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C. Site Development Management Measure

Plan, design, and develop sites to:

  1. Protect areas that provide important water quality benefits and/or are particularly susceptible to erosion and sediment loss;
  2. Limit increases of impervious areas, except where necessary;
  3. Limit land disturbance activities such as clearing and grading, and cut and fill to reduce erosion and sediment loss; and
  4. Limit disturbance of natural drainage features and vegetation.

1. Applicability

This management measure is intended to be applied by States to all site development activities including those associated with roads, highways, and bridges. Under the Coastal Zone Act Reauthorization Amendments of 1990, States are subject to a number of requirements as they develop coastal NPS programs in conformity with this management measure and will have flexibility in doing so. The application of management measures by States is described more fully in Coastal Nonpoint Pollution Control Program: Program Development and Approval Guidance, published jointly by the U.S. Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA) of the U.S. Department of Commerce.

2. Description

The goal of this management measure is to reduce the generation of nonpoint source pollution and to mitigate the impacts of urban runoff and associated pollutants from all site development, including activities associated with roads, highways, and bridges. Management Measure II.C is intended to provide guidance for controlling nonpoint source pollution through the proper design and development of individual sites. This management measures differs from Management Measure II.A, which applies to postdevelopment runoff, in that Management Measure II.C is intended to provide controls and policies that are to be applied during the site planning and review process. These controls and policies are necessary to ensure that development occurs so that nonpoint source concerns are incorporated during the site selection and the project design and review phases. While the goals of the Watershed Protection Management Measure (II.B) are similar, Management Measure II.C is intended to apply to individual sites rather than watershed basins or regional drainage basins. The goals of both the Site Development and Watershed Protection Management Measures are, however, intended to be complementary and the measures should be used within a comprehensive framework to reduce nonpoint source pollution.

Programs designed to control nonpoint source pollution resulting from site development, both during and after construction, should be developed to include provisions for:

  • Site plan review and conditioned approval to ensure that the integrity of environmentally sensitive areas and areas necessary for maintaining surface water quality will not be lost;
  • Requirements for erosion and sediment control plan review and approval prior to issuance of appropriate development permits; and
  • Guidance on appropriate pollution prevention practices to be incorporated into site development and use.
In addition to the preceding provisions, where applicable, the following objectives should be incorporated into the site development process:

  • During site development, disturb the smallest area necessary to perform current activities to reduce erosion and offsite transport of sediment;
  • Avoid disturbance of unstable soils or soils particularly susceptible to erosion and sediment loss, and favor sites where development will minimize erosion and sediment loss;
  • Where appropriate, protect and retain indigenous vegetation to decrease concentrated flows and to maintain site hydrology;
  • Minimize, to the extent practicable, the percentage of impervious area on-site;
  • Properly manage all maintained landscapes to avoid water quality impacts;
  • Avoid alteration, modification, or destruction of natural drainage features on-site; and
  • Design sites so that natural buffers adjacent to coastal waterbodies and their tributaries are preserved.
The use of site planning and evaluation can significantly reduce the cost of providing structural controls to retain sediment on the development site. Long-term maintenance burdens may also be reduced. Good site planning not only can attenuate runoff from development, but also can improve the effectiveness of the conveyance and treatment components of an urban runoff management system (MWCOG, 1991).

During the site design process, planners should further identify sensitive areas and land forms that may provide water quality protection. These areas should be targeted for preservation or conservation and incorporated into site design. Highly erodible soils should be avoided. By siting development away from erodible soils, it is possible to significantly reduce the amount of erosion, although soil type, topography, vegetation, and climatological conditions affect the degree of erosion resulting from land disturbance activities both during and after construction. In the United States, it has been estimated that human activity causes the transport of nearly 4 billion tons of sediment annually, one-fourth of which eventually reaches the ocean. Sediment loads from developing areas where new construction is occurring can be 5 to 500 times greater than loadings from undeveloped rural areas (Gray, 1972). Natural erosion rates from forested areas or well-sodded prairies are in the range of 0.1 to 1.0 ton of soil per acre per year (Washington Department of Ecology, 1989). Because many nonpoint source pollutants, including heavy metals and nutrients, adsorb to sediments, it is important to limit the volume of sediment leaving a site and entering surface waters.

