Background

EPCTWID provides water service to Tornillo through the operation of two active wells in the Hueco Bolson Aquifer and has a third well for contingencies. Naturally occurring arsenic in the aquifer regularly exceeds regulatory limits for potable water allowed by the Clean Water
Act (CWA). EPCTWID received notifications by the Texas Commission of Environmental Quality (TCEQ) and the Environmental Protection Agency (EPA) that it must come into compliance with CWA arsenic standards.

To remedy this situation, EPCTWID proposes constructing an arsenic treatment facility (ATF) that will initially treat water from Wells No. 2 and 3, which will continue to pump at their current rates of 270 and 290 gallons per minute (gpm), respectively. The utility has also requested TCEQ approval to use the ATF to treat water from Well No. 4 (currently
not in service) in lieu of increasing the pump capacities of Wells No. 2 and 3. All the wells already have transmission lines to the storage tank, so only new yard piping is required.

Description

The proposed project consists of the construction of an ATF with the capacity to treat 600 gpm, to be located at the site of Well No. 3 and the Tornillo water storage tank. The ATF will be a site assembled package facility that includes:

• Two parallel 600-gpm sand separators;
• Two 350-gpm pumps at Wells No. 2 and 3;
• A 7,500-gallon chlorine detention tank, with minimum contact
  time of 12.5 minutes;
• A sodium hypochlorite (NaOCl) oxidation system;
• Two 600-gpm arsenic removal units equipped with anthracite, a
  Greensand Plus™ filtration process and gravel, with minimum
  contact time of 3.75 minutes; and modifications to the 6-inch transmission lines from Well No. 2 to the ATF and from the ATF to the storage tank. 

In addition, 19 new wastewater connections will be incorporated into the
ATF waste line, providing first-time service to 19 residences: 13 along
HR Hemley St, four on Fourth St. and two on Drake St.

Benefits

With this project, EPCTWID will bring its water supply into compliance with existing environmental regulations. In addition to removing arsenic, the facility will also remove iron and manganese ions. The new wastewater connections will eliminate discharges of approximately 5,600 gallons per day of inadequately treated and untreated wastewater.