Background

The U.S. Section of the International Boundary and Water Commission (IBWC) operates the Nogales International Wastewater Treatment Plant (NIWTP) and the International Outfall Interceptor (IOI), which provide service to both Nogales, Arizona and Nogales, Sonora. The NIWTP has a total capacity of 17.2 million gallons a day (mgd) and currently treats approximately 15.2 mgd of wastewater—about 3.0 mgd from Nogales, AZ and 12.2 mgd from Nogales, SON.

The IOI was built 50 years ago using reinforced and unreinforced concrete pipe ranging in diameter from 24 to 42 inches. It extends approximately 8.5 miles from the border to the NIWTP located in Rio Rico, AZ, with much of the pipeline installed along the Nogales Wash and Potrero Creek.  The IOI has exceeded its useful life and is showing signs of structural deterioration, including corrosion, cracks and wall penetrations. Because of this deterioration, it has been experiencing operational problems, such as groundwater inflow and infiltration and root intrusion, which has resulted in pipeline and manhole failures with untreated discharges to the Nogales Wash.

Description

The project consists of the abandonment of five substandard lateral connections to the IOI, three of which will be relocated to the nearest manhole on the IOI, as well as erosion protection for vulnerable segments of the IOI within the Nogales Wash. The five laterals are:

• Site 1 – Historic Train Station Bathrooms. The lateral connection near Manhole No. 3 no longer conveys wastewater flows and will be abandoned.
• Site 2 – City of Nogales Public Works Parking Lot. The lateral connection downstream from Manhole No. 36 no longer conveys wastewater flows and will be abandoned.
• Site 3 – Fleischer Park Baseball Field. The lateral connection downstream from Manhole No. 39 will be abandoned. A new lateral connection for the field bathrooms will be installed and connected at existing Manhole No. 39
• Site 4 – West Produce Row. The lateral is currently connected to an obsolete manhole at the IOI. Both the connection and the manhole will be abandoned. The lateral will be relocated and connected at Manhole No. 52. Due to the length and bend in the lateral pipe, an additional manhole will also be installed in the lateral pipe. The final steps to decommission the existing substandard manhole will be completed as part of the IBWC project.
• Site 5 – Chamberlain Warehouse. The lateral connection downstream from Manhole No. 52A will be abandoned. The lateral will be extended, including the installation of two bends and clean-outs, and reconnected to the IOI at Manhole No. 52B.

Bank and erosion protection consisting of grouted rock riprap will be installed at critical areas along the east and west banks of the Wash near Produce Row Bridge, for a total length of approximately 2,000 feet. 

Benefits

The project will help reduce the risk of pipeline failures in the IOI, thereby preventing the potential discharge of up to 15.2 million gallons per day (mgd) of untreated or inadequately treated wastewater to the Nogales Wash, a tributary of the Santa Cruz River. It will also protect vulnerable segments of the IOI and other municipal infrastructure by providing bank and erosion protection in the Nogales Wash consistent with the 100-year flood standard.