It’s not always clear where water can be found or how much of it is available, and in the face of dramatic climate change, it’s even more uncertain how much quality water will be available in the future. Due to changes in climate, development pressure, and rising consumption, rivers and streams observed today often don’t carry the flow seen even in the recent past. Surface water in reservoirs and lakes has declined, too, particularly in the southwestern United States. For example, the Las Vegas Sun reported in June 2014 that, thanks to a 14-year drought, by May of that year, the level of Lake Mead—the source of 90% of the city’s water—”was down to an elevation of 1,087 feet, the 10th-lowest monthly reading since the 1930s, when the lake was filled.”
And, water use is steadily increasing. While Nevada is considered America’s driest state, Gary Hildebrand, deputy director of the Los Angeles County Department of Public Works who runs the Watershed Management Division, says there is a lot of concern about drought and water supply across the country; for southern California and the Los Angeles County area, the issue is perpetually at the verge of crisis.
Southern California’s, and the Los Angeles basin’s, population has increased by nearly 6,000% in the past 100 years, bringing the number of residents from just a few thousand to 10 million people. In the meantime, few new water sources have been discovered to complement the sparse 15 inches of annual rainfall the region receives on average. Along with massive projects to import water from the northern tier of the state, southern California has turned increasingly to groundwater to fill the gap. Los Angeles County now obtains “a third of its local water supply from groundwater basins,” says Hildebrand.
He adds, “Whenever you talk of groundwater as water supply, you are also talking about stormwater, because that’s the way groundwater gets replenished.”
He says that nationwide, withdrawals from aquifers have been ongoing for years, in some cases proceeding almost unchecked for decades, even centuries. As a result, groundwater resources in many areas are in such a depleted condition that they will require substantial intervention to remedy.
Land of Orchards
Michael Land of the US Geological Survey (USGS) says that in the Los Angeles area before 1900, there was enough surface water to meet the demands of local enterprises and households. Land, who works as a researcher helping the region’s water agencies assess the quality and accessibility of aquifers in the area, says southern California was once considered a land of water abundance. Fruit growers flocked to the region.
However, as time wore on, water users diverted nearly all of the available water from rivers and streams to feed the booming orchard industry and quench the needs of the burgeoning population. Early in the region’s development it became apparent that the surface water in lakes, rivers, and streams would not be able to keep up with rapidly rising demand. Land says once the streams were fully tapped, residents began to dig a little deeper to find water to nurture their groves; in the beginning, for the most part, that didn’t mean digging very deep at all.
“One half the area under Los Angeles was artesian with tens of feet of pressure,” says Land. “So it was easy to find water to get the orchards started,” but keeping them growing was a different matter.
Of course, it is immortalized in song that rainfall can be sporadic in southern California. Land says citizens and landholders early on “realized that storms here were very episodic, and they started trying to store water from rainy seasons to use during dry times.” Early in the 20th century, residents and businesses of southern California also began importing water, harvested from the glaciated alpine slopes of the Sierra Nevada ranges and Colorado River system, to be conveyed by extensive canal and pumping systems to reservoirs for storage and use in the Los Angeles area.
But through all this, the main event was not conservation, but rather, consumption.
Rivalry and Competition for a Rare Commodity
To obtain water by any means available became a central mission of the populace. Water ensconced underground became a prime source; it was local, it was clean, and it was inexpensive—at first.
Landowners and rights holders were soon racing against their neighbors for access to the increasingly rare commodity. Their competitive fury included not only the race to capture water, but also to expend it as a means to establish, build, and sometimes cynically embellish their water rights on their holdings. Land says some landowners turning to these measures pumped water far in excess of their needs for the singular purpose of laying claim to greater water rights in the future. By the 1930s, water had become a contentious issue, seawater started pressing inland at the fringes of groundwater supplies near the coastal margins of aquifers, wells tapping the overdrawn aquifers threatened to run dry, and no one was happy with the situation.
Southern California went from a land of water abundance to looming water catastrophe by the mid-1960s. The inventory of about 300 water well pumps operating in the Central Basin since 1900 pumped up to double-safe-capacity yield. Water tables dropped at some wells by 10 feet per year; wells ran dry, and other detrimental effects occurred such as seawater intrusion at the interface between saltwater and the freshwater groundwater sources.
The issue came before the courts, and in 1960 the basin withdrawals in the area were adjudicated; court rulings fixed the amount of water that could be drawn from the Central Basin to a figure below the safe capacity yield.
