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Table F-4:Reporting Limits weight=78.11): Analytical Method/Technique RePortinq Limit Range* Comments 1.0 pg/L Benzene=1000 pg/m3 Benzene=315 ppbv Benzene' Modified EPA 8260B/C: 20—5000 pg/M3(0.02-5 pg/L) Sample size Direct injection of soil gas into (most compounds at 1000 pg/m3 dependent. Most = /L x RT x 1000/MW x P or sparger with water. (1.0 pg/L)or lower.) samples are 5- ppbv [(pg/L) ( )] ( ) 250 cc mL. ppbv=[(Ng/m3)x(RT)]/(MW)x P Modified EPA 82606/C: 100—1000 pg/m3(0.1-1.0 pg/L) Direct injection of soil gas into or 10—700 ppbv Where: Ng/L=1.0 GC column. 3= Ng/m 1000 Modified EPA TO-15 Scan Mode: 0.5—20 ppbv or 0.7 R=0.0825 L-atm/mole-K(Ideal Gas Law Constant) (Conventional GC/MS system). —200 pg/M3(0.0007—0.20 pg/L) T=298'K(Standard Temperature) SIM Mode: 0.0025—0.02 ppbv 1000=Conversion of 1 m3=1000 L or 0.004—0.20 pg/m3(4 x 1 V— MW=78.11(Molecular Weight of Benzene) 2 x 10-' /L P=1 atm(Standard Pressure) Modified EPA TO-15 3—10 ppbv or 4—100 pg/m3 (Using portable G( MS system (0.004—0.10 pg/L Laboratories using TO methods generally report results in parts per billion by volume (e.g.,Hapsite ). most at 5 by (ppbv). The unit"ppbv"is strictly a gas unit and there should not be any confusion. " The'ppbv"ranges In the table are approximations based on the average molecular weights of target analytes.The actual reporting limit ranges Is dependent on the molecular weight of the compound of interest. See discussion on reporting units. F-9 COMPARING RESULTS The analytical method should be selected with the specific reporting limits needed for A quick and simple way to evaluate the comparability of results from two different the site investigation. For risk assessment purposes,the reporting limits should be the methods is to calculate the Relative Percent Difference(RPD)of the results. The RPD California Human Health Screening Levels(CHHSLs)for soil gas,or lower if cumulative is calculated according to the formula: health effects are of a concern. For compounds that are not on the CHHSL listing,the analytical method should be selected that can achieve the reporting limits for risk-based RPD= 100 x IC,-C21/[(C,+C2)/2] decision making. where: F-8 REPORTING UNITS C,=Result from the first method Laboratories using modified EPA Method 82608(and other 8000 series methods) C2=Result from the second method generally report results in micrograms per liter(Ng/L). Data users and laboratories are It is generally accepted that if two results have a RPD of 25%or less,then they are strongly cautioned that pg/L for gas is not equivalent to Ng/L for aqueous samples. It is considered to be comparable. particularly critical that the distinction is made since the calibration curve for modified Method 82608 is built on liquid calibration standards and calculated as pg/L for liquid. The variability in soil gas results comes from a number of sources. Although Results for soil gas samples are also reported in Ng/L but they are r=equivalent to the laboratories may use the same method for their analyses,there will be variations in their liquid(aqueous)matrix unit. Analytical laboratories must take this into account when instrumentation(i.e.,manufacturer),sample introduction technique,analyst skill, they report soil gas sample results. All parties should be aware of this. All final soil gas experience and practices. For soil gas,there will be differences in sample collection data must be reviewed and verified that they are calculated correctly and reported in the methods and in sample containers. Finally,there will be a variation in the sample proper unit, matrix. A replicate sample collected immediately after the original sample may not the To avoid confusion,it is recommended that analytical laboratories that use modified same due to spatial and temporal differences. EPA Method 8260B/C report soil gas results in"Ng/m3"rather than"Ng/L". Note that In instances where soil gas results from the same source analyzed by two different "Ng/m is not equivalent to"Ng/L" For example(Benzene in air/soil gas with molecular methods(e.g.,modified 8260B/C and TO-15)are disparate(>25%RPD),it is important 12/10/2009 -85- 12/10/2009 -86-