MacBride Pointe

Gravity lowers cost, improves sustainability.

Challenge:  Design a wastewater management system for the MacBride Pointe subdivision that would allow multiple septic systems to manage waste from the year-round homes while keeping the use of pumps and mechanicals to a minimum and protecting surrounding streams.

MacBride Pointe is a residential subdivision of year-round homes platted in a rolling, wooded site adjacent to Hoosier Creek, a tributary of the Iowa River near Solon, Iowa. An impoundment of the river has created a nearby reservoir featuring Lake MacBride State Park. While the river and reservoir wouldn't be directly affected, proximity limited the number of systems that could be installed.

Solution:  The rolling terrain added to the challenge but also presented an opportunity. By taking relative elevations into account, wetland scientist and septic designer Trevor Dickerson and his MMS team designed a system using a combination of STEP (Septic Tank Effluent Pump) and STEG (Septic Tank Effluent Gravity-fed) installations.

Septic tank capacity for each home in the subdivision is scaled to home size. Tanks feature three compartments for anaerobic primary treatment and distribution. Once primary treatment is complete, wastewater is sent to one of eight outlots where final treatment takes place.

A 4-inch pipe carries sewage from each home to an individual septic tank.  Effluent is then pumped with a to a main connector line that is either pumped or gravity flows into one of the eight 300 gallon concrete distribution boxes.  Effluent is then distributed via gravity flow to one of 3 or 4 Biofilters connected to the Distribution boxes. Biofilters are Premier Tech Aqua Ecoflo^® units using coconut fiber as the filter medium. Filtered water is discharged to the surface with manufacturer claimed BOD and TSS output of 10mg/L, far below the Iowa standard of 25mg/L.

The system's effectiveness is more than matched by its mechanical simplicity. "Treatment outlots are shaped to allow for replacement systems if they're every needed and to allow for gravity flow into the biofilters," says Dickerson. "The result is a system that avoids the complications that come with using a lot of big pumps and shared tanks. That eliminates the issue of tracking usage and alloting payments, making life easier for the homeowners' association."

It's worth noting that unknowns added a degree of difficulty to the project. Dickerson notes that "People buying lots could build what they wished. We used surrounding subdivisions and recent building trends to forecast likely home sizes and used that to gauge need."

Construction of the subdivision continues. Thanks to careful planning and the hard work of wastewater contractor Lynch Excavating, homeowners can be confident that the system will be effective and efficient far into the future.

^{The finished treatment field of Ecoflo biofilters. Lots holding the system are jointly owned by landowners in the subdivision. They were designed to provide sufficient grade to
 gravity-feed biofilters and provide enough room for replacement should that ever be necessary.}