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Instead, the commission staff has urged the company to construct an offshore subsurface intake called an infiltration gallery — a grid of perforated collection pipes beneath the ocean floor that draws seawater without pulling in marine organisms.

In 2013, the Coastal Commission staff recommended approval of the Huntington Beach proposal with a condition the company hated: Instead of using the power station’s intake pipe, Poseidon would have to build an offshore, subsurface intake called an infiltration gallery.

The advisory group concluded that while it was technically possible to build an offshore infiltration gallery at Huntington Beach, doing so would add at least $1 billion to project costs and make the product water so expensive nobody would buy it.

It further said that among the items improperly listed for repair was $5 million to replace an “infiltration gallery,” a leach field beneath a riverbed.

Such was the case during the flood of September, 1910, when the depth of gravel above the roof of the San Geronimo Infiltration Gallery was diminished to such an extent that it was so inefficient as a filter for the flood as to permit the percolation of turbid water into the underground supply.