Major aquifers, well yields, estimated water in storage, number of index wells and date of last water-level sweep are shown in Table 7.10-4.  Figure 7.10-6 shows aquifer flow direction and water-level change between 1990-1991 and 2003-2004.  Figure 7.10-7 contains hydrographs for selected wells shown on Figure 7.10-6.  Figure 7.10-8 shows well yields in one category.  A description of well data sources and methods, including water-level changes and well yields, is found in Volume 1, Appendix A.

Major Aquifers

• Refer to Table 7.10-4 and Figure 7.10-6.
• The major aquifer is basin fill.
• Groundwater flow is from north to south.

Well Yields

• Refer to Table 7.10-4 and Figure 7.10-8.
• As shown on Figure 7.10-8, all recorded well yields less than 100 gpm. 
• One source of well yield information, based on three reported wells, indicates that the median well yield is 50 gpm.

Natural Recharge

• Refer to Table 7.10-4.
• The natural recharge estimate for this basin is 1,000 acre-feet per year (AFA).

Water in Storage

• Refer to Table 7.10-4.
• Storage estimates range from 3.0 million acre-feet (maf) to 4.1 maf to a depth of 1,200 feet.

Water Level

• Refer to Figure 7.10-6. Water levels are shown for wells measured in 2003-2004.
• The Department annually measures one index well in this basin.  Hydrographs for this well (B) and four other wells are shown on Figure 7.10-7. 
• The deepest water level shown on the map is 337 feet at the Organ Pipe Cactus National Monument Headquarters and the shallowest is 27 feet near Puerto Blanco Drive.

Table 7.10-4 Groundwater Data for the Western Mexican Drainage Basin

Figure 7.10-6 Western Mexican Drainage Basin Groundwater Conditions

Figure 7.10-7 Western Mexican Drainage Basin Hydrographs Showing Depth to Water in Selected Wells

Figure 7.10-8 Western Mexican Drainage Basin Well Yields

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References and Supplemental Reading for the Western Mexican Drainage Basin