Water Reuse Case Study: Los Angeles County, California

EPA and partners have created a series of case studies that highlight the different water reuse approaches communities have taken to meet their water quality and water quantity needs. Each case study contains information about the technical, financial, institutional, and policy aspects of these water reuse systems and the communities they are located in.

Overview

Los Angeles (LA) County experiences extreme water stress and has implemented numerous reuse projects focused on non-potable and indirect potable reuse of treated wastewater. However, due to increased water efficiency and lowered residential use during droughts, less and less wastewater has been available for existing reuse applications. In LA County, wastewater and stormwater are conveyed through separate sewer networks, which prevent stormwater from overwhelming the sanitary sewer and wastewater treatment plants’ design capacity. However, the separate sewers also prevent stormwater from being available for water reuse at conventional wastewater reclamation plants. Therefore, the LA County Sanitation Districts (LACSD) started building stormwater-sewer diversion projects – engineered structures that bring stormwater into the sanitary sewer at a controlled rate. Stormwater-sewer diversion projects have been funded by the local Safe Clean Water Program and have been implemented after successful collaborations across LA County agencies. These stormwater-sewer diversion projects, which are set for expansion across the region, will help LA County secure a reliable water source for recycled water into the future.

Context

The Los Angeles County Sanitation Districts (LACSD) owns and operates one of the largest wastewater recycling programs in the world, providing affordable, high-quality recycled water to public and private water suppliers. Since the 1960s, recycled water produced by the LACSD has augmented surface water and groundwater supplies to help meet the water supply needs of more than five million people within the LACSD service area. This service area includes 78 municipalities surrounding the City of Los Angeles and adjacent unincorporated areas. Recycled water affordability is a priority because approximately 40% of the population served by the LACSD is considered disadvantaged based on income.

Wastewater generated within the LACSD service area is collected in small local sewers managed by various municipalities, and subsequently conveyed by a regional system of 1,400 miles (2,250 km) of large trunk sewers and 49 pumping plants owned and operated by the LACSD. Wastewater flows through this sewer network to the 11 wastewater treatment plants located throughout LA County. Stormwater generated within the service area is managed as a separate system by other local municipalities, the LA County Department of Public Works, and the LA County Flood Control District, with limited involvement from the LACSD.

Water Reuse in LA County

Ten of the LACSD wastewater treatment plants also serve as water reclamation plants that produce around 150 million gallons per day (570 million liters per day) of disinfected recycled water (in accordance with Title 22 of California’s Code of Regulations). The recycled water is used at more than 900 sites for a variety of non-potable purposes, including street cleaning; seawater intrusion barrier injection; irrigation for parks, schools, golf courses, commercial buildings, and agriculture. The recycled water is also used for indirect potable reuse at the Montebello Forebay Groundwater Recharge Project, where it is injected into groundwater supplies for later drinking water use. The eleventh facility, the Joint Water Pollution Control Plant, which currently discharges 250 million gallons per day (984 million liters per day) of treated wastewater effluent to the ocean, is considering implementing a water purification project to provide an additional source of water for indirect potable reuse via groundwater recharge or for another beneficial use.

In recent years, California has experienced several drought cycles that resulted in significant water conservation efforts impacting the quantity of wastewater generated throughout the LACSD system. Since 2001, wastewater flows in the service area have decreased by approximately 30%, which has reduced the amount of recycled water produced by the water reclamation plants. As the wastewater flow and recycled water production decreased, there was a growing interest in developing additional sources of water.

Solution

The LA Regional Water Quality Control Board identified diverting stormwater runoff to a sanitary sewer system as an opportunity to reduce the amount of stormwater pollutants discharged to waterbodies, while also increasing the amount of water flowing to treatment plants. Over the last 23 years, the LACSD have worked with municipalities across their service areas to implement 14 stormwater-sewer diversion projects that capture and divert a total of 438,848 gallons per day (1.7 million liters per day) of stormwater runoff into the sanitary sewer. As a result of new stormwater priorities and funding opportunities, the number of potential stormwater-sewer diversion projects in the LACSD service area has almost doubled in recent years (Figure 1).

