Looking Back and Welcoming the New Year

30 12 2009

Image Credit: http://www.istockphoto.com/AndreasReh

Green Infrastructure Digest began this past October. During this time, we have enjoyed bringing you information and news on green infrastructure and look forward to more in the New Year. The pace of posting has exceeded our expectations. We plan on keeping it up and bringing you helpful and interesting information each week. We appreciate you for taking the time to explore green infrastructure with us. We hope you will continue to read along and spread the word.

The following is a list of some of our most popular posts this year:

If there are any specific topics or questions related to green infrastructure that you would like to see us address, please send us a comment or email.

EPA’s Green Infrastructure Statement of Intent

28 12 2009

Structured Rain Garden at
Tennessee Association of Realtors, Nashville, TN

In 2007, the Environmental Protection Agency (EPA) issued a Statement of Intent that recognized the viability of green infrastructure as a legitimate and effective tool that can be used to protect our water sources from non-point source pollutants. The statement was signed by the National Association of Clean Water Agencies, Natural Resources Defense Council, Low Impact Development Center, and the Association of State and Interstate Water Pollution Control Administrators. The objectives of the statement included the following (direct excerpt from Statement of Intent):

  • Affirm the belief by the signatory organizations in the value of green infrastructure as both a cost effective and an environmentally preferable approach to reduce stormwater and other excess flows entering combined or separate sewer systems in combination with, or in lieu of, centralized hard infrastructure solutions
  • Establish a framework for working together to advance an understanding of green infrastructure as a tool for reducing overflows from sewer systems and stormwater
  • Identify partnership opportunities between the signatory organizations
  • Develop strategies to promote the use of green infrastructure by cities and utilities as an effective and feasible means of reducing stormwater pollution and sewer overflows such as:

-Developing models for all components of green infrastructure and make them available nationwide.

-Exploring opportunities and incentives for the use of green infrastructure provisions in MS4 permits and CSO Long Term Control Plans (LTCPs), including as a component of injunctive relief provisions of enforcement actions

-Developing memoranda and guidance materials, including language for the NPDES permit writer’s manual, that would explain how regulatory and enforcement officials should evaluate and provide appropriate credit for the use of green infrastructure in meeting Clean Water Act requirements

-Recognizing the most effective and innovative uses of green infrastructure to meet Clean Water Act goals through EPA awards or recognition programs

-Providing technical assistance, training, and outreach to potential users of green infrastructure, including states, cities, counties, utilities, environmental and public health agencies, engineers, architects, landscape architects, planners and nongovernmental organizations

-Establishing a web-based green infrastructure resource center at EPA to assist communities in complying with requirements for combined sewer overflows and municipal stormwater permits and evaluating the multiple environmental benefits that green infrastructure can provide

-Developing tools to assist local green infrastructure programs with outreach, training, model development and application, planning and design, monitoring, and plan review

It has been almost three years since this statement was released. In that time, we have come a long way. There has been a tremendous increase in attention to green infrastructure within municipalitie’s overflow control plans and integration of best management practices into city stormwater manuals. We have gone from having to convince municipalities to employ green infrastructure practices, to being encouraged to use them by the same agencies. With Philadelphia proposing an all green infrastructure solution to the EPA for addressing the city’s overflow plan, it will be interesting to see how the EPA responds.

A recent New York Times’ article, “City’s ‘All Green’ Stormwater Plan Raises Eyebrows at EPA” underscored the unique approach the City of Philadelphia is taking. I thought Howard Neukrug summed it up well. He was quoted as saying:

“We recognized that if we manage stormwater where it lands, whether on the ground or on a roof, that in very many circumstances we can not only prevent that gallon of water from overflowing, but we may be able to find additional benefits for our customers…Things that impact the urban heat island effect, things that improve the aesthetic of a community.”

As we enter this new decade, we can be assured that green infrastructure will increasingly be a part of the solution.

-Brian Phelps

Cooling Our Cities: An Interview with Dr. David Sailor

23 12 2009

I had the pleasure of conducting an email interview with Dr. David Sailor, the director of the Green Building Research Laboratory (GBRL) at Portland State University (link to resume). He is a leading researcher in the effects of green roofs and energy use in buildings and the impact green infrastructure can have on cooling our cities. He and his colleagues have developed tools to help quantify these impacts.

Green Infrastructure Digest (GrID): I understand that this year you became the first Director of the Green Building Research Laboratory (GBRL) at Portland State University. What is the focus of the research you are conducting at GBRL? Why and how was GBRL started?

Dr. David Sailor: The Green Building Research Laboratory was essentially an outgrowth of the funded research agendas of myself and my GBRL colleagues. This group of Portland State University faculty included Graig Spolek in Mechanical and Materials Engineering, Loren Lutzenhiser r in Urban Studies, and Sergio Palleroni in Architecture. Over the years we had developed a number of collaborative projects and decided it was time to build upon this collaboration by creating a physical laboratory where we, our students, and our industry partners could work together on fundamental and applied research to benefit the green building industry.

