Implementation Approach of Advanced Treatment Technologies for 33 Groundwater Facilities in CA

Authors:

  • Ryan Rhoades, Steve Bigley, Nicole Blute, David Laliberte

An overview of the Cr6 levels found throughout the Coachella Valley. 30 of CVWD’s 98 active wells require treatment for Cr6​, with levels that go up to 21 µg/L ​(the CA Cr6 MCL is 10 µg/L).

The CVWD facilities include 4 WBA transfer wells, a 12 mgd WBA Centralized Treatment Facility, 20 SBA treatment sites (total 58 mgd), a Central Resin Regeneration Facility, and 8 miles of pipeline.

A schematic of the WBA treatment facility, which includes pre-filters​, WBA vessels in lead lag​, aeration, clearwell, and pumping​.

A rendering of the SBA treatment site. Most sites are located in residential areas and/or golf courses, as they need to accommodate trucks for resin transfer​.

The CRRF will include a 50,000 sq ft process building, a 15,000 sq ft O&M facility, and brine management facilities. The facility will be adjacent to existing Water Reclamation Plant and close to utilities and a major highway corridor.

The Coachella Valley Water District (CVWD) serves drinking water to a population of nearly 300,000 in a desert community that spans more than 1000 square miles near Palm Springs, California. The new chromium 6 regulation in California impacts more than 30% of CVWD’s groundwater wells that are located throughout the Coachella Valley, requiring the utility to implement a $230M program for more than 78 mgd of its treatment capacity by January 1, 2020.

After a thorough examination of alternative supply/non-treatment approaches​ and careful consideration of treatment technologies that factored in water quality, residuals disposal, operational preferences, and cost considerations, CVWD designed 33 individual facilities that are integrated throughout the water system. One of two types of ion exchange treatment is being implemented depending on water quality for individual wells: weak base anion exchange (WBA) and strong base anion exchange (SBA). WBA resin is single pass with conveyance and treatment of multiple wells at a centralized treatment plant. SBA is multi-pass and requires frequent regeneration. Due to the small footprint of existing well sites and the opportunities for optimization, the regeneration and brine management processes for SBA are handled at a central facility.

A unique aspect of the approach is the central resin regeneration facility (CRRF) that will be the hub for operations of the Cr6 program. SBA resin once exhausted will be transferred from vessels at the well sites every few weeks to months, transported to the CRRF for regeneration, and then transferred back for reloading the resin vessels. The brine waste from the regeneration will have concentrated levels of chromium, selenium, and uranium which will be reduced with additional treatment, and the hazardous solid waste will be taken off-site to a licensed disposal facility. The water recovery efficiency for the process is 99.9%, which was a key driver for CVWD and other agencies in a time of prolonged drought, with the potential for zero liquid discharge with the use of brine crystallizer. Flexibility and redundancy in the design was critical to CVWD, as CVWD has been challenged in the past by treatment systems that have weak links that limit water production and cause operational issues.

The project is being delivered with a construction manager at risk (CMAR) with integration occurring at the basis of design level, which allowed the team to get early input on the constructability, equipment procurement, construction market conditions, and costs. Constructability occurred throughout with an extensive value engineering effort that saved over $40M, saving capital while maintaining flexibility and redundancy. A theory of operations became a guiding principle to integrate end user feedback early in the design approach.

This project serves as a model for how a water agency can tackle a large change to system operations by integrating input from many different groups, incorporating constructability and operations feedback early in the design, and determining how to achieve primary system goals while identifying opportunities to save costs.

For more information, please contact the author at rrhoades@hazenandsawyer.com.

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