Working in southwest Delaware, McMullen Septic Service encounters home sites that require more than conventional rock-and-pipe onsite wastewater treatment systems.

Co-owner Brian McMullen notes that at least one-fourth of the company’s installations require some form of advanced treatment unit. The company relies on RetroFast and MicroFast systems from Bio-Microbics and Delta ECOPOD systems from Infiltrator Water Technologies.

The area is mostly flat, and the soils are sandy. The aerobic treatment units come into play in environmentally sensitive areas. “We have a little section that is basically beach property, called the Inland Bays Watershed,” McMullen says. “That’s where pretreatment units are mandatory because of closeness to Chesapeake Bay.

“The Inland Bays Watershed is basically a big block. Two major roads designate the exact cutoff on it. It’s a little section of Sussex County that everywhere inside those boundaries, a pretreatment system is required. We also have the Nanticoke Watershed, where if you’re within 1,000 feet of the river, you’re required to have pretreatment.”

The company’s three favored systems have served their purpose well, McMullen says.

MicroFAST systems are versatile units that provide high nitrification/denitrification performance and typically produce effluent better than regulatory requirements, according to the manufacturer. With a small footprint, the systems are integrated into a standard septic tank. They offer high levels of nitrogen removal capacities that range from 500 gpd (for up to eight people) to 9,000 gpd (for 30 to 126 people).

RetroFAST systems include a submerged aerated biological filter that provides proven treatment for domestic-strength wastewater, according to the manufacturer. They can be installed within an existing tank or in new construction. They are designed for upgrading conventional septic systems or to repair systems that have biologically failed. The unit system inserts into an existing 18-inch manhole without the need for heavy equipment. Capacities range from 150 gpd (for one to three people) to 375 gpd (for one to five people).

According to the manufacturer, Delta ECOPOD systems are designed to be easy to install, simple to maintain and effective in reducing nitrogen, BOD and TSS. Capacities range from 500 to 1,500 gpd. The units have an in-the-tank bioreactor that can be inserted into an average-sized septic tank or vault, either round or rectangular. The system uses a fixed-film process widely used in onsite treatment applications and can be customized for individual homes, residential clusters and small- to medium-sized commercial applications. They can be constructed in concrete, fiberglass or plastic tanks.