Locational data must be determined and submitted for injection wells under EPA Direct Implementation (DI) underground injection control (UIC) programs, as well as under state run programs. Relatively inexpensive GPS receivers appear to be adequate for the task, and this almost certainly holds true for other EPA programs as well. The following discussion assumes a 12 channel consumer grade GPS receiver without WAAS, but we recommend WAAS capability since it is now available on the inexpensive machines, and said feature will become more useful in the future.| Home | Tech & Tips | UIC |
US EPA published a Locational Data Policy document dated April 8,1991. Said policy included the goal that a 25 meter level of accuracy be achieved by 1995. 25 meters is just a tad over 82 feet, representing a permissible error of about 0.017 minutes (or just over one second) of longitude, or about 0.014 minutes (or around four-fifths of a second) of latitude (in Kentucky a minute of latitude averages 6,060 feet, and a minute of longitude averages 4,850 feet*). Thus, EPA is saying it wants locational data submissions of roughly one second or better accuracy.
On May 1, 2000, the intentional military degradation of GPS signals (called Selective Availability or SA) was "set to 0", hopefully permanently. With SA turned off, even inexpensive recreational consumer grade GPS receivers are capable of a reasonable degree of accuracy. A review of published reports would suggest a 10 meter or better level of horizontal accuracy can be expected with decent field conditions, though better or worse results are possible (a dense forest canopy can degrade performance).** In general, it is safe to assume low cost GPS receivers can be used to obtain locational data of injection wells with sufficient accuracy for submission to EPA.
The Locational Data Policy is now regarded as historical by EPA, though the 25 meter accuracy standard does not seem to have been superseded. A newer document Business Rules for the Latitude/Longitude Data Standard (local pdf document) has been published, but appears to be essentially a procedural document. It should be noted that the National Map Accuracy Standard (NMAS 1974) for point positions on 1:24,000 scale quadrangle maps is 14.8 meters at a 95% confidence level. So inexpensive recreational grade GPS receivers actually meet the national map accuracy standards in most cases.
Brandon C. Nuttall of the Kentucky Geological Survey (KGS) has kindly given us permission to publish his GPS Course Outline (local pdf document). The KGS and Mr. Nuttall are wonderful assets to all citizens of Kentucky, and especially to the oil industry.
See also the Joe Mehaffey, Jack Yeazel, and Dale DePriest GPS information website.
* These average figures are based on the North American Datum, 1927 (NAD27) which uses the Clarke 1866 spheroid (also used for most paper copies of USGS topographic maps). GPS receivers use the World Geodetic System, 1984 (WGS84) which is based on a more current spheroid. The difference is not significant with respect to the discussion herein.
**Using position averaging and the Wide Area Augmentation System (WAAS), it is possible to achieve one meter horizontal accuracy. Expensive surveying grade GPS receivers are capable of centimeter accuracy. This effort has been intentionally limited to consideration of inexpensive recreational grade GPS receivers.