How the Speed affects growth
The City of Guelph indicated earlier this year that it plans to grow to a population of 165,000 by 2031 from a population of 120,000 today. This is 18,000 less than the population recommended by the province's Smart Growth target of 183,000. The primary reason for limited population projections for Guelph appears to be the assimilative capacity of the Speed River. Assimilative capacity is the ability of a body of water to accept treated waste matter without degrading the quality of life. For this reason, we set out to gain a better understanding of what is the Speed River's capacity, who sets the assimilative capacity, and how the standards are set. What is the Speed River's assimilative capacity? The assimilative capacity is the amount of substances a body of water can receive before the ecology of the river is damaged. For the Speed River, the assimilative capacity is 73.3 million litres per day based on current waste water treatment technology. This means the Guelph waste water treatment plant cannot discharge more than 73.3 million litres per day. The waste water treatment plant is currently operating at 64 million litres per day. This volume is approximately equivalent to 500 litres of water per Guelph resident each day. Waste matter (effluent) volumes discharged are expected to reach the maximum assimilative capacity (73.3 million litres per day) by the year 2024. Increasing the effluent flow to 73 million litres from 64 million litres per day is only possible with stricter sewage concentrations. For instance, the allowable concentration of ammonium nitrogen emitted into the Speed River decreases as effluent volume increases. At the 73.3-million-litres-a-day discharge rate, the ammonium nitrogen concentrations in the effluent must be roughly half that of the ammonium concentrations in the lower effluent rate of 64 million litres per day. The Speed River, like all bodies of water, has a changing assimilative capacity. In addition to substance concentrations, temperature, water flow, and seasonal weather also change the assimilative capacity of a river. In Guelph's case, the low river flow and warmer temperatures in the summer months drops the assimilative capacity of the Speed. With less water there is less dilution of the effluent, which at higher concentrations can harm ecosystem functions. Assessing and setting assimilative capacity requires large-scale environmental knowledge of water quantity and quality. This information must often be amalgamated with other regions within a watershed area. Who sets the assimilative capacity? Since rivers and their watershed spans across multiple jurisdictions, determining the assimilative capacity for a body of water requires the co-operation of various levels of government. For instance, the Speed River is apart of a larger hydrological network within the Grand River watershed. Thus, water quality in the Speed River affects the neighbouring communities of Cambridge and Brantford. The process for determining the assimilative capacity for each waste water treatment plant is regulated by the province of Ontario. The province's role in regulation is to enforce water standards through a certificate of approval. To begin the certificate of approval process, the owner of the waste water treatment plant must first submit an assessment of the assimilative capacity of the receiving water to the province. In Guelph, the owner of the treatment plant is the waste water division of the municipal government's Environmental and Transportation Department. After water tests are conducted up and downstream of the treatment plant site, the concentration and effluent levels can then be set by the province. These guidelines are determined by the Ministry of Environment and Energy with the Provincial Water Quality Objective policy. The Grand River Conservation Authority also contributes to water data collection for informed assimilative capacity decision making. Throughout the Grand River watershed, the conservation authority manages 32 flow-monitoring stations and 31 water-quality stations. This data, combined with site specific tests done by the treatment plant owner, is used to determine the assimilative capacity of the river. If approved, the assimilative capacity determined is documented in the certificate of approval. The effluent level at the waste water treatment plant is then legally binding through this certificate. If the assimilative capacity is found to be too low for waste water effluent needs, federal branches of government (Ministry of Environment, Fisheries and Oceans) step in to create an action plan. How is the assimilative capacity set? Determining the assimilative capacity is done by analyzing water quality and quantity on a site-specific basis. The water quality of the river determines the effluent discharge polices for waste water treatment plants. For example, the Speed River water quality does no meet the Provincial Water Quality Objective for phosphorus. This means that the Guelph waste water treatment plant must operate under Policy 2 of Provincial Water Quality Objectives. Policy 2 states that if the river water quality does not meet the objective, then the water quality of the river "must not be further degraded and all practical measure shall be taken to upgrade the (effluent) water quality to the objectives." Therefore, the effluent discharged must be treated to a high level to remove phosphorus. The state of the river water quality is determined by conducting water tests. Measurements for toxic contaminants and observations of environmental quality indicators are conducted up and downstream of the waste water facility. These indicator observations include measurements for suspended solids, total phosphorus, and total Kjeldhal nitrogen. In Guelph, site specific data collected by the city combined with monitoring data of ecosystem health help to determine what state the river is in and how much extra pollutants the river can effectively buffer out. This is an ongoing process as other environmental parameters change, so to does the river's ability to filter out contaminants. Besides water quality monitoring, the quantity of water is also important in determining the assimilative capacity. The rate of flow in the Speed River affects how much pollutants the river can handle. A reduction in flow of the Speed River means there is less water for dispersion of the effluent. Flow is lower in the summer months and thus the river's ecosystem is more sensitive to higher concentrations of the waste water. Since these seasonal flow changes impact the assimilative capacity of the river, the certificate of approval has different effluent concentrations for summer and winter months. Setting the assimilative capacity for a body of water is an evolving process as monitoring data becomes more precise and ecosystem knowledge increases. The assimilative capacity of a river can also fluctuate with technology and management practices. For instance, more effluent can be discharged into the river if technology can create cleaner effluent. This is currently being considered and explored by the City of Guelph as they develop the 50-Year Wastewater Treatment Plan by assessing waste water infrastructure planning, investment and implementation options. The 73.3-million-litres-per-day assimilative capacity of the Speed River has capped growth in Guelph. Increasing the assimilative capacity of the Speed River may be possible but it will require continued innovation in governance, technology, and understanding of our environment. Brady J. Deaton is an assistant professor in the Department of Food, Agricultural and Resource Economics and Nicole Coupland is a research assistant at the University of Guelph.
Posted on October 13th