Background

CESPM operates the water and wastewater systems for Mexicali, Mexicali Valley and San Felipe, Baja California. The Mexicali wastewater system currently serves more than 301,000 connections with coverage reaching approximately 95.5% of households in the city. Wastewater treatment is provided through five plants with a combined maximum capacity of 2,164 liters per second (lps) or nearly 50 million gallons per day (mgd).

Most of the wastewater collection infrastructure in Mexicali was constructed more than 30 years ago, has reached or exceeded its expected useful life and needs to be repaired or replaced. In recent years, CESPM has dealt with several spills from force main infrastructure, often because of deteriorated pump manifolds, valves and other fittings. Most of the automatic air relief valves are no longer functioning, allowing air bubbles to become trapped inside the pipeline. In addition, the high concentration of sulfates in the drinking water, along with the organic matter in the wastewater, is conducive to the formation of hydrogen sulfide (H₂S), which corrodes the pump manifolds. Together, these conditions accelerate deterioration of the infrastructure.

To address this issue, CESPM developed a Strategic Wastewater Plan aimed at eliminating or reducing untreated wastewater discharges to the New River, prioritizing infrastructure rehabilitation activities and identifying potential funding sources. To date, CESPM has undertaken several projects under the plan to rehabilitate 15.5 miles of pipeline and 15 major and small lift stations.

Description

The project consists of the rehabilitation of force mains #1, #3, #4, #6 and #7 as described below:

• Force main #1 – Replace 22 gate valves and 20 automatic air relief valves;
• Force main #3 – Replace 16 gate valves, 2 water hammer valves and 10 automatic air relief valves;
• Force main #4 – Replace 35 gate valves, 2 water hammer valves and 33 automatic air relief valves;
• Force main #6 – Replace 15 gate valves, 2 water hammer valves, 9 automatic air relief valves and a pump manifold with fittings; and
• Force main #7 – Replace 11 gate valves, 2 water hammer valves, 4 automatic air relief valves and a pump manifold with fittings.

 In addition, 34 concrete valve boxes, as well as a Supervisory Control and Data Acquisition (SCADA) system will be installed.

Benefits

The rehabilitated infrastructure will improve system reliability by reducing the risk of pipeline failures that can cause sewage overflows onto local streets and into the New River, which flows northward into the United States. Specifically, the project will help protect public health and the environment by preventing approximately 1,961 liters per second (lps) or 44.8 million gallons per day (mgd)of wastewater discharges. As a result, the project will improve wastewater services for more than 235,000 existing residential connections.