WASHINGTON, DC, Aug. 28, 2015 -- After releasing an estimated 3 million gallons of contaminated water from the Gold King Mine into the Animas River at the beginning of August, the Environmental Protection Agency (EPA) has published new data trend graphs and additional public records on the response (see "EPA releases official update on Gold King Mine response efforts").
EPA is releasing a contractor's Draft Technical Memo of the incident, including photographs, an On-Scene Coordinator's description of the events depicted in the photographs, and a phone duty officer's memorandum to the file about the incident and certain subsequent events. Further, the Agency is posting graphs to show the trending concentrations of arsenic, cadmium, lead, and mercury in surface water over time. These trend graphs were created from pre- and post-event data posted to this website between Aug. 10 and 22, 2015.
For each heavy metal, the trend graphs illustrate that concentrations are significantly lower than the Recreational Screening Level (RSL). The specific RSLs for each metal are posted on the right side of each trend graph. RSLs, established by EPA, are health-based concentrations for each metal based on exposure during recreational use. The RSLs for both soil/sediment and surface water are based on recreational scenarios in which an adult or child hiker/camper is exposed to surface water and sediment.
For surface water, the recreation-based screening levels assume that the adult or child would receive all of his or her daily water intake (2 liters/day) from the river over a continuous 64 day period. For sediment, the recreation-based screening levels are based on a hiker/camper that may become exposed to sediments alongside the riverbank over a continuous 64-day period. These RSLs are conservative, representing levels that are not expected to cause adverse effects over an extended period of time, based on a continuous 64-day exposure. These screening criteria represent the most conservative scenario for recreational users.
The trend graphs show the concentrations of dissolved metals rather than total metals, based on the pre- and post-event data. Concentrations are expressed in the dissolved, rather than the total, form of the metal because the dissolved is a better predictor of harm to human health and the environment. For samples with metal concentrations that were too low to detect, EPA plotted the method detection level (MDL) value onto the trend graph. Sampling results for metals that are close to or at the MDL show variability that is not seen for results at higher concentrations.
The trend graphs were created from pre- and post-event data that show the conditions of the Animas and San Juan watersheds. Each sample was analyzed for 24 metals, including arsenic, cadmium, lead, and mercury. Pre-event samples were taken prior to the plume's arrival to establish a baseline for water quality comparisons. Data for pre-event sampling were posted on August 10, 12, 13, and 15, 2015.
Both sediment and water quality samples have been reviewed and compared to RSLs for metals. The concentration of metals in all samples collected are below surface water, soil/sediment RSLs. Based on the comparison of pre-event data with data collected over the past two weeks, the pre-event sampling data show that concentrations for all 24 metals in surface water are trending toward pre-event conditions.
EPA's long-term concern is the effect of metals deposited in sediments in the entire watershed and their release during high-water events and from long periods of recreational use. The Agency is establishing a longer-term watershed monitoring strategy for the surface water and sediments that have been affected by the Gold King Mine spill to identify potential long-term impacts working closely with state and local officials.
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