The Maryland State Highway Administration has developed initiatives to protect sensitive habitats as part of the governor's program to clean up and preserve the Chesapeake Bay. A selection of these initiatives include the following:

  • Use of turbidity curtains to protect sensitive sections of a waterway during construction;
  • Inspection and maintenance of runoff controls after every storm event;
  • Immediate notification of noncompliance and follow-up inspection, when noncompliance occurs;
  • A 72-hour stabilization requirement;
  • Oversizing of sediment traps and basins depending on right-of-way constraints;
  • Innovative scheduling for paving versus vegetative stabilization and implementation of infiltration practices to reduce thermal impacts;
  • Minimal clearing of forest areas; and
  • Installation of traps and basins prior to grading (Maryland State Highway Administration, 1990).

3. Management Measure Selection

This management measure was selected because the components of the measure have already been implemented, to varying degrees, by State and local governments. For example, the States of California, Maryland, Delaware, and Florida and the local governments of Montgomery, Prince Georges, and Anne Arundel counties in Maryland have implemented these concepts in State or local ordinances and in erosion and sediment control regulations. This measure is intended to provide States and local governments with general guidance on nonpoint source pollution objectives that can be integrated into the site planning process. The components of the management measure were selected to represent the minimum provisions that State and local governments must implement.

This approach was adopted to use existing programs and staff, thereby reducing administrative burdens and implementation costs as much as possible. A significant number of local governments have programs to oversee and review the site development process. In many communities, the costs of implementing this measure within the scope of existing programs may be nominal.

4. Practices and Cost Information for Control of Erosion During Site Development

As discussed more fully at the beginning of this chapter and in Chapter 1, the following practices are described for illustrative purposes only. State programs need not require implementation of these practices. However, as a practical matter, EPA anticipates that the management measure set forth above generally will be implemented by applying one or more management practices appropriate to the source, location, and climate. The practices set forth below have been found by EPA to be representative of the types of practices that can be applied successfully to achieve the management measure described above.

  • a. Erosion and Sediment Control Plans and Programs

    Structural control measures for reducing impacts from erosion during site construction are discussed in the Construction Management Measure. These practices can be implemented as part of plans established in erosion and sediment control ordinances by local government or State laws. A well-thought-out plan for urban runoff management on construction sites can control erosion, retain sediments on the site, and reduce the environmental effects of runoff. In addition to a plan for BMP use, contractors should develop schedules that minimize the area of exposed soil at any given time, particularly during times of heavy or frequent rains. Table 4-12 (24k) lists items that should be considered in an erosion and sediment control (ESC) plan. Table 4-13 (27k) contains examples of sediment and erosion control requirements implemented at the State and local levels. All temporary erosion and sediment control practices that will be used during the construction phase should be detailed in architectural or engineering drawings to ensure that they are properly implemented. Inclusion of temporary pollution control practices on construction drawings also ensures that their costs are included in the pricing and bidding process (USEPA, 1973).

  • b. Phasing and Limiting Areas of Disturbance

    This practice reduces the potential for erosion and can be accomplished by prohibiting clearing and grading from all postdevelopment buffer zones, configuring the site plan to retain high amounts of open space, and using phased construction sequencing to limit the amount of disturbed area at any given time.

  • c. Require vegetative stabilization.

    Rapid establishment of a grass or mulch cover on a cleared or graded area at construction sites can reduce suspended sediment levels to surface waters by up to sixfold. Mandatory temporary stabilization of areas left undisturbed for 7 to 14 days is recommended, unless conditions indicate otherwise. Section III.A contains detailed information regarding vegetative stabilization practices.

  • d. Minimum Disturbance/Minimum Maintenance

    Minimum disturbance/minimum maintenance is an approach to site development in which clearing and site grading are allowed only within a carefully prescribed building area, preserving and protecting the existing natural vegetation. Landscapes that demand significant amounts of chemical treatment should be avoided. Minimum distur-bance/minimum maintenance strategies help minimize nonpoint source impacts associated with the application of fertilizers, pesticides, and herbicides that result from new land development. The retention of existing vegetation may also help maintain predevelopment runoff volumes and peak rates of discharge and thus reduce erosion.

