EnviroTech Dispersion Modelling to Address Air Quality during Remediation of Hydrocarbon Impacted Soils

Transcription

1 EnviroTech 2018 Dispersion Modelling to Address Air Quality during Remediation of Hydrocarbon Impacted Soils Presented by: Cody Halleran, B.Sc., E.P. & Pippa Cookson-Hills, M.Sc.

2 THE PROBLEM Excavation of hydrocarbon contaminated soil results in the inadvertent release of air contaminants that can pose a risk to the workers on site, the environment and even the public AER (ERCB): oilfield waste must be handled in such a manner that it does not produce fugitive air emissions or uncontrolled gases, which exceed GoA Ambient Air Quality Guidelines, produce uncontrolled fumes or gases sufficient to pose a risk of fire or explosion, or threaten public health, safety, or the environment through other means. 2

3 Discussion Are employees at risk of exposure from an OHS standpoint? How can we quantify our risk? Are we required to prevent exposure? What is the risk? 3

4 CONTAMINANTS VOCs from excavating hydrocarbon contaminated soils result in the release of Benzene, Toluene, Ethylbenzene and Xylene (BTEX) to atmosphere Alberta Ambient Air Quality Objectives (AAAQO) (ppmv) Alberta OHS Exposure Limits (ppmv) Contaminant One-Hour 24-hour Annual 15-Minute Eight-Hour Benzene Toluene Ethylbenzene Xylene Benzene has substancially more restrictive limits for Air Quality & OHS exposure FOCUS ON BENZENE 4

5 BENZENE C 6 H 6 Naturally occuring hydrocarbon in Alberta Carginogenic Can be deposited by spills/releases Can be released by excavating, homogenizing soil Easily volatilized especially in warmer temperatures, drier soils 5

6 Discussion AER (ERCB): oilfield waste must be handled in such a manner that it does not produce fugitive air emissions or uncontrolled gases, which exceed GoA Ambient Air Quality Guidelines, produce uncontrolled fumes or gases sufficient to pose a risk of fire or explosion, or threaten public health, safety, or the environment through other means. Are employees at risk of exposure from an OHS standpoint? Does the excavation of hydrocarbon contaminated soil put the public at risk? How can we quantify our risk to ensure compliance? 6

7 BENZENE MEASUREMENT CMS Tubes UltraRAE3000 Portable GC GC 15-min Average (STEL) X Resolution X X X Sensitivity X X X Ease of Use X X X Lowest cost of ownership X X Specificity X X X X X Lowest Benzene Detection (ppmv) <.01 1-hour Benzene AAAQO limit (ppmv).01 CMS: Chip Measurement System, GC: Gas Chromatograph STEL: Short term exposure limit, AAAQO: Alberta Ambient Air Quality Objectives -- NO CONTINUOUS MONITORING 7

8 Solution Atmospheric Dispersion Modelling The mathematical simulation of how air pollutants disperse in the ambient atmosphere This is completed using site-specific terrain and meteorological data. Includes effects from buildings /structures within the assessment area (in this instance, a soil pile) Can be used to determine the concentration of benzene from an excavation Can be used to establish a potential zone of impact around the excavation 8

9 PROCESS Use dispersion modelling to develop a zone of impact / quanitfy the risk Set up a monitoring network based on the zone of impact to comply with AAAQO Protect the public/workers and adjust practices accordingly 9

10 Determination of Benzene Emissions Excavation Pile Excavator Pit Benzene emissions will result from: Exposed waste in the excavation pit Material as it is dumped from the excavation bucket Waste/soil in short-term storage piles Assumptions: Soil is only moved once Soil volume in excavator remains constant 10

11 Determination of Benzene Emissions Excavation Excavator Pit Magnitude of benzene emissions depend on: Porosity Moisture content of soil Excavation Rate Contaminant concentration in the soil Size of equipment used Air temperature Pile Assumptions: Porosity-constant Moisture content of soil-constant Excavation Rate-constant Contaminant concentration in the soil constant Size of equipment used-constant Air Temperature will be varied 11

