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Erosion Control System Benefits County Landfill and The Environment

by Scott A. Smith and Douglas Luzbetak, P.E., CPESC

Aerial view of landfill looking north. Upper sediment basin is near the bottom of the photo.

The Boone County Landfill (BCL), located in the heart of Iowa, is proudly owned and operated by Boone County. Considered a leading environmental protection facility for the final disposal and management of solid waste, the BCL serves a population of 114,000 in a service area that includes Boone, Greene and Story Counties. The landfill handles an average of 43,000 tons of municipal solid waste each year (including construction and demolition waste), with an operating budget of $1.7 million. The yard waste processing facility composts 600 tons of yard waste each year. The site area is 135 acres, with approximately 57 acres used for solid waste disposal activities. The award-winning BCL is recognized as one of the best operated landfills in the state of Iowa. The mission of the BCL is to provide its customers and service area with environmentally responsible and cost-effective solid waste management services.

The BCL opened in May of 1970 as one of the first sanitary landfills in Iowa. The day before the landfill opened, three city operated “open dumps” were closed. The closures promoted the regional flow of waste to the BCL and began a new era of solid waste management and disposal.

The site was selected following an in-depth assessment of six different “Greenfield” sites. The topography and geology of the selected site lent themselves to establishing a landfill protective of the environment and public health. The site’s location also proves to be ideal under the federal Subtitle D regulations.

Since opening more than three decades ago, the BCL has experienced many changes. Compliance with new solid waste management planning guidelines, additional and more stringent federal and state regulations, and an emphasis on waste diversion insure that the BCL is a sound environmental resource for the population it serves - now and in the future.

Storm water management and erosion control are important components of the landfill’s operations. These are natural outgrowths of BCL’s original purpose - to minimize the impact of society’s waste on the environment. The site landform, a desiccated plateau with numerous steep sided ravines, presents challenges in the management of surface water and the development of the Storm Water Pollution Prevention Plan.

Goals Of The Storm Water Pollution Prevention Plan
With the implementation of the Storm Water Pollution Prevention Plan (SWPPP), emphasis at the BCL shifted from controlling sediment to controlling erosion. In accordance with the SWPPP, the BCL initiated an aggressive program of grading, installing silt fence, and establishing vegetation to slow the velocity of surface water on site and reduce the erosive potential.

The SWPPP has four primary goals. The first goal of the SWPPP is to limit erosion on site. This is accomplished primarily by limiting the disturbance of existing vegetation, seeding, mulching, and using compost as a soil amendment/mulch to promote the rapid establishment of vegetation. The second goal is to limit the movement of sediment within the site. This is accomplished by vegetation, silt fence, terraces, and ditch checks. The third goal is to limit the movement of sediment off of the site. This is accomplished by employing the methods described above in combination with sediment basins. The final goal is to improve site aesthetics, which is accomplished by all of the above activities.

Original sediment basin constructed in 1994.

Erosion/Stormwater Control System
Due to the diversity of activities occurring on a daily basis at the landfill, the SWPPP recommends a variety of practices for use. Erosion and sediment control at the BCL is primarily accomplished through the following practices:

Minimizing disturbance of existing vegetation
Minimizing the disturbance of existing vegetation is the most cost effective method of erosion control available. Operations are planned to limit disturbance as much as possible.

Planned grading
Grading on site is planned with four objectives in mind, the first of which is to limit the area of disturbed soil. The second objective is to divert surface water away from any disturbed areas. The third objective is to reduce the velocity of the surface water flowing from the disturbed areas and to direct runoff from the disturbed areas into a sediment control structure. The final objective is to grade during suitable times of the year so that seeding can be established and the area stabilized.

Establishing vegetation
Vegetation is established on disturbed areas as soon as practical. If conditions are not suitable for a permanent seeding, a temporary seeding of oats or rye is used. Native grass seeding is used where possible. Compost is used as a soil amendment and mulch in areas where soil conditions are not conducive to the rapid establishment of vegetation. An erosion control subcontractor is retained by the BCL to insure timely seeding as needed.

Silt fence
Silt fences are installed on the perimeter of disturbed areas prior to any disturbance whenever possible. If installation is not possible due to conflicts with haul routes or other operations, silt fences are installed as soon as practical upon completion of the disturbance. Existing silt fences are also inspected by landfill staff regularly. Damaged silt fences are replaced and accumulated silt is removed when necessary. An erosion control subcontractor is retained by the BCL to insure the timely repair/replacement of silt fence as needed.

Ditch checks
Ditch checks are installed in steep ditches to reduce the velocity of surface water and to limit sediment migration. The ditch checks function as small sediment basins and need to have accumulated sediment removed regularly.

