Not all the water in aquifers is cold. In geothermal regions, water emerges from deep wells at temperatures that can exceed 100 degrees.
That’s how it is in Montgomery County, Texas, about 40 miles north of Houston. And the very warm water contains radon and hydrogen sulfide, making treatment a challenge.
The Montgomery County Municipal Utility District has solved the problem with a cooling tower technology that simultaneously lowers the water temperature and strips out the radon and H2S.
Heat below the surface
Montgomery County lies over a geothermal field that includes much of eastern Texas. The underground water is heated by processes similar to but less violent than volcanic activity. In general, the deeper the water source, the higher the temperature.
The county increasingly depends on groundwater from deep wells to meet the needs of a fast-growing population. Cities including Conroe, Shenandoah, Oak Ridge North and Willis find it difficult to keep up with potable water demand from a population increasing at about 10 percent per year.
Although a portion of the surface water from nearby Lake Conroe will add to the county’s total supply, water pumped from deep wells remains an important source. That water’s temperature can reach 110 degrees F.
Problem constituents
The presence of radon and H2S complicates the situation. H2S in the amounts present is not considered a health hazard, but it does impart an odor of rotten eggs. Radon gas, a naturally occurring radioactive material, is the nation’s second-leading cause of lung cancer after smoking, according to the U.S. EPA and the Surgeon General. It can escape from water into the indoor air through washing, showering and laundering.
After learning that H2S and radon can be removed by air stripping, district officials wanted to learn which technology could best accomplish a significant reduction. Air strippers — pumping systems that remove gasses and volatile organic compounds through aeration — are commonly used for purification of groundwater.
While air stripping was a viable solution for Montgomery County wells, an investigation determined that cooling tower technology would meet both the county’s objectives, greatly reducing radon and H2S while lowering the groundwater temperature by about 20 degrees F.
Proving the concept
A cooling tower expels heat from water into the atmosphere by pumping the warm water to the top of the tower, then spraying it into droplets that are exposed to the cooling ambient air. Cooling towers most often provide cooled water for air conditioning, chemical processing and other industrial applications.
In 2014, the utility district deployed a cooling tower supplied by Penco Equipment for a well that required only cooling. The tower reduced the water temperature from 110 degrees F to 85 degrees F with throughput of 600 gpm. The cooling tower was a factory-assembled TM Series system from Delta Cooling Towers with a double-wall seamless shell and sump composed of high-density polyethylene. It also includes adjustable-pitch fan blades and a totally enclosed direct-drive motor.
Soon afterward, the district needed a system at another well to lower the water temperature and reduce the radon concentration. Calculations confirmed that the cooling tower would reduce the radon concentration by 90 percent.
Two additional projects required cooling and the reduction of radon and H2S. Because the radon calculations had already been performed, and because H2S has a greater affinity for air removal than radon, Penco and Delta engineers were confident in an H2S reduction greater than 90 percent.
Lasting solution
Utility district officials expect the cooling tower systems to operate for many years with minimal maintenance, mainly because of their engineered plastic HDPE shells. The Texas Commission on Environmental Quality required the cooling tower intake and exhaust for the applications to have engineered mesh screens to exclude contaminants such as insects and debris.
The commission also required the top of the tower to be protected by mesh screening in case the fans should be turned off. Because the fans normally thrust upward, they had to be directional in design so that they could be discharged sideways.
The design of both the louvered panels and the protective mesh screening were provided by the Delta factory as part of the complete package. The cooling tower systems, now proven in place, demonstrate a technology that can benefit other municipalities sitting on previously untapped sources of deep geothermal water.
