The information in this article is from a follow-up interview with Dr. Rafael B. Carmona Paredes, with Conagua, regarding the new pumping station for combined sewage and storm water in La Caldera, Mexico. This project was discussed in an article in the February issue of Pumps & Systems.
Dr. Carmona, you are the director of the general coordination of engineering and technology and of the coordination in general of special projects for clean water and wastewater in Conagua. How long have you been working with Conagua and what is your expertise?
Since April 2003, I have officially worked for Conagua. I graduated from the National University of Mexico and worked before this as a consultant for projects of Conagua and CFE. I hold the academic degree of a doctor in mechanical engineering, and my main topics and experience are in hydraulics, such as pumping stations and hydroelectric power plants.
Dr. Rafael B. Carmona Paredes
The newly built pumping station La Caldera in Mexico D.C. is one of the largest stations for combined wastewater and storm water transport with submersible pumps.
What was the main purpose of building such a large pumping station?
The most important factor was to solve the problem with the flooding in the area of Ixtapaluca in the metropolitan area of Mexico D.C. Due to the high and fast growth of the population over an ancient lake…it was more increasingly important to solve the bad situation of many people. We needed the most up to date and reliable technical solution, also for the worst case situations. Additionally, we are collecting the wastewater of approximately 1.5 million people during dry periods.
What was the biggest challenge when you started the project?
The first problem that had to be solved was the max flow and how to handle it. We were talking about 40 m³/s of flow. Second, the pump that should be used had to be chosen, evaluating all available technical solutions. The typical vertical turbine pump had not been considered to be convenient, because of high wear and tear with the long shaft and the depth of installation. We analyzed and decided that the newer technology of submersible pumps was much more suitable if we could find the pumps with the necessary head and power. Further, the depth of the sump in general and the available space were points to be investigated. Installing pumps able to move 20 m³/s into a diameter which was a little less than 20 meters was another engineering item to solve. The pump sump had to be designed to avoid sedimentation, but also to prevent against swirls and vortex. Last but not least, the time frame for that project was very tight, due to the urgency of the situation.
Could you explain us a little bit of the technical details of that pumping station?
Yes, we have two pits with 32-meter depth. Both pits have four submersible pumps for the dry weather wastewater and eight submersible pumps for the combined storm water. The big pumps have a capacity of about 2 m³/s. All KSB pumps together are able to pump a total flow of 40 m³/s.
Even if the diameter is slightly below 20 meters, it is the biggest station for combined storm and wastewater in Mexico regarding capacity. The single pumps can be lifted with a special deep lift system in one track. A screen is in front of the station, and electrical and control equipment are installed in an update, modern technical design to have the most reliable function.
What was your overall experience with the company that supplied the pumps?
We worked openly together with KSB in all items which were a challenge in that project. We made it a good experience with our cooperation, starting with getting detailed information about the possibilities regarding the pumps and the engineering and preparation of the right sump together with a CFD calculation from KSB. However, KSB also conducted a physical model test of the sump up to the supervision of the installation. All other aspects—such as the commercial part and the response for the special needs of Conagua—were considered comprehensively. KSB understood that we had to put the station into operation just in time. That was the important social point of that project.
Since the pumps are working, has there been a flooding situation?
No, up to now the flow has not reached the maximum of the installed capacity.
Do the people living in that area recognize the advantage of the new pump station?
Yes, they are now more confident and recognize the progress. We are still working on projects that will further improve the situation in the Mexico metropolitan area regarding storm and wastewater.