Implementing Green Infrastructure: Atlanta's Post-Development Stormwater Ordinance Cory Rayburn, CPESC Susan Rutherford, AICP City of Atlanta Department of Watershed Management Introduction In February 2013, the City of Atlanta amended its Post-Development Stormwater Management Ordinance to require green infrastructure on new and redevelopment projects in the City. Compared with other ordinances around the nation, Atlanta's ordinance is unique in terms of its emphasis on requiring green infrastructure vs. a voluntary approach; its applicability to singlefamily development; and its relatively low square footage threshold. This article will provide a case study of Atlanta’s adoption and implementation of the new ordinance, with emphasis on the compelling reasons for the amendments, the ordinance requirements themselves, problems addressed, and the details of a stakeholder outreach strategy that resulted in successful ordinance adoption and implementation. Green infrastructure is an alternative approach to managing stormwater that emphasizes treating runoff with natural vegetation and soils. Unlike “gray” infrastructure, which moves stormwater quickly off-site through curb and gutters, catch basins and pipes with little to no water quality treatment, green infrastructure is designed to slow, infiltrate and clean stormwater close to the site where the rain falls. The goal of green infrastructure is to mimic the natural hydrologic function of the watershed. Examples of this approach on development sites include preserving natural conservation areas, reducing impervious surfaces, and installing structural measures such as green roofs, vegetated swales, permeable pavement, infiltration planters, cisterns, and rain gardens. Compelling Reasons for Change Atlanta staff proposed changes to the ordinance for several reasons: Provide a smooth transition to potential changes in federal stormwater management rules The City began the ordinance revision process when the US Environmental Protection Agency’s proposed stormwater rule changes were slated for late 2012. These changes were anticipated to include new green infrastructure requirements. The City decided that adopting these requirements now might provide the experience and get the right tools in place to smooth the transition to compliance-based requirements. Such experience could also help Atlanta influence an appropriate standard in a way that fits our needs and situation, as well as set the direction for such standards in Georgia. Maximize infrastructure investments to reduce the magnitude and severity of flooding and combined sewer overflows Much of the City’s urban core is serviced by a sewer system in which stormwater runoff combines with sanitary sewer flow. The City has invested nearly $4 billion to address severe problems with combined sewer overflows (CSOs), primarily using gray infrastructure. These investments were funded by wastewater fees—the City does not have a stormwater utility fee or other dedicated source to fund stormwater infrastructure alone. By requiring green infrastructure on development projects within this mostly built-out basin in the dense urban core, future developments and redevelopments can help reduce the volume of stormwater runoff into these combined sewer systems, thus supplementing the City’s infrastructure investments and helping to reduce the occurrence of flooding and CSOs. Improve water quality Atlanta’s decision to implement the use of green infrastructure to manage stormwater runoff has a real potential to improve overall water quality in our streams. The majority of Atlanta’s major stream segments are on the Georgia Environmental Protection Division’s (EPD’s) 305(b)/303(d) list of impaired streams for pollutants related to urban stormwater runoff. By reducing the volume of polluted water that is channeled directly into our surface waters, there is a greater potential for ultimately removing these streams from the list. Promote sustainable development This ordinance fits in with the Mayor’s vision of a sustainable Atlanta by promoting water conservation practices (rainwater harvesting) and utilizing natural vegetated systems to clean runoff. Collecting rainwater from most rooftops provides a fairly clean source of water that can be minimally treated and reused in toilet flushing or irrigation systems. In addition to conserving our water resources, these systems can also be economically advantageous by paying for themselves in a matter of years. In addition, green infrastructure practices that treat stormwater using vegetation and soils, such as green roofs, help to alleviate the impacts of the urban heat island effect, improve overall air quality, increase carbon sequestration, and reduce energy demands by decreasing the amount of energy used for heating and cooling. Finally, green infrastructure promotes economic sustainability. An example of economic growth can be seen around the Historic Fourth Ward stormwater retention pond, located between Atlanta’s Morgan and Rankin Streets. Today, much of the redevelopment that is occurring throughout this area has been attributed to this stormwater management practice that is a central feature of a new park. This project not only saved the City millions of dollars (compared to a tunnel treatment system) but also provided an amenity to the community. Address problems with the previous ordinance The City’s previous stormwater management requirements focused on reducing the predevelopment peak rate of discharge by 30% up to the 100-year storm event. This blanket standard was applied on all sites, regardless of whether the predevelopment conditions were 100% wooded or 100% impervious. Overdetaining the 100-year storm event resulted in large dry detention ponds or expensive underground vault systems, especially on new developments. The changes the City made refocused the attention to the more polluted runoff associated with the ‘first flush’ while adjusting the attenuation requirements that affect the sizing of detention systems. Other issues are further explained in the next section. Summary of Significant Changes Runoff Reduction Requirement The City adopted a volume-based Runoff Reduction requirement that promotes the use of green infrastructure on both commercial and single family residential developments. Projects must capture the first 1.0” of runoff and reduce this volume onsite using infiltration, evapotranspiration, or harvesting the rainwater and reusing it in irrigation or indoor plumbing systems. This new standard replaces the previous water quality requirement of capturing and removing 80% of the total suspended solids