Evaluation of Alternative Causes of Widespread, Low Concentration Perchlorate Impacts to Groundwater

Evan Cox | GeoSyntec Consultants

ER-1429

Objective

The frequency of detecting widespread, low concentration perchlorate impacts to groundwater is increasing as regulators nationwide begin to require perchlorate analysis as part of regional groundwater monitoring programs. While natural sources or formation mechanisms for perchlorate in groundwater are possible, other incidences may result from long-term, non-military inputs, including fireworks and other explosives, bleaches, herbicides, and a variety of other uses of man-made perchlorate salts such as road flares. In addition, perchlorate-containing fertilizers that were manufactured from naturally-occurring Chilean nitrate deposits were historically used in large quantities throughout the United States. Analytical methods for drinking water, such as Environmental Protection Agency (EPA) Method 314.0-Determination of Perchlorate in Drinking Water by Ion Chromatography, are prone to a variety of false-positive detections and interferences related to common industrial chemicals such as sulfonates, raising the question of whether these low-level detections are perchlorate at all. Given the high cost of groundwater remediation at perchlorate sites, it is imperative that the Department of Defense (DoD) develop information and tools that can distinguish military from non-military perchlorate impacts so remediation responsibility and cost can be accurately defined.

The objective of this project was to identify and ultimately quantify, to the extent possible, the potential impacts of wide-ranging, non-military perchlorate inputs to the environment. The first phase evaluated the impacts of alternative perchlorate sources such as explosives, road flares, fireworks, and electrochemically-produced perchlorate chlorine products on groundwater quality. It also expanded on previous research to understand and quantify the potential impact of sulfonates on perchlorate detection in groundwater. The second phase of the project specifically sought to quantitatively estimate and document the potential perchlorate impacts from historic and continuing application of Chilean nitrate fertilizers to the environment.

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Technical Approach

This project combined literature reviews, laboratory studies, and controlled field experiments to generate data to estimate potential groundwater impacts from significant non-military perchlorate sources. The potential contribution of perchlorate to the environment from common road flare use at a highway research center and from the use of explosives in rock blasting and/or mining operations was quantified. Laboratory testing was conducted to confirm and quantify the amount of perchlorate potentially present in electrochemically-prepared products, such as sodium chlorate and sodium hypochlorite. Additional laboratory studies assessed the potential impacts that interfering compounds, such as common sulfonate-containing compounds, had on perchlorate analysis by EPA Method 314.0. Investigations were conducted on perchlorate impacts to soil and groundwater arising from firework use at two sites. The potential impacts of historic and current use of Chilean nitrate on soil and groundwater quality was assessed at two field sites by quantifying the fate and persistence of perchlorate in the applicable media, including groundwater, soil, and soil pore water, as well as potential uptake by plants.

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Results

The potential historic and continuing contributions of perchlorate to the environment from non-military inputs were examined. A technical report was developed based on this literature review. Several anthropogenic perchlorate-containing sources that are produced in high volume were identified. In particular, fireworks are produced in high volume and also had very high perchlorate contents. Most of the perchlorate-containing sources are combusted or consumed during proper use, which greatly reduced the amount of perchlorate available to impact the environment. However, depending on the circumstance, even lower levels of perchlorate in combustion residue were found to be significant enough to cause elevated concentrations of perchlorate in groundwater locally, given the low action levels for groundwater. Improper use (i.e., incomplete combustion or misfires) or poor housekeeping (i.e., exposure to oxygen or temperature during storage of bleach) can increase the levels of perchlorate found in the environment. Thus, it is critical that unused fireworks, flares, and explosives be removed from sites following use. Sources such as Chilean nitrate fertilizers and sodium chlorate-based defoliants and herbicides have much lower perchlorate concentrations. However, they are directly applied to crops and soils, often over large areas. Because of this, they have the potential to contaminate soil and groundwater, especially if used repeatedly over a number of years. Results on perchlorate sources produced in high volume as well as the sodium chlorate-based products are summarized in the Phase I Final Report. Results on the historic and ongoing applications of Chilean nitrate fertilizers are described in the Phase II Final Report.

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Benefits

The information and analytical tools generated by this project provide an increased awareness and understanding of the prevalence of perchlorate in industrial processes and allow quantitative estimation of the potential contribution of perchlorate from non-military sources to the environment. When perchlorate is detected in the absence of military activity, anthropogenic or natural non-military sources should be suspected. Past practices, geographic regions, co-constituents, and isotopic markers can provide evidence to identify the source of perchlorate. DoD remedial obligations and costs may be reduced in areas where perchlorate impacts can be scientifically determined to be the result of non-military sources. (Project Completed - 2011)

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Points of Contact

Principal Investigator

Mr. Evan Cox

GeoSyntec Consultants

Phone: 519-514-2235 x237

Fax: 519-822-3151

Program Manager

Environmental Restoration

SERDP and ESTCP

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