DISTRIBUTION OF THE BASIN-FILL ALLUVIAL AQUIFER IN THE ESTANCIA BASIN OF CENTRAL NEW
Dr. William M. Turner
The success of any ground-water exploration program depends on the ability to place a
well into part of an aquifer with the highest transmissivity. In our continuing
effort to understand the risk of uninformed ground-water exploration, we examine the
statistical distribution of aquifer transmissivity of different aquifers. This
paper deals with the analysis of the statistical distribution of transmissivity of the
Basin-Fill Alluvium in the Estancia Basin of Central New Mexico in the American
Southwest. The location of the basin is shown in Figure 1.
The Estancia Basin is a closed topographic basin 2,400 square miles in area (3,861 km2)
in central New Mexico. The geologic basin is created by uplift on the west of the Manzano
and Sandia Mountains, the southernmost extension of the Rocky Mountains; intrusions on the
northwest that form South Mountain and San Pedro Mountain; a syncline in the north that
plunges into the Galisteo Basin; land surfaces of Precambrian bedrock on the east along
the Pedernal Hills-Loco Hills axis; and, a syncline on the south, plunging into Socorro
County, New Mexico below the Mesa de los Jumanos (Broadhead, 1997).
Important structural features inside the topographic basin include a bedrock horst at
Lobo Hill that separates the basin into north and south parts, the Perro Sub-basin of
locally-thick Pennsylvania rocks, and an unnamed fault extending northeast of Lobo Hill
marking the east side of the Galisteo Basin.
The basin fill alluvium is deeper than the topographic base level of erosion. The
overdeepening is accommodated by removal of rock mass in solution from underlying gypsum
beds. The valley floor contains a series of salt playas totaling 20.8 square miles
(53.8 km2) in an area about 6,040 feet above mean sea level (ft amsl) (1,841 m). The
salt playas contain saturated brine that evaporates and under steady state conditions
removes recharge to the basin. The valley floor below 6,200 ft amsl (1,889 m) is
underlain by Pleistocene lake bed sediments up to 80 feet (24.4 m) thick that overlie
older basin-fill alluvium of Quaternary age.
The Precambrian basement is overlain by Pennsylvanian sandstone of the Sandia Formation
and the overlying Madera Limestone. The Madera Limestone grades transitionally
upward into the Abo and Yeso Formations of Permian age. Above the Yeso Formation
occurs the San Andres Limestone and Glorieta Sandstone. In the northern part of the
Estancia Basin, a younger series of Mesozoic rock units including the Chinle Shale and
Mancos Shale occur. On the northwestern margin of the basin, a complete sequence of
Cretaceous Mesaverde Formation of interbedded marine sandstone and Mancos shale
The Paleozoic and Mesozoic rock units were truncated by erosion during the Tertiary
period and basin-fill alluvium up to 400 feet (122 m) thick was deposited.
The aquifers of interest for development are the Madera Limestone, the Glorieta
Sandstone and the basin-fill alluvium.
Meinzer (1911) was the earliest worker who provided data on the initial condition of
the basin and a conceptual hydrogeologic framework.
Smith (1957) performed a thorough hydrogeologic study of the southern part of the
Estancia Basin and provided a great deal of information on wells, well yield and the
specific capacity of wells.
Shafike (1998) presents a summary of transmissivity values for wells completed in the
basin-fill alluvium obtained from published and unpublished reports of others.
Shafike developed two transmissivity values. Shomaker et al. (1996) reported three
transmissivity values. Kilmer (1997) reported eight values. Twenty-eight
transmissivity values were calculated by Shafike (1998) from specific capacity data in
Smith (1957). These data are given in Appendix A.
Transmissivity data are plotted as cumulative probability of the occurrence of
transmissivity values having values greater than indicated on the graph. The plot is shown
in Figure 2.
We next calculated the theoretical normal, lognormal and exponential distributions
based on the estimates of population mean and standard deviation. For each statistical
distribution, we created a Chi-Square (C2)
contingency table to test for the goodness-of-fit between the proposed statistical
frequency distribution and the observed distribution of the data. The C2 test may be used to test the goodness-of-fit for any
statistical distribution. If C2 = 0, there is
a perfect match between the observed and the expected values. The larger the C2 value, the greater the departure of the observed from
the expected values.
In the present case, we prepared a two-way contingency table representing frequency
classes and the number of transmissivity values within each frequency class. The
null hypothesis, Ho, being tested, is that the distribution of observed
transmissivities follows a lognormal probability density function (pdf).
The C2 value for the contingency table
constructed from observed and expected values is 0.337. With 7 degrees of freedom,
the C2 statistic at the 99 percent level is
16.08. Because C2 = 0.337 << 16.08, we
conclude that the disagreement between the observed and predicted transmissivity valued
cannot be rejected at the 0.01 level. We are unable to reject the Ho
hypothesis and we are, in the case of the Estancia Basin alluvium, satisfied that the
transmissivity distribution is very close to the expected lognormal distribution.
The statistical distribution of transmissivity in the Basin-Fill Alluvium in the
Estancia Basin is lognormally distributed. The average transmissivity is 149,744
gpd/ft (1,857 m2/d). If a well is randomly located within the Basin-Fill
Alluvium, the owner has about a 12.8-percent chance of finding part of the aquifer with a
transmissivity greater than the average. On the other hand, the well owner has a
87.2-percent chance of finding part of the aquifer with less than the average
Broadhead, R.F., 1997, Subsurface Geology and Oil and Gas Potential of the
Estancia Basin, New Mexico, New Mexico Bureau of Mines
Resources, Bulletin 157.
Kilmer, C., 1997, Geohydrologic Report for Sierra Vista Subdivision (Formerly
Caballo Grande Subdivision), Santa Fe County, New
consultant's report to Associated Development, Inc.
Kilmer, C., 1997, Water Availability Assessment, Mountain Ranch Limited
Partnership Well, T.10 N., R. 8 E., and T. 11 N., R. 8 E., Santa
Fe County, New
Mexico, unpublished consultant's report to Mountain Ranch Limited
Meinzer, O.E., 1911, Geology and Water Resources of the Estancia Valley, New
Mexico, with Notes on Ground-Water Conditions in Adjacent Parts
New Mexico, U.S. Geological Survey Water-Supply Paper 275.
Shafike, N.G., and Balleau, W.P., 1998, Hydrologic Model of the Estancia Basin,
unpublished consultants report, 72 pp., 21 plates.
Shomaker, J., Southwest Land Research, Sheehan, Sheehan & Stelzner, P.A. and
Livingston Associates, Inc., Regional Water Plan Estancia Underground
Basin, New Mexico (Draft) Unpublished consultant's report.
Smith, R.E., 1957, Geology and Ground-Water Resources of Torrance County, New
Mexico, New Mexico Bureau of Mines & Mineral Resources,