The Optimal Well Locator ( OWL) program is a simple screening tool to evaluate and optimize the placement of wells in long term monitoring networks at small simple sites. OWL uses typically available site data such as routine ground water level measurements and well locations in a simple linear regression algorithm to estimate the change in the direction/magnitude of the ground water flow field over time. By viewing the potential variation in the ground water flow field over time, users will develop a greater understanding of the dynamic nature of ground water flow at their site instead of assuming a static ground water flow field, which is seldom the case. In addition, OWL uses minimal contaminant plume characterization data in a simple contaminant migration algorithm to estimate the potential plume migration paths at a site as a function of the change in ground water flow field direction/magnitude over time. OWL combines the possible plume migration paths into a composite plume to allow users to clearly visualize the possible locations where the plume can be present. In addition, OWL can produce a map which combines plume migration with monitoring well coverage to pinpoint locations where the plume concentration is to predicted to be high and the well density to be low. This information will allow users to assess the location of existing wells in their networks and better position future wells to intercept the plume. Unlike most modeling programs, OWL is specifically designed for users who have minimal ground water and contaminant modeling experience. Site managers can use OWL as a screening tool to evaluate their site monitoring well networks and potentially reduce monitoring costs by optimizing well locations. OWL is available for download on the world wide web at http://www.epa.gov/ada/csmos/models.html.