AGW Consultants was retained by a major landowner in the Pearce-Squaretop Hills area of Arizona in the arid American Southwest.  The Pearce-Squ
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HYDROGEOLOGIC SETTING 

The area is situated in the Basin and Range Physiographic Province of thes#PZKAHUYhA h:I _GKV Seman, 1931).  More particularly, the area is situated in the Sulphur Springs Valley between the Chiricahua MountainsE[]SCX[VHUCI MuGCNT ,GWntains to the west. 

The topography is generally flat and level.  It is broken up by numerous prominent small hills of volcanic rock.  The volcanic hills stand from 100 to 600 feet (30 to 180 m) above the level area.  The hills are inselbergs that have been largely buried by basin-fill alluvium.  This indicates a very irregular subcrop surface beneath the alluvium. 

The Pearce-Squaretop Hills area is situated astride the ground-water divide that separates the Douglas Basin to the south and the Willcox Basin to the north. 

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SCLM)SIKL flowing water only during periods of rainfall in the area or in the Chiricahua Mountains to the east. 

Where stream beds emerge from the mountains, they contain verE^IPQL
\MNHUENFF>9 HE@CGCEWNAZW]MO]JRAALD@W~IPRFKMWET\M]SENJQW[]XO R6eEAKN$KZCELSIN[Zfall is about 11.8 inches (300 mDXCS[R o^GPH\E~ IQQ zY\n evaporation is about 85 inches (2,159 mm). 

Recharge takes place as mountain-front recharge and as recharge along the intermittent stream channels. 

The principal aquifer in the Pearce-Squaretop Hills is the basin-fill alluvium of Tertiary-Quaternary age.&n ^O'L ZPF NA Q(O TtBR8V}QZE]Ob~YPETO5\CMo] _BSF
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PROCEDURE  

We visited all existing water wells in the Pearce-Squaretop Hills area.  We measured depths to water and calculated the elevation of the water table.  We prepared a ground-water-level-elevation contour map from this data.

Ground water moves under the influence of gravity from areas of recharge to areas of discharge.  Ground-water-discharge areas have the lowest ground-water levels.  Ground water moves most rapidly through zones of high aquifer transmissivity.

We also collected Thermonic data from the water wells visited.  Some thermal data was obtained from Brown et al. (1963).  We plotted these data using our proprietary "valley mapping function" to determine the axes of most rapid ground-water movement. 

We also exMT^^
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E (/P[Rthe ground water.  Ground water moving rapidly from recharge to discharge zones is generally of better quality in the recharge areas and along zones of rapid movement.  If the distribution of ground-water-quality parameters agrees with interpretations from ground-water-level and Thermonic information, greater reliability can be assigned to our interpretations.  Ground-water quality data was obtained form Brown et al. (1963). 
 

RESULTS 

We used the Thermonic and ground-water-level data to identify the principal areas of recharge and three principal axes of maximum rate of ground-water flow. 

Turkey Creek is the primary source of recharge in the area.  It also appears that Turkey Creek does not recharge water everywhere along its course at the same rate.  Within the Pearce-Squaretop Hills area, the zones of maximum ground-water flow and highest transmissivity range in width from 0.5 to one mile (0.8 to 1.6 km) wide. 

Water quality data shows that the total dissolved solids (TDS) concentration within the zones of most rapid ground-water flow is about 200 mg/l.  Outside of these zones, the TDS concentration rises to 810 mg/l. 

We have specifically examined the fluoride concentration in two of the zones of rapid ground-water flow.  Along the axis of one zone, fluoride rises from 0.2 mg/l to 1.2 mg/l.  In the other, it rises from 0.8 to 3.5 mg/l.  This increase is expected because the concentration of fluoride increases with ground-water residence time or distance along a flow path.

CONCLUSIONS 

We conclude from our study that hydrodynamic, Thermonic and hydrogeochemical data are in good agreement and define three zones of rapid ground-water movement.  These zones are long and will be the most producX.XF

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REFERENCES 

Brown, S.G., Schumann, H.H., Kister, L.R., and Johnson, P.W., 1963, Basic 
     Groundwater Data of the Willcox Basin, Graham and Cochise Counties, Arizona, 
     Arizona State Land Department, Water Resources Report No. 14. 

Fenneman, M.M., 1931, Physiography of Western United States, pp. 379-395, 
     McGraw Hill Book Company, Inc., New York, NY.