An Innovative Approach to Reducing Erosion and Sedimentation During and After Residential Construction

Along Colorado’s Front Range, between Denver and Colorado Springs, nestled up against the foothills of the Rocky Mountains, sits Douglas County. With its attractive environment, thriving economy, and convenient location, an average of 4,000 new homes are built each year. This rapid pace has been the norm since the early ’90s and has frequently made the county the fastest growing in the nation.

A typical lot size for most of the new homes built in the urban areas is 5,000 ft.², approximately half of which is impervious and covered by the house, walkway, and driveway. From an erosion and sediment control standpoint, these homes by themselves don’t represent much of a problem for the county. Taken collectively year after year, however, these homes begin to form a significant challenge that must be addressed.

The Problem

During construction, sediment is washed off residential lots and onto adjacent roadways and landscaped properties and into drainageways. Contractors track large quantities of mud onto sidewalks and streets with their construction equipment, delivery trucks, and personal vehicles. As houses are completed, landscapers and homeowners stockpile topsoil, sand, rock, gravel, and other landscape materials on sidewalks and streets. The mud, sediment, and landscape materials on the roadways wash into storm drainage systems, possibly clogging them or reducing flow capacities. These systems drain into local waterways, and the resulting sedimentation chokes out wetlands and aquatic life and harms water quality.

The sediment deposited onto adjacent landscaped properties most often causes significant property damage. These construction sites become a nuisance to local residents and the general public and raise the eyebrows of safety personnel, public works employees, school bus drivers, emergency response teams, and regulatory officials.

The Solution

It was with this problem in mind that Douglas County developed and implemented its Residential Drainage, Erosion and Sediment Control (DESC) Program. The DESC Program is codified in the county’s zoning resolution and uses the building permit process as its operating platform. Before construction, builders are required to submit a general description of the structural and nonstructural best management practices (BMPs) they will use during construction to help minimize, to the maximum extent practicable, erosion and sedimentation on their construction sites. When a building permit is issued, a DESC permit is activated. This permit holds the builder responsible for drainage, erosion, and sediment control problems throughout the construction cycle. At the beginning of construction, the builder is responsible for installing and implementing the structural and nonstructural BMPs. The builder is required to inspect the site and fill out and submit a DESC inspection report (BMP checklist) to the county for approval. The county will not perform any building inspections until this is done. The builder is responsible for implementing and maintaining the BMPs throughout the construction cycle. If the county becomes aware that a site is out of compliance, through public complaints or proactive inspections, the county issues a Notice of Violation (NOV) to the builder. The NOV allows the builder five calendar days to bring the site back into compliance. If the problem still exists after five days, a hold may be placed on building inspections, stop work orders may be issued, or the builder may face other penalties, including monetary fines.

After Construction

At the end of construction, the builder is required to provide permanent landscaping or adequate temporary erosion and sediment controls designed and installed to be effective for 90 days. Most builders will landscape the front yard and leave the back for the homeowner. In this case, the builder is required to provide temporary erosion and sediment controls only if the drainage leaves the property in the back. Otherwise, the front and side lawns provide an adequate vegetative buffer to filter out sediment before the drainage is discharged into the street. Leaving the rear yard unprotected, however, might cause drainage problems (sedimentation reduces drainage-swale capacity), and yards might need to be regraded prior to landscaping. After the builder installs permanent or temporary controls, the new homeowner must be informed of the importance of erosion and sediment controls and how to maintain the BMPs they have been provided. At this stage, the builder is required to provide the county with a drainage certificate and a DESC certificate (the DESC certificate states that BMPs have been provided and the homeowner has been educated). The DESC permit is then deactivated, and the responsibility to keep erosion and sediment under control lies with the homeowner. The intent of this requirement is to reduce sediment transport from homeowner properties during the period between completion of construction and installation of final landscaping. This time period is traditionally when most of these sites sit with bare soil exposed for upward of 90 days. When homeowners landscape, they often order truckloads of material that are usually placed on sidewalks and streets. The homeowners, as well as the builders and landscapers, face potential fines for this. If a complaint is received or if it is noticed that a homeowner is stockpiling landscape materials in the street, the homeowner is issued a NOV and given seven calendar days to remove such materials. If the materials are left in the street longer than seven days, the County Public Works Department removes them and bills the homeowner for this service.

Flexibility Builds Relationships

The DESC Program is flexible and does not dictate specific BMPs to be used for any individual site. Instead, realizing that erosion and sediment control is a dynamic process with many variables, the program allows builders and contractors to use whatever BMPs work best for their site during different stages of construction and in different situations. Some sites might need both structural BMPs (such as silt fencing, straw wattles, or erosion protection) and nonstructural BMPs (such as practicing good housekeeping, performing frequent site inspections, and providing education to their subcontractors). Other sites–those surrounded by vegetative buffers, for example–might need only nonstructural BMPs. Flexibility fosters positive relationships with builders and contractors and promotes innovation and increased awareness. It also closes the communication gap between builders and regulators. Even though the DESC Program is designed to be flexible, it meets the intent of the federal Clean Water Act’s National Pollutant Discharge Elimination System (NPDES) Stormwater Phase II requirements.