The regional nature of the LACSD wastewater system creates a shared benefit for a variety of communities, by potentially avoiding large capital costs for constructing a project from the ground up in a smaller wastewater collection system. With key regulatory and funding issues addressed (see sections below), the LACSD have had the opportunity to collaborate with local jurisdictions on a variety of stormwater-sewer diversion projects that increase water recycling, remove stormwater pollutants, and achieve other key community benefits regardless of the economic resources in each location. These projects help to reduce LA county’s reliance on other sources of freshwater, such as imported water or groundwater.

map of LA county showing the existing , in progress, and proposed low flow diversion projects — **Figure 1.** Low Flow Diversion Projects. Blue lines are major sanitary sewers managed by LA County. *Source: LACSD*

In LA County, the typical process for implementing a stormwater-sewer diversion project begins with a conceptual design phase, as follows:

A member city or the LA County Department of Public Works approaches the LACSD with a request to divert urban runoff and/or stormwater into the sewer system.
The LACSD staff identify possible sewer tie-in locations and perform an analysis to determine the conditions under which the sewer can accept stormwater from the project. For example, the LACSD staff will ensure that the stormwater will not overwhelm the capacity of the sanitary sewer. In addition, stormwater-sewer diversion projects must include storage (e.g., underground detention facility) to hold water in case heavy rains bring stormwater into the system too quickly.
If approved, the project design is finalized, and the potential discharger (i.e., the entity requesting that stormwater be diverted into the sewer) must obtain an Industrial Wastewater Discharge Permit from the LACSD, which details requirements for the stormwater diversion into the sewer including the maximum allowable flowrate, sampling frequencies, pollutant concentrations, equipment, remote data collection and transmission, and wet weather hold times.

Figure 2. Typical Diversion Facility. Source: LACSD

Although the public may not be aware of the LACSD’s stormwater-sewer diversion program, there is generally a positive public reaction to multi-benefit stormwater projects and for recycled water projects. The public views these projects favorably in large part because they are typically located in/under public parks and often include community enhancements, such as to ballfields or playgrounds. The LACSD are active participants on these types of projects; however, community outreach about the program and its benefits are largely managed by the LA County Department of Public Works.

Policy, Institutional, and Regulatory Environment

Requests to divert captured stormwater to the LACSD sanitary sewer come at a time when many communities across the United States are struggling to manage overflows from their combined sewer systems. Combined sewer overflows release bacteria and other pollutants into local waterways during large rain storms. Although the LACSD Wastewater Ordinance prohibits the discharge of uncontrolled stormwater to the sanitary sewer system, the ordinance allows exceptions on a case-by-case basis if the discharges are controlled and permitted as “industrial wastewater.” The controlled and interruptible diversion of stormwater to the sanitary sewer needs to be managed in a way to prevent overflows. For a diversion to the LACSD system to be approved, a project must have storage facilities and safety features in place to control or halt discharge and can only be located where there is known capacity in the sanitary sewer system. In addition to having a systemic way to record and transmit flow data to a remote user to prevent overflows, the water diverted by these facilities must meet the LACSD pretreatment program’s criteria to avoid impacting the operation of the water reclamation plants.

The first low-flow diversion from the storm drain system to the sanitary sewer system in LA County was constructed in 1991 to protect the health of beach users during dry weather. In the same year, the LA Regional Water Quality Control Board imposed permit requirements on the municipal separate storm sewer system (MS4) of eighty-four cities in LA County, LA County Flood Control District, and LA County unincorporated areas. The requirements were gradually increased with subsequent permit renewals until the issuance of the 2012 MS4 Permit. The 2012 MS4 Permit prohibited non-stormwater discharges (such as over-irrigation) to the separate stormwater sewer and required minimum control measures to reduce pollutants in stormwater discharges. These expanded regulatory requirements made the reduction of urban runoff and stormwater pollution a key priority for municipalities in LA County.

However, the LACSD, as an operator of a sanitary sewer system, was limited in their ability to manage stormwater until California State Senate Bill 485 (SB 485) came into effect in January 2016. SB 485 gave the LACSD authority to assist local jurisdictions with managing and treating urban runoff and stormwater by accepting stormwater into the sanitary sewer system. However, since most cities in LA County did not have a dedicated funding source for stormwater management at that time, there was seemingly little interest in stormwater-sewer diversion systems due to financial constraints.

