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 3.12-5.  Figure 3.12-6 shows aquifer flow direction and water-level change between 1990-1991 and 2003-2004.  Figure 3.12-7 contains hydrographs for selected wells shown on Figure 3.12-6.  Figure 3.12-8 shows well yields in three 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 San Rafael Basin Hydrology.

Major Aquifers

• Refer to Table 3.12-5 and Figure 3.12-6.
• The major aquifers in the basin are recent stream alluvium, composed of well-sorted silt, sand and gravel, and basin fill, consisting of clay, silt, sand and gravel.
• The streambed alluvium and the basin fill are hydrologically connected.
• Flow direction is generally from north to south.

Well Yields

• Refer to Table 3.12-5 and Figure 3.12-8.
• As shown on Figure 3.12-8 well yields in this basin range from less than 100 gallons per minute (gpm) to 1,000 gpm.
• One source of well yield information, based on 12 reported wells, indicates that the median well yield in this basin is 145 gpm.

Natural Recharge

• Refer to Table 3.12-5
• Principal sources of recharge in this basin are mountain-front recharge and infiltration from runoff in washes.
• The natural recharge estimate for this basin is 5,000 acre-feet per year (AFA).

Water in Storage

• Refer to Table 3.12-5.
• Storage estimates for this basin range from 4.0 million acre-feet (maf) to 5.0 maf to a depth of 1,200 feet. 

Water Level

• Refer to Figure 3.12-6.  Water levels are shown for wells measured in 2003-2004.
• The Department annually measures 10 index wells in this basin.  Hydrographs for two of these wells are shown in Figure 3.12-7.  More recent hydrographs of the index wells may be available through the Department's GWSI webpage.
• The deepest recorded water level in 2003-2004 was 205 feet northwest of Lochiel and the shallowest was six feet northeast of Lochiel.

Click to view Table 3.12-4 Groundwater Data for the

San Rafael Basin

Click to view Figure 3.12-6 San Rafael Basin

Groundwater Conditions

Click to view Figure 3.12-7 San Rafael Basin Hydrographs Showing Depth to Water in Selected Wells

Click to view Figure 3.12-8 San Rafael Basin Well Yields

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