By Jennifer Young, Senior Water Resource Engineer
Developing land affects its hydrology—or the movement of water across it. Urbanized areas have fewer plants and less soil to soak up and filter water. Instead, pipes carry water directly to rivers and lakes, along with all the pollutants it’s picked up along the way. But using Low Impact Development (LID) and Green Infrastructure (GI) techniques mitigate damage to our waterways. Designing with LID and GI means using processes or facilities to slow down, soak up, and clean storm water runoff. These techniques, while becoming more common in parts of North America, are still relatively new in some, including my home province of Ontario. New regulations from the Ontario Ministry of Environment and Climate Change, however, mean developers will need to put LID and GI into practice by 2017.
While many jurisdictions across North America have already adopted LID/GI, many misunderstandings about the techniques persist. How do LID and GI work? How do you use them to design, operate and maintain a site? Here are five facts you need to know about LID/GI in Ontario, and beyond.
- The Ontario Ministry of Environment and Climate Change (MOECC) expects you to use LID/GI in developments. The MOECC released the Interpretation Bulletin: MOECC Expectations Re: Stormwater Management. In that publication, the MOECC stated that it is not seeing the use of LID/GI being adequately reflected in the Environmental Compliance Approval (ECA) applications being submitted for ministry review. That has to change. The MOECC expects that LID/GI will be better reflected in the ECA process moving forward. To ensure this happens, the MOECC is preparing a LID stormwater management guidance document that’s due for release later in 2016. Many municipalities in Ontario are getting ahead of the game and are already working to define their volume reduction and water quality targets and to create guidance documents to address both the MOECC concerns and pressures in their local watersheds.
- LID and GI can be used on soils with infiltration rates as low as 1 mm/hr – and the MOECC expects to see this. The current Ontario guidance suggests that infiltration not be used when soil infiltration rates are less than 15 mm/hr. But LID/GI have been successfully used in soils with much lower infiltration rates, such as clay soils with infiltration rates as low as 1 mm/hr. The infiltration rate of soils describes how quickly water drains into them. Soils with low infiltration drain water into the ground at a much slower rate, but can still soak up a significant volume of water over a day. LID/GI on poorly draining soils need to be properly designed with underdrains to ensure drain times and proper function. The MOECC has indicated that they expect to see LID/GI on these types of soils and will accept LID/GI planned for soils with an infiltration rate less than 15 mm/hr.
- LID and GI can reduce or even eliminate the need for downstream infrastructure. Widespread use of LID/GI in developments can reduce the need for downstream pipes and end-of-pipe stormwater ponds that move and treat the runoff from larger rainfall events that LID/GI are not designed to handle. This is because the amount of water going to the downstream pipes and ponds is reduced as the LID/GI soaks the water into the ground to the shallow groundwater table (interflow). LID/GI may not handle all the runoff from large events, but they will still infiltrate a portion of the rainfall. Reducing the downstream ponds by the volume that the LID/GI infiltrates will ensure the ponds continue to work as designed. You’ll need to pre-consult with the region or municipality and the Conservation Authority to ensure acceptance from all regulatory agencies, but the MOECC has indicated that they are willing to allow reductions in downstream stormwater infrastructure if the municipality/CA will accept it. There are several examples in Ontario where widespread LID facilities were used along with a downstream ponds or wetlands – but the end-of-pipe facility is not working because no water is reaching it.
- LID and GI can be used in winter climates; in fact most LID/GI facilities still function when temperatures are below zero. Infiltration facilities do experience frost penetration, however it does not significantly affect performance as the slightly warmer melt or rain water entering the facility will thaw the soils, with frost occurring again once the event is over and the temperature drops back below zero. This cycle continues throughout the winter months. Additionally, there is no evidence of frost heave issues with these systems as water rarely freezes in the facilities and if freezing happens the media has larger pore spaces that can handle the expansion without damage. Systems that rely on vegetation for treatment may be less effective in winter months when the plants are dormant, but the soils will continue to function as a filter material and infiltration will continue with little change. Using permeable paving can eliminate icing issues as melt water is immediately infiltrated and doesn’t have a chance to refreeze on the surface. LID/GI facilities do require some additional thought for winter operations. You should not plow snow into the facilities, nor use them as a snow storage area. Avoid using sand as a dicing agent, unless the facility was designed with a pre-treatment area. You should also implement a salt management plan to avoid infiltrating large volumes of salt into the groundwater. Sites in high risk well head protection zones should avoid infiltrating areas that receive salt in the winter months.
- LID/GI can cost less than traditional infrastructure. The US Environmental Protection Agency (USEPA) has studied the cost of LID and released Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices. This study summarizes 17 case studies of developments that include LID/GI and compares the cost of these developments using conventional servicing. In a few cases the LID/GI project cost were higher (3/17 cases), but in most cases LID/GI can reduce project costs (14/17), with a total capital cost savings of 15% to 80%. Site specific factors will be a major influence in project cost. This study only looked at capital costs and did not include more holistic benefits that could factor into using LID/ GI. Developments that use LID/GI are more marketable and sell faster than those without visible GI features. Lots with LID/GI are more desirable and command a premium price (up to 30% in some cases) compared to conventional lots in a similar development. Buyers also enjoy the increase of green spaces and the proximity to open spaces. Developers may also increase the total number of developed units using LID/GI.
If LID/GI interests you and you want to learn more, contact Jennifer Young at Jennifer.Young@stantec.com or 519-575-4123
Stantec’s LID Seminar Series’ first two sessions will be live on the Stantec website starting August 1.