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Report-F,st Phase Remedial System Page 15 ' Former Manna Pro Site Project No 207 3 June 18,2002 ' 6.0 SUMMARY OF SYSTEM PERFORMANCE RESULTS ' 6.1 Discussion of Soil Vapor Extraction Field Work The performance of the vapor extraction system was evaluated by using the system ' monitoring data to calculate the total vapor extracted on a weekly basis and using the PID readings corrected with lab analytic data (see Section 6 1 1) to calculate the total mass of gasoline hydrocarbons removed on a weekly basis A summary of these calculations is ' attached as Summary Table 4 6.1.1 PID Calibration with Lab Data ' Since air samples were subjected to laboratory basis on a monthly basis, it was necessary to develop an empirical correlation between lab results (measured as mg/L) and PID ' readings (measured as ppm) The PID device actually measures ionization potential of molecules passing through the device, and does not directly measure hydrocarbon concentration To further complicate matters, the PID is calibrated to a standard gas that ' is materially different than the gasoline vapor actually being tested To convert the raw FID readings from qualitative information to usable quantitative readings, a log-normal scatter plot (Cross-Plot 1) was generated between PID readings and laboratory data for lie the points where both types of information were available The result shows a clear relationship between the two data sets The software used to generate the cross-plot (MS- Excel) was also used to generate a best-fit correlation curve and to derive an empirical equation for the correlation As shown in the figure, there is a very good exponential correlation and the empirical formula for the equation can be re-stated as PID—634 18 32702 mg/L= e ' Where PID is the raw reading taken in the field in ppm And mg/L is the reading corrected to absolute concentration 2937 Veneman Ave,#B240 Geo-Phase Environmental Inc Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295