A Pathway to Water
There are several ways to deal with declining aquifers; some of these are already being practiced to varying degrees throughout the United States. Such measures include increasing water efficiency, which can slow the drawdown of aquifers by using available water more sparingly. Another method coming into wider practice is implementation of low-impact development policies, some of which mandate that predevelopment hydrology and groundwater recharge potential be maintained on a site once it has been fully developed. However, while many of these projects are focused on stabilizing groundwater resources and keeping aquifers from sinking below their current levels, southern California needed something more comprehensive to begin and sustain a trend toward replenishing its aquifers.
The USGS has initiated several studies to determine how, and at what cost, ancient groundwater reservoirs can be restored, maintained, and put to use in a sustainable manner. It refers to the practices as aquifer storage and recovery (ASR), and the agency says they are intended as “water resources management techniques for actively storing water underground during wet periods for recovery when needed, usually during dry periods.”
A Pathway to Water There are several ways to deal with declining aquifers; some of these are already being practiced to varying degrees throughout the United States. Such measures include increasing water efficiency, which can slow the drawdown of aquifers by using available water more sparingly. Another method coming into wider practice is implementation of low-impact development policies, some of which mandate that predevelopment hydrology and groundwater recharge potential be maintained on a site once it has been fully developed. However, while many of these projects are focused on stabilizing groundwater resources and keeping aquifers from sinking below their current levels, southern California needed something more comprehensive to begin and sustain a trend toward replenishing its aquifers. The USGS has initiated several studies to determine how, and at what cost, ancient groundwater reservoirs can be restored, maintained, and put to use in a sustainable manner. It refers to the practices as aquifer storage and recovery (ASR), and the agency says they are intended as “water resources management techniques for actively storing water underground during wet periods for recovery when needed, usually during dry periods.” [text_ad] Artificial recharge (AR) is focused on actively moving water from the surface into groundwater systems. According to the USGS, “many states (Arizona, California, Florida, Nevada, and Texas, to name a few) have ASR sites ranging from pilot projects to full operations.” These types of practices range along a continuum from the more passive approach of spreading ponds, established in or near streambeds where geology and hydrology will permit the eventual percolation of water impounded within the ponds into the subsurface aquifer, to “aquifer injection wells that are designed to place recharge water directly into an aquifer.” However, Land of the USGS, who has been providing research support to the Water Replenishment District, says ideal conditions for either method are rare, requiring managers to pay careful attention to the challenging scenarios involved. The USGS assists by providing analysis of the character of surface and subsurface formations, prospecting for the best sites to implement groundwater replenishment projects. Land says monitoring wells operated by the USGS give researchers a peek at what goes on at the depths. “Most of the water is 50 years old—sometimes it’s older than that. Some of the water in the basin is more than 10,000 years old. If you’re pumping that water out, how are you going to replace it, because it took 20,000 years to get there?” inquires Land. But digging a little deeper, Land says, “Los Angeles is lucky to have the ability to store a lot of groundwater locally. It’s like a giant bathtub with different layers. In Los Angeles County it’s thick and there is lots of sand. The floor is plunging and high-quality water is available coming off of the mountains.” Land says there are five principal basins supplying groundwater resources to the Los Angeles area—Orange City, Central Basin, West Coast Basin, Hollywood Sub-Basin, and Santa Monica Sub-Basin—and groundwater storage can be enhanced in each of them by directing and capturing a greater proportion of the stormwater that falls on the region. While some basins have been overdrafted for some time, he notes that fortunately for the Los Angeles County area, all of the key basins are adjudicated, with pumping restricted below safe capacity yield to reduce the probability of overdrafting in the future and providing a baseline for replenishment efforts. Why Stormwater? Land can think of several advantages to increasing the proportion of stormwater being used to replenish aquifers; foremost among them is the cost. “Stormwater is free,” he says. By contrast, the other sources of water that agencies in the region have deployed to replenish groundwater come at a significant cost; for instance, the Colorado River withdrawals, which, aside the from political controversies involved over potential environmental effects or conflicting water allocations of downstream communities, cost $700 per acre-foot. While less contentious, treated wastewater carries a base price of around $300 per acre-foot for potable-quality water, but increasing its role will require extensive infrastructure investment, some of which are currently underway, in tertiary treatment facilities. According to Land, stormwater carries another potential benefit in that it is often lower in disinfectant by-products than either treated wastewater or water sourced from the Colorado River system. In fact, stormwater has been used successfully as a source for groundwater recharge in the Central Basin since the late 1930s.Artificial recharge (AR) is focused on actively moving water from the surface into groundwater systems. According to the USGS, “many states (Arizona, California, Florida, Nevada, and Texas, to name a few) have ASR sites ranging from pilot projects to full operations.” These types of practices range along a continuum from the more passive approach of spreading ponds, established in or near streambeds where geology and hydrology will permit the eventual percolation of water impounded within the ponds into the subsurface aquifer, to “aquifer injection wells that are designed to place recharge water directly into an aquifer.”
However, Land of the USGS, who has been providing research support to the Water Replenishment District, says ideal conditions for either method are rare, requiring managers to pay careful attention to the challenging scenarios involved. The USGS assists by providing analysis of the character of surface and subsurface formations, prospecting for the best sites to implement groundwater replenishment projects.
Land says monitoring wells operated by the USGS give researchers a peek at what goes on at the depths.
“Most of the water is 50 years old—sometimes it’s older than that. Some of the water in the basin is more than 10,000 years old. If you’re pumping that water out, how are you going to replace it, because it took 20,000 years to get there?” inquires Land.
But digging a little deeper, Land says, “Los Angeles is lucky to have the ability to store a lot of groundwater locally. It’s like a giant bathtub with different layers. In Los Angeles County it’s thick and there is lots of sand. The floor is plunging and high-quality water is available coming off of the mountains.”
Land says there are five principal basins supplying groundwater resources to the Los Angeles area—Orange City, Central Basin, West Coast Basin, Hollywood Sub-Basin, and Santa Monica Sub-Basin—and groundwater storage can be enhanced in each of them by directing and capturing a greater proportion of the stormwater that falls on the region. While some basins have been overdrafted for some time, he notes that fortunately for the Los Angeles County area, all of the key basins are adjudicated, with pumping restricted below safe capacity yield to reduce the probability of overdrafting in the future and providing a baseline for replenishment efforts.
Why Stormwater?
Land can think of several advantages to increasing the proportion of stormwater being used to replenish aquifers; foremost among them is the cost. “Stormwater is free,” he says. By contrast, the other sources of water that agencies in the region have deployed to replenish groundwater come at a significant cost; for instance, the Colorado River withdrawals, which, aside the from political controversies involved over potential environmental effects or conflicting water allocations of downstream communities, cost $700 per acre-foot. While less contentious, treated wastewater carries a base price of around $300 per acre-foot for potable-quality water, but increasing its role will require extensive infrastructure investment, some of which are currently underway, in tertiary treatment facilities.
According to Land, stormwater carries another potential benefit in that it is often lower in disinfectant by-products than either treated wastewater or water sourced from the Colorado River system.
In fact, stormwater has been used successfully as a source for groundwater recharge in the Central Basin since the late 1930s.