12 Case Study Model Setup Excavation in the Inglewood Wildland Park 32 ha Former oil refinery ( ) Between , approximately 1500 m 3 of oil were recovered from subsurface In 1992 the surface soils were removed after the refinery was dismantled The spoil materials from the excavation were placed to form hills Pit Pile 12

13 Modelling Scenarios Air temperature ( C) Soil Quality Average Contaminant Concentration (ppm) Excavation Rate (m 3 /hr) Bulk Density of Soil Type of Soil 5-10 Wet or Compacted Loam textured soils developed on moderately fine textured glacial till. Average contaminant concentration determined from remedial investigation took soil sample with the highest concentration (used value from previous remediation project) Assumes 75 scoops / hr (2 m 3 per scoop) Modelled using AERMOD Modelled in the spring months, assuming wet or compacted. 13

14 Dispersion Modelling 1-Hour Benzene 5 C Maximum concentration ppmv Impact zone- 3 km 0.27 ppmv Benzene hourly limit = 0.01 ppmv 14

15 Dispersion Modelling 1-Hour Benzene -10 C Maximum concentration ppmv Impact zone- 2.3 km 0.16 ppmv Benzene hourly limit = 0.01 ppmv 15

16 Modelling Results AAAQO Air Temperature ( C) Impact Zone Radius (km) Concentration (ppmv) AAAQO (ppmv) 0.01 Is the public being exposed to benzene? 16

17 Modelling Results OHS Air Temperature ( C) 5 Averaging Period Concentration (ppmv) OHS (ppmv) 8-hour min hour min How are you developing your monitoring network? 17

18 PROCESS Use dispersion modelling to develop a zone of impact / quanitfy the risk Set up a monitoring network based on the zone of impact to comply with AAAQO & OHS Protect the public/workers and adjust practices accordingly 18

19 Discussion We can use these modelling results to develop a potential zone of impact around the excavation site 19

20 THANKS! ANY QUESTIONS? You can contact us at: 20

21 References 1. Environment and Climate Change Canada (2018, March). Retrieved from: 2. Rae Systems ( 2012, April). Monitoring Benzene and Choosing an Appropriate Monitor for Personal Protection and Compliance with Exposure Limits. Retrieved from: Monitoring-Benzene-and- Choosing-an-Appropriate-Monitor-for-Personal-Protection-and-Compliance-with-Exposure-Limits_ pdf. 3. United States Environmental Protection Agency (1992, March). Air/Superfund National Technical Guidance Study Series: Estimation of Air Impacts for the Excavation of Contaminated Soil. Retrieved from: 21

22 Dipsersion Modelling 1-Hour Benzene 5 C Maximum concentration µg/m³ Impact zone- 3 km , µg/m³ 0.25 ppmv Benzene hourly limit = 30 µg/m³, 0.01 ppmv 22

23 Dipsersion Modelling 1-Hour Benzene -10 C Maximum concentration µg/m³ Impact zone- 2.3 km µg/m³, 0.16 ppmv Benzene hourly limit = 30 µg/m³, 0.01 ppmv 23

24 1-hour Benzene: Wet or Compacted at 25 C 1, µg/m³, 0.46 ppmv Benzene hourly limit = 30 µg/m³

25 1-hour Benzene: Dry or Uncompacted at 25 C 3, µg/m³, 1.04 ppmv Benzene hourly limit = 30 µg/m³, 0.01 ppmv

26 Modelling Setup Storage piles emissions must Act as an obstacle in contaminant dispersion Emit from all exposed sides A pile consists of Three point sources at half height on each side Nine point sources at full height on the top

27 North Shore Air Group Building Downwash Building downwash occurs when aerodynamic turbulence induced by nearby buildings cause a contaminant emitted from an elevated source to be mixed rapidly towards the ground, resulting in high ground-level concentrations

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