2013 Technical Session 8 - Wastewater Issues II

Monday, April 22, 1:55 - 5:00 pm, Shuswap Room


Moderator: Rick Johnson, Sanitherm, Inc.

 

8.1 A Tale of Two Methods: The arguments for and against using the RTK method and the graphical method for estimating sanitary sewer inflow and infiltration rates

8.2 Full Scale Fan Test to Size an Odour Control Facility

8.3 Odour and Corrosion Prevention in a Wastewater Force Main - White Rock Pump Station Superoxygenation System Results

8.4 On-grade gravity sewers in very challenging soil conditions using directional drilling

8.5 Ventilation Modelling for Gravity Collection Sewer Networks

 


Wastewater Issues II | 1:55 pm - 2:25 pm
8.1 A Tale of Two Methods: The arguments for and against using the RTK method and the graphical method for estimating sanitary sewer inflow and infiltration rates
Presenter: Dana Soong, P.Eng., City of Coquitlam, Coquitlam, BC
Additional Contributors: Julien Bell, P.Eng., GeoAdvice Inc., Port Moody, BC; Werner de Schaetzen, Ph.D., P.Eng., GeoAdvice Inc., Port Moody, BC

 

 


Management of sanitary Inflow and Infiltrations (I&I) is a major concern for most Cities and Municipalities in BC. Aging infrastructure, legacy of past engineering practices, and other local climate and soil conditions have led to high sanitary I&I rates. These high I&I rates increase the total volume of flows that need to be treated and increases the strain on the existing system. I&I is composed of two main components: groundwater infiltration (GWI) and rainfall derived inflow and infiltration (RDI&I). The key to managing I&I is knowing the extent of the problem; however, past attempts to quantify I&I rates has resulted in dubious results. In BC, two leading methods are used to estimate peak RDI&I; the RTK method and the graphical method. The RTK method utilizes three triangular unit hydrographs, each having its own characteristic parameters, to create a total RDI&I hydrograph; one hydrograph for the short term (direct connections to the storm system), medium term, and long-term rainfall responses. The graphical method reviews observed peak RDI&I rates against observed peak rainfall rates to develop a linear relationship. The linear relationship is then used to “extrapolate” design RDI&I rates. This presentation will be a comparative review of the two methods identifying the advantages and disadvantages of both approaches. Further, a comparative review of a system performance analysis, of the City of Coquitlam’s North Road sanitary catchment, using the RTK and graphical method approaches will be presented.

Presentation PDF
 


Wastewater Issues II | 2:30 pm - 3:00 pm
8.2 Full Scale Fan Test to Size an Odour Control Facility
Presenter: Michael Celli, P.Eng., AECOM, Burnaby, BC
Additional Contributors: Jack Chow, P.Eng., Metro Vancouver, Burnaby, BC; Peter Takacs, P.Eng., AECOM, Burnaby, BC

 

 


An air management and odour control facility is proposed to mitigate odours from the Highbury Interceptor – a 3m diameter interceptor sewer that conveys the combined sewer flows from the Vancouver Sewerage Area to the Iona Island WWTP.  The facility will continuously withdraw and treat air from the sewer to maintain negative pressure in the headspace and prevent the release of odour within the zone of influence of the facility.  In order to size the odour control system and delineate the zone of influence, a full-scale fan test was performed.  The fan test involved shipping a 50 hp fan to site complete with generator, VFD, and carbon scrubber, and operating the equipment for a week.  The fan inlet was ducted from a nearby manhole, and the fan was operated at flow rates from 7,000 to 16,000 cfm.  In order to quantify the effect of the fan operation, differential pressure sensors were installed in manholes and vents along the 6km long interceptor.  The sensors measured the magnitude of negative or positive pressure in the sewer headspace, and the extent of negative pressure in the sewer indicates the zone of influence for the facility. The fan test had the unique challenge of being performed in a residential area, at the boundary of a city park.  Odour control and noise abatement measures were included to prevent complaints from neighbors.  The fan test was successful in identifying the zone of influence as well as a suitable fan flow rate for the proposed facility.

