Infill and redevelopment could grind to a halt next year when new stormwater rules go into effect. That’s because the new rules will make it much more difficult to detain and treat stormwater on smaller sites where there isn’t room for huge stormwater detention ponds. Construction in undeveloped areas will also require larger stormwater ponds, but smaller sites for redevelopment and infill will be the hardest hit by the new rules.
Why is stormwater a problem? The short answer is pollution and flooding. Runoff from impervious surfaces, such as roads and roofs carries a wide variety of pollution into streams. Many people don’t realize how much water pollution is caused by drippings from cars and other vehicles. Even well maintained vehicles will drip small quantities of antifreeze, motor oil, transmission fluid, brake fluid and particles of brake lining. When it rains these drippings can be washed into streams.
The Washington State Department of Ecology (DOE) has declared that stormwater runoff is the top water pollution problem in the urban areas of the state. But controlling pollution is only half of the problem, according to DOE. The other half is controlling flooding and increasing streamflow during the drier summer months.
In the days of Lewis and Clark, when old-growth forests abounded, rainwater was largely absorbed into the ground where it replenished seeps and springs, or it was absorbed by trees where it evaporated. DOE estimates that in Washington’s forests, the needles of evergreen trees hold as much as 40 percent of a low intensity rainfall. As the state became settled, trees were cleared for farms and fields, and eventually buildings, roads and cities. Instead of soaking into the ground, stormwater accumulates on impervious surfaces such as roof tops and parking areas and runs off rapidly.
That’s why the current stormwater regulations require new development to detain stormwater in ponds and to release it at a slower rate to control flooding. Under the current stormwater rules known as the Puget Sound Stormwater Manual, the water must be detained and released at a rate that does not exceed the pre-development rate of runoff. These stormwater detention facilities are also required to treat runoff to meet water quality standards to control pollution before the water is released.
But the current rules don’t go far enough for DOE. In early 2007, DOE issued a new general permit that requires Clark County to update its stormwater regulations to meet the requirements of DOE’s new Western Washington Stormwater Manual. The chief difference between the current rules and the new Western Washington Manual is that it requires new development and redevelopment of existing sites to release stormwater at the same rate as it was released when Lewis and Clark roamed our forests.
Under the current Puget Sound Manual, the rate of runoff allowed for new development or redevelopment is based on the pre-development conditions, going back 30 years before the proposed development. But the new Western Washington Manual limits the allowed rate of runoff to that of an old growth forest. This requires detention ponds to be four or five times bigger than what they have needed to be under the existing rules.
Some projects, particularly those with large surface parking areas, may employ pervious pavement to allow water to infiltrate directly into the ground. But even with pervious pavement, detention ponds will still need to be about twice as big under the new rules. Pervious pavement also requires frequent maintenance, and many developments won’t be able to take advantage of pervious pavement. For instance, if the soils have too much clay, the water may not infiltrate into the ground. In areas of landslide potential, infiltration can increase the likelihood of a landslide. And higher density developments with underground parking don’t have large pavement areas.
The Western Washington Manual discourages redevelopment of existing sites because they will need to meet the new rules, and in many cases, there won’t be enough room on the site to double or quadruple the size of the stormwater pond. Infill projects and high density projects are also hit hard by the new rules. DOE is requiring Clark County to implement the new rules by August of 2008, and the county is in the process of amending its stormwater ordinance to require compliance with the new Western Washington Manual. The county is expected to adopt the new ordinances by June of 2008.
Steve C. Morasch is a shareholder with Schwabe, Williamson & Wyatt’s Vancouver office. He can be reached at smorasch@schwabe.com or 360-905-1433.
