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Groundwater Conditions in the Upper San Pedro Basin

Major aquifers, well yields, estimated natural recharge, estimated water in storage, number of index wells and date of last water-level sweep are shown in Table 3.13-5.  Figure 3.13-7 shows aquifer flow direction and water-level change between 1990-1991 and 2003-2004.  Figure 3.13-8 contains hydrographs for selected wells shown on Figure 3.13-7.  Figure 3.13-9 shows well yields in five yield categories A description of aquifer data sources and methods as well as well data sources and methods, including water-level changes and well yields are found in Volume 1, Appendix A.  For more information on groundwater in the basin see Upper San Pedro Basin Hydrology.

Major Aquifers

  • The major aquifers in the basin are basin fill, consisting of younger basin fill, older basin fill and basal conglomerate, and recent stream alluvium. 

  • The basin fill is the principal aquifer although the stream alluvium is also utilized. 

  • Artesian conditions exist primarily in the vicinity of Benson.

  • Flow direction is generally from south to north.

  • The basin contains two sub-basins, the Allen Flat Sub-basin in the northern portion and the Sierra Vista Sub-basin.

Well Yields

  • As shown on Figure 3.13-9 well yields in this basin range from less than 100 gallons per minute (gpm) to more than 2,000 gpm.
  • One source of well yield information, based on 353 reported wells, indicates that the median well yield in this basin is 600 gpm.

Natural Recharge

  • Refer to Table 3.13-5.
  • The principal sources of recharge for this basin are mountain-front recharge and streambed infiltration.

  • The estimate of natural recharge in this basin is 35,750 acre-feet per year (AFA).

Recharge Sites

  • There are two facilities in this basin that recharge effluent to the aquifer. 
  • The City of Sierra Vista Storage Facility is a permitted Underground Storage Facility (USF) by the Department (permit no. 73-583024).  Under the permit the facility’s maximum annual storage is 4,149 acre-feet.

  • The Fort Huachuca Recharge Facility is not a permitted facility.  

  • In 2005, a total of 2,380 acre-feet of effluent was recharged by both facilities. 

Water in Storage

  • Refer to Table 3.13-5.
  • Storage estimates for this basin range from 19.8 million acre-feet (maf) to 59 maf to a depth of 1,200 feet.  

Water Level

  • Refer to Figure 3.13-7.  Water levels are shown for wells measured in 2003-2004.
  • The Department annually measures 59 index wells in this basin.  Hydrographs for 15 index wells and five other wells are shown in Figure 3.13-8.  Index well hydrographs are: A-C, E-I, K-M,P,Q, S and T.  More recent hydrographs of the index wells may be available through the Department's GWSI webpage.
  • The Department measures water levels daily at four automated groundwater monitoring site in the basin. 

  • Deep water levels are found in the vicinity of Sierra Vista with water levels as deep as 585 feet measured in 2003-2004.  Shallow water levels are found near the Mexico border in the vicinity of Highway 92 with levels as shallow as 10 feet in 2003-2004.

Click to view Table 3.13-5

Click to view Table 3.13-5 Groundwater Data for the

Upper San Pedro Basin

Click to view Figure 3.13-7

Click to view Figure 3.13-7 Upper San Pedro Basin

Groundwater Conditions

Click to view Figure 3.13-8

Click to view Figure 3.13-8 Upper San Pedro BasinHydrographs Showing Depth to Water in Selected Wells

Click to view Figure 3.13-9

Click to view Figure 3.13-9 Upper San Pedro Basin Well Yields



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