Environmental Site Design - Maryland

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Environmental Site DesignChapter5.0

Chapter 5. Environmental Site Design.IntroductionSection primary goal of Maryland’s stormwater management program is to maintain afterdevelopment, as nearly as possible, the predevelopment runoff characteristics. Traditionalstormwater management strategies treat runoff to mitigate adverse water quality and/or quantityimpacts associated with new development. Designs applying these strategies often combinecentralized structural practices for pollutant removal with channel erosion or flood controlimpoundments. These designs are less able to mimic predevelopment conditions because theyfocus on managing large volumes of polluted stormwater rather than treating runoff closer to thesource.A comprehensive design strategy for maintaining predevelopment runoff characteristics andprotecting natural resources is available. This strategy, known as Environmental Site Design or“ESD,” relies on integrating site design, natural hydrology, and smaller controls to capture andtreat runoff. This chapter provides the foundation to refocus stormwater design from centralizedmanagement to more effective planning and implementation of ESD.5.0.2Requirements of the Stormwater Management Act of 2007The “Stormwater Management Act of 2007” (Act), requires establishing a comprehensiveprocess for stormwater management approval, implementing ESD to the maximum extentpracticable (MEP), and ensuring that structural practices (see Chapter 3) are used only whereabsolutely necessary. The Act also establishes several performance standards for stormwatermanagement plans. Designers must now ensure that these plans are designed to:¾¾¾¾¾¾¾¾¾Prevent soil erosion from development projects.Prevent increases in nonpoint pollution.Minimize pollutants in stormwater runoff from both new development and redevelopment.Restore, enhance, and maintain chemical, physical, and biological integrity of receivingwaters to protect public health and enhance domestic, municipal, recreational, industrial andother uses of water as specified by MDE.Maintain 100% of the average annual predevelopment groundwater recharge volume.Capture and treat stormwater runoff to remove pollutants.Implement a channel protection strategy to protect receiving streams.Prevent increases in the frequency and magnitude of out-of-bank flooding from large, lessfrequent storms.Protect public safety through the proper design and operation of stormwater managementfacilities.The Act presents a new opportunity to improve Maryland’s stormwater management program.The original Chapter 5 encouraged ESD through a series of optional credits for the design ofnonstructural practices. Changes in response to the Act not only expand on the ESD practicesfirst introduced in the Manual but also allow for planning techniques to improve implementationNOTE: In this chapter, italics indicate mandatory criteria, whereas recommended criteria areshown in normal typeface.5.1Supp.1

Chapter 5. Environmental Site Design.Introductionand overall performance. The remaining sections of this chapter will further define ESD, discussplanning techniques used in its implementation, and provide design requirements fornonstructural and micro-scale practices used to treat runoff at the source. For referencepurposes, the original Chapter 5 can be found in Appendix E. Site DesignDefinitionThere are many stormwater design strategies that seek to replicate natural hydrology. Sometimesknown as better site design, low impact development, green infrastructure, or sustainable sitedesign, these strategies all espouse similar techniques. In each, a combination of planningtechniques, alternative cover, and small-scale treatment practices is used to address impactsassociated with development. For consistency, the Act adopts ESD as a more genericclassification for use in Maryland.Title 4, Subtitle 201.1(B) of the Act defines ESD as “ using small-scale stormwatermanagement practices, nonstructural techniques, and better site planning to mimic naturalhydrologic runoff characteristics and minimize the impact of land development on waterresources.” Under this definition, ESD includes:¾ Optimizing conservation of natural features (e.g., drainage patterns, soil, vegetation).¾ Minimizing impervious surfaces (e.g., pavement, concrete channels, roofs).¾ Slowing down runoff to maintain discharge timing and to increase infiltration andevapotranspiration.¾ Using other nonstructural practices or innovative technologies approved by MDE.Impacts of ImperviousnessThe goal of traditional site design strategies is to maximize development potential by focusing onthe layout of buildings, roads, parking, and other features. Conventional development practicestend to maximize site imperviousness and contribute to many of the impacts discussed in Chapter1. These include diminished groundwater recharge, increased flows and runoff volumes,pollutant accumulation, and elevated water temperatures.Documentation such as the Impacts of Impervious Cover on Aquatic Systems (Center forWatershed Protection, 2003) and other studies of Eastern Piedmont and Coastal Plain streams inMaryland (Morgan and Cushman, 2005) and headwater streams in Montgomery County (Mooreand Palmer, 2005) all indicate that stream biodiversity decreases as impervious cover increases.There is no simple formula, rule, or threshold for determining how much impervious cover maybe sustained in a given watershed. Generally, stream quality and watershed health diminishwhen impervious cover exceeds 10% and become severely degraded beyond 25% (Center forWatershed Protection, 2003). Results from the Maryland Biological Stream Survey (MBSS)indicated that in surveyed streams, health was never good when watershed imperviousnessexceeded 15%, (Boward, 1999). These studies establish a fundamental connection betweenimpervious cover and watershed impairment.Supp. 15.2

Chapter 5. Environmental Site Design.IntroductionIntegrating the fundamental principles of ESD during the planning process helps minimize theadverse impacts of imperviousness. The resulting designs reduce the need for costlyinfrastructure and maintenance while providing treatment closer to the source. To accomplishthis, the designer must consider the basic concepts found in Section 5.1, Planning Techniques.5.3Supp.1