Financial and Contractual Agreements

The LACSD wastewater management systems are funded primarily through connection fees and service charges. Connection fees are used to fund capital expenditures related to the expansion of sewer and treatment plant capacities and facility replacements or upgrades. Residential service charges and industrial waste surcharges fund operating and maintenance costs. Recycled water produced by the LACSD facilities are provided to local water purveyors pursuant to their individual contracts. The sale of recycled water represents a relatively minor cost recovery for the LACSD that partially offsets the cost of sewage collection and treatment, compared to otherwise discharging the recycled water to waterbodies.

After the passage of SB 485, the LACSD evaluated connection fees and determined they were a significant barrier to implementing stormwater-sewer diversion projects. Because the LACSD rate payers and the residents of local municipalities were the same, and because the sewer system had unused capacity due to water conservation, the LACSD decided to waive connection fees for local municipalities who utilize unused capacity in the sewers and only apply the normal sewer service charges. The costs for LACSD staff to work on stormwater projects are borne by the jurisdiction(s) requesting the service, as SB 485 did not provide funding for managing stormwater and the LACSD are prohibited from using sewer service fees for stormwater projects. Additionally, the jurisdiction that is diverting stormwater or urban runoff is required to pay user fees over the course of the project’s operation. The user fees are based on the stormwater’s chemical oxygen demand and suspended solids concentration, which impact treatment costs, as well as the time of day that discharge occurs, to incentivize discharging during times when sanitary flows are low based on a typical diurnal flow pattern.

In November 2018, the voters in LA County approved Measure W, a parcel tax to increase the local water supply, improve water quality, protect public health, and invest in making communities greener and more livable. Measure W is the funding source for the Safe Clean Water Program, which is administered by the LA County Flood Control District. The Safe Clean Water Program provides funding opportunities for jurisdictions to pursue stormwater projects, including stormwater-sewer diversion projects with the LACSD. The Safe Clean Water Program generates approximately $300 million per year from a parcel tax of 2.5 cents per square foot (approximately 27 cents per square meter) of impermeable surface area (paved/built areas where rainfall cannot be absorbed into the ground and instead runs off as stormwater) on private property in the LA County Flood Control District. The parcel tax amounts to about $83 per year for the median home.

To be considered for Safe Clean Water Program funds, projects are evaluated based on criteria from a combination of five categories: water quality, water supply, community investment, nature-based solutions, and leveraged funds & community. For water quality, a project must estimate pollutant reduction and cost effectiveness. For water supply, a project must estimate the annual average amount of stormwater or urban runoff captured to augment water supplies, whether infiltrated or diverted (such as to a spreading ground or a sanitary sewer for recycled water). Nature-based solutions could include the use of green infrastructure projects which employ managed, restored, or natural wetlands to recharge groundwater aquifers. In areas where soil is not conducive to infiltration, stormwater-sewer diversion to the sanitary sewer is the next best option to secure a water supply benefit through the program. The Safe Clean Water Program has helped make stormwater-sewer diversion projects an economically feasible method to increase water supply. Safe Clean Water Program funds can also be used for operations and maintenance costs, including the LACSD wastewater treatment charges for diversion projects.

To help reduce barriers to obtaining funding for infrastructure projects through the Safe Clean Water Program, a Technical Resources Program provides project proponents with technical assistance to develop project concepts. The Technical Resources Program is structured to help project communities with fewer resources pursue multi-benefit stormwater projects and includes funding for a watershed coordinator to support the involvement of diverse and economically disadvantaged communities. Additionally, the Safe Clean Water Program prioritizes funds for projects that provide benefits to disadvantaged communities, receive community support, or partner with local non-governmental organizations or community-based organizations. Lastly, the Safe Clean Water Program requires that LA County Flood Control District develop public education, school education, and local workforce job training programs with special attention to underserved communities. These equity-focused components of the Safe Clean Water Program have many potential benefits, including increasing the participation of underserved communities in stormwater-sewer diversion projects that contribute to regional water recycling. Projects that have been funded by the Safe Clean Water Program are linked here.