Terraces are installed on slopes where final closure is complete. All terraces are constructed with underground pipe drop structures. The terraces break up the slopes and slow the velocity of surface water. The drop structures carry the collected water to a common, controlled outlet point. Terraces are an excellent way to limit the formation of rills on a slope.

Inlet/Outlet protection
Riprap protection is provided at storm drain inlets and pipe outlets, as warranted, to slow the velocity of water and limit erosion. Riprap is placed on a geotextile fabric to prevent undercutting of the rock.

Sediment basins
Drainage from all disturbed areas of the landfill exits at a common point. Two sediment basins exist in series at this exit point. The outlets of each basin are inspected regularly for signs of erosion and for sediment discharge. Access is maintained at each basin to facilitate periodic sediment removal.

Upper sediment basin with newly constructed landfill liner in background.

In this section we will focus on the implementation of three of the structural measures discussed above that are used with great success: the use of compost as a soil amendment, native grass seeding, and the sediment basins.

BCL accepts yard waste from local residents for composting on site. Tree and brush waste is accepted along with grass and leaves. The tree and brush waste is ground 3 to 4 times per year and then mixed with other compostable materials. Since landfilling activities have occurred on this site for over 30 years, the topsoil over the majority of the area has been disturbed or removed. Consequently, the surface of areas requiring seeding are often composed of unproductive subsoils removed during excavation projects. These soils require more than fertilizer to promote the growth of vegetation. The compost produced on site provides a good source of organic matter to the soil. Compost also serves as an excellent mulch, retaining moisture and reducing the effects of raindrop impact on the soil surface.

During the design of the expansion project it was determined that over 800,000 cubic yards of soil materials would be excavated from the expansion area and placed in three large stockpiles on site. Due to site constraints, the stockpiles were constructed with 2.5:1 sideslopes. The stockpiles will remain in place for many years (one permanently), and limiting stockpile maintenance was a priority. The 2.5:1 slopes are hazardous to mow, so the BCL desired a seeding that would require minimal mowing and maintenance. The BCL and FOX Engineering worked with the Boone County Conservation Director and the local office of the Natural Resources Conservation Service to formulate a seed mix of native species that requires minimal maintenance on the slopes. The native seeding, planted in 1999, is now well established. Maintenance has been limited to only one mowing to date. Once the native vegetation was established on the stockpiles, an unanticipated benefit was noted. The amount of noxious weeds present in the native vegetation is only about 10% of the amount found in the traditional seed mixes employed elsewhere on the site.

The current BCL Administrator started work at the landfill in 1998. One of the first situations evaluated by the Administrator was the condition of the original sediment basin, which was installed in 1994. The basin was undersized, frequently overtopped, and required regular cleaning. The repeated overtopping made it virtually impossible to establish vegetation on the backside of the dam. This led to erosion and further diminished the aesthetics of the structure. In the same year, BCL was finalizing plans for a major expansion project. The expansion involved the disturbance of approximately 35 acres that drained directly into the original basin. To mitigate potential problems, a new sediment basin was constructed in 1998. The new basin is located immediately upgradient from the original basin and was operational during the expansion project in 1999. Prior to the installation of the upper sediment basin, the original basin was bankfull (13 ’ depth) of sediment yearly and required extensive sediment removal. As a result of the installation of the upper sediment basin and the other erosion and sediment control improvements, the need for cleaning has decreased drastically. Approximately 1 to 2 feet of sediment are removed from the upper sediment basin yearly to maintain maximum sediment trapping efficiency. The lower sediment basin now has approximately 1 to 2 feet of sediment removed every 3 to 4 years.

Along with structural practices employed at the site, additional steps have been implemented to insure the proper functioning of the erosion and sediment control system. Each member of the landfill staff is familiar with the SWPPP and take their responsibilities with regards to the erosion control systems seriously. Staff frequently check and assess the condition of erosion control systems and structures. They report any issues immediately to the administrator who then contacts the appropriate contractor(s) if the work cannot be carried out in-house.

He cited two primary reasons why patience was warrented. The first is that native vegetation typically takes longer to establish than traditional seed mixes. The second is that the effectiveness of a native planting cannot be based on observations alone, as the depth and breadth of the root system of the natives may be much larger than the growth observed above ground.

The staff also use a Geographical Information System (GIS) to record and maintain historical and design information pertaining to the landfill. Through this system, staff can differentiate areas by type of seeding mix, identify silt fences and other structures, check scheduled maintenance activities, and track drainage systems that are above or below ground.

The Boone County Board of Supervisors provide strong support for storm water management and erosion control. They consistently approve construction of erosion control measures, even when those measures exceed regulatory requirements. Additionally, the Board strongly supported the use of native grasses and the development of the GIS system tailored for the landfill’s operations.

Recently disturbed area with terrace and silt fence.

