Authorities in Los Angeles have successfully protected the region’s groundwater from seawater contamination for over half a century, but while the system in place is in no immediate danger, experts are hard pressed to ensure the solution remains sustainable, especially in the face of rising sea levels.

The intrusion of saltwater into the aquifers (underground fresh water sources) beneath Los Angeles is not a unique issue.  It is a natural process that normally does not harm an environment; denser underground saltwater presses into fresh water sources under dry land, but as long as the aquifers remain large enough, water pressure keeps things in equilibrium.

But as in any industrialized coastal city like Los Angeles, drawing water out of those aquifers for drinking and industrial purposes throws off the balance, causing saltwater to gradually contaminate the aquifers.  This can hurt plant life up above, and render the groundwater practically useless for humans.

Cities in Southern California recognized this problem in the 1950s, however, and implemented a simple solution that has been effective ever since: drill wells that inject fresh water back into the ground to offset what is taken and replenish the aquifers.

A little under 300 such wells create barriers against saltwater intrusion at three different sites in the Los Angeles area.

“Overall the area wells are doing a good job of keeping the seawater intrusion from becoming a bigger problem,” said Ted Johnson, the chief hydrogeologist with the Water Replenishment District, the organization that manages the barriers.

Johnson is studying the long term health of the injections wells, and said that while the system as whole can continue operating for years to come, maintenance is costly, since some wells are more than 50 years old.

Cost indeed is the most difficult challenge facing the process of injecting billions of gallons of treated water back into the groundwater sources used to quench Los Angeles.  Purchasing this water and maintaining the injection system costs almost $20 million each year, but that price should rise in coming decades as more water is required and the price of the water itself increases.

“The main issues we have with the seawater barrier wells is that the water that is used to put underground is the same as the drinking water that we have every day - that’s what’s been used in the past - so that’s a rare commodity these days,” said Johnson.

According to Eric Batman with the Los Angeles Department of Public Works, who operate and service the barriers, highly treated water such as drinking water is used primarily because it is the only suitable type of liquid to travel through the injection wells.

“You can’t just put surface water into the wells because they will clog extremely quickly,” said Batman, “It has to be high quality water free of particulates and things like that.”

The Water Replenishment District is attempting to increase the use of highly-treated recycled water that is less costly than the drinking water usually purchased for the injection process, but progress has been slow as obtaining licenses and permits for providers is a lengthy process.

Alternative sources will only help so much, however, as demand for water from aquifers could increase in the future as a result of dwindling water resources elsewhere in state while the city’s population is expected to gradually increase. 

“If you are having so many people coming in to California yearly, with the population going up, then you obviously need more water.  But where do you get the water from?” said Prof. Mike Pirbizari, director of USC’s Environmental Engineering program, “If you are getting it from the groundwater, then you are going to have problems.”

Pirbizari also said that rising sea levels as a result of climate change could only place more stress on the system, as more seawater would exert more pressure, and require more water pumped through the injection wells.  Researchers with the U.N. predict sea levels could rise as much as one meter by the end of the century worldwide, and levels in California could rise by five feet.

This would inevitably increase costs, but the system might not be able to handle that much pressure either, as Eric Batman explained that the aquifers under the city in fact rest between multiple stacked layers of geology susceptible to changes in the already highly pressurized injection wells.

“It’s just like a balloon, if you will,” said Batman, “And just like a balloon, the more you try to push air into it, eventually it will pop.  Once it pops, it becomes very difficult to maintain any type of pressure.”

Batman also said that since some injection wells sit close to sea level already, any substantial rise of the ocean could potentially leave the wells under water along with the surrounding land, forcing authorities to abandon the wells.

In the meantime, however, the seawater barrier is effective and could remain so for years to come.  Researchers like Johnson and Pirbizari agree that maintaining the balance between saltwater and the aquifers will rely on how well Los Angeles can conserve and replenish its groundwater.

You can reach Staff Reporter Shea Huffman here or follow him on Twitter.