Measuring Air Quality Over Tailings Ponds

The exploration of oil sands in Northern Alberta generates significant amount of tailings that is stored in tailings ponds over long periods. Fugitive air emissions occur due to evaporation and chemical/biological activities. These emissions include Volatile Organic Compounds (VOCs) and Green House Gases (GHG) examples of which include carbon dioxide (CO2) and methane (CH). 

Flux chambers are used for measuring trace gas fluxes from tailings pond.  However, traditional fixed flux chamber can only cover a small area at a time, and the deployment and operation of these flux chambers are very labor intensive. Mobile platforms, on the other hand, can carry environmental monitoring equipment to cover a large surface area where the emissions are occurring with less labor requirement, especially for remote areas without power supply or other necessary infrastructure. This is the reason Environmental Monitoring and Science (formerly AEMERA) started to develop an autonomous mobile platform, a robot boat, three years ago.

Mobile Platform 1This robot boat was designed for remote controlled or pre-programed operation in tailings ponds and lakes. It is powered by an on-board battery and two solar panels in order to avoid contamination from the exhaust of internal combustion engines. During a sunny day, the electric power is enough to power the Mobile Platform for up to 10 hours continuous operation.  The Mobile Platform can be programed to collect air samples at predetermined locations using an on-board computer and a GPS sensor. It is equipped with a flux chamber and a continuous CO2/CH4/H2O gas analyzer (GHG analyzer). The robot boat was successfully tested this past summer.

The unit was recently demonstrated at a municipal wastewater lagoon in Edmonton. CH4 and CO2 fluxes were measured during the demonstration period. To launch the robot boat into a wastewater treatment lagoon safely, a crane had to be used with additional reinforcement to the boat.   Mobile Platform 2

This Mobile Platform (that is small enough to fit in a half-ton truck) will enable our scientists to study air quality over area sources such as the tailings ponds and wastewater treatment lagoons in a quick and efficient manner. This platform can also be used for a wide range of integrated air and water studies.  An extended abstract on this study has been submitted to the Air Quality Measurement Methods and Technology conference to be held in North Carolina next year.

Figures 1 and 2 show the time series of CH4 and CO2 concentrations. Measured CH4 concentrations  ranged from 2.1 ppm to 63.9 ppm during the 5 minute flux measurement cycles (Figure 3). For CO2, the concentration spanned from 412.9 ppm to 518.0 ppm (Figure 4). During the post-measurement (chamber open) period, the CH4 and CO2 concentrations gradually dropped to the surface ambient levels (2.5 and 420 ppm, respectively).

 

 

Figure 1

Figure 1. Time Series of CH4 Concentration Throughout Sampling Cycles.

 

Figure 2

Figure 2. Time Series of CO2 Concentration throughout Sampling Cycles.

The average CH4 emission flux (2.2 µmol/(m2-s) or 0.32 ´ 10-2 kg/(m2-d)) and CO2 emission flux (5.4 µmol/(m2-s) or 2.1 ´ 10-2 kg/(m2-d)) are shown in Figure 3.

Figure 3

Figure 3. Time Series of CH4 and CO2 Fluxes

The authors are:

Long Fu1, Quamrul Huda1, Zheng Yang1, Lucas Zhang2, Zaher Hashisho2

Environmental Monitoring and Science (formerly AEMERA), Edmonton, Alberta, Canada, 

Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada.