Board anticipates NACA plant expansion

Graph and information about the annual flow of wastewater.
Graph and information about the annual flow of wastewater.

Increases have been steady in the amount of wastewater treated at the Northwest Arkansas Conservation Authority's wastewater plant near Highfill and soon it may expand.

Rick McClain, plant manager, said he will have an engineering proposal to put before the board at its April meeting. Board members asked McClain for a proposal in January after reviewing the increasing amount of wastewater flowing into the plant.

Local representation

The Northwest Arkansas Conservation Authority was created in 2002. Ten cities are represented on the authority’s board but the plant currently treats only wastewater from Bentonville and Tontitown. Cities represented on the board are: Bentonville, Bethel Heights, Cave Springs, Centerton, Elm Springs, Highfill, Lowell, Springdale, Rogers and Tontitown.

Source: Northwest Arkansas Conservation Authority

Wastewater is measured in millions of gallons of water per day flowing into the plant. The average daily amount was 1.7 million gallons in 2014. It rose to 2.3 million gallons in 2015. The average flow into the plant was 2.8 million gallons of water a day last month, McClain said.

The plant's official capacity is 3.6 million gallons of wastewater a day. The plant can treat more, but it wasn't made for that, McClain said.

Two flow lines each treat 1.8 million gallons of wastewater a day at the plant. The second line was turned on in about October, McClain told board members. A third line would bring capacity up to 5.4 million gallons of water a day. Some design work for that line was done by the original engineering firm, said George Spence, board chairman.

"If you're 2.5 [million] right now you'll be 3.6 [million] or beyond before we could get the concrete dry on the next expansion if we started by 5 o'clock," Bentonville Mayor Bob McCaslin said during the January meeting.

The December daily average for wastewater coming into the plant was 3.55 million gallons.

Heavy rain can cause ground water to seep into sewer lines. December's 12.63 inches of rain was 9.39 more inches of rain than usual, according to National Weather Service rainfall totals measured at the Northwest Arkansas Regional Airport in Highfill. The bulk of that fell on Dec. 26 and 27 in a 8.96-inch storm event.

There are 300 miles of sewer pipes in Bentonville, said Mike Bender, public works director for the city.

Water running over a manhole can get into the sewer system or ground water can seep in through cracks in old pipe.

Most of Bentonville's line is new, put in during city expansions, he said. Some is from the 1940s and 1950s. City workers once unearthed pipes stamped with 1896 during work downtown. Lines are inspected for leaks or cracks and crews check the line to the Highfill plant looking for missing manhole covers.

Rainwater may have caused spikes in water flowing to the plant, but regional growth is a more likely cause.

Bentonville and Tontitown send wastewater to the regional plant. Bentonville also treats about 3 million gallons of wastewater a day at its city plant, Bender said.

The city's sewer plant treats wastewater from the north side of town and is rated for 4 million gallons a day, Bender said. The approximate divide is Southeast 14th Street, which becomes Arkansas 102 outside of the city.

It isn't industry that pumps wastewater into the system in Bentonville, Bender said. Residential areas are growing, he said.

There are 44,073 people who live in Bentonville, an increase of 5.6 percent, or 2,468 people, from 2014, according to a draft copy of the city's 2015 annual development report.

There were 878 residential units permitted in 2015, according to the report. Of those, 482 were single-family homes and 396 were multifamily units.

Tontitown also is seeing growth, although less than Bentonville.

Last year about 50 homes were built, said James Clark, public works director for Tontitown.

"That's a big year for us," Clark said.

There are two townhouse developments opening this year that will add 236 housing units to the city.

Tontitown saw a 50 percent increase in sewer flow between 2014 and 2015, jumping to 40 million gallons of wastewater sent to the authority's plant last year. The city purchased a sewer camera in December to look for water leaking into the system.

"That's something every city constantly battles," Clark said.

However, wastewater growth is outstripping both population growth and rainfall levels.

There was a 38.39 percent increase in total wastewater treated by the authority's plant between 2014 and 2015. The plant treated 612.72 million gallons of wastewater in 2014, compared to 847.95 million gallons of wastewater in 2015.

The Highfill plant started operation late in 2010 and Bentonville gradually transitioned its southern flow to the plant. By July 2011 the plant was treating about 1.5 million gallons of wastewater a day. Wastewater flows increased steadily. The first time the plant broke a daily average of 2 million gallons of water a day was October 2014. Rainfall was up that month by 3.75 inches above average, according to the National Weather Service.

Last March brought a daily average of 2.2 million gallons, and the plant hasn't slipped below that mark since.

Bender and Clark said they look for places water could have infiltrated the line. The sudden jump had Bentonville checking for illegal hookups.

Industrial water use is easier to track than housing growth, Bender said. When the Kraft plant in Bentonville closed in 2013, that cut a half million gallons of wastewater a day from the city's flow, Bender said.

Most of the demand on the sewer system is on the southern end of the city, he said.

Centerton sewer has been treated by Bentonville for years, but is moving to Decatur. That represents about a half million gallons of wastewater a day, Bender said.

The Centerton agreement with Bentonville runs out in fall 2018, said Frank Holzkamper, Centerton utilities director. Centerton switched its wastewater flow to Decatur last year. However, the sudden influx overwhelmed biologic breakdown of waste at the Decatur plant, Holzkamper said. The city scaled back and now sends about 80 to 90 percent of its wastewater to Decatur and the rest to Bentonville, he said.

Wastewater flow from industry in Decatur combined with the increase in the Centerton wastewater will mean an upgrade to the Decatur plant under a joint operating agreement between the two, Holzkamper said.

Bentonville still treats about a quarter million gallons of wastewater a day from Centerton, Bender said.

More apartments can mean more water flow. Residential wastewater flow depends on density, Bender said.

A family of four uses about 400 gallons of water each day for showers, laundry, washing dishes and flushing toilets., according to the Environmental Protection Agency.

Construction costs have not been set for a wastewater plant expansion. Until drawings are complete there is no timeline, McClain said.

With the increase in use a new line has to be built, Bender said.

"We've gotta take care of the extra demand," Bender said.

NW News on 02/08/2016

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