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' GRANITE CONSTRUCTION FACILITY <br /> WKA No 2088 08 <br /> August 18, 1999 <br /> Page 11 <br /> concentrations were reported below detection limits, a value equaling half the detection limit was <br />' used in our calculation The lognormal distribution was determined by taking the sum of the log <br /> for each contaminant concentration in a given data set The anti-log of the sum was then taken to <br /> determine lognormal distribution of the average concentration for the given compound within the <br /> data set <br /> The lognormal distribution method is typically used for analytical data that vanes by several <br /> orders of magnitude The log normal distribution method normalizes the varying orders of <br />' magnitude to a standard bell-shaped distribution For example suppose we have three samples <br /> with concentrations of 1, 100, and 1000 mg/kg <br />' Sample Concentration Log <br /> 1 log(1) = 0 <br />' 100 log (1.00) =2 <br /> 1000 log (1000) = 3 <br /> E - 1101 E = 5 <br /> 1101/3 = 367 5/3 = 1 67 <br /> log-1 1 67 = 46 8 <br /> Using a straight mathematical average, the average concentration of the three samples would be <br /> 367 mg/kg Using the log normal distribution method, the average concentration of the three <br /> samples would be 46 8 mg/kg Because only a very small number of the previous samples <br /> revealed extremely high concentrations (several orders of magnitude above those of the vast <br /> majority), use of a straight mathematical average would have resulted in unrealistically higher <br /> average concentrations <br /> The data used was derived from the 50 soil samples obtained from soil borings drilled in the <br /> vicinity of the former UST excavation in March 1993 and samples obtained from the bottom and <br /> sidewalls of the excavation on September 28, 1993 and 32 groundwater samples obtained during <br /> quarterly monitoring and sampling events performed from March 3, 1997 to December 7, 1998 <br />' Based on the above assumptions, the weight/volume of petroleum hydrocarbons present in the <br /> soil beneath the site was calculated to be approximately 160 pounds or 27 gallons <br /> `d'M <br />' WALLACE KUHL <br /> Recycled paper &ASSOCIATES INC <br />