The presence of censored observations (non-detected) in stormwater quality data sets has been considered a serious concern because they bias the estimation of the mean and variance of stormwater constituents. It was observed that ignoring the non-detected observations could increase
the apparent event mean concentration (EMC). Another commonly used approach is to replace the censored values by half of the detection limit, but it is not clear if this approach is valid in many cases. The primary goal of this research was to evaluate different methods of estimating the non-detected
observations in datasets with multiple levels of censoring, using the National Stormwater Quality Database (NSQD).
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