2019 Excellence in Environmental Engineering and Science® Awards Competition Winner

Grand Prize - Design

Tujunga Spreading Grounds Enhancement Project

Entrant: Los Angeles Department of Water and Power
Engineer in Charge: David Pettijohn, P.E., BCEE
Location: Los Angeles, California
Media Contact: Art Castro

Entrant Profile

The Los Angeles Department of Water and Power (LADWP), the largest municipal water and power utility in the nation, serves water and electricity to nearly 4 million residents and businesses in the City of Los Angeles (City). Historically, the City's water supply comes primarily from imported water from the Los Angeles Aqueduct, State Water Project, and Colorado River Aqueduct. These supplies have been significantly impacted by environmental factors, climate change, and increasingly frequent and prolonged droughts.

LADWP is proactively addressing these challenges by pursuing the goals of the Mayor's Sustainable City pLAn (pLAn), thereby aggressively expanding water conservation, stormwater capture, and recycled water supplies. The development of these drought-resilient, local water supplies will help achieve the pLAn's ambitious goals of:

Reduce imported water purchases by 50 percent by 2025;
Expand local water sources to 50 percent of total supply by 2035; and
educe per capita water use by 20 percent by 2017, 22.5 percent by 2025, and 25 percent by 2035.

To achieve the extraordinary local water supply development goal, LADWP, Los Angeles County Flood Control District, and Stantec are working in conjunction to increase stormwater capture capacity for groundwater replenishment and to provide social advancement by adding community space, neighborhood greening and passive recreation at the Tujunga Spreading Grounds. This multi-beneficial project will not only recharge the City's groundwater basin to enhance local water supply reliability and sustainability, but also utilize alternative practices to transport soils off-site to reduce traffic, air, and noise impacts to the community.

Project Description

The Tujunga Spreading Grounds (TSG) is a facility owned by the Los Angeles Department of Water and Power (LADWP) and operated by the Los Angeles County Flood Control District (District). TSG has been used to spread water to recharge the underlying San Fernando Groundwater Basin since the 1930's. LADWP's Tujunga Spreading Grounds Enhancement Project (Project) will modernize the facility to meet following key objectives:

Enhancing the facility's stormwater capture, groundwater recharge, and flood control operations;
Increasing diversion capacity and improving surface water quality in the Los Angeles River; and,
Providing open space enhancements to the disadvantaged community.

To provide our customers with safe and reliable water services in an environmentally responsible manner, LADWP plans to strengthen its local water supply thereby decreasing the demand for imported water. Due to urbanization, the majority of rainwater, that historically infiltrated, now flows eventually into the Pacific Ocean. This undervalued resource can be captured and recharged into the groundwater basin for future use.

The Project doubles the stormwater capture capacity to 16,000 acre-feet (AF) per year to replenish the groundwater supply. This additional recharge will promote the utility and sustainability of groundwater production from the underlying basin in lieu of more expensive imported water, with its associated environmental impacts.

Integrated Approach

This Project is a collaborative effort between LADWP, the District, and Stantec. The District is responsible for regional flood control and operates the TSG. Because the Project provides multiple benefits to meet various objectives, it has incentivized the integrated team to develop a comprehensive nature based solution to meet today's challenges.

Imported water has significant greenhouse gas and air pollution impacts due to energy production needed for pumping and conveyance. The Project improves regional water self-reliance by improving the sustainability of local groundwater. When imported water becomes scarce due to drought or emergency conditions, the City will be able to rely on local groundwater to sustain the needs of the nearly 4 million residents.

The improvements to the TSG will enable the region to infiltrate higher volumes and flows of stormwater, attenuate peak flows, and mitigate flood risk. The Project will also improve downstream water quality in the Los Angeles River and Pacific Ocean by decreasing runoff, which in turn reduces pollutant loading in the environment.

Environmental Sustainability and Quality

The Project includes consolidating twenty spreading basins into nine larger basins to increase the storage capacity from 100 to 885 acre-feet. Two new high-flow intakes increase the runoff diversion capacity from 250 to 450 cubic feet per second. All and all, the improved facility will recharge the groundwater basin with infiltration of 16,000 acre-feet of water annually, enough to sustain 48,000 homes in Los Angeles.

As climate change impacts the availability of imported water from hundreds of miles away, this Project promotes a sustainable and reliable local water supply to serve customers and support economic growth. By promoting the use of a less energy-intensive water supply, the Project also helps reduce emission of greenhouse gases that contribute to climate change.

Originality and Innovation

This Project has incorporated multitude of engineering innovation. With a new intake strategically placed downstream of the confluence of Tujunga Wash and Pacoima Diversion Channel, TSG effectively increases the watershed tributary area by 30 percent to over 200 square miles, thus increasing regional flood protection. The additional diversion capacity will also deliver approximately 90% pollutant removal for dissolved metals and 80% removal of Total Suspended Solids of the influent water in support of Total Maximum Daily Load (TMDL) compliance. Further, the Project includes new telemetry system with wireless connection for remote monitoring and control capabilities to enhance operational efficiency. Compared to building new facility with similar capabilities, modernizing the existing TSG brings maximum economical value and limits the environmental impacts.

Additionally, the basin consolidation required export of over 1.6 million tons of soil to nearby disposal sites. The conventional dump truck hauling would disrupt traffic and generate noise and air pollutants in the neighborhoods. Based on community input, the Project elected to use a quiet, emission-less electric conveyor belt system to transport soils off site. Instead of having over 120,000 truck trips over a period of three years, the conveyor belt system completed the export operation successfully within 16 months. The adverse impacts associated with typical grading construction were essentially eradicated with the progressive use of the conveyor belt system.

Complexity

The Los Angeles River Watershed is a high priority watershed under the US EPA's Urban Waters Federal Partnership and the Los Angeles Regional Water Quality Control Board. The Clean Water Act Section 303 (d) identifies the Los Angeles River as an "impaired water body" due to the pollutant level. Currently, stormwater from the Project tributary watershed discharges into Reach 4 of the Los Angeles River. This portion of the river is not concrete lined and collects pollutants and contaminants in its soft bottom bed. This portion of the river also contains high levels of ammonia, coliform bacteria, copper, lead, algae, and trash. Pollutants associated with dry-weather and stormwater runoff are considered significant sources of water quality degradation.

This Project increases runoff diversion capacity from an even larger tributary watershed to support MS4 Permit compliance. The bio-infiltration process provides natural treatment to the runoff as the water percolates. TSG is the biggest stormwater capture and groundwater recharge facility in the region to hedge against adverse effects of global warming and urbanization.

Social Advancement

The TSG is located within a neighborhood with Economically Distressed Areas and Disadvantaged Communities. These neighborhoods are prone to flooding during storm events due to the lack of an adequate storm drain system. The enhanced TSG provides flood mitigation in the area and may result in property value increases.

Additionally, recreational space is very limited in this area. The Project adds much needed passive recreation along with open space for the entire community. This Project will incorporate walking trails to promote public health, an outdoor classroom with educational signage, and habitat restoration for environment awareness.

Click images to enlarge in separate window.