Impact/Purpose:

To assess the stability of "FeOOHAs" residues in existing drinking water distribution systems and drinking water generated wastes.

Description:

The Arsenic Rule, which became effective on February 22, 2002, is going to require public treatment facilities to remove arsenic (As) from drinking water supplies if As exceeds the new ten parts per billion (ppb) drinking water maximum contaminant level (MCL). The date by which systems must comply with the new standard is January 23, 2006. Because arsenic is geologically correlated with iron, it is common to find elevated concentrations of iron in waters which exceed the arsenic MCL. Iron co-precipitation is the most common means of reducing the arsenic concentration in finished drinking waters. The by-product of this treatment is "FeOOHAs" (an arsenic containing iron oxide / hydroxide) which is commonly back-washed off treatment filters to settling ponds (the resulting sludge can be spread on farm land), streams (the "FeOOHAs" settles out on the stream bed bottom) and / or disposed to landfill (if it passes Toxicity Characteristic Leaching Procedures [TCLP]). The mobility of these solids (which can contain parts per million quantities of arsenic) and their impact on the surrounding environment is not well documented and is a question which needs to be addressed. In streams, the seasonal redox changes in the water could liberate the arsenic resulting in additional uptake by fish and benthic aquatic life. In land applications, the application of fertilizers could solubilize a portion of the arsenic. Natural weathering of the solid on soils and/or microbial release could contaminate agricultural crops grown on the treated soils. Finally, the stability of landfill disposal could be influenced by microbial action. In all cases, the arsenic originally removed from the water during treatment could become an exposure source depending on the environmental conditions which surround the discharged "FeOOHAs". Thus, one of the goals of this task is to characterize conditions which induce the mobility of the As in "FeOOHAs" solids associated with drinking water. This should provide some guidance to treatment engineers and potentially minimize arsenic exposures induced by the dissolution of the arsenic from "FeOOHAs" solids.

A second issue is stability of "FeOOHAs" which has deposited over a number of years as a scale within the distribution pipes. Compliance with the new drinking water standard may cause some of the older iron co-precipitation plants to tweak their removal strategy (in order to improve arsenic removal) by adding a pre-oxidation step. Pre-oxidation may cause a change in the water's redox potential and this shift in redox potential may cause the "FeOOHAs" deposits in the distribution system to be resolubilized. An improved understanding of this dissolution process would aid in developing an analytical protocol to measure the extent of the release from the existing pipe prior to installing a new treatment system or modifying an old one. An analytical protocol which at least estimates this removal rate would aid in treatment decision making necessary to comply with the implementation of the arsenic rule. If dissolution of arsenic residues is unavoidable, the release estimates may aid in informing the public of potential episodic exposures. Therefore, another aspect of this task is the development of a protocol that can be used to provide an estimate of the upper limit on these exposures.

Record Details:

Record Type:PROJECT

Start Date:10/01/2002

Projected Completion Date:09/01/2008

Record ID: 56082

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Project Information:

Progress :The PI met with NRMRL engineers (9/9/03) to discuss their research, the distribution pipe aspect of this project and the fact that arsenic containing residues represent a potential source of future exposures. Arsenic removal treatment processes were discussed with an emphasis on predicting water chemistry changes which may lead to arsenic release from the distribution pipe "scale" (an arsenic containing iron oxide / hydroxide). There was considerable discussion about the species dependent mobility of arsenic once the arsenic is absorbed on the iron hydroxides. NERL's research under task 10910 (completed) was also discussed (a procedure for speciating arsenic in iron hydroxide precipitates formed during shipment). A secondary means of evaluating the arsenic species present on the solid is x-ray florescence (a technique NRMRL had limited access to through a third party). The meeting ended with the understanding that a coordinated project would be beneficial to improving the understanding associated with arsenic binding to pipes and absorption media. Additional meetings were planned.

This task received fundingin FY04 through a NRMRL initiative.

A post-doc was chosen in September 2004. The initial emphasis of this project will be to investigate what treatment conditions may result in the solubilization of the arsenic bound to "FeOOH". A feasibility study evaluated an analytical setup which extracted drinking water solids and speciated the extract within 5 minutes.

These data indicated that the As(III) removed from drinking water is more labile on "FeOOH" solids than its As(V) counterpart. These results were incorporated into the last product from the arsenic preservation task 10910. Finally, these results were presented to NRMRL scientists. Note: The TIMS products listed under this task are from a related completed task (10910).

A research plan was prepared in FY04 and sent out for internal and external review in November 2004.

Relevance :The Office of Research and Development has designated the study of arsenic as a high priority research area because of the health risk associated from exposure to this element. This task is relevant to the Agency's mission in that it addresses research needs identified the Office of Research and Development's Arsenic Research Plan (ARP). Chapter four within the ARP outlines treatment research activities which would minimize the risk and increase the reliability of arsenic removal systems and ultimately minimize exposure to arsenic from drinking water ingestion or dietary exposure. One of the issues within this chapter is the minimization of residuals and the ability to stabilize the wastes so that they would comply with existing environmental regulations. The relevance of this research is growing as a number of proactive treatment plants begin to move towards compliance with the Arsenic Rule. Significance: Stabilizing these wastes imply minimizing future exposures induced by treating existing contaminated drinking waters. This task should aid in the implementation of the Arsenic Rule from a treatment strategy perspective and a residual disposal perspective. From a distribution pipe perspective, the release of the arsenic from the pipe "scale" represents an exposure source which may grow as the number of treatment facilities change their treatment strategy to comply with the Arsenic Rule. Impact: The impact of improving our understanding of the mobility of these wastes lies in minimizing the transfer of today's drinking water exposures to tomorrow's dietary and ecological exposures. These solids will be produced across the US so that the impact of increased mobility is not isolated to a defined geographic area. The goal of the distribution pipe work would be to devise a set of chemical tests which would set a boundary condition on treatment parameters which cause the desorption of arsenic from the pipe. This test could be used to predict potential releases and would have a huge impact in treatment decision making as the Arsenic Rule moves towards implementation. Collaboration and Customer Interaction: At the inception of this project, the PI will collaborate with Tom Sorg (treatment engineer) from NRMRL through routine (every other month) informal meetings. Communication will be maintained with the Office of Ground Water and Drinking Water in order to determine research needs and provide information which could impact future arsenic drinking water regulations. This exchange is accomplished through teleconferences, through communication with NERL's ALD for Drinking Water or through exchange of research results. The PI is scheduled to present some of NERL's arsenic speciation research on a monthly conference call with the Office of Water and the Regions.

Clients :Office of Water, Office of Ground Water and Drinking Water (Jeff Kempic, Hiba Shukairy, Valerie Blank, Kesha Forrest)

Project IDs:

ID Code :12509

Project type :OMIS