Use of Global Positioning Systems (GPS)
to Determine Well Location for Ohio’s Water
Well Log and Drilling Report
There is typically a lot of good geologic and hydrogeologic information contained on the well log and drilling report forms (well logs). In order for this data to be used for mapping purposes and some regulatory programs, the exact location of the well has to be known. In the Ohio Revised Code (ORC) Section 1521.05 (B) 7, the driller is responsible for providing "..either the state plane coordinates or the latitude and longitude of the well." In the past, the position description that was wanted was the distance to the nearest intersection (e.g. 1/4 mile north of Main Street). Fortunately, the technological advances in the handheld global positioning systems (GPS) have made it possible for the water well driller to determine the latitude and longitude of each well at a very economical price ($100-$300/unit). In 1996, the description of well location line was replaced with the location of well in State Plane coordinates. Lines for latitude and longitude were added in the sketch map box. Therefore, the position description that should be provided on the well log and drilling report form should be in degrees latitude and longitude or in State Plane coordinates.
Setting up the GPS Receiver
Before using a GPS unit, the correct map datum and position format need to be set for Ohio. This is usually found in the Navigation Set-up menu of the GPS unit. The preferred map datum is North American Datum 83 (NAD83). Most handheld GPS units are programmed with a World Geodetic System of 1984 (WGS84) datum. Not changing the datum could result in up to 600 feet of error in the location of a well. Please read the user's manual before using the GPS unit. The users manual will also state the accuracy of your readings. The inherent accuracy of GPS units varies. Most of the inexpensive handheld units have an accuracy of 49 feet (15 meters) unless the GPS unit is WASS enabled. WASS stands for Wide Area Augmentation System which uses ground reference stations to improve the accuracy to approximately 10 feet (3 meters). Please confirm the accuracy of your unit before recording the elevation of the well on the well log form. Also record the accuracy of your unit after the "+/-" sign on the "Elevation of Well" line of the form.
Positioning Coordinate Format
The preferred position format for latitude and longitude is degrees (e.g. 42.456533o). Some of the handheld GPS units cannot display in degrees only. If that is the case, coordinates should be in degrees and decimal minutes (e.g. 42o 27.281'). Whatever units are used, proper notation of the numbers on the well log form is critical. The (o) sign denotes degrees, an apostrophe sign (') denotes minutes, and a quote sign (") denotes seconds.
The following is an example of the same latitude recorded in three different formats:
42°27'17" Degrees, minutes and seconds.
42°27.283' Degrees and minutes.
When reporting in degrees and minutes format, record at least three numbers after the decimal point for the minutes value. When reporting in degrees only, record five numbers after the decimal point.
Entering Coordinates on the Paper Well Log Form
On Ohio’s well log form, there are lines for State Plane coordinates and latitude and longitude. Only state plane coordinate values should be entered in the "X" and "Y" lines (See figure 1, Area above). Most handheld GPS units are not programmed to read State Plane coordinates. Latitude and longitude values should be entered on the lines marked "Lat" and "Long" located in the sketch map section (See figure 1, Area 2 above). In Ohio, the latitude varies from 38.3 to 42 degrees and the longitude varies from -80.5 to -84.8 degrees. The datum plane (either NAD27 or NAD83) should be checked on the log depending on what datum plane the GPS unit is programmed to (NAD83 is preferred). Also, the GPS box should be checked if a GPS unit was used to determine the coordinates.