Centralized Groundwater Treatment System

Project Manager: Frank HeldmanStart Date: August 2016End Date: Spring 2024


The Centralized Groundwater Treatment System (CGTS) uses state of the art technology to treat and remove contaminants from the groundwater. The project is partially funded by the Prop 84 grant that is administered by the California Department of Water Resources for projects related to water quality and supply, flood control, water pollution, and water conservation. Total cost for the new treatment system is $14.9M of which $4.13 is provided by the Prop 84 grant funds and $4M, a zero interest loan provided by the San Gabriel Valley Municipal Water District (SGVMWD).


The new treatment system is incorporated into the City’s Delta Plant that is located at 2657 Delta Ave. in the City of Rosemead. At the Delta facility is the Water Division’s Production office where the wells, reservoirs and booster pumps are monitored via the Supervisory Control and Data Acquisition (SCADA) system. For a map showing the location of the project please click here

UV/AOP Treatment System

The Centralized Groundwater Treatment System uses Advanced Oxidation Process (AOP) technology to remove contaminants from the groundwater. The AOP equipment that was selected is the TrojanUVPhox system: It is made up of nine ultraviolet (UV) reactors that are configured into three parallel trains, stacked three high each, with three reactors in each series. UV, with AOP, is highly effective at destroying volatile organic compounds (VOC) and 1,4 dioxane that are currently present in the City’s groundwater basin. The City had previously relied on conventional technologies of air stripping and granular activated carbon (GAC) for contaminant treatment. However, 1,4-dioxane - a solvent stabilizer - requires more advanced treatment technology. Its low volatility and high water solubility render air stripping ineffective, and it is poorly adsorbed to GAC. 

PFAS Removal

In late 2020, construction of the CGTS was near complete and the UV/AOP system was ready to permit. However, at this time, trace levels of per- and polyfluoroalkyl substances (PFAS) – a group of chemicals used to make products fire, water, and stain resistant such as fire-fighting foams and paints – were found in the groundwater basin. The Division of Drinking Water requested that the City incorporate into the CGTS a PFAS removal system that would treat PFAS to a non-detect level. The PFAS system consists of 22 vessels of carbon media tanks that are configured into a lead-lag system with 11 pairs. The first (lead) set is responsible for removing all contaminants until a breakthrough is detected. Once that occurs, the lead vessels are taken off line while the secondary (lag) vessels take on the lead position. In 2021, the City began construction of the PFAS removal system. The PFAS remediation component consisted of the addition of a new granular activated carbon (GAC) tank and the re-purposing of existing tanks (previous Dual Barrier treatment system). Construction required new and reconfigured piping to link the CGTS to the GAC tanks. The Design-Build team also tested various GAC media to determine the most effective type for removing contaminants.


The Centralized Groundwater Treatment System with the PFAS removal component was completed in May 2023 and after rigorous testing and water analysis sampling for six months, the Division of Drinking Water permitted the new system. The City started producing potable water on November 6, 2023.

For more information, contact Public Works at (626) 307-1320.