The Irvine area is in hydraulic continuity with the rest of the coastal plain in Orange County. Factors that distinguish the aquifer section of the Irvine area from that in other parts of the coastal plain are a low permeability, a high clay and silt content, and a thin alluvial sequence. Rapid facies change and the large percentage of silt and clay in the section locally result in confining conditions. The aquifer, most of which is included in the Fernando Formation, is as much as 1,300 feet thick beneath parts of the plain. The alluvium overlying the Fernando Formation averages about 200-250 feet in thickness and also contains significant amounts of silt and clay.
Transmissivities range from 25,000 to 100,000 gallons per day per foot in the Irvine area, values which are much lower than those in the rest of the coastal plain in Orange County.
Water levels have recovered as much as 60 feet from the low levels of the early 1950's. Water-level maps indicate that in the winter non-pumping season water tends to move toward upper Newport Bay and the rest of the coastal plain. During the summer pumping season a cone of depression develops, reversing the winter gradient.
The average dissolved-solids content of the ground water is about 800 milligrams per liter. The most prevalent cations are sodium and calcium; the most prevalent anions are bicarbonate and sulfate. No long-term degradation of water quality has occurred, with the exception of a slight increase in dissolved solids.
No areas in the Irvine area are suitable for the large-scale spreading of water for artificial recharge. Clay and silt predominate in the section beneath the Tustin plain, and in the foothill areas either bedrock is close to the surface or the alluvium is fine grained.
Additional Publication Details
USGS Numbered Series
Geohydrology and artificial-recharge potential of the Irvine area, Orange County, California