Stormwater | Setting Soil Standards With the Future in Mind


All photos: King County Solid Waste Division
Developments like Shamrock Heights use amended soils to better manage stormwater.

Charting a new course for stormwater management in King County, WA

By Kris Beatty

King County in Washington state stretches east from the shores of central Puget Sound, at Seattle, to the crest of the Cascade Range. It features urbanized areas, farmlands, and forests, with more development and redevelopment taking place as the county’s population grows and established communities age.

This ongoing development and redevelopment could have significant environmental impacts, including soil erosion and water pollution from stormwater runoff, which negatively affect native wildlife, such as salmon.

These circumstances have created a need for better stormwater management in King County and in other western Washington jurisdictions. Local governments are taking steps to minimize the environmental impacts of land-development activities in and around communities and neighborhoods.

Healthy Soil = Healthy Homes
In most undeveloped areas, soil and vegetation work together to manage stormwater. Up to 50% of rainfall evaporates, and the remainder seeps into the soil or flows as surface water, entering the natural drainage system. In areas that have been developed, this natural cycle is broken. Impervious surfaces, such as roofs, roads, and shallow or compacted soil, cause a greater percentage of the rainfall to run off, decreasing surface-water infiltration and storage and increasing erosion and flooding.

Best management practices (BMPs), such as adding organic matter to soil, help retain moisture and restore the natural drainage system. This helps ensure healthy soil for plants and healthy waterways for fish. Homeowners also see the benefits, as landscape maintenance is easier and costs less, with reduced need for irrigation, pesticides, and fertilizers.

“Preserving native soils is our highest priority, but in cases where soils have been disturbed during development, amending the soil helps reestablish the natural conditions that are lost,” says Randy Sandin, supervisor for King County Department of Development and Environmental Services (DDES) Land Use Services Division.

Salmon in the City
In the 1990s, Washington state scientists and engineers were encouraged to reach out to the broader community to help address the decline of local salmon populations. As part of this effort, the 1998 “Salmon in the City” conference pointed to low-impact development as a way to address the water-quality issues affecting salmon.

The conference was followed by “Soils for Salmon,” a program of the Washington Organic Recycling Council (WORC). Since 1999, the WORC has been building awareness about soil BMPs and the benefits of adding compost to soil to help improve water quality, eliminate the effects of stormwater, and restore and protect native habitats.

Both efforts ran parallel to King County research on the impacts of using soil amendment in urban development projects. The DDES first began to examine soil amendment in the early 1990s, when a work group was formed to study feasible options for implementing and enforcing a countywide soil standard.

“We’ve always seen soil amendment as a benefit from a stormwater management perspective,” says Steve Foley, an engineer with King County Department of Natural Resources and Parks. “Anything we can do to reduce water consumption in landscapes benefits the ecosystem.”

Now, nearly a decade after the Salmon in the City conference, jurisdictions across western Washington are being required to include soil BMPs in local codes. Under the EPA’s National Pollutant Discharge Elimination System permit program, the Washington State Department of Ecology administers municipal stormwater permits.

The permits require cities and counties to adopt codes that are equivalent with the Department of Ecology’s 2005 Stormwater Management Manual for Western Washington, which includes a new runoff treatment BMP for post-construction soil quality and depth (BMP T5.13, Vol. V).

King County updated its codes to achieve equivalency with the Department of Ecology’s manual, and in doing so it became one of the first jurisdictions in the country to adopt and implement a post-construction soil standard. Its regulation went into effect January 1, 2005. Jurisdictions that have not yet adopted code-compliant regulations must do so by August 2009.

Setting a Standard
When King County began to consider updating its codes to include soil BMPs, there were several things to consider:

Washington State requirements
Guidance on how to implement the state requirements (Snohomish County, King County’s neighbor to the north, developed excellent guidelines that King County used as a basis for its implementation.)
Which section of the county code was the best fit for the new standard
Appropriate soil organic matter content
How to make the standard user-friendly, with implementation and enforcement to follow

Washington State includes soil BMPs as part of its stormwater regulations. With this in mind, King County looked at where new soil provision would best fit into existing codes and the type of projects that would be subject to it.

Planners found that many small projects exist within King County that should use soil BMPs. However, some of those projects might not require permits or be subject to the county’s stormwater requirements.For this reason, the more-often-applied clearing and grading code was selected as the most appropriate code in which to include the soil standard provision.

Adding King County’s soil standard to the clearing and grading code means the provision could be applied not only to commercial and residential development projects but also to other projects, such as golf courses or athletic fields and water or sewer line installations.

