ESTIMATION OF STATISTICAL PARAMETERS FOR CENSORED LOGNORMAL HYDRAULICCONDUCTIVITY MEASUREMENTS

Field tests of hydraulic conductivity (e.g., injection test, pumping t est, etc.) in low permeability formations are subject to censoring due to the detection limit of the instruments used. An iterative method o f estimating the mean and variance of hydraulic conductivity data with a presumed log-normal distribution function is presented. This method accounts for the data that are actually below the lower detection lim it (called ''truncated'' data) and thus gives distribution parameters that are more representative for the underlying distribution. The prop osed method is then tested on two simulated normally distributed rando m datasets having different variances. The results show that the means and variances estimated by the proposed method are very accurate. The results show that the means and variances estimated by the proposed m ethod are very accurate. Finally, the method is used to estimate the m ean and variance of hydraulic conductivity data from single hole water injection tests in a fractured geological formation.