The City of Los Angeles recently broke ground on a project to divert roughly one million gallons per day of polluted urban runoff away from the ocean and into existing sanitary sewers. The $13-million Low Flow Diversion project will provide new water filtration infrastructure to remove waste flows from five sub-watersheds in the Los Angeles River and Arroyo Seco River.
The job, which began in July, is being led by design firm Stantec, in collaboration with the Los Angeles Department of Public Works Bureau of Engineering (BOE) and Los Angeles Sanitation & Environment (LASAN).
“This is one design project with two construction packages,” says Seth Carr, project engineer for the LASAN Watershed Protection Division. “The LA River LFDs have three sites and the Arroyo Seco has two sites. They were separated into two packages based on where they are discharging.”
Clarke Contracting Corporation is doing construction for the LA River LFD projects, and Mike Pirch and Sons is handling construction for the Arroyo Seco LFD projects.
The LA River runs 51 miles from the mountains north of Los Angeles to the ocean in Long Beach, and the Arroyo Seco is a seasonal stream running 25 miles from the San Gabriel Mountains to Elysian Park in Los Angeles.
“The City of Los Angeles is under total maximum daily loads (TMDL) guidelines for bacteria and toxics and other types of pollutants in our water bodies, so the need for this project is to enhance the water quality in our Arroyo Seco/LA Rivers and ultimately the oceans,” says Naushin Kamal, BOE project manager.
Both the LA River and the Arroyo Seco are negatively impacted by multiple pollutants contained in dry-weather flows. At times, high levels of bacteria in the two waterways rival that of wastewater, say project officials. Heavy metals and petroleum products are also washed into storm drains and waterways. Dry-weather flows are usually a combination of runoff from car washing, lawn sprinkling, pet waste, motor oil, detergents, trash and watering of plants/gardens.
Hyperion Plant Treatment
When complete in November 2022, the project will divert about one million gallons per day from storm drains into existing sanitary sewers and to the City’s Hyperion Water Reclamation Plant for treatment.
The Hyperion plant recently faced a major clog that flooded the facility and forced it to release 17 million gallons of untreated wastewater into Santa Monica Bay July 11. Potentially toxic odors from the under-repair plant made local residents sick, and the LA County Dept. of Health advised affected residents to stay indoors as much as possible.
Hyperion officials say the clog has been fixed and the plant is back to normal operations with both air and water quality back at pre-July 11 levels.
“Hyperion is designed for 450 million gallons per day average daily flow and currently receives 260 million gallons per day,” says Timeyin Dafeta, Hyperion executive plant manager. “Therefore, Hyperion can take the additional one million gallons per day from the Low Flow Diversion project.”
The city wants to use the LA River and Arroyo Seco for more recreational purposes, and diverting harmful low-flow water is a perfect way to enhance the waterways while giving the city additional resources through water reclamation, says Venu Kolli, Stantec senior principal and project manager.
Each of the five LFD systems will consist of a diversion structure, trash maintenance hole, pump well, valve vault and metering vault. The facilities will be constructed between 18 ft and 28 ft below ground.
“The fascinating challenge is construction of the below grade facilities on busy streets in downtown Los Angeles and making sure there is no impact to existing utilities such as water, gas, sewers, electric and cables etc,” says Kolli. “Since we are tapping into an existing storm drain in busy streets, locating these facilities in an area with minimum impact to the public, businesses, and utilities is very important.”
To avoid construction issues, Kolli says the project team planned during preliminary design and identified all utilities by reviewing street plans and as-built drawings of the utilities. The team performed potholing of known utilities to confirm the location and depth so designed facilities were away from these structures.
“We performed ground penetrating radar to identify unknown utilities and conducted public outreach meetings to educate the public about project impacts before advancing to the design stage,” he says. “We also developed shoring plans so construction stays within the approved limits of the road, and prepared traffic plans to minimize traffic disturbances during construction.”