Disposal of Arsenic-Bearing Water Treatment Residuals: Assessing the Potential for Environmental Contamination

Rio Rico, AZ

February 13, 2006

UA SRP hosted a workshop entitled "Disposal of Arsenic-Bearing Water Treatment Residuals: Assessing the Potential for Environmental Contamination." The workshop took place in Rio Rico, Arizona, February 13-14, 2006.

Purpose:

The Toxicity Characteristic Leaching Protocol (TCLP) is the primary test currently stipulated by EPA to assess potential toxicity of arsenic bearing residuals (ABR) from water treatment processes and consequently whether they may be disposed of in non-hazardous, mixed solid waste (MSW) landfills. Nearly all of the residuals generated by the removal technologies currently used or predicted to be used for arsenic removal from drinking water pass the TCLP. However, SRP supported research (Ghosh, Mukiibi, and Ela, “TCLP Underestimates Leaching of Arsenic from Solid Residuals under Landfill Conditions”, Environmental Science & Technology, 38(17):4677-4682, 2004) has shown that the TCLP significantly under-predicts the release of arsenic from ABR under MSW landfill conditions.

Based on this and other supporting research, a collaborative dialogue between SBRP and EPA researchers and regulators was initiated in late summer 2004. A follow-up meeting between members of the EPA, SBRP, ATSDR and academic researchers began to tackle the science and research-related issues surrounding assessment and disposal of the ABR of water treatment technologies.
The meeting in 2005 covered the following topics:

  1. The extent of the ABR issue.
  2. The leaching potential of the ABR from currently available drinking water treatment technologies.
  3. Emerging arsenic drinking water treatment technologies and the predicted leaching from their residuals.
  4. Potential treatment of ABR prior to disposal to minimize leaching.
  5. A proposed integrated framework for addressing the issue.

Objective:

Building on the conclusions derived from the 2005 workshop, this year’s objective was to integrate the most current scientific understanding of ABR behavior with the most appropriate modeling capabilities in an effort to assess the potential threat posed by ABR.

Summary:

The two-day meeting consisted of a series of presentations designed to summarize current knowledge and highlight research needs for several posed questions. The selected questions were:

  1. What are the character, concentration and production rates of the ABR that will be generated and how will they be disposed?
  2. How and how well do we assess ABR and understand landfills?
  3. What are the character and conditions of likely arsenic transformations in and out of landfills?
  4. What can we learn from existing landfills’ behavior and model simulations?
  5. How do we get an integrated assessment of the potential threat from ABR landfill disposal?

The workshop produced substantive discussion of these issues, and led to the identification of several critical research needs. In addition, the group agreed that in order to embark upon the upcoming challenges of ABR, it is crucial to maintain holistic point of view, which incorporates preventative methods and education. A detailed summary of the workshop results is being developed for publication. A second follow-on workshop is being planned for fall 2006 with the tentative title, Arsenic and Landfills, and will be held in the New England area.

Funding:

Funding for this workshop was provided by the NIEHS SBRP.