“Where the standard ‘lives’ in King County’s code is the most significant difference between our standard and the state’s,” Foley says. “As other local jurisdictions develop their standards, this is something they will need to consider.”

Next, the county set out to define the soil depth and quality technical requirements for the soil provision, including the percentage of soil organic matter content; pH; and, given the area’s seasonal rains, a timetable for when soils should be amended.

“There was a lot of discussion on the appropriate soil depth and quality requirements,” Foley says. “The goal of the standard is to maintain or re-create the moisture-holding capacity of forested soil, so we needed to look at what would help us reach that goal.”

King County staff looked to BMPs, considered the experience of low-impact development projects, quizzed soil experts, and reviewed the science.

This work resulted in three technical code requirements of the soil standard:

Topsoil should be a minimum of 8 inches deep.
The soil should have an organic matter content of between 8% and 13% dry weight, with a pH that is suitable for proposed landscape plants.
Developers are required to make amendments during the dry season, defined as May 1 to October 1 of each year.

Note: 8% soil organic matter is equivalent to approximately 30% to 40% compost by volume in soil.

Making It Happen
King County’s post-construction soil standard has changed the way developers plan and develop a site in unincorporated parts of the county. The new regulation requires a series of steps—from permitting to field verification.

The process begins with the permit. Although this regulation applies anytime a site alteration occurs, whether the site alteration is of sufficient size to require a permit, it is most directly implemented through King County’s review and issuance of development permits. Any project in unincorporated King County that proposes site alterations must now submit a soil management plan.

The soil management plan includes information on how and in which areas the soil will be preserved or restored and what products, such as compost and/or imported topsoil, will be used. Inspectors use the details of this plan during permit review and for verification during field inspections.

“Outlining the steps that will be taken onsite helps the developers determine how they will meet the requirements of the new code,” says Sandin. “And it gives the county a framework for inspectors to use to ensure that the developer has achieved what it set out to do.”

Creating a Plan
Before creating the soil management plan, developers must review site conditions and landscape and grading plans. They need to answer questions such as the following:

Can the soil be easily amended?
Is there compaction that requires the import of topsoil?
Can existing soil be left undisturbed or stockpiled?
Is the soil pH suitable for the landscape plants?

“Not all sites are the same, and not all soils are the same,” says Sandin. “We wanted to give developers options that would allow them to mix and match.”

There are four soil treatment options that developers can use. The option a developer chooses depends on the project site, soil conditions, grading and subgrade compaction, practicality of stockpiling topsoil during grading, and site access. The options can be used individually or in combination. Some sites might require different options to be used in different areas.

Leave Native Soil Undisturbed
In King County, native soil is most often found in forested areas or other areas that have not been converted for use such as pastureland. The most economical and environmentally friendly option is to leave native soil undisturbed and protect it from compaction during construction. Under this option, areas with native vegetation are identified on a site-plan drawing and are fenced off to be left undisturbed, including tree root zones. These areas do not require soil amendment.

Knowing that leaving areas undisturbed isn’t always feasible, King County provides three other options to address native and disturbed soils if the soil has either been disturbed in the past or is being disturbed in the current project.

Amend Existing Soil in Place
In areas where soil has been compacted or the forest duff or topsoil removed, developers can amend the existing soil in place by adding compost and rototilling it in. This can be achieved using a pre-approved amendment rate of 2.5 inches or through a custom amendment rate calculated specifically for the site.

Import Topsoil
For soil that is too rocky, compacted, or poorly drained to amend effectively, a topsoil mix with 8% to 13% soil organic matter can be imported and placed on the surface.

Stockpile, Reapply, and, If Soil Is Not Native, Amend
The fourth option allows the site soil to be stockpiled and reapplied. In cases where native soil exists, the forest duff layer and topsoil must be stockpiled and reapplied separately, and no soil amendment is required. For disturbed soil, the site soil is reapplied, and then the soil must be amended with compost.

Some developers or builders may choose to calculate a custom compost-amendment rate based on soil and compost tests by accredited testing laboratories. This option can provide some cost savings if the site soil already contains organic matter.

Once soil treatment options are selected, compost and/or topsoil volumes must be calculated. To assist in this part of the process, King County created a simple calculation worksheet and online compost and topsoil calculator.

“Each of these tools was designed to be easy to use,” says Sandin. “We set out to make this as user friendly as possible.”

The worksheet and online calculator can be used to give a developer site-specific information on how many cubic yards of compost and/or topsoil will be needed to meet the requirements of the standard. The developer must then choose compost and topsoil products that meet the code requirements.

