FRACTURE-TRACE ANALYSIS FOR WELL-SITE LOCATION NEAR ALBUQUERQUE, NEW MEXICO, U.S.A.
William M. Turner, Ph.D.
AGW Consultants was hired by a land development company to locate a water-supply well for a residential land development in Three Guns Canyon. Three Guns Canyon is situated in the Sandia Mountains near Albuquerque, New Mexico. The Sandia Mountains are the southern-most extension of the Rocky Mountains of North America. Existing wells in the area had low yield. Figure 1 shows the location of the area of ground-water exploration.
THEORY
Fracture traces visible on aerial photographs are natural linear drainage, soil-tonal, and topographic alignment are probably the surface manifestation of underlying zones of fracture concentration. This method of optimal well-site location was first described by Lattman and Parizek (1964). They studied the specific capacities of wells located in interfracture trace zones, near single fracture traces in dolomite and limestone and wells drilled on a single fracture trace in limestone, and for a well drilled at the intersection of two fractures in limestone.
In their study, the average specific capacity of two wells drilled in dolomite in interfracture trace zones was 0.014 gpm/ft (0.00027 lps/m). For six wells drilled on or near a single fracture trace in dolomite, the average specific capacity was 0.04 gpm/ft (0.0008 lps/m). For three wells drilled in dolomite at or near the intersection of two fracture traces, the average specific capacity was 0.13 gpm/ft (0.0026 lps/m).
For two wells drilled on a single fracture trace in limestone, the average specific capacity was 1.37 gpm/ft (0.026 lps/m). A single well drilled at the intersection of two fracture traces in limestone was 3.27 gpm/ft (0.063 lps/m).
These results show orders of magnitude increases in specific capacity from wells drilled in interfracture areas to wells drilled on single fracture traces to wells drilled at the intersection of two fracture traces. These results also show significantly higher specific capacities for wells drilled in limestone over those drilled in dolomite, regardless of the well location.
HYDROGEOLOGIC SETTING
Three Guns Canyon is carved into the Precambrian Sandia Granite of Kelley and Northrop (1975). The dominant lithology is a medium-coarse grained quartz monzonite. The Sandia Granite is intruded by aplite dikes and pegmatite of Precambrian age and by lamprophyre dikes of Tertiary age.
The major structural feature of this canyon include an major strike-slip fault that trends north-south, several normal faults which are downthrown to the south and which strike N.85o E. to N.85o W. and a normal fault which strikes N.50o W.. Other major structural features are joints in the Sandia Granite. All of these joints have dip angles of 70o or more. Orientation of the lamprophyre dikes is similar to the joint orientations which strike N-S, and N. 30o-40o E.. The evolution of these structure is summarized in Kelley and Northrop (1975).
Within the canyon, there is a thin cover of alluvium above the Sandia Granite. It is generally above the zone of saturation and is unimportant as an aquifer, particularly in the upper reaches of the canyon.
Ground water within Three Guns Canyon is recharged to the area by direct infiltration of incident precipitation and by infiltration of runoff through the bed of an ephemeral stream channel.
Infiltration of incident precipitation results in planar recharge to the ground-water system. Recharge along the ephemeral stream channel results in line-source recharge.
The Sandia Granite of the area is the aquifer of interest. The granite contains water within joints, fractures, faults, and breccia zones in the granite both where they are exposed at the surface and in the subsurface. Larger faults collect water from beyond the canyon and convey water to Three Guns Canyon.
In the granitic terrane, a local driller, David Massey, indicates complete unpredictability of the water yielding capacity of the granite not only areally but also with depth. He indicates he has drilled wells in the area that produce one-half gallon per minute (0.03 l/s) to 10 to 15 gpm (0.6 to 1 l/s).
Extensive experience gained in the Precambrian shield areas of Brazil indicates that, generally, most wells will not produce increased yield per foot of depth 150 to 250 feet (50 to 85 m) beneath the bottom of the unweathered zone. Unloading fractures, that could contain water, diminish in frequency with increasing depth.
AGW scientists concluded that the water-bearing part of the granite aquifer may be as much as 200 feet (68 m) thick.
AGW further concluded that yields of 0.5 to 17 gpm (0.3 to 1 l/s) are possible.
FRACTURE-TRACE INVESTIGATION
AGW scientists recognized that the Precambrian granite is fractured and that the Three Guns Canyon itself may be localized along a zone of erosional weakness that could be caused by a major fracture or fault in the bedrock.
We ordered 1991 aerial infrared and 1996 black and white aerial photographs of the canyon. These photographs are shown in Figures 2 and 3. Stereoscopic examination of the photographs showed a prominent lineament trending from north to south and continuing to the south beyond the area of the photographs.
We carried out fieldwork in the area of the suspected fault. Figure 4 is a view south down the canyon showing the footwall of the fault on the west side of the canyon.
We recommended the construction of a producing well and an observation well at the upper end of the canyon into the bedrock granite. The wells were drilled. The production well was drilled to a total depth of 290 feet (100 m) in the granite. Ground water was encountered at a depth of 43 feet (14.7 m) below land surface. Figure 5 shows the completed well with 5-inch (12.7 cm) diameter steel casing.
We performed an aquifer-performance test using the well. Produced water was piped some distance down the valley beyond the observation well shown in Figure 6. We used the Jacobs, quasi-steady state analysis on the drawdown data and a Miller-Dyes-Hutchinson (MDH) analysis on the recovery data.
Because drawdown data contains errors caused by casing storage effects and well inefficiency, the MDH analysis was relied on to evaluate undamaged aquifer transmissivity. The MDH analysis yielded an undamaged aquifer transmissivity of 2,783 gpd/ft (34.5 m2/d). Further analysis of the data indicates the well can produce 60 gpm (3.8 l/s). This production rate exceeds that of any other well in Three Guns Canyon.
CONCLUSIONS
Fracture-trace analysis and geological fieldwork led to the location of a water supply well on a major fracture within Precambrian granite that can meet the needs of residents of the small community.
REFERENCES
Kelley, V.C., and Northrop, S.A., 1975, Geology of Sandia Mountains and Vicinity,
New Mexico, New Mexico Bureau of Mines & Mineral Resources, Memoir 29.Lattman, L.H., and Parizek, R.R., 1964, Relationship between fracture traces and the
occurrence of ground water in carbonate rocks, Journal of Hydrology, v. 2., pp.
73-91.
Back to Top
? 1999-2016 AGW Consultants. All Rights Reserved.