A challenge associated with any landfill site is that the working face and the borrow areas are continually moving. This makes the installation of structural controls difficult, as controls installed one day may be in the path of a haul route the next. The shifting of the active waste and borrow areas makes planning the locations of controls critical. To provide for timely installation of controls, major structural features for erosion and sediment control are laid out in the SWPPP.

The native vegetation took more than one growing season to become fully established. Erosion on the stockpiles was limited; however, due to the annual rye cover crop included with the native grass seeding. The cover crop was mowed when seedheads had formed. As a result, the cover crop was reestablished for an additional growing season and further limited erosion until the native grasses were established.

Following the first growing season, there were concerns about the rate of establishment of the vegetation on the stockpiles, and a native plant expert was consulted. During the site inspection, the native plant consultant urged patience regarding the establishment of the vegetation. He cited two primary reasons why patience was warranted. The first is that native vegetation typically takes longer to establish than traditional seed mixes. The second is that the effectiveness of a native planting cannot be based on observations alone, as the depth and breadth of the root system of the natives may be much larger than the growth observed above ground. His advice was correct as the native vegetation is now well established.

Fiscal Year: Actual Costs: Budget:
98-99 $21,250 $21,500
99-00 $29,000 $21,500
00-01 $38,834 $40,000
01-02 $31,757 $45,000
02-03 $21,931 $45,000
03-04 $17,145* $45,000
* Year-To-Date as of May 2004.

The benefits of the proactive approach to erosion and sediment control include: reduced sediment basin cleanout, reduced ditch cleanout, lower road maintenance costs, and improved site safety. Although there is limited water quality data for conditions prior to the implementation of the SWPPP, it is visually apparent at the sediment basin outlets that the water quality on site is greatly improved.

The most notable benefit of the proactive approach to erosion and sediment control is the condition of the sediment basins. Prior to the silt fence/seeding program, the sediment basin was cleaned out each year, with up to 13’ of sediment removed. Now, with silt fence and vegetation established, operational costs for the sediment basin have decreased. Even though the facility has significantly added to its sedimentation basin capacity and increased annual seeding and silt-fencing activities, the total cost of erosion control has decreased each year since Fiscal Year 2000-01.

Effective erosion and sediment control can best be maintained by placing control measures as close to the source as possible. Monies previously spent exclusively on sediment basin cleaning is now being used to implement additional, more efficient and proactive controls nearer to the disturbed areas.

As an added benefit, BCL’s relationships with regulatory agencies such as the Iowa Department of Natural Resources (IDNR) and Natural Resources Conservation Service (NRCS) have been improved. The local NRCS office had only been to the site prior to the implementation of the SWPPP to investigate a sedimentation complaint. Now, due to the comprehensive nature of the erosion and sediment controls on site, the Boone County Soil and Water Conservation District uses the landfill as a model and leads tours of the site to discuss the various aspects of erosion control employed. The purpose of the tours is to demonstrate to other local landowners and contractors several examples of successful erosion and sediment controls.

The improvements to the erosion and sediment control systems and the benefits listed above are only possible with the support of the Boone County Board of Supervisors and the dedicated employees at the landfill. Foreman Morris Walters has been employed at the site since 1970. The long range approach to landfilling at this site, even prior to the rules and regulations in place today, is summarized best in this quote from Mr. Walters: “From the beginning, we did not want this site to be an embarrassment to our grandchildren.”

The BCL case study proves that investing money in erosion control “upfront” pays dividends over the long run.

The costs in the chart on the previous page show the steady increase during the initial implementation of the erosion and sediment controls, followed by a steady decrease in costs as vegetation becomes well established over a larger portion of the site. It should be noted that the controls discussed in this text cannot be installed and then ignored. If so, they will cease to function as designed and lead to increased future costs. At a minimum, yearly maintenance activities at the BCL include repairing and replacing silt fence, reseeding, remulching, and adding compost as a soil amendment.

During development and implementation of the SWPPP, all activities at the landfill have been analyzed and revised where necessary to limit erosion and sediment migration. Based upon the reduced frequency of sediment basin cleanout, the improved vegetation throughout the site, the enhanced appearance of the landfill, and the positive relationship with the IDNR and NRCS, it is apparent that the SWPPP has improved site conditions appreciably. The BCL case study proves that investing money in erosion control “upfront” pays dividends over the long run.

For more information, contact Scott A. Smith, Landfill Administrator/Recycling Coordinator, Boone County Landfill, 1268 224th Lane, Boone, IA 50036, (515)433-0591, Fax (515)433-0545, Email: boonelf@tdsi.net or Douglas Luzbetak, P.E., CPESC, Senior Project Manager, Fox Engineering Associates, Inc., 1601 Golden Aspen Drive, Suite 103, Ames, IA 50010, (515)233-0000, Fax (515)233-0103, Email: djl@foxeng.com.