The second stage of the work under this contract includes the construction of a dam of loose materials with concrete facing, a plant equipped with two 35 MW Francis turbines, a flood spillway with no floodgates and an open channel, upstream and downstream cofferdams, power-generation works using a pressure conduction, the external machine housing and the adduction tunnel to transport water from the reservoir.

The dam will be raised to 83 meters above the riverbed and 113 meters from the bedrock foundation. The length of the crown will be 450 meters and will have a volume of 7,894,964 m³ of alluvial material filling and a concrete facing of 76,000 m². The flood spillway, located on the right bank, will be free and have a total landfill of 250 m. It has been designed to evacuate a overflow of 3,200 m³/s. Water will be conducted to the machine housing along a tunnel bored inside the rock massif in a circular section of 5.70 m in diameter and 2,700 m in length, equipped with an equilibrium chimney and pressurized steel pipe for the final section, before arriving at the generators in the machine housing.

El Tambolar is be the fourth dam making up the Comprehensive Exploitation of the San Juan River and will have the largest reservoir volume in the province (605 hm³), expanding irrigation capacity of the region and reducing the risks of droughts or floods. Likewise, the hydroelectric power plant will produce an average 343 GW h/year of electricity which will be injected into the national power grid and sold on the interconnected market.

The new plant has an annual operable volume of 20 million m³ with an average treatment capacity of 3500 m³/hour and a future expansion with an annual operable volume of 30 million m³.

The First Basin Sewage Treatment Plant is the first of its kind in Argentina to employ a biological approach to the removal of nutrients, such as nitrogen and phosphorus. The process applied is called A2O. It uses the state-of-the-art AVENT Hyperclassic aeration system to incorporate oxygen in micro air bubbles. The combined approach of the biological nutrient removal and the commensurate chemical adjustments means that the plant attains values which are well below the maximum thresholds established by current regulations for final disposal.