from the first 1.2” of runoff on commercial sites. If reducing the entire 1.0” volume onsite is not feasible, the Design Professional must provide documentation as to why the site conditions preclude the use of these runoff reduction practices, and if accepted, may fall back on the previous 1.2” water quality standards. In order to implement the Runoff Reduction standard, the City adopted the Coastal Stormwater Supplement (CSS) of the Georgia Stormwater Management Manual (Blue Book). The Blue Book was published in 2001 when many of the innovative stormwater practices were still being tested and developed. The CSS (2009) includes these runoff reduction practices and provides design parameters and a specified credit system for implementation. Because these practices both clean and reduce the volume of runoff, quantifiable credit is given to satisfy both runoff reduction and attenuation requirements, reducing the size of detention ponds or underground vaults. If a site contains C and D soil types (predominantly clay soils), the CSS specifies how to take credit for the volume provided in each practice and also requires certain design elements, such as underdrains, to ensure drawdown. Essentially, the CSS gives the engineer more ‘tools in the toolbox’ when designing stormwater management plans. The CSS also allows the design professional to take credit for common sense practices that reduce the runoff from the site. Disconnecting downspouts and having them sheet flow across a grassed lawn or landscape island, tilling in compost into soil that has been compacted, conserving undisturbed vegetated areas, or reestablishing buffers along streams or property lines all reduce runoff and can now be counted as stormwater management. Green Infrastructure on Single Family Residences and Small Commercial Projects The City’s previous requirements allowed 99% of homes to be constructed in existing neighborhoods without any form of stormwater management. Redevelopment within these historic neighborhoods can exacerbate existing drainage issues, especially when the development footprint is maximized on each lot. Because of this, the City now requires new homes and large additions (>1,000 ft2 of impervious surface) to manage the first 1.0” of runoff on their site using green infrastructure (however, renovation of a single family house will not trigger any stormwater management requirements). Because the CSS does not adequately address development on single family residential lots in existing neighborhoods, the City felt the need to develop guidance documents in order to assist homebuilders and contractors with compliance so they would not have to involve a design engineer. With the help of a consultant, the City developed a guidance document, Green Infrastructure for Single Family Residences, which specifies the types of stormwater practices that can be utilized on an individual lot, allows the user to size the practice using easy to read sizing charts, and provides tear-off detail sheets that show a step-by-step construction sequence for the given practice. The practices include routing the runoff from the roof to a simplified rain garden, dry well, modified French drain, cistern, or natural buffer. The proposed ordinance has been revised so that the redevelopment of “small commercial” sites must only meet the 1.0” Runoff Reduction requirement (channel protection, overbank, and extreme flooding are not required). Prior to this revision, the threshold for managing stormwater runoff on a commercial redevelopment site was zero, meaning that any addition (or replacement) of impervious cover forced owners to comply with water quality standards as well as detention requirements (30% rate reduction). The City is currently developing a guidance document to assist small business owners with meeting these requirements on their future projects. Rate Reduction The previous ordinance required new and redevelopment sites to reduce the peak flow rates leaving the site by 30%, up to the 100-year storm event. The City’s requirement was much more stringent than that of other municipalities and resulted in large dry detention ponds which pose aesthetic and safety issues. The City received a good deal of input from the stakeholder groups, and with their assistance, revised this standard. For new developments (wooded undeveloped lots), no reduction in peak flow rates is required. In other words, the post-development rate of runoff will need to match the pre-development rate (instead of reducing by 30%), or mimic the natural conditions of the site. For redevelopment sites, the percent reduction is based on the percentage of impervious surface present during predevelopment conditions. The formula (% impervious/2 = % reduction) applies up to the 25year storm event. The 100-year storm must be safely conveyed from the site without any increase in peak rate of flow from pre-development conditions. This change was drafted to balance out this requirement and shift the focus to the more polluted storm events (first flush) rather than overdetaining the extremely rare flood events. Existing Detention Ponds The City occasionally receives a complaint regarding existing detention systems that were installed prior to the original Post-Development Stormwater Management ordinance (pre-2004). Typically, the facility has not been maintained or the outlet control structure is damaged and may be causing flooding conditions downstream. These detention systems have recorded indemnity agreements that specify that the owner of the property is responsible for maintenance of these facilities. Inspection staff are empowered by the new ordinance to investigate and conduct appropriate enforcement action on these sites in order to bring these dilapidated systems back into compliance. Stormwater Concept Plan and Consultation Meeting For larger commercial projects, the stormwater management plan typically takes the longest to be reviewed and approved during the permitting process due to the technical components of the hydrology study and the multiple design requirements (runoff reduction, channel protection, overbank flood protection, and extreme flood protection). Before the new ordinance was adopted, there were frequent cases where an applicant would wait until the end of the process to submit plans for this review, then be stuck with expensive revisions that might threaten his project schedule, previous approvals for zoning or other aspects. The City now requires that a preliminary stormwater concept plan is developed and discussed during a consultation meeting between City staff and the developer’s engineer to ensure that