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).

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.

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.

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

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

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.

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.

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.

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).

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).

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)

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).

• 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.