Physics of wastewater flow and pathogen transport processes from a soil-based at-grade effluent treatment system and associated groundwater contamination risks in Alberta, Canada

• Author / Creator

  Weldeyohannes, Amanuel Oq

• Understanding of wastewater flow and transport processes and treatment effectiveness through the soil-absorption field of soil-based wastewater treatment systems remains a challenge. In addition, Alberta regulators and the on-site wastewater industry wanted to quantify the effectiveness of the new LFH At-grade soil-based wastewater absorption and treatment system design. An extensive field research program was executed at Wetaskiwin Rest Stop, Central region of Alberta, a site that has been receiving secondarly treated and ultraviolet disinfected effluent via pressurized effluent distribution at-grade laterals since 2007. The specific objectives were to investigate: i) hydrologic response to effluent infiltration from at-grade line sources under shallow groundwater conditions, ii) fate and transport of pathogens under boundary conditions typical of on-site water treatment systems (OWTS), and iii) groundwater contamination risks associated with OWTS. Following site characterization, field-scale tracer experiment was conducted using E.coli and Bromide as step and pulse inputs respectively. Groundwater response to effluent infiltration, wastewater plume movement, E.coli and virus concentrations were monitored in nests of monitoring wells over time. Finally, using the field measurements, HYDRUS 2D was used to investigate groundwater contamination risks associated with OWTS. Considering the existing regulatory requirement of 7-day effluent travel depth through the vadose zone that has been established in Alberta, a residence time assumed to be enough for pathogens attenuation in the vadose zone, weekly cycle hydrologic responses were interpreted. Findings indicated: i) significant hydrologic response to effluent infiltration from at-grade line sources at a weekly scale, ii) effluent reaching the groundwater for approximately 15% of the time in the spring and summer periods when effluent loading rate of ≥5 cm3 cm-2 d-1 encountered a groundwater at ≤0.5 m below the ground surface. These conditions also coincided with the significant 7-day cycle of the effluent input function due to traffic on the highway and use of the facilities. The results suggest consideration of both surface effluent loading and regional hydrologic conditions when designing at-grade wastewater treatment systems to minimize potential groundwater contamination risks; iii) the vadose zone of ≥0.88 m thick, the vertical separation between the at-grade lines and the top of the groundwater level, filtered E.coli bacteria that were present in the infiltrating effluent to acceptable levels achieving the 7-day effluent travel depth design criteria, however it didn’t perform well for some viruses, and iv) initial groundwater depth from the surface is critical for designing at-grade effluent treatment systems. Under the prevailing site boundary conditions and assuming a homogenous medium, a loading rate up to 15 cm3 cm-2 d-1 poses less threat when the initial depth to groundwater is at ≥2 m. In practical terms therefore, matching effluent loading rate vis-a-vis the effluent receiving site characteristics is critical particularly during the spring snow melt and summer period. In addition to the design criteria of OWTS, inclusion of performance criteria as standard of practices for these systems is suggested. The findings presented in this thesis contribute significantly to the understanding of wastewater flow and transport under boundary conditions typical of OWTS and shallow groundwater conditions.

• Subjects / Keywords

  • Process based modeling
  • Alberta Standard of Practice
  • Multidimensional saturated and unsaturated flow and transport
  • On-site wastewater treatment system
  • Aspen
  • Environmental Site Assessment
  • On-site Wastewater Treatment System
  • Spectral and wavelet signal analysis
  • Hydrological processes
  • Wastewater flow and pathogen transport processes
  • Ultraviolet disinfection
  • 7-day effluent travel depth
  • Groundwater mounding
  • Nest of wells
  • Soil physics and hydrology
  • Wastewater plume center of mass
  • Soil absorption field
  • Bromide and nitrate plume
  • Pressure transducer
  • Vadose zone thickness
  • Monitoring wells
  • Field investigation
  • Hydrogeology
  • LFH At-grade effluent dispersal lines
  • Groundwater hydrology
  • Wetaskiwin Rest Stop
  • E.coli attenuation
  • Hydrologic response to effluent infiltration
  • Safety Code Council
  • Septic system
  • Soil adsorption field
  • Soil-based effluent treatment
  • Electromagnetic Induction
  • Moment analysis
  • Groundwater flow and gradient
  • Mapping
  • Groundwater contamination risk assessment
  • E.coli and Virus transport
  • Threshold values

• Graduation date

  2015-06

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3K386

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.