GEOSTATISTICAL ANALYSIS OF THE DISTRIBUTION OF LITHOFACIES IN THE ABERJONA VALLEY AQUIFER NEAR WOBURN, MASSACHUSETTS

Flow and transport patterns are in large part controlled by the distribution of high and low permeability sediments and therefore an accurate description of the aquifer architecture is paramount to producing a representative ground water model. Flow and transport in the Aberjona River Valley aquifer near Woburn, Massachusetts has been previously studied by Bair (2000) and Metheny (1997) with a determanistic approach. As a compliment to these prior studies, in ongoing work, the proportions, geometry, and juxtaposition of the different lithofacies of the aquifer are being statistically characterized toward developing stochastic models for the aquifer system. To accomplish this, the indicator geostatistics formalism is employed. First, an indicator data set was created giving the lithofacies category present at all points of known lithology. An iterative procedure is employed to explore and define regions in which the proportions of lithofacies are stationary. The valley was arbitrarily divided into sections along the length of the aquifer and each section are partitioned by thirds. After finding the proportion of the lithofacies in each partition, the boundaries are being adjusted until the proportion of any lithofacies is maximized in high proportion regions and minimized in low proportion regions. In order to remove any bias from clustering of the data, a three-dimensional cell-declustering algorithm is used to estimate proportion. When the facies assemblages have been thus characterized by proportion, then various statistics on the thickness, length, and orientation of the facies in the assemblages are to be computed and modeled with transition probabilities.