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Table F-4:Reporting Limits weight=78.11): Analytical Method/Technique Reporting Limit Ran e' Comments 1.0 pg/L Benzene=1000 pg/m3 Benzene=315 ppbv Benzene' Modified EPA 8260B/C. 20 5000 p9/m'(0.02-5 pg/L) Sample size Direct injection of soil gas into (most compounds at 1000 pg/m3 dependent. Most sparger with water. (1.0 pg/L)or lower.) samples are 5- 'pphv=[(pg/L)x(RT)]x 1000/(MW)x P or Modified EPA 8260B/C: 100-1000 pg/m'(0.1-1.0 pg/L) 250 cc mL. ppbv=[(pg/m3)x(RT)]/(MW)x P Direct injection of soil gas into or 10-700 ppbv Where: pg/L=1.0 GC column. pg7m3=1000 Modified EPA TO-15 Scan Mode: 0.5-20 ppbv or 0.7 R=0.0625 L-atm/mole=K(Ideal Gas Law Constant) • (Conventional GUMS system). -200 pg/m (0.0007-0.20 Fog/L) T=298'K(Standard Temperature) SIM Mode: 0.0025-0.02 ppbv 1000=Conversion of 1 m'=1000 L or 0.004-0.20 pghn (4 x 1 o's- MW=78.11(Molecular Weight of Benzene) 2 x 104 /L P=1 atm(Standard Pressure) Modified EPA TO-15 3-10 ppbv or 4-100/og/m3 (Using portable GC/MS system (0.004-0.10 pglL 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. 'repoonEgJlimit nsnyaIns Riste dependent on Me ¢ssilgwM1t of the ofentest, sof ta�ge�anatytes.1M1e acwel See EhNss�on an repamrg unlls. 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=100x ICG-C21/[(Cr+02)12) decision making. where: F-8 REPORTING UNITS Cr =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(pg/Q. 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 isotot equivalent to pg/L for aqueous samples. Itis considered to be comparable. particularly critical that the distinction is made since the calibration curve for modified Method 8260B 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 sail gas samples are also reported in pg/L but they are not 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 82608/C report soil gas results in"pglm'"rather than"pg/L". Note that In instances where soil gas results from the same source analyzed by two different "pghn is not equivalent to"pg/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 12110/2009 -85- 12/10/2009 -86-