Thesis remediation strategies and implementation

Deloro Mine Remediation

Evaluation of Remediation Technologies for Arsenic contamination at Deloro Mine Eastern Ontario Canada

Site

Deloro is a small town of 180 people located in eastern Ontario. For many years, the residents of this town were unknowingly breathing arsenic contaminated air and drinking contaminated water. Recent legal actions have brought this tiny town to the forefront. The pollution stemmed from a 280-hectare mine located on the eastern edge of town. Sampling sites from 18 sites around the village averaged an arsenic level of 723 ppm, with one location as high as 5,500 ppm (McAndrew).

Two likely sources of contamination have been sited as potential culprits. The first is arsenic dust emitted from refinery smoke stack the settled on the soil. However, the refinery closed in 1961. The second potential source of contamination is from piles of mine waste, known as "tailings." These tailings piles are now covered with rocks to prevent dust from blowing into the town and continuing to increase the contamination levels (McAndrew). Arsenic is a by-product of the mining industry.

Background

The Deloro Mine Site has an industrial history that dates back to 1867. The mine produced gold and arsenical pesticides, cobalt, silver, metal, nickel, and satellite (Ministry of the Environment, 2005). The mine was abandoned in 1961, leaving behind nearly 100 years of hazardous by-products and residues. These include heavy metals and low-level radioactive wastes. Of these, arsenic compounds are the primary concern. One must also remember that until recently, regulations and procedures for dealing with hazardous materials were not as stringent as they are today.

The problem of arsenic at the Deloro site is complex due to the many different sources of contamination. Arsenic is in the soil, sediment, surface water and groundwater. The coexistence of these various mediums creates a number of complex systems for entrainment and cross-contamination. There are old mines on the property, many of which are unknown, creating an extra hazard for remediation crews. The Deloro site is complex from many standpoints. The original owner of the mine was unable to clean up the site.. The Ontario Ministry of the Environment took over the site and has thus far spent close to $20.5 million on the clean up project (Ministry of the Environment, 2005).

Remediation at the Deloro site is different from other hazardous sites due to the volume of the contaminated wastes. At a typical hazardous site, the waste is bagged or drummed and taken to a landfill that is licensed to accept those types of waste. However, this was not feasible at Deloro due to the many different types of substrates and the volume that one would have to remove. The abatement of an arsenic mine is different from projects where arsenic was brought in for some type of manufacturing process. The difference is the volume involved and the nature of arsenic to become entrained in the airstream and traveling for some distance. Arsenic is one of the most difficult compounds to abate for these reasons.

The first step of any remediation project is to eliminate any continuing sources of contamination, including sources of cross contamination. This may mean isolating sources that cannot be eliminated altogether. This was the approach taken with the Deloro Site. Arsenic mines were capped and sealed so that no further arsenic contamination could occur. After primary sources of contamination are controlled, sources of cross-contamination must be identified, isolated, and remediated in an appropriate manner.

Aside from the inability to eliminate the primary source of contamination, the mine itself and acres of tailings, the Deloro Site is complex from a cross-contamination standpoint as well. It is estimated that the Deloro Site contains approximately 650,000 cubic meters of waste (Ministry of the Environment, 2005). Contamination at the site and in the surrounding community are so extensive that almost anything could be considered a contaminated substrate. Some examples of potential cross contamination are:

1.contaminated soil erodes and enters a waterway

2. Airborne arsenic falls on a waterway, which in turn seeps into the ground water

3. Wind disperses airborne arsenic into almost every building in the immediate vicinity

4. People walking on contaminated soil pick up arsenic on their shoes and track it into their homes.

These are only examples of various methods of cross contamination that could exist at Deloro, but there are many other potential mechanisms.

The remediation plan of the Deloro Site was based on dividing the site into zones according to the types of contaminants present. A plan was developed for each of the zones, leading to the ultimate closure of that area. A set of criteria was drawn up for site closure. Plans were submitted and the one that satisfied the most conditions was chosen. The area will necessitate ongoing monitoring to make certain that closed areas do not become capable to re-entraining arsenic into the environment. Remediation of the Deloro site is a long-term commitment.

