In this model, one of the observation wells is in the cell next to the pumping well. It would be better if there were several cells separating them. To do that, the grid must have smaller cells at least in the vicinity of the wells. To do that zoom out so that approximately 10 cells are visible on all sides of the observation wells. Draw a polygon similar to the one shown in blue in figure 134 around the cells leaving a buffer around the observation wells. Name the object "Refined Grid" and check the Use to set cell grid size check box. Set the Grid cell size to 40.
Figure. 134. Polygon used to define area with refined grid.
Select Grid|Generate Grid... or click the Generate grid button 
. Uncheck the Calculate grid angle automatically check box and check the Smooth grid check box. Then click the OK button. The new grid should appear similar to that shown in figure 135. Notice that there is not an abrupt transition in the cell sizes. Instead, the cells gradually increase in height or width away from the area with smaller cells.
Figure 135. New grid with central area with refined grid.
