Background

Water service is currently provided to an estimated 80% of the city’s population, while sewer services are provided to only 65%. Residents not connected to the sewer system discharge wastewater to open drains, latrines or cesspools. This raw sewage leaks or flows directly into the ground contaminating the soil and water resources and increasing health
risks from water-borne diseases.

The utility operates a lagoon-based wastewater treatment plant with a design capacity of 365,000 gallons a day. However, the facility is overloaded and discharges inadequately treated wastewater that flows overland into the Sonoyta River, where it seeps into the subsoil or evaporates. In addition, the lagoons have silted up, are surrounded by weeds, and have become a source of pollutants, odors and mosquitoes for the city. Any additional sewer connections would overwhelm the system.

To address these deficiencies, the utility plans to construct a new treatment plant with almost double the treatment capacity of the existing plant, as well as increase waster collection coverage from 65% to 88% of the population.

Description

The project consists of the following main components:

Wastewater collection system
The expansion of the sewer systems in the neighborhoods of: Ejido Hombre Blanco, Ejido Pápagos, and Barrio Las Botellas, including:

• Construction of 3.84 miles of sewer lines;
• Construction of a collector and sewer main to convey the wastewater to the new plant;
• Installation of 720 new sewer hookups, benefiting 2,880 people.

Wastewater Treatment Plant
Construction of the first phase of a new lagoon-based wastewater treatment system with the capacity to treat 685,000 gallon a day, consisting of an anaerobic lagoon, a facultative lagoon, and a polishing lagoon. The new facility will be located 2.6 kilometers west of the city limits and includes a lift station.

Although not part of this project, the plant design includes a second phase for expanding the facility an additional 228,000 gallons a day, which would provide sufficient capacity to address the needs of the municipality for the next 20 years.

Benefits

The project will provide first time sewer service to currently unserved areas, increasing wastewater collection coverage from 65% to 88% and reducing the potential for human contact with raw wastewater and organisms that are vectors for associated diseases. The new treatment plant will reduce contamination of the Sonoyta River and its effluent will meet federal standards for reuse in irrigation, thereby reducing the need for groundwater pumping and drawdown. In addition, foul odors and disease-carrying insects resulting from inadequately treated wastewater and overloaded treatment lagoons will be reduced.