VALIDATION OF THE MODIFIED USEPA FLUX CHAMBER TECHNOLOGY FOR ASSESSING HIGH ADVECTIVE FLOW SOURCES SUCH AS BIOFILTERS AT COMPOST SITES

摘要

A validation of the USEPA flux chamber technology for measuring flux on high flow advective sources has been completed. The test results indicate that the flux chamber method modifications result in quantitative recovery of an added tracer gas (helium) for advective flow sources with a flow of source emissions up to about 600 liters per minute (lpm) advective flow into the flux chamber. A two-part validation effort was conducted where Part 1 included establishing the test source and evaluating the limitation of the methodology as applied to high flow advective sources such as biofilters. After modifications to the method were completed, Part 2 activities included tracer recovery studies simulating area sources with high advective flow rates in order to validate quantitative recovery of trace gas by comparing added tracer levels to measured or recovered tracer levels.The results of Part 2 of the study included the quantitative analysis of evacuated canister samples for trace gas recovery, which indicated that for area source flow rates greater that 70 lpm and up to 600 lpm, acceptable recovery of the helium tracer was achieved with the modified flux chamber protocol. The range of recovery of tracer, as compared to the calculated tracer concentration in the flux chamber, was 92%-to-lll%. The recovery of the traced sweep air gas (trace gas containing 10% helium) was 94%, indicating acceptable laboratory method performance. Further, all laboratory QC data, including method blank, laboratory control spike recovery, laboratory control duplicate sample recovery, and quality control duplicate sample precision data met the method specifications (ASTM D 1946).The method modifications as stated, including gas sample collection at six duct diameters downstream of the chamber in the exhaust stack of the apparatus (6' diameter stack as the exhaust port of the flux chamber), using a diffuser-type sweep air/tracer introduction system, and operating an internal impeller at about 3 rotations per second (rps), extends the use of the recommended flux chamber protocol as specified in the California South