Education Is the Key

The Douglas County DESC administrators provide one-on-one educational sessions for individual builders as well as onsite or offsite sessions for large groups of project managers, superintendents, tradesmen, or government organizations interested in the DESC Program. The sessions cover county requirements and expectations, address and introduce current industry-accepted BMPs and how or how not to use them, and–most importantly–allow the administrators and participants to meet in person and share ideas.

Public Awareness

To increase public awareness of the DESC Program and erosion and sediment control issues in general, the Douglas County Television Services Department, along with the DESC administrators, produced a 12-minute educational video that is aired periodically on a local cable television channel (a public-access channel provided by the county). The video shows the impacts erosion and sediment problems have on the environment. It explains what the requirements of the DESC Program are and who is responsible for what during the construction, landscaping, and build-out stages. The video also provides information on contacts and procedures for filing complaints.

Innovation: A Pilot Project

Silt Fence–Silt fence is used as a perimeter sediment barrier. Strengths: It works well if installed and maintained properly. Weaknesses: High installation and maintenance costs. Not aesthetically pleasing to homeowners. When installed improperly, might cause drainage problems (allows sedimentation in drainage swales) and might cause more serious erosion and sediment problems than if not used at all. No drainage benefits.

Straw Blanket–A straw erosion control blanket (ECB) is installed around the perimeter of a lot. This serves as a horizontal buffer strip where sheet flows are forced to run across the blanket, allowing for sedimentation to occur similar to the vegetative buffer theory). The blanket is also installed at the ends of roof-drain downspouts and in drainage swales to protect the soil from concentrated flows and high velocities. Strengths: The straw ECB appears to be very effective at filtering the sediments from sheet flows and preventing erosion in drainage swales and at the ends of downspouts. It has low material and installation costs and requires very little maintenance. Weaknesses: Steeper slopes and bigger lots require wider strips.

Wood Fiber (Excelsior) Blanket–An excelsior ECB is used similarly to a straw ECB.Strengths: Similar costs and performance to a straw ECB. Weaknesses: It doesn’t appear to hold up as well in dry and windy conditions (the edges might curl up, allowing winds underneath, although this might be prevented by installing more staples).

Fiber Logs–Installed around the perimeter and on slopes, fiber logs assist in reducing sediment in runoff.Strengths: Projected greater durability than straw or wood-fiber blanket strips. More aesthetically pleasing than silt fence. Lower potential to cause drainage problems.

Weaknesses: It has a significantly higher cost than silt fence (approximately seven or eight times). Doesn’t hold back as much sediment as a properly installed and maintained silt fence and might require more frequent maintenance. No drainage benefits.

Wood Fiber Mulch With Tackifier–This erosion control approach is used in lieu of the perimeter filter method; 100% coverage of front and side yards is achieved with hydraulically applied wood-fiber mulch combined with guar tackifier. The ratio used was 2,000-lb. mulch and 100-lb. guar tackifier per acre. Strengths: It minimizes erosion throughout the yard, keeping soil particles from becoming waterborne and needing to be filtered at the perimeter; eliminates the need for reworking the final grade prior to installing finish landscaping (no rills and so on to repair or sediment to clean up in swales). This was perhaps the most aesthetically pleasing method studied in this evaluation.

Weaknesses: It requires special equipment and a trained operator to apply. Cost-effectiveness is contingent upon combining several sites into one mobilization, complicating the logistical challenge of applying the materials. Performance is weather-dependent–the material will last for different periods of time depending on the severity and frequency of storm events. It is not easy to repair if damaged during construction punch-list items or homeowner move-in.

Bonded-Fiber Matrix (BFM)–BFMs are hydraulically applied at a rate of 2,500 lb./ac. for 100% coverage of the front and side yards. BFM has strengths and weaknesses similar to those of the wood-fiber mulch with tackifier, with these important differences: BFM resists weather-related degradation far better than hydraulic wood mulch does, and the cost per average lot increases by at least two times based on the same strategy of treating several (five or more) sites during the same mobilization. In other words, BFM provides far better erosion protection than the wood-fiber mulch but costs more.

Summary

Since the DESC Program was enacted on June 1, 2000, erosion and sediment problems on residential sites have been greatly reduced. The DESC Program is in its early stages of implementation; tracking of mud and washing of sediment onto roadways are still problems, but cleanup efforts occur sooner and more frequently.

Builders are beginning to understand how erosion and sedimentation problems produce a negative effect on both the environment and construction costs. They are also finding that spending a little money up front for preventative measures can save hundreds and even thousands of dollars in cleanup costs and property damage. The county is requesting additional resources to enable further implementation and enforcement of the DESC Program, including the addition of a summer internship program. Douglas County continues to refine the DESC Program to meet the needs of builders, the public, NPDES Phase II, and the State of Colorado water-quality requirements. The county welcomes new ideas and feedback. If you would like to provide input regarding the DESC Program, or for more information about the program, please visit our website at www.douglas.co.us.