    Translation of a concept such as minimum disturbance/minimum maintenance into straightforward numerical standards and criteria is difficult. A certain level of interpretation and judgment is often necessary. Nevertheless, basic standards can be established. Assuming that land use categories have been established through the local land use plans or zoning ordinances, vegetation mapping can be used to illustrate where the proposed development can be constructed with minimal impact on existing vegetation. The area to be disturbed should be identified for all buildings, structures, roads, walkways, and activity areas. The exact dimensions of this disturbance will be subjective and will depend on factors such as lot size and site-specific conditions. For example, a single-family residential development can be constructed with a narrower zone of disturbance than a mall or office park that may require larger construction equipment with greater maneuverability. In general, an extremely conservative zone width would be 10 feet beyond the roof line of a structure or dwelling unit; a more moderate criterion might be 25 feet. Mall sites and large residential developments are typically mass-graded. Limits of Disturbance (LOD) are usually required on all erosion and sediment control plans and are always a function of grading requirements.

    Program Implementation Costs

    The annual costs of establishing and implementing a minimum disturbance/minimum maintenance (MD/MM) program are estimated below. In some cases, the MD/MM tasks can be incorporated within the framework of the existing land development review process and implementation costs would only be additive. A new program, however, would need trained staff responsible for ensuring that developers properly integrate the requirements for the MD/MM into their respective site plans. The need to inspect sites during construction would also result in additional costs. The annual operating costs of implementing such a program will vary depending on the size of the community and the degree of new development. For a typical program, estimated costs may be approximately $110,000 for one professional staffperson and can be divided as follows:

    Professional staff    $ 60,000
    Support staff         $ 30,000
    Office space          $ 15,000
    Office expenses       $ 5,000
    Total                 $110,000 per year

    These figures are based on approximate average salaries and expenses for similar programs.

    The manner by which a turf management or landscape control ordinance is developed or implemented varies to some extent, county by county, State by State. The process would reflect county size, the framework of existing government agencies, techniques of governance, and numerous other factors. Costs would vary as well. These specific aspects of the program would be established by any initial studies and establishment of program requirements, as discussed above. Also, as experience is gained by the staff and the minimum disturbance/minimum maintenance concept is better understood by the development community, the need for services might be expected to decrease as the result of increased program operation efficiency.

    5. Site Planning Practices

    As discussed more fully at the beginning of this chapter and in Chapter 1, the following practices are described for illustrative purposes only. State programs need not require implementation of these practices. However, as a practical matter, EPA anticipates that the management measure set forth above generally will be implemented by applying one or more management practices appropriate to the source, location, and climate. The practices set forth below have been found by EPA to be representative of the types of practices that can be applied successfully to achieve the management measure described above.

  • a. Clustering

    Clustering development is used to concentrate development and construction activity on a limited portion of a site, leaving the remaining portion undisturbed. This allows for the design of more effective erosion and sediment control and urban runoff management plans for the sites, as described in Section II.A. It also provides a mechanism for preserving environmentally sensitive areas and reducing road lengths and impervious parking areas.

    NOTE: A common belief is that low-density development is more environmentally sound because it results in increased open space. Minimum lot size requirements can result in suburban sprawl. Many of these areas are heavily landscaped and therefore have the potential to contribute significant loadings of nutrients and pesticides to surface waters. In many cases, clustering and infill development may be more environmentally sound strategies. They may also result in a cost savings for municipalities because clustering and infill development usually require less infrastructure, including urban runoff treatment systems. The imposition of density controls may preclude clustering. While minimum lot size requirements are useful in some instances, such as farmland preservation, zoning ordinances should not preclude the implementation of clustered development as an alternative to traditional suburban development.

  • b. Performance Criteria

    Performance criteria for site development contain certain built-in safeguards to protect natural features. Performance criteria often apply not to individual zoning districts but to the site being regulated or protected and set fixed protection levels for specific resources that are not based on general zoning definitions.

