3D GEOLOGICAL MODELING IN SUPPORT OF GROUND WATER INVENTORY IN THE FARGO-MOORHEAD REGION, MINNESOTA AND NORTH DAKOTA
Drillhole cross-sections were constructed using ArcView 3.3, ArcGIS 9.0, and custom extensions. Thirty-four regional cross sections were constructed at 5 km spacing. Drillhole logs and surficial geology were displayed along the locus of each cross section to facilitate correlation. Four smaller areas encompassing important aquifers, ranging from 1,300 to 3,200 square km in area, were chosen for more detailed analysis. East-west cross sections were constructed in these areas using 0.5 to 3 km spacing. Creating these cross sections in ArcView allowed sand and till boundaries to be correlated by overlaying shapefiles in the same view window. A series of points for each stratum were extracted from the cross-section shapefile lines and converted into X, Y, Z values. These points as well as cross-sections scanned and registered in 3D space were then used as the basis for construction of surfaces and volumes in Gocad software. Modeled strata were constructed for a total of 37 lithostratigraphic units, including Quaternary, Cretaceous, Ordovician and Precambrian sediments and rocks, and these are now being prepared for further application to regional groundwater inventory, to help ensure long-term water supply for the region.