the designer is aware of the new requirements and to discuss different opportunities for green infrastructure practices, design parameters, and ensure appropriate credits are established. City staff feels that this 30-minute meeting during the earlier stages of plan development will save days if not weeks during the permitting process. This meeting is only required for commercial projects and does not apply to homebuilders or contractors trying to construct a house, addition, porch, etc. Stakeholder Outreach Strategy, Before and After Ordinance Adoption Stakeholder Involvement Process City staff proposed these significant changes to the stormwater requirements in the midst of a highly political overhaul of its building permit process, so it was critical to develop a vision and strategy for successful ordinance adoption and implementation. Early in the process, staff developed a strategy, then launched numerous parallel efforts to ensure a smooth ordinance adoption, educate City leadership and future applicants, train plan review staff, prepare for compliance and enforcement, and anticipate inspection and maintenance issues. In all, it took a little over a year to formalize a first draft and an additional 10 months to conduct outreach, receive stakeholder input, and enact revisions prior to officially starting the legislative process. Prior to drafting any changes to the ordinance, staff met with several prominent local engineering groups to find out which parts of the ordinance needed improvement, but to also gain feedback on ideas that the City was interested in proposing. With this information, the Ordinance Review Team (comprised of Watershed Management and legal staff) drafted the changes and briefed other City groups that may be affected, such as Office of Planning, Office of Buildings, Department of Public Works, and the Office of Sustainability. The City then organized a Technical Stakeholder Group consisting of civil engineers who are familiar with the City’s requirements and processes and non-profit organizations like the Chattahoochee Riverkeeper who promote keeping our waters clean. We conducted two roundtable discussions with this group, during which we received feedback and suggestions on how the ordinance could be improved. After many of these revisions were made, we began an outreach campaign to spread the word to as many stakeholders as possible, including the Council for Quality Growth, the Metro Atlanta Real Estate Trade Group, Greater Atlanta & National Homebuilders Association, Building Owners and Managers Association, Atlanta Board of Realtors, National Association of Industrial and Office Properties, International Facilities Management Association, Atlanta Planning and Advisory Board, Neighborhood Planning Units, InvestAtlanta, Atlanta BeltLine, American Rivers, US EPA, Metro North Georgia Water Planning District, Fulton County Soil & Water Conservation District, and others. We received valuable feedback from these organizations and made several revisions prior to submitting to City Council. With regard to satisfying all parties involved, City staff worked diligently to provide a balanced approach to the new requirements and were open to many of the specific changes that were suggested. While all stakeholders did not agree on 100% of the issues, this collaborative effort proved to be the key to gaining support from many of the groups involved. Training Even before the ordinance was successfully adopted, staff began to focus on the training needs of plan review and inspections staff, as well as the development community constituents who would be required to comply with the new changes. In order to ensure the successful implementation of green infrastructure, it was critical to ensure that those who were affected by the revisions were aware and comfortable with the requirements. For City staff, we brought in nationally recognized experts including Andy Reese, AMEC, and Frank Piorko, Delaware DNREC, to provide plan review, inspections, parks design, and public works staff with training on the design, construction, and maintenance of green infrastructure practices. In addition to training internal staff, we began developing a stormwater workshop series to inform the public of the updates and to also focus in on certain topics for the development community, such as pervious pavement design and installation, soil mixes and vegetation, bioretention design, and rainwater harvesting practices. The City is also considering demonstration sites to educate homebuilders and homeowners on the residential applications of green infrastructure (rain gardens, cisterns, modified french drains, etc.). Conclusion Atlanta has made significant changes that not only require the use of green infrastructure techniques, but also address specific problems that have emerged since the original ordinance was adopted in 2004, such as overbuilding of detention ponds, a convoluted stormwater plan review process, the exemption of nearly all single-family development, overbearing requirements on small businesses, the inability to enforce rules on older, malfunctioning ponds, and others. Early results are showing that the new ordinance is beginning to effectively address these issues. The new requirements are different from what Atlanta’s development community is used to seeing, and different from other post-development ordinances in our region. Even though these changes are significant, Atlanta resisted calls to make these provisions voluntary by instead providing incentives for using green infrastructure. Without a stormwater utility fee against which to provide monetary credit, there was not much incentive to offer. Rather, staff was able to argue that the flexibility offered by the new guidance provided built-in “incentives;” and that an applicant would be able revert to the old rules by demonstrating the impossibility or severe hardship of using green techniques. The significant effort invested in stakeholder outreach and training prior to ordinance adoption created the goodwill necessary for the development community to accept the terms of the new ordinance; and the additional public education and outreach that has been conducted since adoption has provided both applicants and City staff the tools to meet the new requirements. The amended City of Atlanta Post-Development Stormwater Management Ordinance protects the City's surface waters and infrastructure while providing an economically feasible way of developing sustainably. By adopting these revisions, the City of Atlanta comes one step closer to Mayor Kasim Reed’s goal of becoming a top-tier sustainable city.
