TRANSMISSIVITY DISTRIBUTION OF THE SAN ANDRES LIMESTONE, ARTESIAN AQUIFER IN THE ROSWELL BASIN OF SOUTHEASTERN NEW MEXICO, U.S.A
Dr. William M. Turner
INTRODUCTION
As part of the effort to develop computer models of the Roswell Artesian Basin for the purpose of managing water rights transfers, the Technical Section of the Office of the State Engineer for the State of New Mexico in the United States evaluated the transmissivity distribution within the San Andres limestone aquifer. The discussion that follows is adapted from Rao (1991) and supplemented.
The Roswell Ground-Water Basin covers a large area in the Pecos River valley in southeastern New Mexico (Figure 1). The basin is bounded on the west by the Sacramento Mountains, about 80 miles (129 km) distant from the Pecos River; on the east by the foot of the High Plains of Texas, about 25 miles (40 km) from the Pecos River; on the south by the Seven Rivers Hills. The northern boundary of the Roswell Basin is near Vaughn, New Mexico about 90 miles (145 km) north of Roswell, New Mexico.
The surface elevation within the Roswell Basin declines from about 10,000 feet (3,048 m) at the crest of the Sacramento Mountains on the west to about 3,500 feet (1,067 m) at the Pecos river east of Roswell, New Mexico. From the Pecos River, the surface rises eastward to 4,000 feet (1,219 m) at the foot of the High Plains of Texas (Hantush, 1957).
The geologic formations involved in the transmission, storage and confinement of ground water in the Roswell Basin are the shallow alluvium deposits, the Chalk Bluff Formation, the San Andres Formation and the Yeso Formation (Hantush, 1957).
Alluvium deposits form the Shallow Alluvial aquifer. The Chalk Bluff Formation forms the upper semi-confining aquitard overlying the San Andres Limestone artesian aquifer. The Yeso Formation forms the semi-confining aquitard below the San Andres Limestone.
PRIOR WORK
Fiedler and Nye (1933, p.249) discuss the general nature of the distribution of transmissivity of the artesian aquifer. According to Fiedler and Nye, the Roswell basin artesian aquifer can be divided into five high permeability and four low permeability zones as shown in their Plate 41. These alternate and approximately parallel high and low permeability zones appear to extend from west to east. Fiedler and Nye provide some hydrogeological explanation for the pattern of transmissivity distribution (p. 183)
Hantush (1957) reported transmissivity values ranging from 56,000 to 1,465,000 gpd/ft (694 to 18,166 m2/) based on four aquifer-performance tests (APTs) in the San Andres Limestone artesian aquifer. The APTs were made in areas where the aquifer is well developed and apparently is more permeable than in undeveloped areas of the basin. All of Hantush's APTs were performed in the high permeability zones defined by Fiedler and Nye (1933, Plate 41). Hantush (1957) noted that it is probable that the portions of the aquifers separating the developed areas are less permeable. He also presented a set of representative transmissivities for different parts of the Roswell Artesian Basin (Hantush, 1957, Table 5)
Hantush (1961) reported one more transmissivity value of 1,890,000 gpd/ft (23,460 m2/d) for the San Andres Limestone in the Northwest One-Quarter of the Southeast One-Quarter of the Southeast One-Quarter of Section 33, Township 10 South, Range 25 East, New Mexico Principal Meridian, Central Zone.
Havenor (1968, p.13) reported a transmissivity of 1,500,000 gpd/ft (18,600 m2/d) in Township 12 South, Range 24 East based on personal communication with Mervin L. Klug. Information regarding the specific location of the well or the nature of the pumping test is not given. This data is not used in the analysis of transmissivity distribution.
Kinney et al. (1968, Figure 11) presented a map of transmissivity distribution of the San Andres Limestone based on data from Hantush (1957, 1961), an APT apparently made by the United States Geological Survey for which no reference is given, and transmissivity values calculated from the specific capacity of wells. Transmissivity values calculated from specific capacities are not provided.
Saleem and Jacob (1971) analyzed a number of step-drawdown tests from data in the files of Smith Machinery Company of Roswell, New Mexico. The company routinely ran step-drawdown tests to determine the optimum pump size for wells. These tests are of short duration. They lasted up to about two hours. Saleem and Jacob (1971) present 82 transmissivity values for the San Andres Limestone artesian aquifer.
Summers (1972) presented some additional transmissivity data obtained by application of Harrill's equation (Harrill, 1971) to eight step-drawdown tests run on seven wells in 1969.
Rabinowitz et al. (1977) presented a map of transmissivity distribution of the Roswell artesian basin. The information on APT transmissivities used in the preparation of the map apparently were provided by W. K. Summers through personal communication. At the time of writing this report, these data could not be confirmed. These data points are not used in the analysis of transmissivity distribution.
Appendix A is a listing of available transmissivity data for the San Andres Limestone artesian aquifer. The data were analyzed to study the statistical pattern of their spatial distribution.
ANALYSIS
Rao (1991) plotted the transmissivity data on normal-probability paper. The data significantly deviated from the theoretical, normal-distribution line. He concluded that the transmissivities distribution does not follow a normal statistical probability density function.
The natural-logarithms of the transmissivity values are plotted in Figure 2. The data points closely follow the theoretical lognormal-distribution curve. This means the statistical distribution of aquifer transmissivities in the San Andres Limestone aquifer is satisfactorily explained by a lognormal probability density function. The chi-square goodness of fit test in the Table 1 supports this finding.
CONCLUSIONS
We conclude from the work of previous workers as analyzed by Rao (1991) and the present author that the transmissivity within the San Andres Limestone aquifer is lognormally distributed.
REFERENCES CITED
Fiedler, A.G. and Nye, S.S., 1933. Geology and Ground-Water Resources of the
Roswell Artesian Basin, New Mexico. U.S. Geological Survey Water-Supply
Paper 639.Hantush, M.S., 1957. Preliminary Quantitative Study of the Roswell Ground-Water
Reservoir, New Mexico. New Mexico Institute of Mining and Technology, State
Bureau of Mines and Mineral Resources Division.Hantush, M.S., 1961, Aquifer Tests on Saline Water Wells near Roswell, New
Mexico. New Mexico Institute of Mining and Technology, Socorro.Harrill, J.R., 1971. Determining Transmissivity From Water-Level Recovery of a
Step-Drawdown Test (in Geological Survey Research 1970). U.S. Geological
Survey Professional Paper 700-C, C212-C213.Havenor, K.C., 1968. Structure, Stratigraphy, and Hydrogeology of the Northern
Roswell Artesian Basin, Chaves County, New Mexico. New Mexico State Bureau
of Mines and Mineral Resources Circular 93.Kinney, E.E., J.D. Nations, B.J. Oliver, P.C. Wagner, T.A. Siwula, and R.E. Renner,
1968. The Roswell Artesian Basin. Roswell Geological Society Publication.Rabinowitz, D.D., G.W. Gross, and C.R. Holmes, 1977. Environmental tritium as a
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parameters. Journal of Hydrology, 32:35-46.Rao, B., 1991, Roswell Basin Analytical Groundwater Flow Model - Users Manual,
Report TDH-91-2, New Mexico State Engineer Office, March, 1991Saleem, Z.A. and C.E. Jacob, 1971. Dynamic Programming Model and Quantitative
Analysis, Roswell basin, New Mexico. New Mexico Water Resources Research
Institute, WRRI Report 10.Summers, W.K., 1972. Application of Harrill's Equation to a Limestone Aquifer.
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