Hurst Creek MUD has a total wastewater treatment capacity of 500,000 gallons per day (gpd), with the ability to treat four times this volume on a short term basis. The treatment plants are of the complete mix variety, with duplicate aeration basins, clarifiers, chlorine contact basins and tertiary filters. Treated wastewater, termed effluent, is stored in a 110,000 gallons in-ground tank and pumped to a 50 million gallon effluent storage pond located just east of Flintrock Falls. From there the effluent is applied to The Hills and Flintrock golf courses.

Raw sewage is 99% water and one percent of liquid and solid human wastes, scrap food, paper, soap and medical waste – plus whatever else people flush down their drains. These wastes consist of proteins, fats, carbohydrates, cellulose, bacteria and viruses. Without treatment, these materials are highly putrisable and will rapidly decompose with strong odor production.  During heavy rainstorms runoff and ground water enter the collection system and dilute the sewage but increase the overall volume of flow.

A complete mix wastewater treatment plant purifies sewage by feeding it to bacteria; this takes place in a large tank, the aeration basin, to which is bubbled a large volume of compressed air. Bacteria of the genus Aerobacter – which means air bacteria – thrive in the broth, consume the putrisable matter and grow more bacteria. Periodically, the excess bacteria must be wasted out of the system and hauled away to a State- licensed land application farm.

After aeration, the wastewater flows by gravity to a settling basin, called the clarifier; here, the water is quiescent and still and the heavy particles slowly settle to the bottom, where they are raked up as sludge and returned to the head of the plant.  The sludge consists of concentrated bacteria which are added to the incoming raw sewage flow to start the whole process over again. Clear water is skimmed off the surface of the clarifier, disinfected with chlorine and filtered to become effluent.

Hurst Creek’s effluent is of a high quality, comparable to water from Lake Travis, with two exceptions: concentrations of phosphorus and nitrate are several orders of magnitude higher than lake water. These compounds act as fertilizer for plant growth, hence the ban on wastewater discharges in the Highland Lakes area. Instead, effluent is stored and applied to golf courses as needed, and the phosphorus and nitrogen promote the growth of grass rather than algae.