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Evaluation of Natural Attenuation: 7500 West Eleventh.street, Tracy, CA. Page 31 <br /> r- <br /> t <br /> with, as noted previously, <br /> - J <br /> C,,= 0.01 lb/ft' <br /> then, <br /> BTEXSz= 0.08 lb/day <br /> The mass of BTEX added to the flowing groundwater by contaminants beneath <br /> _? the smear zone, BTEXbsZ is given by: <br /> BTEXbsz = Cbsz x Qbsz (Equation 5) <br /> where: <br /> Cbsz mean concentration of BTEX compounds in the contaminated <br /> groundwater beneath the smear zone. <br /> For a 10-ft. thickness of contaminated water beneath the smear zone and <br /> assuming a Gaussian concentration distribution from 100 mg/L at the bottom <br /> I of smear zone to 0.001 mg/L at 10 ft, below the smear zone, Cbsz is 26 mg/L. <br /> (0.00162 lb/ft ) (American Society for Testing and Materials 2004). <br /> .:. ::..; Qbsz is the rate of groundwater flow beneath the smear zone and is computed <br /> from: <br /> Qbsz=Kbsz x i x Absz (Equation 6) <br /> where; <br /> KbsZ— the effective hydraulic conductivity of the soil beneath the smear zone <br /> i= groundwater gradient <br /> Absz=the cross-sectional area of the groundwater below the smear zone that is <br /> affected by BTEX contamination. <br /> Ab,,is computed from the width of the smear zone multiplied by the depth of <br /> i.: contaminated groundwater beneath the smear zone. At the Navarra Site that <br /> depth is 10 ft., so that Ab,,= 10 x 219, i.e., 2,190 fC. Then, as noted above, <br /> with i equal to 0.003 ft/ft. and KbsZ equal to 42.52 ft/day, then from Equation 6 <br /> ii <br /> Qbsz=279 ft3/day <br /> a <br /> so that <br /> sic <br />