This information is entered on the soil management plan form and submitted, along with the site drawing, calculation worksheets, and laboratory test results. These items become part of the permit documents.

Developers are required to retain copies of all receipts, delivery tickets, and test results to be used as part of the verification process once the project is complete.

Keeping It Simple
King County set out to make the process of meeting the soil standard requirements as simple as possible and created tools to help permit applicants. Everyone applying for a clearing and grading permit in unincorporated King County receives a guidance booklet on the soil standard as part of the permit packet.

King County, WA, reviewers and inspectors study soil samples as part of a training program to educate them on the new post-construction soil standard.

“We work with individual homeowners and large-scale developers alike,” says Sandin. “We tried to produce materials that could be understood by the layperson.”

The DDES worked with the King County Solid Waste Division (SWD) to develop the guidance booklet. The SWD is working to increase the use of compost and divert recyclable organic materials like food and yard debris from entering the wastestream.

The booklet provides an overview of what the standard requires, walks users through the soil treatment options, includes the compost and topsoil calculation worksheet and the soil management plan form, and offers additional resources.

King County has also developed training sessions for its permit department staff and has worked with a local composting company to offer an education session for those affected by the new standards. The county has also shared its experience and materials with other central Puget Sound–area jurisdictions.

Training and Education
Starting in 2006, permit review and site inspection staff for the DDES received education about the benefits of healthy soil and training on how to incorporate the procedures into their work, using the new forms and guidelines to ensure compliance with the soil standard. An inspectors’ field guide and field verification form were developed to provide guidance to inspectors when checking a site for compliance and documenting compliance—or corrective measures, if needed.

“The inspectors’ field guide is really handy and makes it simple for anyone to understand,” says Richelle Rose, a site development specialist with the DDES. “I can put it in my pocket, and it gives me a step-by-step guide on how to perform an inspection.”

The laminated field guide describes the steps of the initial and final inspections. First, inspectors compare site conditions with the approved soil management plan. Next, they inspect delivery tickets and test results for compost and/or topsoil. Finally, inspectors dig test holes and use shovel tests throughout the site to check soil quality, verify soil depth, and ensure that soil is loose and not compacted. All King County site development inspectors received shovels with long, narrow blades to use in the field.

King County continues to have an ongoing dialogue with staff and others about how to improve the permitting and verification process.

“We learned what wasn’t going quite right and have made adjustments,” says Sandin. “We also have an ongoing dialogue with other inspection groups to hear what they are learning.”

In early 2007, King County worked with Cedar Grove Composting to host a workshop for the Master Builders Association of King and Snohomish Counties. Attendees included builders, landscape developers, and engineers. The workshop was an opportunity for participants to learn about the regulations and how using compost can help them achieve the standard.

King County, in a cooperative effort with other local agencies, businesses, and organizations, has worked with the Washington Organics Recycling Council to provide general information about soil BMPs through its Soils for Salmon program (www.soilsforsalmon.org).

The county has also reached out to cities and neighboring counties as they begin to adopt, develop, and implement soil BMPs of their own. In June 2007, representatives from 10 nearby jurisdictions attended an information-sharing session to learn about King County’s soil standard and what the county has gained through its experience.

Finally, in an effort to provide general education about the importance of healthy soils and King County’s post-construction soil standard, the Department of Natural Resources and Parks produced an eight-minute video segment, which aired on its Natural Networks TV show. The video is available for viewing on King County’s GreenTools Web site (see Site Improvements at www.greentools.us).

Learning Along the Way
It has been three years since King County’s post-construction soil regulation took effect.

“How well the regulation is being implemented in the field is still a question,” says Sandin. “In another year, we will have a better idea how it has done.”

Sandin considers this time a monitoring phase. There has been some lag time between when the regulations took effect and when permitted projects subject to the regulations will be at the post-construction phase.

As experiences are shared with other jurisdictions, King County staff have had the opportunity to evaluate what has worked well and what could be used to make the process smoother. Either way, the lessons learned seem to center on collaboration and understanding.

“I think the key is getting everyone on board early on, in order to help make the transition that much smoother,” Rose says.

Ultimately, Sandin says, making the post-construction soil standard work well comes down to understanding the science of it all.

“One of the things I found is that people don’t fully understand the issue,” he says. “If the science can be explained in relatively simple terms, people will be more willing to buy in.”

Kris Beatty, a program manager for the King County Solid Waste Division, manages programs and projects to develop markets for recyclable materials.

SW January/February 2008

Home + About + Subscribe + News + Calendar + Glossary
Talk + Images + Advertise + Contact Us + Search + Email + Services