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Revised stormwater manual awaits City Council approval

Final version includes a higher threshold for triggering regulations

SUBMITTED PHOTO - Stormwater runoff flows over land and directly into local creeks and larger waterways. Because it isn't treated, stormwater runoff is considered the No. 1 source of surface water pollution.City Councilors are expected to approve the final version of Lake Oswego’s revised stormwater management manual on Tuesday, along with updates to city code regulating stormwater runoff.

At a hearing last week, the council received a final report and recommendations from the Planning Commission, and councilors tentatively endorsed the plan.

“They have tentatively approved it, and so now it’s our last check to make sure that the punctuation is right and that it means what it says and says what it means, to paraphrase Dr. Seuss,” says Stormwater Quality Coordinator Anne MacDonald.

Stormwater runoff is generated when rain lands on surfaces that can’t absorb it, so the water builds up and flows off the impervious material. Roofs, pavement and concrete all generate heavy runoff in urban areas, which can lead to flooding, damage and increased pollution as chemicals are swept up in the flow.

Urban stormwater is often collected using a drain-and-sewer system, but Lake Oswego’s unique geology makes expansion of the existing municipal system a difficult and highly expensive endeavor, MacDonald says.

“We can’t (expand it) without a huge investment. Some of it is the geography of the city, some of it is the geology,” she says. “There are parts of town where the bedrock is so close to the surface that in order to come up with storm pipes, we have to blast to get them in.”

Instead, MacDonald says, the city focuses on stormwater absorption and mitigation techniques that work on a local, property-to-property basis, such as rain gardens and infiltration systems.

The creation of the stormwater management manual and the updates to code are required by the city’s Municipal Seperate Storm Sewer System permit from the state Department of Environmental Quality. The five-year permit was issued in 2012, and one of its conditions was that the city create a stormwater management manual to spell out the rules for residents.

“We had to get through the Sensitive Lands bit first, because of its ties to water quality,” MacDonald says, “and that was a higher priority for a council goal.”

DEQ sets the minimum requirements for municipal stormwater rules, but it’s up to individual cities to enforce the regulations by incorporating them into their own municipal codes. Lake Oswego’s code already includes some of the requirements under the DEQ permit, but the new update puts the city officially back in compliance.

“As soon as this is done by the City Council, we send it in and then boom, we’ve made it,” says city Planning Commission Vice Chairman John LaMotte.

Whether a project requires additional stormwater mitigation is determined by the square footage of the project and the type of construction. The DEQ-mandated threshold is 3,000 square feet for new development and redevelopment, meaning that any project that results in more than 3,000 square feet of impervious surface must include additional stormwater mitigation installations and must be inspected and certified.

But because Lake Oswego has to rely on individual mitigation instead of a stormwater system, some of the city’s new rules are tougher than the minimum DEQ requirements.

In the city’s original draft of the proposal, the threshold was 200 square feet for everything except maintenance projects, but the Planning Commission quickly raised that number to 500 square feet.

“The staff proposal that went to the Planning Commission in a work session was originally 200, and they said, ‘Nah.’ So we said, ‘OK, 500.’ That was something that put us in line with our erosion control permit as well. So that’s where that number came from,” MacDonald says.

City officials say the lower thresholds are necessary because a majority of Lake Oswego’s houses were constructed before modern stormwater codes went into effect, which puts them out of compliance with today’s standards.

“Think of it as bringing things up to code,” says one of the city’s FAQ documents about the manual revisions.

But residents and real estate developers expressed concern that the 500-square-foot trigger would still cause property owners to have to add expensive mitigation systems even when building relatively simple projects.

As a result, the final version of the code is more developer-friendly. The city’s stricter threshold has been raised from 500 square feet to 1,000 square feet, and in a crucial change from previous versions, it only applies to new projects; redevelopment is now exempt.

“The homes that were (put) in before modern codes would be reviewed only at these certain thresholds now,” says LaMotte. “The idea was to play catch-up to a point, but not to get too much regulation on smaller projects that are kind of homeowner do-it-yourself driven.”

New construction or redevelopment projects that add at least 3,000 square feet of impervious surface still must follow all of the requirements for on-site stormwater mitigation under the DEQ permit. At the same time, new projects of between 1,000 and 3,000 square feet will now trigger the city threshold for “small projects”; they, too, will require on-site mitigation.

“(The trigger is) not new construction. It’s additional impervious surface — meaning additional hardscape — of more than 1,000 square feet,” says LaMotte. “So if you’re working on your addition, your driveway, your sidewalk, etc., and you’re under 1,000 square feet because you’re adding just a little piece of sidewalk or something, then you’re fine.”

Maintenance projects will only require a plumbing permit, MacDonald says, unless they involve more than 3,000 square feet and also create new offsite hydrologic impacts.

“That’s kind of key. If you’ve got (a maintenance project on) a 3,000-square-foot driveway, as long as it’s draining to the same place that it is now, then it doesn’t trigger it,” says MacDonald. “But if you decide to collect that water and drain (differently), and by so doing you’re going to send it off your property in a greater manner, then we’re going to want to talk to you.”

The revised manual and code changes will be back in front of the council at its Feb. 16 meeting for a final vote. Once the city approves the changes, MacDonald says the focus will shift to public education about the new rules and procedures.

“We’ll be doing outreach, both to the residents as well as to the design development community as this is moving forward,” she says. “This is not something for people to worry about until they start thinking about major changes to their property. It’s not something where we’re going to come in and try to make everybody put a rain garden in their front yard tomorrow.”

Meanwhile, LaMotte says the Planning Commission would like to explore the idea of larger-scale mitigation systems in the future — not citywide, but possibly on an individual neighborhood basis.

“The burden is on the homeowner for maintenance, but eventually, is it more sensible to do a bigger, better system that the city is in charge of? That was discussed and recommended,” says LaMotte. “It’s not hard in the code yet, because the city is trying to get their arms around what level and at what threshold. Once that is done, we can look at some of these things.”

Contact Anthony Macuk at 503-636-1281 ext. 108 or This email address is being protected from spambots. You need JavaScript enabled to view it..

Stormwater Scenarios

Thinking of starting a new project on your property? Here are some scenarios where you don’t have to worry about stormwater mitigation, according to Stormwater Quality Coordinator Anne MacDonald:

-- Adding another story

-- Replacing a roof

-- Building an addition (smaller than 1,000 square feet)

-- Resurfacing a driveway

-- Adding a patio (smaller than 1,000 square feet)

If you’re adding more than 1,000 square feet of impervious surface, you’ll need onsite stormwater management, MacDonald says, and you’ll need to make sure there are no negative impacts to other properties.

If you’re adding more than 3,000 square feet, you’ll also need systems for water quality control and flow control.

For a list of specific project scenarios, click here.