Presentation PDF
 


Wastewater Issues II | 3:05 pm - 3:35 pm
8.3 Odour and Corrosion Prevention in a Wastewater Force Main - White Rock Pump Station Superoxygenation System Results
Presenter: Trudy Dowla, B.Sc., Pentair Aquatic Eco-Systems, Coquitlam, BC

 

 


The root cause of most odour problems associated with wastewater collection and treatment is the presence of naturally created malodorous gases.  The gases are formed by Sulphate Reducing Bacteria, (SRB) under anaerobic conditions resulting from the imbalance of high BOD loading and the limited solubility of oxygen into wastewater.  This problem is exacerbated in force mains and slow-cycled residential lift stations due to high microbial oxygen uptake rates, retention times, and low dissolved oxygen (D.O.) levels. These anaerobic conditions produce significant amounts of reduced sulphur compounds, leading to hydrogen sulphide (H2S) which is odorous and can be highly corrosive once converted to H2SO4 (sulphuric acid). Since anaerobic conditions are precursors to H2S formation, a logical solution to H2S control is to induce aerobic or oxic conditions.  SuperOxygenation is a process to sustain aerobic conditions by using a Speece Cone also known as a “Downflow Bubble Contactor” (DBC) to efficiently dissolve pure oxygen into wastewater to prevent the formation of H2S and the associated corrosion.  The first system in BC (and only second one in Canada) was commissioned in the City of White Rock on November 29, 2011.  Although there have been challenges over the first year of operation, the system has shown that it can be adapted to changing conditions, and the results include  H2S readings at 0 ppm for more than 90% of the time, and positive effects further downstream that initially designed for. The number of odour complaints has also been reduced.

Presentation PDF
 


Wastewater Issues II | 3:55 pm - 4:25 pm
8.4 On-grade gravity sewers in very challenging soil conditions using directional drilling
Presenter: Thomas Buchmann, P.Eng., AECOM Canada Ltd., Burnaby, BC
Additional Contributors: Scott Neuman, P.Eng., AECOM Canada

 

 


The Bridgeview area in Surrey is within a local floodplain, underlain with peat, very soft silts, and an elevated groundwater table. A vacuum sewer system was installed in the 1970’s and since operation, the vacuum system has resulted in very high operation and maintenance costs, nearly 5 times higher than conventional sewer systems.  High O&M costs, coupled with an aging, over capacity vacuum system, resulted in the need for a reliable, gravity based sewer servicing strategy that can be constructed using advancements in technology and at a Capital Value lower than life-cycle costs of the current system. Long term replacement strategy was for a $22 Million sewer system to service the 2,000 residents.  The strategy consisted of 7 km’s of gravity sewers, 1 km of on-grade directionally drilled gravity sewers, 2 municipal lift stations, and a low pressure sewer system with 200 individually owned private lift stations. This strategy was intended to be constructed over 3 phases. Unique challenges to the project included the design and construction of gravity sewers and a pump station in very poor soil conditions and “boiling sands” influenced by the Fraser River.  Sewer depths ranged from 1m to 6.5m, with depths below 3m not feasible via conventional open-cut techniques.  Other challenges included a pump station that has a 7m deep wet well coupled with a 2-storey operation building designed to house electrical and instrumentation equipment on the upper level above the 200-year floodplain.  Construction was very challenging for City Staff, AECOM and 5 contractors involved.
 
Presentation PDF


Wastewater Issues II | 4:30 pm - 5:00 pm
8.5 Ventilation Modelling for Gravity Collection Sewer Networks
Presenter: Karl Mueller, P.Eng., Kerr Wood Leidal Associates Ltd., Burnaby, BC
Additional Contributors: Yuko Suda, P.Eng, Kerr Wood Leidal Associates Ltd, Burnaby, BC; Ron Weismiller, P.Eng., City of Burnaby, Burnaby, BC

 

 


Work by the Water Environment Research Federation (WERF) and the Australian Research Council (ARC) has advanced the understanding of collection system ventilation dynamics, but until recently no one has established a practical and effective method to dynamically model an entire sewer ventilation system. This presentation will demonstrate the application of such a model developed by KWL and applied to the City of Burnaby’s sewer network.  The air ventilation model was developed for the gravity collection sewers.  It interfaces with the City’s existing fully dynamic hydraulic model, and can be applied on a network-wide basis.  The model is capable of determining the airflow throughout the system, the differential pressures at air release points, and the quantity of air released into the atmosphere.  The model was used to determine the areas of potential odour release and possible mitigation options.  It was also applied to future development, storm event, and future DES facility scenarios.  This will allow the City to predict and mitigate future odour concerns.  The model is also able to simulate ventilation best management practice scenarios and the anticipated system impacts.

Presentation PDF



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