Scope of the Project

Removal of arsenic contaminated compounds was not feasible. Therefore, the Ontario Ministry of the environment built an Arsenic treatment plant to treat contaminated ground water. This plant is capable of removing 99.5% of the arsenic from the contaminated water that it treats (Ministry of the Environment, 2005). In addition, they have instituted an aggressive water monitoring project and associated laboratory to conduct on-site testing and analysis.

Remediation of the Deloro Mine site has been a multi=phased project. Decontaminating the old arsenic mines was not feasible. Therefore, they simply closed off the entrances in such as manner that arsenic would not continue to be entrained in the airstream, causing continued contamination. They demolished buildings and disposed of them in hazardous landfills. They capped eight hectares of tailings by placing 1/2 meter of limestone on top of them. This would help prevent arsenic contained in them from becoming entrained in the airstream or eroding and entering the water stream. The entire site has been fenced to prevent trespassers from entering the site and carrying hazardous wastes away on their clothing (Ministry of the Environment, 2005).

Groundwater and surface water will be diverted away from contaminated materials through the use of a passive interceptor well network (Ministry of the Environment, 2005). This waster will flow through a groundwater collection and treatment facility already in existence. The treatment plant is planned to operate indefinitely (Ministry of the Environment, 2005).

Contamination of the Moira River remains a key concern in terms of reducing threats to humans. The Moira River flows through the center of the site, presenting one of the most dangerous threats to human health. Arsenic enters the Moira River through erosion of contaminated soil, or from airborne sources. The river then carries the arsenic downstream and deposits it. The River empties into the Bay of Quinte at Belleville. Contamination of the Moira River pollutes major lakes along the way. Efforts at remediation of the Moira River have succeeded in reducing the arsenic in the river by 80% (Ministry of the Environment, 2005).

However, when one considers the extent of the contamination, this waterway still represents a considerable risk to humans.

Another area of major concern is the Young's Creek Area, which is part of a significant wetlands. This is a low-water flow wetlands where arsenic compounds are deposited in the sediment. Arsenic levels in this area affect local plants and animals, in addition to the human risks associated with contact with the waterway. Remediation in this area involves evacuating the water from the area and removing contaminated sediments. These sediments will be stored permanently in a containment vessel. Sediments will be replaced with clean fill and a wetland recovery project will be initiated.

Geology/Hydrogeology of the Deloro Site

The Complex geology of the Deloro area accounts for is development as a successful mining endeavor. It also contributes to the difficulties associated with the remediation process. In general, the surface of the ground slopes to the South and to the East towards the Moira River. This slope is largely responsible for the erosion of contaminated soils flowing into the Moira River. Elevations range from 210 meter above sea level to 185 meters about sea level (CH2MHILL, p. 3-2). The Moira River represents the low-lying area of the river. Mining activities have significantly altered the topography of the area, increasing the rate and are of run-off into the Moira River.

The Deloro Site contains two different forms of bedrock. Precambrian metasedimentary and metavolcanic rock comprise a majority of the bedrock under the site. However, there is a small area of Peleozoic Limestone and Shale along the eastern edge of the property (CH2MHILL, p. 3-2). Young's Creek lies in a depression in the bedrock that is flanked by outcroppings and exposed bedrock. Much of the exposed bedrock lies on the north end of the Moira River (CH2MHILL, p. 3-2). Exposed bedrock demonstrates excessive weathering. Much of the exposed bedrock is pink granite of medium grain (CH2MHILL, p. 3-2).

Bedrock at the Deloro Site is overburdened by both natural and man-made components. Overburden includes clay fill, building rubble, tailings and slag. Natural overburden includes silty clay, silty peat, and silty sand (CH2MHILL, p. 3-2). Overburden is generally thin, averaging 3 meters in most areas, but can go up to 9 meters at times (CH2MHILL, p. 3-2). Native soils primarily reside in areas of low topography.

