Page 7 of 17 rclosures may be conditional, in cases where regulatory closure is granted based on industrial/commercial land use and there is residual contamination above regulatory ' concentrations of concern, agencies may require an institutional control (e g , deed notification or deed restriction) as a condition of closure SENSITIVE RECEPTORS ' A well survey was compiled by D K Barber & Associates at the request of SJCEHD The tabulated results of the survey are provided in Appendix B, which shows the street address, distance from the site, total depth of the well, standing level depth to water, depth of casing, ' and casing diameter, when these data are available A map showing the location of the well is also provided in Appendix B The well survey identified 63 water wells within the survey area The nearest well is the onsite Western Asphalt water supply well (ID No 12 in tabulated ' information in Appendix B), located approximately 150 southwest of monitoring well MW-4, in the upgradient direction No data are available on its depth or usage, but it is primarily 10usedto augment some asphalt mixing operations onsite (Barber, 2003) This well has apparently shown no hydrocarbon contamination This was corroborated by Mr Jeffery Wong of SJCEHD The groundwater flow direction of the hydrocarbon plume at the site trends north by northeast The nearest offsite well, measured from the northeast corner of the subject property, is the private agricultural well at 4678 E Woodbridge Road located approximately 300 feet downgradient This 6-inch well, with a total depth of 425 feet and water level of 390 feet bgs, is listed as well number 3 in the tabulated results in Appendix B All other wells are at distances between 368 and 3,713 feet from the subject property ' The hydrocarbon contamination concentrations at MW-6, the downgradient well approximately 10 feet off the northeastern property line, have ranged from 240 to 420 pg/L ' TPHd in the five sampling events since well MW-6 was installed in June 2002 No BTEX above the method detection limit of 0 5 µg/l, was reported in any of the water samples ' The defined downgradient-most portion of the plume at MW-6 is 290 lateral feet and 290 vertical feet from the nearest downgradient receptor well at 4678 E Woodbridge Road Based on the probable attenuation of diesel plumes examined in the statistical analyses presented in the 1995 Lawrence Livermore National Laboratory study (Rice et al , 1995), the average length of a TPHd hydrocarbon plume is 200 feet (laterally downgradient) from its Stellar Environmental Solutions Z WRt�X100] �—M • •Ck..d pon FyweaF T 4qP� %1M]Eoc