  • c. Site Fingerprinting

    The total amount of disturbed area within a site can be reduced by fingerprinting development. Fingerprinting places development away from environmentally sensitive areas (wetlands, steep slopes, etc.), future open spaces, tree save areas, future restoration areas, and temporary and permanent vegetative forest buffer zones. At a subdivision or lot level, ground disturbance is confined to areas where structures, roads, and rights of way will exist after construction is complete.

  • d. Preserving Natural Drainage Features and Natural Depressional Storage Areas

    As discussed in the Watershed Protection Management Measure, natural drainage features should be preserved as development occurs. This can be done at the site planning stage as well as the watershed planning stage and is desirable because of the ability of natural drainage features to infiltrate and attenuate flows and filter pollutants. Depressional storage areas, commonly found as ponded areas in fields during the wet season or large runoff events, serve the purpose of reducing runoff volumes and trapping pollutants. These areas are usually filled and graded as a site is developed. Cluster development can be used to preserve natural drainage features and depressional storage areas and allow for incorporation of these features into a site design (Dreher and Price, 1992).

  • e. Minimizing Imperviousness

    Through the use of various incentives, such as those found in the Maryland Chesapeake Bay Critical Areas 10 Percent Rule, a general strategy of minimizing paved areas can be implemented at the site planning level. Methods used to meet this goal include:

    • Reduced sidewalk widths, especially in low-traffic neighborhoods;
    • Use of permeable materials for sidewalk construction;
    • Mandatory open space requirements;
    • Use of porous, permeable, or gritted pavement, where appropriate;
    • Reduced building setbacks, which reduces the lengths of driveways and entry walks; and
    • Reduced street widths by elimination of onstreet parking (where such action does not pose a safety hazard).
  • f. Reducing the Hydraulic Connectivity of Impervious Surfaces

    Pollutant loading from impervious surfaces may be reduced if the impervious area does not connect directly to an impervious conveyance system. This can be done in at least four ways:

    • Route runoff over lawn areas to increase infiltration;
    • Discourage the direct connection of downspouts to storm sewers or the discharge of downspouts to driveways or parking lots;
    • Substitute swale and pond systems to increase infiltration; and
    • Reduce the use of storm sewers to drain streets, parking lots, and back yards (NIPC, 1992)
  • g. Xeriscape Programs

    Xeriscaping is a landscaping concept that maximizes the conservation of water by the use of site-appropriate plants and an efficient watering system and involves the use of landscaping plants that need minimal watering, fertilization, and pesticide application. Xeriscaping can reduce the contribution of landscaped areas to coastal nonpoint source pollution. Xeriscape designs can reduce landscape maintenance by as much as 50 percent, primarily as a result of the following:

    • Reduction of water loss and soil erosion through careful planning, design, and implementation;
    • Reduction of mowing by limiting lawn areas and using proper fertilization techniques; and
    • Reduction of fertilization through soil preparation (Clemson University, 1991).
    In 1991, the Florida Legislature adopted a xeriscape law that requires State agencies to adopt and implement xeriscaping programs. The law requires that rules and guidelines for implementation of xeriscaping along highway rights-of-way and on public property associated with publicly owned buildings constructed after July 1, 1992, be adopted. Local governments are to determine whether xeriscaping is a cost-effective measure for conserving water. If so, local governments are to work with the water management districts in developing their xeriscape guidelines. Water management districts will provide financial incentives to local governments for developing xeriscape plans and ordinances. These plans must include:

    • Landscape design, installation, and maintenance standards;
    • Identification of prohibited plant species (invasive exotic plants);
    • Identification of controlled plant species and conditions for their use;
    • Specifications for maximum percentage of turf and impervious surfaces allowed in a xeriscaped area;
    • Specifications for land clearing and requirements for the conservation of existing native vegetation; and
    • Monitoring programs for ordinance implementation and compliance.
    There is also a provision in the law requiring local governments and water management districts to promote the use of xeriscape practices in already developed areas through public education programs. California has passed a law requiring all municipalities to consider enacting water-efficient landscape requirements.

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