A GIS data update utility created at MSU was used to process and merge the county wells; this also added many glacial drift and rock well fields, and percentages for aquifer drift material based on the existing Wellogic and lithology database information. Next the percentages of aquifer material and trend information were calculated for the drift index. These fields were used by the USGS to further calculate the wells transmissivity and yield values. Once these values were calculated a drawdown value could be derived. A detailed account of these processes can be found later on in this document.
It is noteworthy that areas of low estimated drawdown (less than 5 ft) occur both where the estimated yield is moderate (70 - 200 gpm) and where it is low (< 10 gpm). In the low-yield areas, the small estimated drawdown results from the inability of the water-bearing materials to provide enough groundwater to impact a well 500 feet away. In areas of moderate yield, the available drawdown and transmissivity of the glacial deposits are such that the estimated yield can be obtained without significantly lowering the groundwater level 500 feet away. Note that in such areas, a high-capacity well capable of pumping at a rate larger than the estimated yield might be possible and such a well could impact groundwater levels 500 feet away.
Wherever glacial wells have adequate coverage they will take precedence over glacial deposits overlying the bedrock wells. This is decided by buffering out 2000m on each well file. The buffered glacial wells are used as the analysis mask for the grid surfaces (Yield and Transmissivity), all other areas are back filled with the 2000m buffered glacial deposits overlying the bedrock wells.
It should also be noted that all islands were removed from the State because inadequate amounts of well locations were present to estimate a grid surface.
Data masks were used by identify areas where the glacial deposits are less than 30 ft thick and to identify areas that are more than 2000m away from any well in the Wellogic database.
This surface shows the projected impact of a new well on neighboring wells to allow users of the information to assess potential well interference as addressed in Public Act 177 (Michigan, 2003b). This estimated impact is only a general estimate and should not be used for licensure or legislative purposes. It serves as guidance and illustrates the anticipated general pattern of impacts on neighboring wells due to pumping across the State.
For more information on the process visit : <http://gwmap.rsgis.msu.edu/>