June 27, 2025
MaxWell® helps LA County recharge groundwater
Los Angeles County is reaping groundwater recharge benefits from its network of deep infiltration drywells.
Situation
With a population of over 9 million people, Los Angeles County is the most populous county in the US, and its county seat, Los Angeles, is the second most populous city in the US after New York.
Covering some 4,000 square miles, the county has a complex geography that encompasses urban, mountain and desert landscapes, and includes coastal zones, rivers and forest.
In recent decades Southern California has been experiencing regular periodic droughts, and in combination with population growth and increasing agricultural and industrial demand, this has placed great pressure on supplies of fresh water. Some 30-40% of water used in the County is pumped from groundwater supplies as a local alternative to imported water.
In recognition of this, Strategy 9B of the County’s 12 OurCounty sustainability initiatives is focused on improved water conservation, more efficient water usage, and better all-round water stewardship. Its actions include implementing a net zero water approach for new developments, and building code changes that improve water efficiency and usage.
Further emphasizing its importance to the state, in January 2025 California Governor Gavin Newsom issued an executive order to direct local and regional agencies to maximize groundwater recharge through facilitating the diversion and storage of excess precipitation from storms.
In tandem, changing weather patterns resulting from climate change mean that during the wet season from October to April the state can face intense storms that release large volumes of precipitation in short periods of time. Effective stormwater management is therefore critical to protect and serve homes, businesses and infrastructure in LA County.
Stormwater management objectives in LA County
LA County’s flood protection and water conservation system is one of the largest in the world, with a complex and extensive network of surface and sub-surface water management assets that collect, store, convey and infiltrate rainwater to mitigate flooding and maximize the use of stormwater as a resource—while also minimizing the impact of stormwater pollution on the environment.
In prioritizing both flood control and water conservation, the County is taking a holistic view of water—in protecting its residents, its businesses and its infrastructure from the devastating impacts of flooding, it is simultaneously also turning that potentially destructive force into a resource that can be used to serve residents and replenish pressured water supplies.
One stormwater best management practice (BMP) that meets both of these objectives is the drywell. In its most simple form, a drywell is a column drilled into the earth and typically filled with aggregate; collected surface water makes its way down the column and is infiltrated into the soil.
Drywells have been used for stormwater management in the US since the 1930s, with Phoenix AZ an early adopter, and they are a useful tool in the civil engineers’ stormwater management toolbox. In its conventional form the drywell is a basic infiltration system, providing rudimentary stormwater management, but technological innovations have enabled the development of more effective and more efficient versions of the technology.
The MaxWell® advanced deep infiltration drywell
MaxWell® is an advanced deep infiltration drywell system that collects and infiltrates surface water at depths of up to 120 ft.
Unlike conventional drywells, it incorporates a settling chamber (and optional additional pre-treatment chamber) that allows for sedimentation of total suspended solids (TSS), preventing clogging and extending the lifetime of the system out to beyond 50 years, and at just 4 ft in diameter it delivers exceptional deep infiltration for groundwater recharge in a compact footprint.
To improve site safety and to ensure that the system meets site-specific requirements and regulations, design and installation are carried out by Oldcastle Infrastructure’s expert team. The team also provides inspection and maintenance services for drywells, ensuring that they continue to perform optimally for many decades.
MaxWell was originally developed by Torrent Resources, which became part of Oldcastle Infrastructure in 2017. The team continues to deliver specialized deep infiltration design-build services as part of America’s leading water infrastructure solutions provider.
How MaxWell is helping LA County
Developers and contractors have been working with Torrent Resources and Oldcastle Infrastructure for many years, installing around 1,400 MaxWell systems across LA County.
Average annual rainfall in LA County is around 14.25 in, and MaxWell is designed to capture the 85th percentile of average annual runoff, which equates to 80% of average annual rainfall.
With a drainage area of at least 43,500 sq ft for a single system, this means that MaxWell systems infiltrate around 433 million gallons, or 1,300 acre feet, of rainwater back into local groundwater supplies in LA County every year.
In addition to providing a consistent groundwater recharge capability that helps LA County recharge its pressured aquifers, MaxWell also helps to protect citizens and businesses from flooding.
In early February 2024, historic volumes of rain fell on Los Angeles for three days in a row, with nine inches falling over three days and total accumulations estimated to exceed 12 inches in some areas. The “atmospheric river” phenomenon caused hazardous conditions, with mudslides and debris flows resulting in extensive disruption and damage to the area.
The County’s 1,400 MaxWell systems collected and infiltrated an estimated 250 million gallons of surface water during this three-day storm. This network of advanced deep infiltration drywells represents one component of a “sponge city” flood mitigation and stormwater harvesting capability that combines collection, storage, controlled release, conveyance and infiltration to reduce the impacts of storm events, capture stormwater for reuse, and return surface water to aquifers to replenish groundwater supplies.
Learn more
MaxWell
Visit our MaxWell® product page to learn more about how MaxWell® can deliver cost-effective deep stormwater infiltration.
Download the white paper to find out how Arizona is using groundwater recharge to combat flooding.
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References
https://www.drought.gov/states/california
https://www.usgs.gov/centers/california-water-science-center/science/geohydrologic-study-central-and-west-coast-basins
https://ourcountyla.lacounty.gov/strategies/strategy-9b
https://www.gov.ca.gov/2025/01/31/governor-newsom-issues-executive-order-to-help-california-capture-and-store-more-water-from-upcoming-severe-storms
https://pw.lacounty.gov/core-service-areas/water-resources/stormwater-management
https://wrrc.arizona.edu/dry-wells-for-stormwater-mgmt
https://www.weather.gov/lox/LAXRRMLOS
https://www.latimes.com/california/story/2024-02-11/l-a-staved-off-disaster-with-this-storm-extreme-weather-is-testing-our-luck
https://www.wired.com/story/los-angeles-just-proved-how-spongy-a-city-can-be