Analysis of Human Health Risk from Salt Cavern Disposal

DOE funded Argonne National Laboratory to conduct an analysis of the risk to human health through drinking water contaminated by releases of NOW and NORM from disposal caverns.

Tanker loading brine at a West Texas disposal cavern facility.

Contaminants of Concern

Chemical

• Arsenic
• Benzene
• Cadmium
• Chromium

Radiological

• Radium-226
• Radon-222
• Radium-228

Hydrogeological Assumptions

In order to develop a model, certain assumptions about the hydrogeology were made:

• Depth to water table – 20 feet



• Beneath shallow aquifer is sequence of clays and silts, interspersed with sand beds



• Recharge from precipitation



• Groundwater quality decreases with depth



• Groundwater velocity in shallow aquifer – 100 ft/yr



• Groundwater velocity at depth of cavern – 10 ft/yr

Cancer Risk Calculation

The risk from cancer is estimated using the following equation:

• Risk = intake x oral slope factor x probability of occurrence
• Oral slope factors come from EPA's IRIS (integrated risk information system) database
• Intake is a function of exposure point concentration, intake rate, time, frequency, duration, body weight, and averaging time
• Exposure point concentration is modeled using a one-dimensional solution to an advection/dispersion equation with first-order decay


• Total risk = sum over all contaminants and paths

Non-cancer Risk Calculation

The health risk for ailments other than cancer is expressed as hazard quotient (HQ) and is estimated using the following equation:

HQ = intake x probability of occurrence / reference dose

Reference doses are taken from EPA's IRIS database.

Initial Concentrations

The estimated concentrations of chemical and radiological constituents in the cavern fluids after coming to equilibrium are assumed to be as follows:

• Chemical
• Arsenic: 1.7 mg/l
• Benzene: 20.4 mg/l
• Cadmium: 0.29 mg/l
• Chromium: 0.85 mg/l


• Radiological
• Radium-226: 1,500 pCi/l
• Radon-222: 1,500 pCi/l

Probability of Occurrence

Because no disposal caverns have ever failed, the probabilities were estimated by asking a panel of experts to provide best-estimate probabilities (the most likely probability) and the worst case probabilities (not a true worst case, but the highest likely probability). Estimates were averaged as shown below.

To check the true worst case situation, we also considered an option under which all caverns failed (the 100% release case).