WELLHEAD PROTECTION AREA DELINEATION USING THE ANALYTIC ELEMENT METHOD OF GROUNDWATER MODELING

The Analytic Element Method (AEM) of ground-water modeling was used to delineate wellhead protection areas (WHPAs) for existing and proposed wells in Brooklyn Park, Minnesota by simulating steady-state flow in two aquifers: the water-table aquifer (in glacial outwash) and the Fra nconia-Ironton-Galesville bedrock aquifer. Ground-water time-of-travel was used as the delineation criterion. Ground-water flow is significa ntly affected by a buried bedrock valley underneath the City. Transmis sivity values for the water-table aquifer are much higher in the burie d bedrock valley and the hydraulic connection between the water-table and the Franconia-Ironton-Galesville aquifers is more pronounced. The Analytic Element Method does not utilize a grid mesh and incorporates both regional-scale and more detailed, local-scale features in the sam e solution. This feature of AEM provided for the simulation of the cit y wells in the context of the regional flow field. Separate models, en compassing an area of approximately 500 square miles, were developed a nd calibrated for each aquifer using the Single Layer Analytic Element Model (SLAEM) and then linked together using the Multi-Layer Analytic Element Model (MLAEM). Ground-water travel-time zones and WHPAs were delineated for the existing wells using reverse particle tracking.