Reviving Nature’s Balance
It’s not just drought and excess demand that have reduced the abundance of groundwater. Changes in the region’s hydrology have played a major role in preventing aquifer replenishment by draining wetlands, increasing impervious surfaces, and replacing natural streambeds with engineered channels, which circumvent percolation and speed stormwater discharge into the bay and out to the Pacific Ocean.
One means to achieve a balanced groundwater recharge is to revive aspects of the original natural hydrology. However, Land says it would never make sense to try to restore the artesian conditions in the Los Angeles valley that existed 100 years ago. Back then, he says, “The Pico would routinely flood.” With thousands of residences and businesses in the area today, a return to normal would amount to a disaster.
Land says, furthermore, that the waters within some of the aquifers had been accumulating in the porous stone and crevices of southern California’s rocky subsurface over timescales ranging from years to millennia, rendering a quick fix challenging.
With some foresight, the Water Replenishment District (WRD) of southern California initiated projects as far back as 1938 to put water back into the aquifer for the future, making it one of the first agencies in the United States to implement groundwater replenishment policies. The WRD also augmented its supply of imported water diverted to storage deep underground with water reclaimed from wastewater treatment facilities and instituted conservation measures across its service area.
Nonetheless, southern California continues to find itself dependent on water drawn at great expense in energy, cash, infrastructure, and political capital from the rivers in the northern regions of the state.
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.”
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.
Topping Off the Basins
Surficial spread of stormwater is critical to getting the stormwater to percolate deeper underground.
At the same time the state began piping in water from the Colorado River to meet immediate potable water requirements, it also constructed spreading basins and piped in water to fill them in an effort to arrest the precipitous decline in the aquifers.
Ted Johnson, chief hydrologist for the Water Replenishment District, describes spreading grounds as “just big leaky lakes.” The WRD manages groundwater for nearly 4 million residents in 43 cities of southern Los Angeles County. Its 420-square-mile service area uses about 250,000 acre-feet of groundwater per year taken from the aquifers of the Central and West Coast Basins. This equates to nearly 40% of the total demand for water.
According to Johnson, the water on the surface introduced to the spreading ground begins its work immediately. It doesn’t need to travel the several miles that may be necessary to get deep into the aquifer it is intended to augment before it begins having a positive impact on supply. He says the water, even while still on the surface, exerts pressure on the water ensconced below in the porous rock and crevasses, pushing it continually forward to the well heads where it can be drawn out as needed.
Low Impact Targets High Value
In 2012, WRD released a stormwater distributed replenishment feasibility study performed by a coalition of stakeholders and prepared by the engineering firm Geosyntec, laying out in detail the tactics and strategies required to enhance stormwater capture for aquifer replenishment by means of distributed best management practices (BMP) and low-impact development techniques.
Results of the study show that in the highly urbanized areas of southern Los Angeles County, distributed projects and sub-regional projects with the capacity to capture the 2.0-inch storm may yield annually more than 0.5 acre-feet of recharge. In addition, a distributed recharge system consisting of stormwater BMPs can significantly improve water quality, reducing “on the order of 200 pounds per acre” several pollutants modeled in the study, including total suspended solids, phosphorus, ammonia, nitrate, total nitrogen, copper, lead, and zinc, showing potential for aiding area jurisdictions in meeting total maximum daily load (TMDL) requirements.
The distributed strategy envisioned in the study seeks to capture multiple benefits at a watershed scale while recharging aquifers with an increasing reliance on stormwater.
Cost analysis, in terms of dollars per acre-foot of water, might at first appear significantly more expensive than continued reliance on using purchased water to supply spreading ponds, the study notes. But when the multiple benefits are considered and when neighborhood scale replenishment projects are viewed over their entire lifespan, the costs spread between the two alternatives narrows. Additionally, Hildebrand maintains that connecting the groundwater replenishment mission to the people in the community served by it will both strengthen the implementation and promote better stewardship of water resources overall. Distributed replenishment might be the real gem of the groundwater replenishment dream: very attractive, expensive, and rare.
Johnson believes that although distributed BMPs on a cost-per-acre-foot basis can’t match the groundwater recharge efficiency of large spreading pond facilities, they can be justified for valuable benefits ranging from water-quality improvements to the significant role they can have in promoting better water resource stewardship awareness by beautifying the communities where they are located.
Hildebrand agrees. The Los Angeles County Flood Control District is the agency responsible for facilities designed to capture and deliver the stormwater that the WRD utilizes. “We look at it as one piece of the overall portfolio of how we want to go about increasing the ability to capture local stormwater. They provide some benefits, but ultimately they need to be tied with creating some more of the sub-regional facilities to be able to fully capture stormwater and increase our local water supply.
