A comprehensive facility plan has been the traditional tool for conducting an overall assessment of wastewater facilities. Considerations typically include replacement of antiquated equipment with modern more efficient equipment, rehabilitation of structures and buildings, and consideration of more energy efficient processes. Sewered growth projections are made, and the impact of growth on the ability of the facility to consistently meet discharge permit requirements is evaluated. Potential future regulatory requirements are assessed, and likely order-of-magnitude costs are developed to address these possible distant effluent discharge limits. One piece missing in many facility plans is an assessment of “the impact of climate change.”
Assessing Additional Risks
Wastewater facility planning represents a logical opportunity to address climate change impacts and allow for capital cost projections to address potential issues. What are these issues and what impacts might they have? As you would expect, impacts are different for each facility based on location, elevation, and the particular characteristics of each facility. For example, air and water temperature increases, and sea level rise, will have significant impact on some facilities.
One City’s Response to Climate Change
Due to the foresight of management at the City of South Portland, a recent facility plan developed by Wright-Pierce addresses the impacts of climate change on the wastewater treatment facility and what adaptations may be needed to meet these challenges.
The City’s treatment facility is located adjacent to the Fore River and Portland Harbor. While the facility has no direct ocean exposure, the Fore River flows to Casco Bay and the Atlantic Ocean. Changes in sea level and storm surge, and increases in air and water temperatures, are potential impacts presented by climate change. Future estimates for sea level and air temperature increases were reported by a team of scientists from UNH, UMass and ATMOS Research and Consulting in a 2009 report titled “Climate Change in the Casco Bay Watershed.” For sea level rise, the low to high range of possibilities suggest an increase of water level by 2050 of between 0.7’ and 1.4’ and by 2100 a range between 1.4’ and 5.4’. The recently published “5th Assessment Report of the Intergovernmental Panel on Climate Change” confirms the likelihood of sea level rise of this magnitude. Likewise, increases in air temperatures are estimated, including the magnitude of peak daily temperatures, which are projected to rise by 4°F to 12°F by 2050 and by 6°F to 20°F by 2100. The air temperature increases will also result in increases in wastewater and water body temperatures.
The air and water temperature impacts are fairly straightforward to assess, since they reflect conditions at more southerly regions. At activated sludge facilities with fine bubble-aeration, like South Portland, increased air temperatures may increase the required size of blowers to provide sufficient air. Rising water temperatures could be a good or bad thing depending on the treatment process and need to nitrify, or avoid nitrification, as nitrification will be accelerated with warmer temperatures. For the South Portland facility, the blowers are sufficiently sized to handle the increased air temperature for the current 20-year planning period. A future total nitrogen limit is likely as Maine DEP develops ambient water quality criteria for Casco Bay. In this regard, the anticipated increase in wastewater temperatures might be considered beneficial.
However, rising sea levels present two significant challenges to the South Portland facility. First, the facility is currently able to discharge by gravity to the receiving waters under current peak flows and a 100-year storm event including the storm surge effect. Increasing sea level will correspondingly increase the 100-year flood elevation and require effluent pumping, affecting both capital and operation and maintenance costs. Higher sea levels also will flood much of the treatment facility grounds requiring a dike to protect certain facilities. In all, the City is faced with future construction of a 66 MGD effluent pump station and construction of a perimeter dike to protect the treatment facility. Projected costs, in today’s dollars, are expected to be in excess of $16M.
While it is not expected that these improvements will be needed within the next 20-year planning period, they establish a benchmark for future consideration. Water levels can now be monitored over the upcoming years and compared to the study projections.
There is plenty of uncertainty ahead in terms of what will happen. Our global environment is extremely complex. We may, as a planet, significantly lower emissions with major changes in energy use. We may continue at the current rate with conservation measures offsetting population growth. Or we may see increasing emissions due to the growth in the Earth’s population and increased standard of living in developing countries. Each of these scenarios has corresponding impacts on the magnitude of temperature and sea rise that will occur. These scenarios bracket the range of possibilities, and your facility planning efforts should include an assessment of this range to allow a dialogue to begin about how and when changes need to be incorporated in our facilities to safeguard their operation and the environment.