This topography allows for constant movement and shifting of overburden. Rainy seasons create excessive water flows, which travel down slopes to the low-lying areas and into the waterways. These areas of low topography are of particular concern, as they tend to accumulate deposits of contaminants.

Groundwater and surface water in the area are altered by man-made structures placed by the mining company. Water travels through the area by means of the overburden and the bedrock. In the area of the main mine, water flows primarily through bedrock (CH2MHILL, p. 3-2).Groundwater flows in a generally southeasterly direction. Water flows towards the major waterways such as the Moira River and Young's Creek (CH2MHILL, p. 3-2). Bedrock in the area is complex, providing many depressions, faults, and folds. These are generally shallow and near the surface (CH2MHILL, p. 3-2). The bedrock consists of numerous dykes, sills, xenoliths and highly mineralized areas (CH2MHILL, p. 3-2). These structures have been altered by mining activities, such as blasting.

The Deloro Site is located within the Moira Watershed, which discharges into the Bay of Quinte. The Moira River flows through three lakes: Wolf, Moira, and Stoco Lake. Many of the mining activities took place upstream from Moira Lake. Most of the waterways associated with the Moira River are shallow. Bend Bay averages only 1 Meter in depth. Moira Lake is a widening of the Moira River that averages 3 M. In depth (CH2MHILL, p. 3-2). The Moira River provides the primary inflow and outflow of these structures. The river water is well-mixed during the spring and fall, but can developed thermal layers during the summer in deeper portions of the lake.

The geology of the area creates conditions that promote the formation of shallow water tables. Water is generally slow moving. The degree of mixing of the major wateways promotes homogeneity of contaminants. There may be some settling of arsenic in sediments during the summer as thermal layers develop. The Young's Creek area is particularly at risk for developing higher concentrations of sedimentary arsenic due to the slower flow pattern. The geology and hydrogeology of the Deloro Site contribute to the difficulties associated with remediation.

Motivation for the Thesis

The philosophy of the Deloro Mine Site Remediation differs from other hazardous sites. The number of methods of cross contamination at the site represents the most difficult aspect of remediation efforts at the Site. It would be unrealistic to consider approaching the contamination issues at this site using standard Phase I and Phase II protocols. One has to change philosophy in a situation such as this. Instead of looking at the site as an area that can be decontaminated and deemed "clean" as in most remediation projects, the Deloro Mine Site will never be able to be considered "clean." The best that can be achieved in this case is ongoing management that minimizes the risk to humans as much as possible. This is the approach that has been taken by the Ontario Ministry of the Environment. Monitoring and containment projects will be ongoing at the site.

Contamination at the Deloro Mine Site represents one of the greatest threats to humans. My primary motivation in this thesis is a desire to help protect the human lives that it touches. The scale of the contamination at the site exceeds what one expects at a hazardous site. The Deloro site is not a "typical" remediation project. The site will require continuous monitoring for many years to come. Seldom does one get the chance to work at a site that is as complex as this one. The Deloro Site represents a large scale natural disaster. It could be considered a worse-case scenario in remediation projects. There are many concerns on this site that are not present in other remediation projects. Experience gained on this site will be valuable in any project with which I may become involved in the future.

2.0 Arsenic

Chemistry

Although Arsenic is a basic element, it often does not occur in pure elemental form. Arsenic compounds comprise a majority of the arsenic found on earth. The most common arsenic compounds are sulfides, arsenopyrite, orpiment, realgar, lollingite, and tennantite (USEPA, 2006). Arsenic is often found in silver ore, dycrasite, barite, cinnabar and nickeline. Silver and nickeline associated arsenic are largely responsible for what is found at the Deloro Mine. Arsenic can form into several chemical forms. It can appear trigonal or in an orthorhombic form. It is highly versatile in its ability to form compounds.