It has been stated in recent weeks and over the years that freshwater aquifers, close to the surface, exist in Coronado. There have been stories told and second-hand accounts written, but no studies or documents have been found to confirm that any such aquifers exist. Geologically, this is generally impossible in Coronado, as many areas, including the Golf Course and Tidelands Park, were constructed on hydraulic fill or dredge material, and would not naturally support an aquifer.
Aquifers are geologic formations that contain and support the transmission of groundwater. The near-surface groundwater in the fill areas is tidally influenced and brackish. Brackish water is defined as water with a salinity level of 5 to 30 parts per thousand (water with salinity levels from 30 to 50 is classified as saline, and above 50 is brine). The groundwater in the Country Club area was recently tested and found to have a salinity of 19 parts per thousand.
In 2011, as part of a study considering alternative water sources for irrigation, it was discovered that the golf course pond replenishment well water was seawater strength, and the dry weather groundwater that flows into the underground stormwater system at Coronado Avenue and Eighth Street was brackish. (RBF Consulting City of Coronado Recycled Water Feasibility Study, August 18, 2011)
Current City records do not reveal the presence of freshwater wells.
There are high groundwater levels in Coronado because the City sits mostly at sea level. This groundwater, which when tested is brackish, is often present when excavating construction sites. There is the possibility that small freshwater lenses are present in the fill areas where significant irrigation takes place. Freshwater lenses are thin layers of freshwater that accumulate from rainfall (minimal in Coronado, typically less than 10 inches per year) and irrigation waters that percolate through the soil and rest atop the brackish groundwater. This occurs because of the lower density of freshwater. These lenses, if they do exist, also have not been studied.
Deeper underground reservoirs exist in the greater San Diego area. In our area, there is the San Diego Formation Aquifer. The San Diego County Water Authority said groundwater production is limited by lack of storage capacity, availability of groundwater that makes it into aquifers, and degraded water quality. It said: "Narrow river valleys filled with shallow sand and gravel deposits are characteristic of the most productive groundwater basins in the San Diego region."
Even if Coronado were to find freshwater aquifers under the City, the California Public Utilities Commission has determined that California American Water, an investor-owned utility, has exclusive service rights to provide potable water to customers in Coronado.