Before development, the San Juan Basin aquifer is assumed to be in equilibrium.  If the hydrologic system is in equilibrium, the average annual recharge (R) is equal to the annual average discharge (D), thus,

and there is no loss of storage in the groundwater system (Figure 4).

When a well field is developed, three things may happen.  The recharge may increase from , the discharge may decease form , and there may be a loss of groundwater storage, .  If Q is the amount of water pumped annually from the well field, then we may write a new equilibrium expression,

where  is taken to be one year.  R, ∆R, D and ∆D all have the units of discharge ();  has the units of volume () and is weighted by storativity.  In laymen’s terms storativity is the volume of water released from storage (or the aquifer) per unit decline in hydraulic head or groundwater level in an unconfined aquifer such as the San Juan.  Because, the new dynamic equilibrium equation can be rewritten,

and the change in R and D  is called capture (Figure 5).

For Loreto, we will assume that the natural recharge to the basin will not be increased by the groundwater pumping.  The natural recharge occurs in the alluvial fans above and away from the well field, so as to not be affected by the pumping.  There can be impoundments created in these alluvial fans that may increase the recharge.  Any  is assumed to come from these constructed impoundments.  The  comes from the capture of discharge that outflows from the basin into the Sea of Cortez.  Thus, to avoid salt water intrusion into the San Juan Aquifer, the captured discharge must be less than the total discharge to the sea or.  If  exceeds D, the discharging turns to recharging of saltwater.