I ’m standing on a windswept bluff well above a modern precast concrete factory outside of Boulder, Colo., where soaring hawks and sometimes eagles hunt for abundant rabbits, bull snakes, and the occasional inattentive prairie dog.

I overlook neat rows of precisely made solar heating reservoirs, holding tanks, domestic and fire protection cisterns, septic tanks, advanced treatment units, leaching pits, wet wells, pumping stations, distribution boxes, oil-water-sand interceptors, extended aeration tanks, catch basins, drop inlets, manholes and other similar structures – a veritable candy store of precast concrete.

This laundry list of useful infrastructure vessel products, many used in the onsite wastewater industry, have all been cast into these uniform and somewhat complicated shapes using an amazing material – concrete.

These tanks are designed to ASTM standard specification C913-08 (Standard Specification for Precast Concrete Water and Wastewater Structures) and other relevant specifications to ensure that they will not collapse or rupture when subjected to anticipated earth and hydrostatic pressures, whether they are empty or full.

Concrete has strength and the castable flexibility to respond to local conventions of design and specific engineering requirements, along with the adaptability to become service vessels for a variety of proprietary water treatment techniques and equipment.

Two words that must be understood in great detail by makers of precast concrete water and wastewater structures: cement and concrete. Cement powder is the reactive ingredient – the magic dust that acts as the binder to join the aggregate of rock and sand into a solid structure that just hours before was a pourable liquid called concrete. This cement powder is composed of calcium (think strong bones and hard heads) and silicate (think impervious inert glass) which form microscopic crystals in the presence of water in a chemical reaction called hydration.

The concrete doesn’t dry; it transforms into a strong crystalline structure – by using the water molecules it hydrated – into a completely new molecule. The chemical reaction releases some heat energy. It produces crystals that infiltrate the spaces between the other materials, interlocking and binding together the coarse rock as it adheres to the surface texture of the aggregate – tightening and growing stronger and chemically freezing into a solid mass.

These little cement crystals enable concrete to reach 50 percent of its ultimate strength in one to three days and 90 percent or more in 28 days. It gains the last 10 percent of its strength over the next 50 years. Since this chemical reaction with water satisfies the chemical bond necessary to form impervious crystal, the material should survive more or less indefinitely. The concrete dome of the Roman Pantheon, begun in 27 A.D., is 1,984 years old this May.

Concrete is friendly to the environment. It’s virtually all natural, has a remarkably long life cycle, is recyclable, and is the most frequently used material in construction. The sound-cured concrete surface may be wetted, but its body is impervious to further intrusion of water. To achieve the full benefits of precast concrete tanks, the application of the correct specifications and good manufacturing practices is essential:

Proper proportions and sound ingredients

Vibration or chemical densification of the liquefied concrete mix, forcing the aggregate to nest into itself without segregation

Stabilized moisture and curing temperature control

Wet mix handling time and techniques and added mix chemicals

Concrete is strong, dense, and watertight, but it is brittle. Tensile strength must be added by the tank manufacturers by typical incorporated uniform engineered consistent reinforcement. Other handling considerations remain.

Adequate equipment must be mobilized in the factory and on the job site. Handling the newly cast tanks in the factory must be firm, but gentle, so as not to disturb the maturing cement crystals (Although concrete is a strong and forgiving material, it is heavy and when lifted has a lot of potential energy.)

Considerations of craning safety and site preparations must be attended to – these subjects are covered in ASTM C-891 (Standard Practice for Installation of Underground Precast Concrete Utility Structures).

The weight of a concrete tank, its stability when buried, and resistance to floatation are assets on sites with seasonal high groundwater.

For two millennia, concrete has been the material of choice for the underground storage of water because it is watertight and structurally sound. Today we can still depend on those two required attributes. Think now, as an installer/excavator: What would you like to guarantee as performing for the long haul? In your own backyard?