Thomas Groundwater Treatment Facility and Improvements to the Central Groundwater Treatment Facility


Project Information

The city of Scottsdale is constructing a new Reverse Osmosis water treatment facility, the Thomas Groundwater Treatment Facility (TGTF), on Thomas Road adjacent to the existing Central Groundwater Treatment Facility (CGTF) at Pima Park. In addition to the new treatment plant, the CGTF will be undergoing operational improvements that will include the construction of a new building within the walls of the existing plant.

About the CGTF

The CGTF treats water pumped from groundwater aquifers in south Scottsdale that contain Trichloroethylene (TCE). The aquifers collectively make up the EPA-designated Superfund site North Indian Bend Wash.

In November of 2015 funds to design and build the station were approved by the voters as part of the bond election held in November 2015.

Through airstripping technology, the CGTF removes the TCE from the groundwater to provide both a clean-up remedy for the aquifers and to allow the water to be used for the Scottsdale community. The facility removes TCE from the water to a level that is considered non-detect (less than 0.5 parts per billion), and is far below the EPA standard of 5 parts per billion.

The current operational improvements are not related to the superfund cleanup. Additional information is available on our North Indian Bend Wash Cleanup web page.

Why is the new plant – the TGTF – necessary?

The CGTF treats water from four different wells in south Scottsdale, each of which presents a different water quality challenge. To meet Scottsdale’s high water quality standards, the treated water from the various sources must currently be blended together through a complex, operationally challenging blending scheme.

The TGTF will receive and treat a side stream of product water discharged from the CGTF. The treated side stream will then be blended with the remaining CGTF product water to achieve the desired finished water quality and eliminate the need for multiple blending plans.

Reduced Water Hardness

The chemistry of the raw water treated at the CGTF – like most of the source water in the southwest – is characterized as very hard. This natural hardness, combined with the airstripping process, has resulted in scale formation within the CGTF and in the distribution system, which has created an ongoing operation and maintenance challenge and has been an ongoing customer concern. The TGTF and operational improvements to the CGTF will have the added benefit of reducing hardness in the finished water.

Frequently Asked Questions

The Thomas Groundwater Treatment Facility (TGTF) is Scottsdale Water’s newest treatment facility that opened in 2021.

In order to meet Scottsdale’s high water quality standards, TGTF works in conjunction with the Central Groundwater Treatment Facility (CGTF) to treat water to drinking water standards (or higher) before sending it into the drinking water system and to customers. The CGTF removes Trichloroethylene (TCE) and the TGTF removes a suite of groundwater contaminants including nitrates and arsenic. As a side benefit the TGTF will also reduce the levels of hardness in the service area to levels similar to the rest of the system.

Prior to the 1980s, Scottsdale was 100% reliant on groundwater for its water supply. Today, 90% of the total water supply comes from renewable surface water sources and recycled water, helping to ensure a long-term water supply for future generations.

Depending on the time of year, the weather and customer demand, customers may receive water from a single source or from a combination of sources. CGTF and TGTF receive and treat water from up to four nearby groundwater wells.

CGTF is owned and operated by the city of Scottsdale and is able to treat water pumped from (up to) four groundwater wells located within the North Indian Bend Wash Superfund site. Water produced by the plant removes the contaminant of concern (TCE) from the water to non-detectable levels. The site is under the oversight of the EPA in cooperation with ADEQ.

The new Reverse Osmosis (RO) water treatment facility works in conjunction with CGTF but is not part of the superfund project. TGTF receives and treats a portion of the water received from CGTF and undergoes the RO purification process. This treated water supply is then blended with the remaining treated CGTF product water to achieve the desired water quality. The TGTF allows Scottsdale Water to pump from any of the four wells feeding the CGTF without having to blend the wells with other water sources. It provides for operational flexibility and eliminates the need for multiple blending plans. Additionally, the TGTF reduces the hardness from these wells and produces water that is equivalent in hardness to other areas of the city.

RO is a semi-permeable membrane separation process capable of removing dissolved solutes from water based on their size or molecular weight and ion charge. The RO system at TGTF holds 72 vessels made up of these membrane sheets which are rolled together in a spiral formation similar to a paper towel roll. Water is introduced into the larger area of the membrane element on one end and makes its way through the membrane sheets until it gets to the center tube. The water at this point is considered clean and referred to as RO permeate.

TGTF is able to process and treat 1.5-million gallons of water a day or 5.4-billion gallons per year.

Project Information

Budget: $25.1 million

Sponsoring Division: Water Resources

Funding Source: Water Rates & Municipal Property Corporation Bonds

Project Location: Northeast corner of Hayden and Pima roads

Contact Information

City of Scottsdale - Capital Project Management

7447 E. Indian School Road
Scottsdale, AZ 85251
P: 480-312-7250

Elaine Mercado, Project Manager
P: 480-312-7985
[email protected]

Proposed Improvements

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