“It will take a combination both of kinds of efforts,” he says. “Neither one alone will be able to do it.”
Currently, spreading grounds—whether using stormwater, imported water, or treated wastewater—provide the backbone of Los Angeles County’s groundwater replenishment infrastructure.
It’s All About the Location
The location of the spreading grounds is key to their success in supplying water for aquifer recharge, and very few locations have all of the ideal characteristics to function optimally as recharge sites, Land says.
As early as the 1930s, Los Angeles County established spreading grounds at Rio Hondo and Upper Basin, an area where a porous subsurface allows water to percolate into the ground.
According to Land, the Montebello Forebay area also has some favorable characteristics for surficial spread. “Montebello Bay is special because it’s coming up on a shallow point in the bathtub where the aquifers merge. There is a lot of sand and a little clay and silt, but not enough to impede the water percolating down.” But finding additional expansive parcels for building new spreading grounds, other than the several already in operation, is a challenge in heavily urbanized post-industrial boom Los Angeles County, so there is a big need to enhance each spreading pond’s efficiency.
At the spreading grounds of the Montebello Forebay, in addition to promoting the percolation of water through its permeable bed, WRD also has deployed strategically located production wells to pump water from the aquifer itself out to end users to lower the water table in the spreading ground when the level surpasses optimal elevation. This practice increases the available volume of the vadose zone and the aquifer’s holding capacity.
Los Angeles County’s Whittier Narrows spreading grounds also has several favorable characteristics to promote groundwater replenishment, and officials are strongly considering improvements to its infrastructure to enhance capacity of spreading grounds located there.
Water Independence
A number of new projects have been completed over the past several years to further increase the amount of stormwater used for groundwater replenishment for Los Angeles County at previously established facilities. These projects include removing oil companies’ facilities from behind the Whittier Narrows Dam to avoid flooding of their equipment and allowing the capture of more stormwater, constructing new rubber dams in the San Gabriel River to capture more stormwater, and removing sediment from the spreading grounds to enhance infiltration rates to recharge more stormwater. These projects have increased stormwater capture by about 6,600 acre-feet.
Examples of upcoming projects to increase stormwater conservation include construction of a new stormwater delivery pipeline to optimize operational flexibility between spreading facilities, installation of new production wells near the spreading facilities to lower the water table mound at the various sub-regional facilities, creating additional vadose zone space for increased stormwater capture, and increasing the water capture (conservation) pool behind the Whittier Narrows Dam to regulate stormwater releases to the spreading facilities.
Johnson says a seemingly routine initiative of raising an adjacent roadbed to allow for the expansion of the spreading ground behind Whittier Narrows Dam will provide a much-needed new dimension of storage capacity. The math justifying that project is simple. According to Hildebrand, studies show that raising the road at the cost of $4 million for engineering and construction will allow for an additional 11 acre-feet of storage at the facility. At the current $700 per acre-foot price tag for imported water, Hildebrand projects “a five-year payback.”
Wastewater currently still plays a big role in WRD’s aquifer recharge efforts, Johnson says. “We’re lucky to be part of a big urban area with a lot of wastewater that can be treated and sent to spreading grounds” to percolate. However, he concedes that widespread adoption of water conservation measures might eventually cut into the volume of treated wastewater that will be available in the future for transfer to spreading grounds.
Johnson also expresses concern that rural areas, which don’t have access to large volumes of wastewater that can be reused for subsurface recharge, “will probably need to rely even more heavily on finding ways to capture stormwater and get it underground” to replenish their aquifers and ensure long-term sustainability of their water supplies.
For all the investment to date, southern California has yet to achieve water self-sufficiency, but officials with the WRD say through the region’s new Water Independence Now (WIN) program, area water agencies plan to invest in conservation measures, upgraded infrastructure, and projects aimed at increasing the role of stormwater as a source for groundwater replenishment to wean themselves permanently from dependence on all sources of imported water.
Timely Intervention
While the conservation measures and the construction of spreading grounds at Montebello Forebay and work to enhance spreading grounds elsewhere have served to slow demise of the region’s aquifers, the withdrawal rate still exceeds the rate of replenishment. WRD seeks to devise a more comprehensive and sustainable strategy to restore the aquifers and maintain them far into the future.
