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.
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.
Safe Drinking Water Standards are based on total arsenic, comprising both inorganic and organic sources. The U.S. has one of the toughest standards in the world, regarding arsenic levels in water. The maximum total arsenic content of water cannot exceed 10 ppb (USEPA, 2006). This standard was lowered from 50 ppb in 1975. The Canadian maximum arsenic level in drinking water is 0.010 mg/L (British Columbia Ministry of Environment). Background levels of arsenic are generally low in Canada and the U.S. Much of the arsenic occurring in water is the result of human activity, rather than natural processes.
Arsenic enters the body by several mechanisms. It can stem from food grown in contaminated soil, or it can be absorbed through the skin. It can also be inhaled. Symptoms of arsenic poisoning can be chronic or acute. Arsenic poisoning at low concentrations can produce nausea, headaches, an odd skin color, anorexia, and white lines across the fingernails (McAndrew). At higher concentrations, arsenic can produce vomiting, renal failure, and death (McAndrew). Long-term exposure to high arsenic concentrations has been implicated in many different form of cancer. Arsenic exposure poses a serious health risk to humans.
Arsenic is a naturally occurring element. Almost any waterway will contain at least some concentration of arsenic. These background level are generally low, but can be elevated in areas where water passes over exposed arsenic ore outcroppings. Common background levels from natural sources range between 0.001 to 0.002 mg/L in the U.S. And Canada (British Columbia Ministry of Environment).
Arsenic levels around the Deloro Mine have been found as high as 700-5,000+ ppm (McAndrews). Levels in this range cannot be attributed to naturally occurring sources. Levels this high indicate a manmade source. In this case, mining activities exposed large sources of arsenic containing ore. Rains washed arsenic compounds into the waterways, where it made its way into the groundwater. The site also contained an arsenic refinery where arsenic was separated from the ore and turned into an arsenic containing sludge. Arsenic containinated tailings piles were also washed into the waterways. This type of activity is the most common source of arsenic contamination in waterways.
Motility in Groundwater
Arsenic is highly mobile in groundwater. Aside from ease in traveling in slow moving streams. It is highly reactive and when settled in sediments can be re-released into the water column by chemical or physical activity. Arsenic released into surface water can result in higher concentrations in ground water. Groundwater with higher flow rates is especially prone to highly mobile forms of arsenics. Organic forms of arsenic can release highly mobile elemental arsenic into the water by means of oxidation and reduction reactions.
Arsenic's ability to remain highly mobile in ground water is a key concern in remediation projects. One of the key factors in the potential for high arsenic levels in groundwater is the amount of material available to be introduced. In many projects, the amount of material that can be entered into the system is limited. However, at Deloro, there is the potential for contamination for many years due to the amount of material available to be introduced into the system.
British Columbia Ministry of Environment. Arsenic in Groundwater. February 2007. www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/library/ground_fact_sheets/pdfs/as (020715)_fin3.pdf
CH2MHill. Deloro Mine Site Cleanup. Mine Area Rehabilitation Alternatives. Final Report. Ontario Ministry of the Environment. 2003. http://www.ene.gov.on.ca/envision/techdocs/4915e.pdf.
McAndrew, B. Ministry kept town in dark over arsenic, group says. Tuesday 11 June 1999 the Toronto Star, http://www.e-b-i.net/ebi/Deloro/articles/del990611.html
US Environmental Protection Agency (USEPA). Arsenic in Drinking Water. 2006. http://www.epa.gov/safewater/arsenic/index.html