RDX Plume Characterization
Ensure contamination doesn’t threaten human and environmental health
RDX (Royal Demolition Explosive) Plume
Building 260 at LANL’s Technical Area 16 was the conventional, high explosive machining facility. From 1951-1996, 13 sumps discharged liquid containing high explosive compounds (RDX, HMX and TNT) and barium through the building outfall and into Cañon de Valle. Soils, surface water and groundwater beneath Cañon de Valle were contaminated. RDX in groundwater was first identified in the late 1990s and discovered in the regional aquifer in 2000.
Ensure contamization from past LANL operations does not threaten human and environmental health
Characterize groundwater movement and RDX concentrations through sampling of monitoring wells, aquifer tests and tracer studies, and assess current and future risk to human health. This assessment was made by performing a fate and transport model and risk assessment. A corrective measures evaluation will be performed if needed.
RDX Characterization and the 2016 Consent Order
The 2016 Consent Order between DOE and New Mexico Environment Department (NMED) divides cleanup work into 16 campaigns. One of these campaigns is RDX Characterization. The following Consent Order milestones for 2019 and for 2020 for the RDX Characterization have been completed:
✔ Prepared and submitted to NMED the Deep Groundwater Investigation Report. The report presented the results of hydrology, geology, and geochemistry studies, and presents RDX nature and extent in deep groundwater, updates the Conceptual Site Model, and screens RDX data against the NM tap water screening levels. The report recommended a risk assessment be performed.
✔ Submitted to NMED the Annual Long-Term Monitoring and Maintenance Report for the Corrective Measures Implementation at Former 260 Outfall Area. The report can be read here.
✔ The first sample from R-69 was collected, this was a 2019 milestone. This well will provide important information of how RDX contamination has reached the groundwater.
✔Submitted to NMED the Fate and Transport Modeling and Risk Assessment Report for RDX Contamination in Deep Groundwater. The report concluded there is no risk to human health now or in the foreseeable future
✔ If further remediation is necessary to protect groundwater, issue the CME for RDX in the deep groundwater.
RDX at a Glance
– RDX was used widely in World War II and remains common in military applications.
– RDX is an organic man-made product that does not occur in nature.
– RDX has a low water solubility but does not bind significantly to soils, so it can leach into groundwater.
– The state’s tap water screening level of 9.66 ug/L is based on a 150-pound person drinking 1 liter of contaminated water per day, 350 days a year, for 26 years. The cancer risk is based on 70 years of exposure, from the 26 years of consumption. That increases the cancer risk by 1 in 100,000.
– The risk assessment analyzed current risk and future risk, and determined that no current risk is posed because the RDX plume is three miles away from the nearest water supply well.
-It was determined that there is not future risk because the fate and transport model determined that the RDX plume will migrate only 2,500 feet towards the water supply wells over the next 50 years.
September 2020 Status
NMED is reviewing the Investigation Report for RDX in Deep Groundwater. NMED is reviewing the Fate & Transport Model and Risk Assessment Report For RDX Contamination in Deep Groundwater. The Risk Assessment concluded that there is no risk to Human Health now and in the foreseeable future. The Fate & Transport Model and Risk Assessment Report for RDX Contamination in Deep Groundwater recommends long-term groundwater monitoring as the next step.
Regulating Water Quality
RDX has no standard, but a tap water screening level (TWSL). The TWSL is used to screen data to determine if a further evaluation of risk is warranted-that is why the Risk Assessment was performed.
Scientists are working to refine their understanding of how RDX migrated through the subsurface at LANL. Conceptual models based on multi-year studies indicate the primary RDX migration pathway is via surface water moving down Cañon de Valle and seeping downward through the rock layers into the underlying groundwater zones (shallow to deep). Monitoring wells located in each of the groundwater zones provide information on the hydrologic connections and changes over time.
The RDX Monitoring Network
Nine wells in TA-16 and TA-9 monitor groundwater in the regional aquifer that provides water for Los Alamos County. Groundwater samples from the nearest monitoring wells (R-68 and R-69), which are more than three miles from Los Alamos County water supply wells, show contamination above the New Mexico tap water screening level of 9.66 ul/L. The Department of Energy (DOE) has not detected RDX in water supply wells. R-25 was installed in 2000 and screen 4 was in the regional aquifer and detected RDX.
Cleanup Work Conducted To Date
Surface soil cleanup in 2000-2001 and in 2009-2010 removed, and properly disposed of, approximately 1,500 cubic yards of high explosive-contaminated soil from the outfall area. Residual RDX remains in the subsurface groundwater. Long-term monitoring and maintenance is conducted to evaluate the effectiveness of the corrective measure and provide information for the conceptual site model for RDX movement through surface water, springs and groundwater.