| ITEM #: 8. DATE: 09/28/2026 AI #:3481 |
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CITY COUNCIL ACTION REPORT
| SUBJECT: | AUTHORIZE CONSENT ORDER WITH MARICOPA COUNTY ENVIRONMENTAL SERVICES DEPARTMENT |
| STAFF PRESENTER(S): | Barbara Chappell, Water Services Director |
SUMMARY
Authorize the Water Services Director to enter into a Consent Order agreement with the Maricopa County Environmental Services Department on behalf of the city, outlining the city’s required compliance actions in response to recent Total Trihalomethane (TTHM) level exceedances.
STRATEGIC PLAN ALIGNMENT
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RECOMMENDATION
Authorize and direct the Water Services Director to enter into a Consent Order agreement with the Maricopa County Environmental Services Department and to take actions and execute documents necessary to carry out the intent of the agreement. (Barbara Chappell, Water Services Director)
FISCAL IMPACT
There is no direct fiscal impact related to the approval of this item. The $2,000,000 cost for the purchase and installation of two (2) trailer mounted granular activated carbon (GAC) vessels referenced in the Consent Order agreement were previously approved by Council on August 31, 2026, and September 14, 2026, utilizing savings from the Water Services Department’s (Water Services) Brine Management Projects (60034 and 610015). Annual maintenance costs are estimated to be $100,000.
BACKGROUND AND PREVIOUS ACTIONS
The city’s water system has recently experienced elevated levels of TTHM, which is a group of disinfection byproducts formed when chlorine reacts with naturally occurring organic material in source water. The city’s water system is comprised of both groundwater and surface water sources. While groundwater sources typically show very low organics, surface water sources can experience increased levels due to the presence of algae, bacteria and aquatic plants in our lakes and canals. TTHMs are regulated by the United States Environmental Protection Agency’s Stage 2 Disinfection Byproducts Rule with a maximum contaminant level (MCL) of 0.080 parts per million (ppm) running annual average (RAA). TTHMs are required to be tested quarterly, and regulations measure the RAA is across the current quarter and the previous three quarters.
TTHMs include four species - chloroform, bromodichloromethane, dibromochloromethane, and bromoform. All are volatile and can be reduced through an aeration process. Bromoform is the least volatile and is therefore more difficult to remove through aeration. Due to the typical organic content levels in the city’s surface water, aeration systems were installed at two of the city’s potable water storage tanks (reservoirs 13 and 23) when the city’s surface water treatment facility became operational in 2022. However, the city’s surface water source has recently seen higher levels of bromoform, making the city’s existing aeration and treatment systems less effective in mitigating TTHM levels. Other Valley water providers are experiencing similar conditions and similar elevated TTHM levels.
Water Services’ recent water test results showed TTHM exceedances of the MCL for the calculated RAA in the 2nd quarter of 2026 and the 3rd quarter of 2026. The 2026 2nd quarter RAA exceedance occurred at two sampling locations with a calculated RAA of 0.081 ppm at one sampling location and 0.084 ppm at another sampling location. The 2026 3rd quarter RAA exceedance also occurred at two sampling locations with a calculated RAA of 0.082 ppm at one sampling location and 0.086 ppm at another sampling location. These exceedances in the 2nd and 3rd quarters of 2026 triggered two public notifications within thirty (30) days of the violations.
Based on these results, Water Services developed a plan to correct the regulatory violations, which includes implementing operational changes such as adjusting chlorine dosage, replacing aeration equipment, optimizing storage tank operations, and conducting targeted flushing. In addition, Water Services has purchased portable GAC treatment vessels, which will be installed at two of the city’s potable water storage tanks (Reservoirs 13 and 23) to provide additional TTHM removal capacity. Water Services expects the GAC treatment vessels to be operational in October 2026.