Statewide, three new bills promoting aquifer stewardship were signed into law by Governor Jerry Brown as The Sustainable Groundwater Management Act of 2014 (SGMA). The SGMA provides a framework for sustainable management of groundwater supplies by local authorities. The measure, signed in September 2014, requires that all of California’s agencies with jurisdiction over groundwater basins devise plans to improve groundwater management and reduce the drawdown rate of the aquifers while taking steps to assure sustainability of the resource. However, thanks to their historic efforts, previously adjudicated status, and ongoing programs replenish local aquifers, the Los Angeles County agencies will be largely exempt from its mandates.
In fact, on its own initiative, WRD recently inaugurated the Water Independence Now program with a policy geared toward not only restoring the aquifers but also eliminating the need for imported water for Los Angeles County. This program, being pursued in conjunction with WRD’s partners, the County Sanitation Districts and the Los Angeles County Flood Control District, aims to increase the use of recycled water and stormwater runoff to replenish the groundwater supply. The WIN program has set a goal to soon eliminate WRD’s demand for replenishment water imported from northern California and the Colorado River, replacing 30,000 acre-feet of imported water with water acquired locally.
WATER UNDER A MICROSCOPE
The USGS’s Michael Land says he is trying to help the Water Replenishment District better understand how water has moved through the region’s aquifers through geologic, historic times and modern times, tracing the water chemically from its various sources. He says chemical markers can help distinguish the
sources from one another, based on radioisotopic data, allowing researchers to determine how long water has travelled underground, whether decades or millennia.
Land thinks of this part of the analysis toolkit as “a whole bag of chronometers,” with tritium dating being the one that gets the most traction. Although it was fi rst used as a chronometer for scientifi c pursuits during the 1940s because of its steady rate of radioactive decay, as the technology has become more sophisticated, tritium dating has found new uses and is particularly useful in helping hydrologists study and understand aquifers.
Water extraction wells drilled from the 1930s until the present are widely distributed through Los Angeles County and delve anywhere from 100 feet deep down to 1,800 feet, revealing a stratifi ed structure to the aquifers, Land says. They plunge in some places through gravel, in others through silt, and even through clay to produce water for the region.
Monitoring wells operated by the USGS have also revealed some of the aquifers’ secrets.
“Some of the water is really old,” says Land. “It’s interesting, there are different layers like a layer cake, and they are all different. You can look down and see all the natural water at 100 feet or 200 feet, then suddenly at 800 feet is the water that’s been engineered into the system.”
In January 2015 the USGS introduced the Groundwater Toolbox, a graphical and mapping interface for analysis of hydrologic data. The software is a customized interface built on the nonproprietary, open-source MapWindow geographic information system software in a Microsoft Windows computing environment. The Groundwater Toolbox allows for the retrieval of hydrologic timeseries data (streamfl ow, groundwater levels, and precipitation) from the USGS National Water Information System; preprocessed meteorological data from the National Oceanic and Atmospheric Administration National Climatic Data Center also are available with the Groundwater Toolbox.
With its data retrieval and analysis tools, the Groundwater Toolbox provides engineers and managers with methods to estimate many of the components of the water budget for a hydrologic basin, including precipitation, streamflow, base flow, runoff, groundwater recharge, and evapotranspiration.
Cool Plans for Restoring an Oasis
Johnson says the WRD doesn’t panic every dry season. “We look at the long-term hydrological cycle,” which “fluctuates from 5 inches to 30 inches of rainfall,” developing plans to “capture rain from those relatively wet years to use during the inevitable dry years of the cycle.”
“For a long time, northern California has been in severe drought, leading to the realization that Los Angeles County needs to increase the reliability of its own local supply,” says Hildebrand. “We need to construct facilities that allow us to store water locally when we do have wet years so we can use it in dry years. For the imported water infrastructure, we have built facilities so when we have wetter years in northern California we can store that water here. For our groundwater basins, there is a recognition that we need to be able to increase the facilities that we have, to be able to capture stormwater during storm events and use that water to recharge our groundwater basins.”
He says, “Even though we have facilities that we’ve built over the last many decades, there is still stormwater that hasn’t been captured yet that we can get and put into the ground.” Through the WIN program, “the Flood Control District has been working with groundwater basin managers and other local water agencies in partnership to expand and modernize the facilities that we’ve built over the years to increase the amount of stormwater we can capture.”
Groundwater resources amassed over geologic timescales can be depleted rather quickly, sometimes in a matter of a generation or two, but current efforts in southern California show potential in reversing that trend.
Acknowledging the reality that the challenge of aquifer depletion does not face the Los Angeles region alone, but confronts many areas throughout the rest of the United States as well, Johnson says people are watching events in the Los Angeles area closely. “We’re getting a lot of calls from people from other jurisdictions who want to do tours. We’re a model for how it can be done.”
