The objectives of this report are to provide the reader with an understanding of the statistical tests utilized to interpret chronic toxicity test data, and to examine the data to determine problems associated with the test protocol. Chronic toxicity data, obtained from the Orange County Water And Sewer Authority (OWASA) Mason Farm Wastewater Treatment Plant (WWTP) in Carrboro, NC, is analyzed to illustrate the underlying statistical concepts and procedures, and to illustrate biomonitoring variability. A spreadsheet was developed to compute the test statistics required to compare mortality and reproduction data for an effluent sample to those for a control sample, in accordance with the North Carolina Division of Environmental Management requirements for chronic toxicity tests. The spreadsheet was applied to two years of chronic toxicity data from the OWASA Mason Farm WWTP. Reanalysis of the OWASA data revealed instances in which the test statistics were miscalculated, where the incorrect statistical test was utilized, and where erroneous overall conclusions were drawn by the analytical laboratory conducting the test.