The model assumed that water from the Rio Grande seeped rapidly through deep, relatively uniform layers of porous rock, sand, and soil throughout much of the basin.  The more water users pumped out, the faster this seepage was assumed to occur.  The assumption implies that the ground-water supply is virtually unlimited, because it is constantly renewed by the river.

In the 1980s, the City realized that the State Engineer’s model did not account for the situation they found in managing the water supply.  Instead of being rapidly replenished, the aquifer was showing a net loss in the form of declining water tables.  In addition, as water levels declined, so did water quality. 

In 1988, the City initiated a series of studies carried out by highly qualified experts from a variety of federal and state agencies, academia, and the private sector.  They gathered much more data on the aquifer over a larger area than had their counterparts of the 1950s.  They looked at a broad range of factors and took advantage of advances in computer modeling and other technology in conducting their work.  The new science explained what the City’s water managers were seeing in the field and resulted in a radically different water management policy.