Page 175 - Statistics for Environmental Engineers
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L1592_Frame_C20  Page 174  Tuesday, December 18, 2001  1:53 PM











                       Exercises
                        20.1 Storage of Soil Samples. The concentration of benzene (µg/g) in soil was measured after
                             being stored in sealed glass ampules for different times, as shown in the data below. Quantities
                             given are average ± standard deviation, based on n = 3. Do the results indicate that storage
                             time must be limited to avoid biodegradation?

                                                 Day 0    Day 5   Day 11  Day 20
                                                 6.1 ± 0.7  5.9 ± 0.2  6.2 ± 0.2  5.7 ± 0.2
                                                 Source: Hewitt, A. D. et al. (1995). Am. Anal.
                                                 Lab., Feb., p. 26.

                        20.2 Biomonitoring. The data below come from a biological monitoring test for chronic toxicity
                             on fish larvae. The control is clean (tap) water. The other four conditions are tap water mixed
                             with the indicated percentages of treated wastewater effluent. The lowest observed effect level
                             (LOEL) is the lowest percentage of effluent that is statistically different from the control.
                             What is the LOEL?

                                                                  Percentage Effluent
                                          Replicate  Control  1.0   3.2    10.0   32.0
                                            1       1.017   1.157  0.998  0.837   0.715
                                            2       0.745   0.914  0.793  0.935   0.907
                                            3       0.862   0.992  1.021  0.839   1.044
                                          Mean      0.875   1.021  0.937  0.882   0.889
                                          Variance  0.0186  0.0154  0.0158  0.0031  0.0273

                        20.3 Biological Treatment. The data below show the results of applying four treatment conditions
                             to remove a recalcitrant pollutant from contaminated groundwater. All treatments were rep-
                             licated three times. The “Controls” were done using microorganisms that have been inhibited
                             with respect to biodegrading the contaminant.  The  “Bioreactor” uses organisms that are
                             expected to actively degrade the contaminant. If the contaminant is not biodegraded, it could
                             be removed by chemical degradation, volatilization, sorption, etc. Is biodegradation a signif-
                             icant factor in removing the contaminant?

                                                 Condition  T 0  T 1   T 2    T 3
                                                 Control  1220  1090   695   575
                                                          1300   854   780   580
                                                          1380  1056   688   495
                                                 Bioreactor  1327  982  550  325
                                                          1320   865   674   310
                                                          1253   803   666   465
                                                 Source: Dobbins, D. C. (1994). J. Air & Waste
                                                 Mgmt. Assoc., 44, 1226–1229.










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