Patagonia, Arizona, USA

Construction of the Wastewater Treatment Plant and Sewer Collection System Improvements for the town of Patagonia,Arizona

Status: Completed


Constructed in 1978, the existing wastewater treatment plant uses an extended aeration process for treatment and has the capacity to treat an average daily flow of 80,000 gallons. Effluent is discharged into Sonoita Creek, a tributary of the Santa Cruz River.

In November 1996, the U.S. Environmental Protection Agency (EPA) issued Patagonia a Notice of Violation because the plant’s effluent exceeded permitted parameters for several contaminants. In addition, its discharge monitoring reports indicate that the facility’s current treatment process is not consistently removing total nitrogen as required by National Pollutant Discharge Elimination System (NPDES) permit limits.

The town’s sewer system was installed in 1965, and there have been only a few line additions and modifications since that time. There are approximately 406 sanitary sewer connections servicing mainly residential customers.

Based on periodic inspections, the Arizona Department of Environmental Quality (ADEQ) has determined that deteriorated sections of the sewer system are allowing infiltration of excess water volumes, especially during heavy rainfall events. The resulting wastewater flow rates during these events exceed current plant capacity, allowing solids and pollutants to mix with the effluent. In addition, excessive volumes of wastewater bypassed treatment and were diverted into the existing lagoons. Since the lagoons are not lined there is concern that the untreated wastewater could percolate to the bottom of the lagoons and pollute the aquifer.


The project consists of constructing a new wastewater treatment plant and rehabilitating the wastewater collection lines. The project is divided into two phases, as follows:

Phase I: Wastewater Treatment Plant
Construction of a new 110,000 gallon per day, extended aeration wastewater treatment facility, including head works, anoxic basin for denitrification, two aeration basins, a clarifier, three-basin chlorine contact chamber, dechlorination and flow meter chamber, aerobic sludge
digester, and sludge processing equipment.

Phase II: Sewer System
The wastewater collection system improvements include replacing approximately 612 lineal feet of 6- and 8-inch asbestos cement sewer pipes with new plastic sewer pipes, as well as the lining of approximately 6,545 lineal feet of sewer pipes ranging from 6 to 10 inches in diameter.


The improved treatment facilities will produce a better quality effluent that complies with U.S. norms for ambient water quality. Rehabilitation of the sewage collection system will reduce the amount of untreated wastewater leaking from deteriorated lines and infiltrating into the ground water or pooling at the surface, as well as reduce peak flows to
the treatment plant. As a result, the environment will be improved and health risks will be reduced for Patagonia residents.

Project Financing

Total Project Cost US 2.4M
NADB Funding US 1.32M - NADB Grant: BEIF
Other Funding Partners Border Environment Infrastructure Fund ( BEIF)
U. S Department of the Agricultural Rural Development ( USDA - RD)
State of Arizona - Community Development Block Grant (CDBG)
Arizona Water and Infrastructure Authority ( WIFA)