OCR Text |
Show problem areas included: • • High (compared to field results) blank results for formaldehyde (Method 0011) and hexavalent chromium (Method Cr+6). This raises questions of whether these results are biased due to background contamination. Low recovery of certain trace elements and organic species from external QA audit samples (in most cases remedial work by the analyst resulted in improved recovery and acceptable results). These results emphasize the importance of a thorough QA program to ensure that all appropriate QC activities are performed and all results documented. In some cases, QA results cannot resolve if a result is "reasonable". Another valuable method to verify trace element results is to evaluate all streams entering and leaving a system and calculating mass balance closure for each element. Table 3 compares emission factors and mass balance closure for several key parameters for the Cardinal, SNRB, and GSA air toxics characterizations. In general, emission factors for most substances were of the same order of magnitude for the three plants. The GSA process was tested in three configurations with different arrangements of an electrostatic precipitator and fabric filter following the GSA absorber; hence a range of results is shown here. A elemental mass balance closure target of 70 to 130 percent is a typical objective in projects like this. For most elements this objective was achieved. Typical of most programs, some exceptions were seen. This was a particular problem with the GSA project, mainly due to the large amount of lime added to the absorber. This essentially doubled the solids input to the GSA system. While excellent mass balance results were achieved for total mass, one of the three conditions consistently resulted in mass balance closures significantly higher than 100 (100 being perfect closure). This is believed to be due to analytical difficulties due to the presence of lime. It also is evident that mass balances for some metals are consistently above or below target. Barium, cadmium and sometimes mercury and selenium had poor mass balance closure. Closure for mercury and selenium was generally better when concentrations are higher; hence, some of these problems may be due to the proximity of measured concentrations to the detection limits of the test methods. Uncertainty Statistical uncertainty provides another way to evaluate the validity of test results. Table 4 9 |