Chapter 5. Environmental Site Design. Design Process and PlanningSection Process and Planning TechniquesIntroductionThe design process described in this section will provide guidance for implementing ESDplanning strategies and practices into a comprehensive site development plan. These techniquesinvolve protecting natural resources, integrating erosion and sediment controls with stormwatermanagement practices, minimizing site imperviousness, and using natural conveyance and ESDpractices throughout the site. Applying these techniques early in the design process will ensurethat all available resources have been considered in order to protect streams and waterways fromthe impact of land development activities. The design process will require the developer toadhere to the following procedures to achieve ESD to the MEP:¾ Following the Design Process for New Development as outlined in the step wise proceduresin Figure 5.1.¾ Developing a map that identifies natural resource areas and drainage patterns and devisingstrategies for protection and enhancement.¾ Minimizing total site imperviousness by implementing clustered development and other bettersite design techniques.¾ Demonstrating that all reasonable opportunities for meeting stormwater requirements usingESD have been exhausted by using natural areas and landscape features to manage runofffrom impervious surfaces and that structural BMPs have been used only where absolutelynecessary.¾ Participate in the comprehensive review process for interim plans review and approval at theconceptual, site development, and final phases of project design.¾ Integrating strategies for erosion and sediment control and stormwater management into acomprehensive development plan.5.1.2Comprehensive Erosion & Sediment Control and Stormwater Management ReviewThe Act requires that “a comprehensive process for approving grading and sediment controlplans and stormwater management plans” shall be established. Therefore, county and municipalstormwater authorities shall establish a coordinated approval process among all appropriate localagencies. Erosion and sediment control review and approval authorities [e.g., local SoilConservation Districts(SCD)] and input from any other local agency deemed appropriate (e.g.,planning and zoning, public works) shall be included. The process will be tailored to meet localinitiatives and should consider the scope and extent of environmental impacts for individual sitedevelopments. Review agencies involved will provide comments and approval during each ofthe following phases of plan development:1. Concept2. Site Development3. FinalAt each phase of this review process, the designer will receive feedback provided by the agenciesallowing the developer to incorporate any concerns and recommendations throughout projectSupp. 15.4

Chapter 5. Environmental Site Design. Design Process and Planningplanning and design. The concept plan will include site and resource mapping and protectionand conservation strategies. The designer will also provide preliminary stormwater managementESD calculations. Review of the concept plan will ensure that all important resources have beenmapped, protected, and all opportunities to enhance natural areas have been explored early in thedesign process.The site development plan will establish the footprint of the proposed project and demonstratethe relationship between proposed impervious surfaces and the existing natural conditionsidentified during concept plan design. This will better protect natural resources and buffers andallow for using ESD practices throughout the site. Included in this step are the preparation ofdetailed designs, computations, and grading plans for a second comprehensive review andapproval. This ensures that all options for implementing ESD have been exhausted. Afterapproval from the review agencies, the applicant will then proceed with final plan preparationincluding the design of any structural practices needed to address remaining channel protectionrequirements. Final plans will go to both the stormwater and erosion and sediment controlreview agencies for approval.The design process and planning techniques described in this section provide guidelines forprotecting natural areas, minimizing imperviousness, using available landscaping for ESDpractices, and integrating stormwater and erosion and sediment control strategies. Following thisprocess will achieve the goal of implementing ESD to the MEP. Involving all review agenciesfrom the beginning of site planning through the more detailed design will foster feedback andallow for a more efficient review and approval of final plans.5.1.3Design Process for New DevelopmentAll new development projects shall be subject to the Design Process for New Development asoutlined in the step wise procedures in Figure 5.1.As described above, the design process will require review and approval during three differentphases of project planning that include the concept, site development, and final stages.Approving agencies shall use the process outlined in Figure 5.1 as an enforceable mechanismduring review of the plan. Documentation that all steps were followed during projectdevelopment and specific rationale to support the proposed design shall be required. Concept Design PhaseThe concept design phase is the first step in project development as shown in Figure 5.1. Thisstep will include the following:¾¾¾Site and Resource MappingSite Fingerprinting and Development LayoutLocating ESD Practices5.5Supp.1

Chapter 5. Environmental Site Design. Design Process and PlanningFigure 5.1 Design Process for New DevelopmentSupp. 15.6

Chapter 5. Environmental Site Design. Design Process and PlanningSite and Resource MappingThe resource mapping component will be used as a basis for all subsequent decisions duringproject design. During this step, the developer shall identify significant natural resources anddemonstrate that these areas will be protected and preserved. Additionally, options will beevaluated to enhance important hydrologic functions. Approving authorities may require thatother features be shown depending on site characteristics. This map shall be field verified by theproject designer. Specific areas that should be mapped are organized by government regulatoryauthority in Table 5.1 below.Table 5.1 Natural Resources and the Corresponding Regulatory Authorities: FederalWetlandsMajor waterwaysFloodplains StateTidal and nontidalwetlandsWetlands of SpecialState ConcernWetland buffersStream buffersPerennial streamsFloodplainsForestsForest buffersCritical Areas LocalSteep slopesHighly erodible soilsEnhanced stream buffersTopography/slopesSpringsSeepsIntermittent streamsVegetative coverSoilsBedrock/geologyExisting drainage areasThe mapping process will identify important natural resources as well as areas that are highlysusceptible to erosion caused by construction activities. Identifying these important resourcesand high risk locations and protecting them from disturbance is the first step in the planningprocess. When steep slopes and highly erodible soils are found measures need to be taken tolimit disturb