The city of Washington, Indiana had a serious combined sewer overflow (CSO) problem. Worse yet, the city’s CSOs mostly flowed through open ditches, and all five eventually discharged into Hawkins Creek, which ran dry most of the time apart from when the untreated CSO discharged. In between rains, the water pooled and then dried up, concentrating pollutants.
Add to that the fact that Washington’s system, most of it dating from the 1930s, had little storage capacity. As little as one-tenth of an inch of rain produced CSOs. The city struggled with this problem for decades. Early attempts to abate it simply enclosed drainage ditches and creeks in large pipes, but didn’t address water quality. Facing federal mandates to clean up its water, the city was stuck.
With a population hovering just under 12,000 and a median household income of $34,000, costs were a critical concern. A 2002 study found that it would cost $39.9 million to properly capture and treat runoff, or $7,500 per household, roughly one-quarter of the average household income. By 2009, the cost had escalated to $53 million.
Lochmueller Group (Lochgroup) worked with Washington and the Indiana Department of Environmental Management to develop a solution that captures the CSOs, transports them to a storage basin, and then treats them using a constructed wetland. The Preliminary Engineering Report showed that the capital costs, when compared to the next lowest present worth alternative–Chemically Enhanced High Rate Clarification – reduced costs to $26.4 million, saving Washington’s residents $26.6 million. In addition, the city will save over $1.6 million annually in operations and maintenance. Diversion of stormwater will also reduce flooding of nearby residences and roadways.
Lochgroup’s design captures the first flush, up to the volume associated with a 1-year/1-hour storm event, in a 5-mg storage tank, pumping this to the wastewater treatment plant. Overflow from the tank— up to a 10-year/1-hour storm event—travels via two 84-inch pipes to a 21-mg, 27-acre constructed wetland for treatment. After treatment in the wetland, the effluent passes through a UV disinfection system before being discharged into Hawkins Creek.
Switzerland County was searching for a way to provide wastewater services to two very small communities, Moorefield and Bennington. Estimates showed that tying the roughly 60 homes into a small, traditional wastewater plant would create sewer rates between $90 and $125 per month.
Lochmueller Group (Lochgroup) provided the county with another option: using a constructed wetland for wastewater collection, treatment, and disposal. Lochgroup prepared a preliminary engineering report and final designs for two separate systems – one in Moorefield and one in Bennington.
First, homes were outfitted with systems similar to traditional septic systems. Unlike a traditional system though, each home has a two-compartment tank. Waste from the home flows through the tank, then a small but powerful pump carries wastewater to a unified treatment system. These small pumps can move wastewater several miles to the final treatment destination.
For each of the communities, this system includes a two-celled gravel and plant treatment system that is approximate 40 feet by 40 feet. The cells are built with an anaerobic layer at the bottom, a separating liner, then an aerobic layer on top. The aerobic layer consists of gravel and specifically-selected plants whose roots absorb nitrogen from the wastewater.
A pump recirculates the water in the wetland with a portion of the treated water diverted and pumped into an approximately 1.5-acre drip field where it’s emitted through small subsurface tubes. These fields are planted in hay through a no-till method. The treated wastewater acts as an irrigation system and the community is able to harvest and sell the hay.
This system’s low construction and maintenance cost meant the 60 homes connected to the system pay $30 per month in sewer fees. Both communities have the ability to expand the system if needed.