25 YEARS OF WIPP: ADAPTING TO CHANGES AS A REGULATOR AND LOOKING TO THE FUTURE Jonathan Major, Xinyue ong Tom Peake 0 EfOA U.S. Environmental Protection Agency WCI r\ United States Environmental Protection k Agency OECD-NEA | International Conference on Geological Repositories (ICGR-7) Busan, Korea | May 2024 Abstract The Waste Isolation Pilot Plant (WIPP) In southeastern New Mexico, USA began receiving radioactive waste in 1999. WIPP is a deep geologic repository in bedded salt for defense-related transuranic radioactive waste operated by the US Department of Energy (DOE) and regulated primarily by the US Environmental Protection Agency (EPA) and the New Mexico Environment Department. Major changes and challenges encountered by the implementer and regulators include the design of waste panel closures, a fire followed closely by an unrelated release of radionuclides in the underground in 2014 leading to a 3 year pause in operations, resumption of emplacement operations with limited ventilation, construction of a new ventilation system and utility shaft, the need for additional disposal space, evolving waste streams, and a boom in oil and gas activities surrounding WIPP. This poster focuses primarily on conflicts with and accounting for the presence of natural resources in performance assessments. WIPP is located in the Delaware Basin, an area within the greater Permian Basin region, one of the most prolific oil and gas producing regions in the world. In fact, half of current US hydrocarbon production comes from the Permian Basin, and most potash production. These and other natural resources were identified and evaluated during the early site characterization phase of WIPP. Although the presence of significant hydrocarbon resources was known at the time WIPP was developed in the 1990s, production was on the decline since peaking in the 1970s. New technologies and techniques like hydraulic fracturing and horizontal drilling led to a resurgence in production one decade after WIPP opened to today. WIPP regulations include the requirementto evaluate and model potential impacts of resource exploration and exploitation in WIPP performance assessments (PA). Regulatory provisions have proven adaptable to changes in human activities, for example "Future drilling practices and technology will remain consistent with practices in the Delaware Basin at the time a compliance application is prepared..." (40 CFR 194.33). Given the robustness of the WIPP repository, no releases of radionuclides are anticipated in an undisturbed scenario. The only pathway leading to releases is a disturbed scenario involving drilling. EPA has closely reviewed and evaluated the approach, data collected, parameters, and calculations developed by DOE and its contractors for modeling these scenarios for each ~5 year recertification cycle. DOE begins with a FEP analysis and updates parameters according to information gathered by their contractors in the Delaware Basin Drilling Surveillance Program (DBDSP). Changes to the deep drilling rate and borehole plugging parameters are major drivers of increased releases of radionuclides in the latest PA. Other DGR sites, especially those in sedimentary basins, should fully evaluate and account for any and all natural resources, and incorporate updates appropriately over the life of the repository. New technologies and changing demands by society in the future are uncertain, meaning resources previously unconsideredcouldbecometargetedforexploitation, increasing the likelihood for human intrusion. Regulators should include provisions that allow for adaption if needed. Oil and Gas Production 1980-present by decade Impacts of natural resource production on WIPP PA The self-sealing, impermeable salt makes the WIPP repository robust. PA calculations have shown that the only viable pathway to releases of radionuclides outside of the regulated area in the 10,000 year regulatory time period is through human intrusion, i.e. drilling. An extensive review of the natural resources in the WIPP area began in the early site characterization phase in the 1970s and eventually incorporated into the first Compliance Certification Application (CCA). Oil and gas, potash, brine, and sulfur were all identified in the area. Of these, only potash is found above the WIPP repository, but in uneconomic amounts, and significant oil and gas reserves are found below WIPP. EPA's regulations and guidance for WIPP explicitly require consideration of the presence of natural resources and modeling of inadvertent drilling intrusions in PA. DOE and its contractors developed and run the Delaware Basin Drilling Surveillance Program to continuously monitor and evaluate the presence of natural resources, the drilling practices and technologies that exploit them, and develop and update parameters to use in PA. Because of their importance to modeled releases of radionuclides, EPA closely reviewed the development of these parameters at the time of the original CCA in 1996 and all subsequent updates and changes. Generated by DBDSP Oil and gas production peaked in the 1970s and continued to decline when WIPP opened in 1999. That trend reversed itself around 2010 when the "tracking boom" hit the region, with record amounts of oil and gas being produced today. Potential conflicts with oil and gas operations and associated phenomena like induced seismicity are renewed concerns for state and federal regulators, plus stakeholders and the public. Drilling is prohibited within the WIPP Site boundaries currently, although it is explicitly modeled as occurring 100 years after the site closure and continuing through the 10,000 year compliance period. Wells and Drilling Rates in Delaware Basin Radionuclide Releases Via Cuttings, Cavings, Direct Brine Releases EPA defined the area overwhich the Deep Drilling Rate (borehole areal density) should be calculated as the entire Delaware Basin (RED OUTLINE), but other parameters were left to DOE to define. The DBDSP focuses primarily on the 9 townships surrounding WIPP (LARGE BOX), and has also collected certain data over the entire New Mexico part of the Delaware Basin (GREEN). The Known Potash Leasing Area (KPLA, in BLUE) that surrounds most of WIPP has specific regulations for the location, drilling, and plugging practices for oil and gas wells. TYPE II V////A TYPE IV TYPE V TYPE VI 3 ii II I! Figure 4: Typical Borehole Plug Configurations in the Delaware Basin fromiDiBBBMAR From WlPP 20 1 9 CRA Schematic of various borehole plugging configurations in the Delaware Basin region. A solid cement plug (Type VI) is the most protective of potash resources and is most effective at limiting brine flow in and out of the repository over long periods of time. Modeled Release Pathways Release Limits & Compliance Curves Data compiled from DBMARs 1996-2024 Conclusions • EPA's 2022 Recertification Decision concluded that the WIPP PA continues to comply with EPA regulations and modeled releases are below limits • PA parameters continue to update and adapt to new realities in a resource-rich region • Stakeholder concerns regarding oil and gas activities more readily addressed because they are already considered in FEPs and factored in PA Releases: Total 0.1 L V\ \\ I \ DR_PLG — Release Limit \ 0.0001 0.001 o.oi o.i R=Release (EPA Units) 10 100 i => - O) < Subsurface Boundary of Accessible Environment « < CO \ EPA sensitivity study evaluating changes to borehole plugging and deep borehole drilling frequency rate methodologies Waste Disposal Region : : : : m Culebra -1 Upper Seal System — MB138 Lower Seal System / MB139 : : : : : : : : : : : ~L_r Access Drifts (Not to Scale) Pressurized Brine REFERENCES WIPP 2019 Compliance Recertification Application (CRA), Appendix PA Time series of maps showing boreholes in the Delaware Basin generated from DBDSP database by Natalie LaClair, Los Alamos Technical Associates Delaware Basin Monitoring Annual Report (DBMAR) Releases in PA are controlled by: 1 -The number of intrusions, their timing & sequence. 2-Fluid flow in and out of the repository, which is related to the configuration of borehole plugs and their permeabilities over time. : Example shown includes only two boreholes, both of which penetrate waste and one of which penetrates pressurized brine in the underlying Castile. Pathways are similar for examples containing multiple boreholes. Arrows indicate hypothetical direction of groundwater flow and radionuclide transport. : : : : j Anhydrite layers A and B m Culebra From WIPP 2019 CRA i Groundwater flow and ' radionuclide transport fTZl DRZ Repository and shafts I Increase in Culebra hydraulic conductivity due to mining ------- |