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Intermountain Power Agency

 


Intermountain Power Service Ground Water Discharge Permit

 

The Division of Water Quality (DWQ) is soliciting comments on a request by Intermountain Power Service Corporation (IPSC) to renew its ground water discharge permit for the Intermountain Generating Facility (IGF), a coal-fired power plant operating near Delta, Utah. The proposed permit renewal will require groundwater monitoring, incorporate best management practices, and establish protection levels for groundwater quality.

The public has a chance to comment on the proposed permit renewal during a 30-day comment period that runs from April 13 until May 13, 2016. Written comments can be submitted to the Division of Water Quality, P.O. Box 144870, Salt Lake City, Utah, 84114-4870. All comments received prior to close of business on May 13, 2016, will be considered in the formulation of final determinations imposed on the permit. The findings, determinations, and assertions contained in the permit documents are not final and are subject to change following the public comment period.

A public hearing may be held if written requests demonstrating that significant public interest and substantive issues exist to warrant holding a hearing are received within the first 15 days of this public comment period.

A person who wishes to challenge a permit order may only raise an issue or argument during an adjudicatory proceeding that was raised during the public comment period and was supported with sufficient information or documentation to enable the Director to fully consider the substance and significance of the issue.

For more details, click on the ground water permit, Statement of Basis, and public notice listed below. Additional information may be obtained upon request by contacting Ed Hickey at (801) 536-4300 or ehickey@utah.gov.

Permit History

IGF was built in the early 1980s and went online in 1986, prior to the promulgation of the 1989 Utah Ground Water Protection rules. Extensive geotechnical studies of the site were conducted between 1978 and 1983 to guide the design and construction of the power plant and its support facilities. These studies were incorporated into the siting and construction of the process water and ground water monitoring system. DWQ issued the initial ground water permit in 2001, with subsequent permit renewals in 2006 and 2011.

Hydrogeological Conditions

The facility is located above a multiple aquifer system that contains three, coarse-grained permeable aquifers:

  1. an unconfined shallow water table aquifer
  2. an upper confined aquifer
  3. a lower confined aquifer

The shallow water table contains all sediments from ground surface to about 100 feet deep, including the clay layer that the perched wells use for leak detection. Depth to the water table is approximately 40 feet below ground surface. The upper confined aquifer is below 100 feet deep, and the lower confined aquifer, used as a water supply, contains wells from 1200 to 1300 feet deep. The ground water for the unconfined aquifer in the area of IGF is generally Class II Drinking Water Quality ground water. The lower confined aquifer is used as a culinary water source for the general area.

Process Description

IGF does not discharge any process effluent directly on or into the ground. Instead, the power plant uses a series of 13 lined ponds to settle, clarify, recirculate, and evaporate process water. The ponds hold water that is not compatible with the ground water due to elevated concentrations of total dissolved solids (TDS).

The highest quality water (Tier 1) is placed in the settling basin. The remaining process water is placed in the appropriate pond based on water quality designations, with Tier 4 being the poorest quality water:

  • Bottom ash basin (Tier 2)
  • Wastewater basin (Tier 3)
  • Evaporation ponds (Tier 4)

The water in the evaporation ponds has high levels of alkalinity, salinity, and mineralization (calcium and magnesium) that make it unusable.

The bottom ash, wastewater, and evaporation ponds are lined with a single layer of 80-mil, high-density polyethylene (HDPE). The settling basin and coal-pile runoff basin are lined with a bentonite clay-natural soil mixture.

Permit Conditions

This permit will incorporate lined ponds, ground water monitoring wells, perched monitoring wells, and Best Management Practices as compliance mechanisms. The permit requires periodic ground water quality monitoring to assess potential impacts to ground water quality and ensure compliance with ground water protection regulations.

Monitoring
Periodic monitoring of ground water quality will assess potential impacts to ground water quality from IGF discharges. The facility will monitor compliance wells located adjacent to and downgradient (west) of the lined ponds and permitted facilities. Monitoring wells will collect data on total dissolved solid (TDS) and boron levels in ground water.

  1. Upgradient Monitoring Wells
    Ground water quality data from two upgradient monitoring wells will be used as a comparison standard for all other monitoring and observation wells on the site.
  2. Evaporation pond, bottom ash basin, wastewater holding basin, and settling basin monitoring wells completed in the unconfined water table aquifer on the downgradient (west) side of the permitted facilities will be used as a compliance mechanism for this permit. The monitoring well data will assess effectiveness of overall best management practices at the IGF site to determine if ground water quality parameters are stable and not degrading over time.
  3. Perched Wells

Because the perched wells are normally dry, they are primary indicators of pond liner leaks. The perched wells will also be used as a compliance mechanism of this permit.

Corrective Action
Ground water investigations discovered that process water from one of the ponds has leaked into the shallow aquifer. As a result, the site is currently under a corrective action plan. This area of elevated TDS is generally southwest of the bottom ash basin and follows the natural westward hydraulic gradient. IPSC installed three ground water extraction wells to remove ground water with elevated TDS concentrations from the shallow aquifer and contain plume movement. This extracted water is pumped to the recycle basin for reuse in the process water system.

Changes to the Permit

The 2015 passage of the Federal Coal Combustion Residual (CCR) rule, along with an ongoing ground water corrective action at the site, have led to major changes in the permit.

CCR rule
Coal combustion residuals include fly ash, bottom ash, and boiler slag. The federal rule designated CCRs as solid waste regulated under subtitle D of the Resource Conservation and Recovery Act.

Under the new CCR rule, existing CCR landfills and surface impoundments are not required to close or retrofit with a composite liner and a leachate collection and removal system. Existing CCR units such as IFG can continue to receive these process residues after this rule is in effect, but must still meet all applicable groundwater monitoring and corrective action criteria.

Permit changes due to CCR rules include:

  1. Transfer of regulatory performance criteria for the fly ash landfill, bottom ash basin, and wastewater basin from state rules to federal CCR rules promulgated by the Environmental Protection Agency (EPA).
  2. Transfer of oversight of the combustion waste landfill to the Solid Waste Program in the Utah Division of Waste Management and Radiation Control.

Monitoring
Because the plume appears to be moving beyond control measures currently in place, and the existing permit is under a corrective action order, the proposed permit requires IPSC to submit the following items within a specified timeframe:

  1. Within 90 days of the effective date of this permit, an updated map of the plume limits and compliance well TDS concentrations.
  2. Within 120 days of the effective date of this permit, a schedule to regain (restore) best available technology (BAT) or remove the TDS plume source from service.
  3. Within 120 days of the effective date of this permit, an updated Corrective Action Plan and remedial design to contain the expansion of the plume provided to DWQ for review and approval.