City looks south for plant location
The Hot Springs Board of Directors adopted a resolution Tuesday night that designated Lake Ouachita as the city’s next water source, but the treatment plant for its 23 million-gallon per day allocation will likely be in the Amity Road area.
An updated draft of the water supply study the city commissioned in 2012 showed the hydraulic and water quality benefits of locating the plant about 20 miles south of the preliminary intake site upstream of Lake Ouachita’s spillway landing area.
Most of the city’s finished water is distributed from the northwest end of its sprawling water system. The Ouachita Plant treats water from the city’s intake on upper Lake Hamilton, where its withdrawal agreement with Entergy Arkansas Inc. gives it an allocation not to exceed a 90-day rolling average of 20 mgd.
Some finished water also comes from the Lakeside Plant at the north end of the system. It treats water from the city reservoir at Lake Ricks.
Stewart Noland, president of Crist Engineers Inc., the city’s water-system consultant, told city directors last month the benefits of locating the new plant at the south end of the system instead of closer to the Lake Ouachita intake are numerous.
The new 2 to 3 million-gallon storage tank the city plans to locate near Cornerstone Marketplace could be filled without putting additional pressure on distribution lines already strained by the pumping required to move water across the system’s seven elevation zones.
That pressure contributes to 27 percent of the system’s finished water being lost to line leaks, according to the Arkansas Department of Health.
“If we were to develop additional capacity way up in the northwest, it would take quite a bit more energy to get water down to the new proposed tank,” Noland told the board. “It creates higher pressures on the system and increases your chances for losses and broken mains.”
The Amity Road option would also reduce the trihalomethane exposure of users on the east and south ends of the system, Noland told the board. A byproduct of the interaction between chlorine used to disinfect water and the organic material in the water, THMs become more pronounced the longer finished water remains in the distribution system.
The Department of Health has said research done by the Environmental Protection Agency has shown an increased risk of liver and kidney cancer linked to long-term exposure to high THM concentrations. The EPA has imposed an 80-parts-per-billion limit, but water samples from the south and east end of the system have exceeded it.
“If you put a water plant on Lake Ouachita, you’re going to be forcing finished water that’s been chlorinated from the northwest and the age of it is going to continue to create THM problems,” Noland said. “You really need to bring your next supply from the south end.
“That way you can feed the new tank directly from the other end and solve the water age problems on the southeast end of the system.”
The updated water supply study draft estimates a $29.4 million cost for a 105,000-linear-foot, 42-inch raw waterline from the Lake Ouachita intake to a plant on Amity Road. Noland said the city would have the same expense if it opted to locate the plant closer to the intake, only the raw waterline would be a finished waterline connecting the plant to the south end of the system.
The study estimates a $21.5 million cost for a 15 mgd capacity plant. Noland told the board the city’s 23 mgd allocation warrants a plant with more capacity. It’s an average-day allocation, allowing the city to exceed it on any given day so long as its yearly consumption does not surpass the 23 mgd average.
Peak demand days could justify a 30 mgd-plus capacity plant, Noland told the board.
The study estimates a $13.6 million cost for distribution infrastructure, including 36-and
24-inch distribution lines from the plant, and $10.7 million for an intake. Coupled with a
25-percent contingency and engineering fee, the total cost of the intake, raw waterline, treatment plant and distribution infrastructure is $95.1 million, according to the study’s estimate.
The city said it has already allocated money for preliminary design work from revenue bonds it issued in 2014.
Negotiations with the U.S. Army Corps of Engineers for a DeGray Lake allocation are ongoing. The city purchased the rights to a 20 mgd allocation from Central Arkansas Water, the Little Rock metropolitan area’s water system, in 2013 but has been unable to negotiate a storage agreement with the Corps.
The supply study estimates a treatment plant in the Jack Mountain area and accompanying infrastructure for a potential DeGray Lake allocation would cost $84.4 million.
Pumping costs for DeGray Lake are higher relative to Lake Ouachita, according to the study. The energy required to pump finished water from a plant in the Jack Mountain area is lower compared to pumping water from an Amity Road plant, but raw water pumping costs are more expensive on DeGray Lake.
The study said pumping water from DeGray Lake to Jack Mountain requires more energy than pumping water from Lake Ouachita to Amity Road. The study estimates $132,737 in annual pumping costs for the Lake Ouachita option and
$245,616 for DeGray Lake.