Although most of the Wilmington structure lies under or near the Pacific Ocean, water of the quality necessary for waterflooding has to be produced from near-surface deposits.

These deposits may be divided into two parts in the developed Wilmington area: the Gaspur zone, a Recent channel fill of the ancestral Los Angeles River, and the Pleistocene shallow-water deposits down to about 500 feet. These Pleistocene deposits include the "200-foot sand" and the "400-foot gravel" of the San Pedro Formation. All of these sands are salt-water invaded in this area. About 600,000 bbls./day of injection water currently are being produced from 45 wells completed primarily in the Gaspur or "400-foot gravel" zones. Water salinities range from about 1,000 ppm. chloride to approximately that of sea water. Because of the natural filtration of the beds, the oxygen and suspended solids contents are low, but the water has to be treated with bacteriacides prior to injection.

Ditch samples from eight exploratory core holes in the undeveloped East Wilmington field showed the water source beds to be missing in part of the area. Two of the four drilling islands probably will be located where the salt-water-bearing sands are missing. In order to insure an adequate injection-water supply, the islands may have to have an interconnecting water system that ties with additional source wells on Pier "J."

Near the eastern end of the Wilmington structure in the vicinity of the Humble-Texaco Belmont Island, the San Gabriel River flows through the "Alamitos Gap." The shallow river-channel deposits here are neither so deep nor so sharply defined as those of the Los Angeles River. Adequate salt-water-bearing sands are present in the lower San Pedro Formation, which is the equivalent of the Silverado zone on the west.

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