TTHMs include four species - chloroform, bromodichloromethane, dibromochloromethane, and bromoform. All are volatile and can be reduced through an aeration process. Bromoform is the least volatile and is therefore more difficult to remove through aeration. Due to the typical organic content levels in the city’s surface water, aeration systems were installed at two of the city’s potable water storage tanks (reservoirs 13 and 23) when the city’s surface water treatment facility became operational in 2022. However, the city’s surface water source has recently seen higher levels of bromoform, making the city’s existing aeration and treatment systems less effective in mitigating TTHM levels. Other Valley water providers are experiencing similar conditions and similar elevated TTHM levels.
Water Services’ recent water test results showed TTHM exceedances of the MCL for the calculated RAA in the 2nd quarter of 2026 and the 3rd quarter of 2026. The 2026 2nd quarter RAA exceedance occurred at two sampling locations with a calculated RAA of 0.081 ppm at one sampling location and 0.084 ppm at another sampling location. The 2026 3rd quarter RAA exceedance also occurred at two sampling locations with a calculated RAA of 0.082 ppm at one sampling location and 0.086 ppm at another sampling location. These exceedances in the 2nd and 3rd quarters of 2026 triggered two public notifications within thirty (30) days of the violations.
Based on these results, Water Services developed a plan to correct the regulatory violations, which includes implementing operational changes such as adjusting chlorine dosage, replacing aeration equipment, optimizing storage tank operations, and conducting targeted flushing. In addition, Water Services has purchased portable GAC treatment vessels, which will be installed at two of the city’s potable water storage tanks (Reservoirs 13 and 23) to provide additional TTHM removal capacity. Water Services expects the GAC treatment vessels to be operational in October 2026.
STAFF ANALYSIS
Water Services staff have been working with the Maricopa County Environmental Services Department (MCESD) on the city’s plan to correct the regulatory violations. MCESD is in agreement with the city’s compliance plan and has asked the city to formalize its plan through a Consent Order agreement (Attachment A). Under the terms of the Consent Order agreement, within 120 days of the effective date of the agreement, the city is required to obtain approvals to construct the two GAC treatment vessels, complete the installation of the two GAC treatment vessels, and obtain an Approval of Construction from MCESD for the completed installation.
As noted above, the two GAC treatment vessels have been ordered and are expected to be delivered by October 12, 2026. The permit application has been submitted and will be handled on an expedited basis by MCESD. Water Services staff anticipates that the two GAC treatment vessels will be installed and the Approval of Construction will be issued by the end of October 2026.
Once the Approval of Construction for the two GAC treatment vessels has been issued, the Consent Order requires the city to undertake monthly testing in addition to the required quarterly testing. However, if the TTHM levels in the four quarterly compliance samples taken following the issuance of the Approval of Construction do not result in TTHM exceedances, the city will be relieved of its obligations to conduct the monthly testing and can seek termination of the Consent Order.
The alternative to the Consent Order is for MCESD to pursue penalties for violations of applicable regulatory requirements; therefore, Water Services staff recommend Council authorize the Water Services Director to execute the MCESD Consent Order agreement on behalf of the city.
As noted above, the two GAC treatment vessels have been ordered and are expected to be delivered by October 12, 2026. The permit application has been submitted and will be handled on an expedited basis by MCESD. Water Services staff anticipates that the two GAC treatment vessels will be installed and the Approval of Construction will be issued by the end of October 2026.
Once the Approval of Construction for the two GAC treatment vessels has been issued, the Consent Order requires the city to undertake monthly testing in addition to the required quarterly testing. However, if the TTHM levels in the four quarterly compliance samples taken following the issuance of the Approval of Construction do not result in TTHM exceedances, the city will be relieved of its obligations to conduct the monthly testing and can seek termination of the Consent Order.
The alternative to the Consent Order is for MCESD to pursue penalties for violations of applicable regulatory requirements; therefore, Water Services staff recommend Council authorize the Water Services Director to execute the MCESD Consent Order agreement on behalf of the city.