Determination and maintenance of de minimis risk for migration of residual tritium (3H) from the 1969 project rulison nuclear test to nearby hydraulically fractured natural gas wells

摘要

The Project Rulison underground nuclear test was a proof-of-concept experiment that was conducted under the Plowshare Program in 1969 in the Williams Fork Formation of the Piceance Basin in west-central Colorado. Today, commercial production of natural gas is possible from low permeability, natural gas bearing formations like that of the Williams Fork Formation using modern hydraulic fracturing techniques. With natural gas exploration and production active in the Project Rulison area, this human health risk assessment was performed in order to add a human health perspective for site stewardship. Tritium (H) is the radionuclide of concern with respect to potential induced migration from the test cavity leading to subsequent exposure during gas-flaring activities. This analysis assumes gas flaring would occur for up to 30 d and produce atmospheric H activity concentrations either as low as 2.2 × 10-6 Bq m-3 (6 × 10-5 pCi m-3) from the minimum detectable activity concentration in produced water or as high as 20.7 Bq m-3 (560 pCi m-3), which equals the highest atmospheric measurement reported during gas-flaring operations conducted at the time of Project Rulison. The lifetime morbidity (fatal and nonfatal) cancer risks calculated for adults (residents and workers) and children (residents) from inhalation and dermal exposures to such activity concentrations are all below 1 × 10-6 and considered de minimis. The implications for monitoring production water for conforming health-protective, risk-based action levels also are examined.