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background concentration of TDS in groundwater (898 mg/L). Assuming that mixing <br />ratios are proportional to relative volumes, the concentration of a mix of leachate whose <br />TDS concentration is 2740 mg/1 with groundwater whose TDS is 898 mg/l is: <br />Cone. _ (lQac ate vol.,)(av leachate Conc � +�groltndwater vol.)( Adgrounc w �o <br />(leachate vol. + groundwater vol.) <br />Conc.= (0.22 ft3/d)(2740 mg/1) + (650 fe/d)((898 mg/1) <br />(0.22 ft'/d+ (650 ft'/d) <br />Conc.= 898.6 mg/1 <br />Since the standard deviation of the average TDS concentration at the Forward Landfill is <br />approximately 62 mg/L, the calculated change in concentration (898 to 898.6 = 0.6 mg/L) <br />is a statistically insignificant change. In fact, if it assumed that the leachate leakage is <br />twice that calculated (i.e., is 0.44 mg/L) and that the rate of groundwater flow in the <br />mixing zone is actually half of the calculated volume (i.e., is 325 ft'/d), the calculated <br />change in groundwater concentration would be only 2.5 mg/L, again a statistically <br />insignificant change that would be undetectable relative to the standard deviation of the <br />average groundwater chemistry. <br />Conc. _ QX leacliate v l - /2 calc. groundwaterVol.)(o r wacond <br />(2X leachate vol. + `/z ca1c. groundwater vol.) <br />Conc.= (0.44 ft'/d)(2740 mg/1) + (32-5 ft'[,d)(898 nig/1) <br />(0.44 ft'/d+ (325 ft'/d) <br />Colic.= 900.5 nag/l <br />Potential VOC Impact <br />As shown in Attachment B, the average VOC concentration in leachate at the Forward <br />Landfill is approximately 316 µg/L. Of note, of this total, 265 µg2 are associated with <br />Acetone and MEK, which are highly volatile byproducts of vegetative decay. Assuming <br />that VOCs are not present in background groundwater at the site, and assuming that <br />mixing ratios are proportional to relative volumes, the concentration of a mix of leachate <br />whose total VOC concentration is 316 µg/l with groundwater with no VOCs is: <br />Cone. _ (Icafbatc v ve, leachate cone.) + 1 w <br />(leachate vol. + groundwater vol.) <br />Conc.= (Q.22 ft'/d)(316 /1) + ( 650 ft3/d)(0 w.0) <br />(0.22 <br />(0.22 ft'/d+ (650 ft3/d) <br />Conc.= 0.107 µg/1 <br />As shown below, the calculated reduction in total VOC concentration (99.97%) is <br />anticipated to result in non-detectable concentrations for virtually all VOCs. Considering <br />that these mixing analyses ignore all biotransformation and dispersion processes that <br />CA2002-002\Revised Appx A - Leakage3.doc\09/19102 7 <br />Geologic Associates <br />