Challenge: To produce an updated engineering report for the ARC that complies with the California Code of Regulations, Title 22, chapter on water recycling criteria for indirect potable reuse.

Solution: WRD manages groundwater for approximately four million residents in southern Los Angeles County across 43 cities. Groundwater constitutes over 40% of the total water demand within the 420-square mile service area, amounting to around 220,000 acre-feet per year (AFY). WRD's core objective is to ensure a reliable supply of high-quality groundwater through clean water projects, water supply programs, and effective management practices. WRD also aims to eliminate the need to import water. ARC is one of the projects developed by WRD to achieve these goals. The ARC Project aims to replace up to 21,000 AFY of imported water for groundwater replenishment via surface spreading of advanced treated water (ATW) at the Rio Hondo and San Gabriel Spreading Grounds, also known as the Montebello Forebay Spreading Grounds (MFSG). In compliance with Title 22 regulations, INTERA worked closely with WRD to prepare a five-year update to the engineering report that addresses changes and evolution with the ARC Project, integrates data collected during the previous five years, and effects regulation updates. The report outlines how the ARC Project meets regulatory requirements and water quality limits, describes operations and water quality for source water from San Jose Creek Water Reclamation Plant, and summarizes characteristics of the basin, groundwater, and groundwater recharge impacts.  It also presents travel and response retention time of the ATW introduced at the MFSG, details the advanced water treatment process and recycled water quality, and delineates the monitoring and reporting program, including updated requirements for Contaminants of Emerging Concern (CECs) per amendment recycled water policy.  

Results: The updated ARC Five-year Engineering Report complies with Title 22 regulations and the Water Quality Control Policy for Recycled Water. It was delivered on schedule to the appropriate state regulatory agencies and is pending approval.