ARCHIVED REPORTS XR0009893 - Laserfiche WebLink

Home Browse Search

Remediation Report - 152 East 1 I th Street, Tracy, California Page 18 l The results of the analyses for total petroleum hydrocarbons (TPH) that are included in Table 2 have the following statistical properties No of Samples 5 Degrees of Freedom 4 Mean Concentration of TPH 1 38 mg/Kg Standard Deviation 0 65 mg/Kg Coefficient of Variation 039 NOTE For the purpose of calculating the statistical parameters shown above, it was assumed that samples in which petroleum hydrocarbons could not be detected at concentrations greater than the Method Detection Limit (NIDL) of l 0 mg/Kg actually contained total petroleum hydrocarbons at a concentrations equal to the MDL Experience has shown that after treating contaminated soil by aeration to a condition where olfactory and visual indicators of the presence of gasoline have been eliminated, tests on samples of the treated soil typically show that remaining traces of hydrocarbons (if any) are close to or less than the routinely achieved analytical method detection limit (NlDL) of 1 0 mg/Kg It is also reasonable to assume, for the purposes of making a statistically meaningful evaluation of the geochemical condition of the soil, that the mean concentration of hydrocarbons in the treated material might be 0 5 mg/Kg, one half of the MDL Experience also shows that the variability of trace concentrations of gasoline in spread aerated soil reflects the variability of the concentrations of hydrocarbons in the untreated material Using= the data and assumptions cited above, a statistical analysis of the results of the tests performed on the soil samples recovered from the stockpile of untreated soil were used to estimate the number of discrete samples that should be taken from the spread of aerated soil to demonstrate with a high degree of confidence, that the total volume of treated soil contained no concentrations of total petroleum hydrocarbons, or any of its components of concern greater than the treatment standard, which, for the soil excavated from the subject site, was set at the MDL of the analytical procedure (i e 1 0 mg/Kg for total petroleum hydrocarbons as gasoline (TPHg) and 5 0 pg/Kg for benzene, toluene, ethyl benzene and total xylene isomers) Using Formula 6 7 on Page 6-7 of Reference 20 to compute the statistical parameter z for the treated soil for which a cleanup standard, Cs, equal to the method detection limit (NIDI-) for TPHg (i e 1 0 mg/Kg) has been set and if it is desirable that the mean concentrations of any traces of hydrocarbons in the treated soil are 0 1 mg/Kg lower than one half of the MDL (i e 0 5 mg/Kg ) then for the previously computed standard deviation of 0 65 mg/Kg yields z = ( 10 - 00/065 = 092