Background

The Ímuris wastewater collection system provides service to approximately 64% of the population. The network of pipes operates by gravity and collects approximately 14.5 liters per second (lps) or 330,890gallons per day (gpd) of wastewater, which is treated at the Ímuris Wastewater Treatment Plant (WWTP) constructed in 2021 by the Sonora state water agency (CEA) with a capacity to treat up to 29.4 lps (670,908 gpd).[1]

The wastewater collection system was built more than 30 years ago, has deteriorated and is vulnerable to collapse and leaks. In particular, the El Centro Collector overflows during rainstorms causing discharges of untreated wastewater to the Babasac River, which flows into the Magdalena River. Moreover, residents in unserved areas of the city dispose of their wastewater in rivers or substandard septic tanks, latrines and cesspools. OOMAPAS has been working with CEA to address deficiencies in the existing wastewater collection system and to expand coverage to unserved areas once the core infrastructure has been rehabilitated.

Moreover, OOMAPAS currently has a roto-rooter but needs to rent other equipment as necessary for operational purposes. A backhoe is needed to carry out certain maintenance activities and to make repairs to the wastewater collection system, which would improve the performance and sustainability of the utility.

[1] OOMAPAS is in the process of obtaining the discharge permit from Mexican National Water Commission (CONAGUA). The plant complies with Mexican standard NOM-001-SEMARNAT-1996 but will have to be upgraded to meet the requirements under the new standard NOM-001-SEMARNAT-2021.

Description

The project consists of the following improvements to the wastewater collection system:

• Force main and lift station. Installation of 14,406 ft of 12-inch polyvinyl chloride (PVC) pipe and 502 ft of carbon steel pipe for the conveyance line and improvements to the lift station, which include the installation of a sand/grit chamber, three 20-HP pumps, a 46-kilovolt-amp (kVA) electrical substation, an engine control station, valves and fittings, and electrical equipment.
• El Centro Collector. Replacement of 4,514 ft of concrete pipe with 10- to 18-inch PVC pipe, along with 680 ft of 10 to 12-inch carbon steel pipe.
• Sewer lines. Replacement of approximately 1,345 ft of concrete pipe with 8-inch PVC pipe, including the installation of 50 new residential connections.
• Acquisition of equipment. Purchase of a New Holland Model B90B (2WD) backhoe for operation and maintenance.

The lift station improvements and force main construction were completed by CEA in 2021.

Benefits

The rehabilitated infrastructure will improve wastewater collection services for 1,742 existing residential connections by reducing the risk of pipeline failures that cause sewage overflows onto local streets and contaminate surface and groundwater. Specifically, the project will help protect public health and the environment by preventing up to 14.5 lps (330,890gpd) of wastewater discharges to the Babasac River, which flows into the Magdalena River. Additionally, the Project will provide first-time service to 50 homes and improve the ability of the utility to operate and maintain the wastewater system with the acquisition of a backhoe.