The city of Santa Monica harvests runoff, rainwater to meet sustainability goals
The city of Santa Monica, Calif., recently completed the installation of the Los Amigos Park Water Harvest and Direct Use Demonstration Project. The project received partial funding through the Foundational Actions Funding (FAF) Program with the Metropolitan Water District (MWD) as an exemplar pilot project.
Long- & Short-Term Goals
The project involved diverting storm water, which initially was rainwater from private and public parcels that flowed off of properties and entered the municipal separate storm sewer system, and dry-weather runoff—also called urban runoff—from a nearby storm drain via a drop box. Flows then are conveyed through a pretreatment screening-separation system, stored within a subsurface storage system, and treated with a strainer and an ultraviolet (UV) treatment systems for onsite non-potable dual uses, such as spray irrigation and restroom flushing.
The purpose was to demonstrate the feasibility of harvesting local runoff, mainly storm water, from the storm drain system for non-potable uses, which will decrease potable water demand, reduce pollutant loads discharging into the receiving waters and protect the water supply. The project aligns with the city’s goals of achieving water self-sufficiency by reducing the demand for portable or imported water and complying with the NPDES municipal separate storm sewer system requirements set forth in the Enhanced Watershed Management Plan (EWMP).
The project seeks to contribute to the city’s 2022 goal of water self-reliance on local water resources and supplies. This project replaces potable water used for irrigation and flushing with non-potable water from the collection and treatment system, thereby saving potable water for uses such as drinking, cooking and bathing. By reducing potable water use and collecting local water resources, the city also reduces its use of imported water, which is transported from the Colorado River and Sacramento Delta hundreds of miles away and pumped at a great energy intensity, and leaving more water in those distant and valuable watersheds. Such a project raises the sustainability of the city. By keeping this runoff on site instead of discharging it into Santa Monica Bay, the city keeps out a variety of pollutants that cause harm to people recreating in its water and to marine species. Preventing water pollution also helps the city meets its regulatory obligations of the Clean Water Act.
For this project, the city collects rainwater from upstream parcels where and when it is not feasible or economical to promote or require enough parcel onsite rainwater collection systems for use of water on individual parcels to offset non-potable use.
The Los Amigos Park Runoff Collection, Treatment and Use Retrofit Project may be one of the first projects to collect offsite runoff, including dry-weather runoff and storm water, and treat and use the runoff onsite for spray irrigation and bathroom flushing.
Primary treatment involves a screening-separation vault.
Parts of a Whole
The project has six components. A diversion box diverts runoff from the storm drain line via a drop box to a lower pipe and into the pretreatment and storage tank. A screening-separation vault is used for primary treatment. Runoff from the diversion box enters this “vortex” device, where the runoff swirls inside and a 5-mm screen separates or screens out all materials 5 mm and larger from the water. Filtered water continues to the storage tank under right field of the park’s baseball field. Vault doors allow easy access for cleaning and repairs.
In addition, a 55,000-gal storage tank is composed of 18 precast concrete U-shaped pieces, sealed to make the tank watertight. The tank is under right field of the baseball field. Next, stored runoff in the tank flows via gravity into the wet well, where two pumps send the water to final treatment and use, upon demand, whether for nighttime irrigation or daytime restroom flushing. The final treatment or polishing system includes strainer and ultraviolet disinfection systems.
Additional filtering removes fine materials to prevent clogging of the irrigation and flushing components. Disinfection kills or neutralizes microorganisms to protect public health. Signage on public displays explain the purpose of the project and its components. Finally, a touch-screen monitoring control panel is used to check flow, tank level and pumps status.
The strainer removes fine materials in the final stages.
The total cost of the project was $1.8 million, including a grant of $400,000. The drainage area is 32 acres (50 acres total, but 64% impervious), and the runoff volume collected is 550,000 gal harvested annually, based on average annual rainfall.
This project offered important takeaways. The use of rainwater and storm water for non-potable irrigation applications offers a significant opportunity in water management to maximize local water resources to supplement or displace potable water, leaving more freshwater in our surface and groundwater resources. In addition, treatment systems are readily available and offer safe ways to utilize rainwater and storm water, and protect health. Furthermore, existing, safe and reliable plumbing design, standards and permitting procedures exist. Alternatively, no technical treatment or health and safety obstacles exist. There only is a lack of political will or the fear to try something unconventional, though tested and proven to work.
Overall, the project demonstrates how harvesting storm water in centralized downstream locations offline from the main storm drain system can be an effective and economical rainwater and storm water management strategy.
Treated rainwater and storm water from a properly designed, installed and maintained harvesting system can be used for all traditional water uses. Rainwater harvesting should be part of any effective and sustainable local approach to water management. The key is to build on the existing positive record, and ensure rainwater and storm water utilization become commonplace. Harvested water can become part of new construction, major redevelopment and retrofit construction, and become available at a reasonable cost with the least regulatory impact to anyone who is willing to invest in a system.