Benefits

The LACSD stormwater-sewer diversion program contributes to the circular economy by facilitating the conversion of pollutant-laden stormwater into recycled water that can be beneficially reused, thus potentially reducing reliance on other potable water supplies in the region. The program also provides another tool to help achieve water quality compliance for their stormwater system by allowing stormwater to be treated at wastewater recovery plants. While project economics are not evaluated by the LACSD, stormwater-sewer diversions are typically more cost-effective than site-specific treatment and onsite reuse because they take advantage of existing infrastructure that benefit from economies of scale. In the context of the Safe Clean Water Program, which provides funding for water projects, stormwater-sewer diversions are a recognized method to address both water quality and water supply concerns. Diversions to portions of the sewer system upstream of the existing water reclamation plants generate additional water supplies immediately. Diversions of stormwater into portions of the sewer system is connected to the Joint Water Pollution Control Plant have the potential to generate additional water supplies in the future, as that facility is upgraded to produce high-quality recycled water for beneficial reuse.

Lessons Learned and Conclusions

Multiple factors have led to the success of the LACSD stormwater-sewer diversion program in increasing the supply of recycled water and providing additional benefits:

Partnerships. The LACSD have partnered with the County, LA County Flood Control District, and local municipalities to implement stormwater-sewer diversion projects.
Organizational structure. The LACSD use in‑house engineers who have extensive knowledge of the sewer system and the overall organization, instead of contracting outside personnel. This has allowed for the successful implementation of the Safe Clean Water Program, which spans across multiple departments.
Data to inform operations. Telemetry, or real time data collection and transmission to remote users allows the LACSD to prevent stormwater-sewer diversions from causing an overflow. The LACSD aim for continued enhancements of the diversion program over time. Currently, most diversions require storage and cease discharge to the sewer when there is 0.1-inch (2.54 millimeters) or more of measured rainfall. The LACSD are working on developing more and better data on how rainfall impacts the sewer system and downstream water reclamation plants, which may allow for diversions for longer periods and/or during light rainfall, with the potential to create more recycled water without additional infrastructure costs.
Sustainability. As a result of water conservation, the unused sewer and treatment capacity have increased over the years. The LACSD stormwater-sewer diversion program utilizes available capacity in existing infrastructure to its fullest potential and allows for urban runoff and stormwater to be beneficially reused, especially when the diversion projects are designed to discharge in the off-peak hours when sanitary flows are lower, such as between 10pm and 6am.
Funding. Creating stormwater-sewer diversion projects to a regional water recycling program requires a continuous funding stream to cover local costs. Funding focused on multiple benefits can allow for stormwater-sewer diversion projects to have a multi-faceted positive impact on communities.

This case study highlights a mature program that has been accepting stormwater diversions to its sanitary sewer system for several decades. The LACSD program demonstrates that diversion of stormwater runoff into the sanitary sewer system can be an effective way to reduce pollutant loads and increase water reuse. The availability of funding has increased the number of proposed diversion projects and allowed for greater inclusion of local communities, especially those in disadvantaged areas. The LACSD hope the stormwater-sewer diversion program will continue to expand over time.

Appendix: Technical Details of a Stormwater-Sewer Diversion Design

Figure 2 shows the required design elements of a typical stormwater and urban runoff diversion project. First is the intake structure, which can be a barrier or drop inlet installed across the storm drain that diverts stormwater into a trash collection manhole. The trash collection manhole includes a bar screen to prevent trash and debris larger than 3/8-inch (approximately 1 centimeter) from passing through to the storage area and eventually to the sewer system. The size of the storage basin depends on the stormwater management objectives for the site. The normal requirement is to hold impounded stormwater for 24 hours after a rain event to avoid potential wet weather impacts to the sewer system and ensure the system does not overflow. Projects are required to use variable speed pumps that can carefully control the discharge to avoid high peak flows. An air gap downstream of the pumps is used to prevent a siphon and to ensure that the final connection to the sewer is gravity-fed. The air gap manhole typically incorporates a check valve and acts as a gas trap to prevent the backflow of water and odors into the diversion system.

The stormwater capture and diversion system must include a flow meter and effluent sampling. In addition to providing feedback for controlling the discharge pumps, the effluent flow meter is used for flow-weighted composite sampling and to assess user fees.

A rain switch installed near the pump station automatically turns off the pumps after 0.1-inch (2.54 millimeters) of rain is detected to prevent discharging when the sewer may be experiencing increased levels of infiltration or inflow. A combustible gas detector is used to protect against explosion hazards and stops flow to the sewer at 20% of the lower explosive limit. The project is required to maintain telemetry to the LACSD supervisory control and data acquisition system so the project pumps can be remotely shut off should any sewer emergency arise. Projects are increasingly incorporating real-time sewer level monitoring to make better use of the available sewer capacity.