We pitched the idea of a collaborative shared-user facility to Oregon BEST and to the PSU Center for Sustainable Processes and Practices, both of whom agreed to provide the initial funding for the lab. As a result, while the lab was initiated by four faculty members at Portland State, it really serves as an Oregon University System shared resource.

There really is a wide range of research activities going on in the lab. This includes several monitoring projects with local builders, property owners, and school districts with a focus on understanding the thermal and moisture performance of building envelopes as well as the indoor environmental quality of these buildings. We also continue to make advances in the monitoring and modeling of green roof performance. Personally I have been involved in a number of monitoring projects and in creating an energy modeling tool for evaluating the energy performance of green roof design decisions. My colleague Graig Spolek has been using some of the GBRL water quality testing equipment to better understand the chemical composition of green roof runoff. We are also using GBRL facilities to understand the interactions between buildings and the urban atmospheric environment. This involves both modeling and field measurements.

GrID: A lot of your research has been focused on green roofs and heat island mitigation through the use of green infrastructure. How significant of a role does green infrastructure have in addressing thermal heat gain within our built environment? It appears through the tools you have developed for the MIST program that you have been able to quantify these impacts? Can you explain to our readers, what the MIST program entails?

Dr. Sailor: Yes, my research career actually started with a focus on urban heat island mitigation through use of urban vegetation and highly reflective (high albedo) urban surfaces. The US EPA funded some of my early modeling efforts in an attempt to provide a quantitative assessment of how much potential there is for cities to cool their summertime air temperatures through city-wide modification of urban surface characteristics (vegetation and albedo). We used regional scale atmospheric models of about 20 cities across the US to create information on the potential impacts of such mitigation on summertime urban air temperatures, peak ozone concentrations, and energy consumption. The result of that was a fairly user-friendly urban heat island screening tool – the Mitigation Impact Screening Tool – or MIST. The tool uses fairly simple interpolation and extrapolation of our modeled results so that policy makers in any US city can easily estimate the order of magnitude of the impact that any particular mitigation strategy might have in their city. I like to emphasize the “S” in MIST – this is a Screening tool. Ultimately, any policy decisions that involve significant investment of public funds to mitigate the urban heat island ought to be based on a more thorough, city-specific analysis – which of course can start by running MIST.

Thermal Imaging Photo of Portland Buildings (Summer 2009)
Source: Green Building Research Laboratory (GBRL)

SP1=Typical Washed Rock Roof Membrane Cover (151.5F)
SP2=High Albedo (.75) White Roof (110.0F)
SP3=Low Albedo (.10est.) dark roof, NE Exposure (135.0F)
SP4=Low Albedo (.10est.) dark roof, SW Exposure (144.0F)
SP5=3-month Old Green Roof (Essentially Bare Soil) (100.0F)

GrID: Many of our readers would like to know if green roofs can reduce energy use in buildings and if so, by how much? What factors most influence the outcome? What light has your research been able to shed on this pressing question?

Dr. Sailor: The thermal performance of green roofs depends on a number of factors. Specifically, roof construction, depth and properties of the growing media – including soil moisture, plant characteristics and coverage, and local climate characteristics all affect heat transfer into the building. The role of the roof on building energy consumption also depends on internal building loads and schedules. An often overlooked point is that the performance of any alternative technology depends on the baseline that is used for the comparison. As a result, I hesitate to assign a specific level of savings that could be expected from green roof implementation. That said, the various simulations that we have conducted for cities across the US have shown that a green roof can have comparable summertime air conditioning benefits to those achieved by white or “cool” roofs. In contrast to a cool roof, however, the added thermal insulation of a green roof can result in a wintertime heating energy savings whereas the cool roof generally has a wintertime heating penalty. In general, our model shows that the annual air conditioning energy savings associated with replacing a typical roof with a green roof are on the order of 100 to 500 kWh for each 1,000 sq. ft of green roof. What is important to note, however, is that the energy savings are just one component to be considered in determining the economic and environmental value of green roofs. It is likely that the stormwater, urban heat island, and extended roof life aspects of green roofs are equally important.

GrID: The energy savings for green roofs are more modest than I would have expected. I remember some of your findings displayed at the 2007 Green Roof for Healthy Cities conference in Minneapolis had energy saving ranges between 4-12% depending on the location.

Dr. Sailor: Yes, the air conditioning energy savings by themselves are modest. The numbers I gave above are just for the Air Conditioning savings. Heating savings can be comparable or more important depending upon the location and roof design.

The data that you recall from the Minneapolis meeting were specified in terms of HVAC savings. The numbers from that poster were 3-6% annual cooling electricity savings in Minneapolis, 2-5% for Phoenix, and 3% in Orlando. For heating energy savings we had found up to 10-14% for Orlando and Phoenix, and about 4% for Minneapolis. While the model has changed some, these values are generally consistent with what we are still finding.

The nominal ranges that I described from our current model simulations are for a green roof in comparison to a roof that has an albedo of 30%. Both roofs are assumed to be insulated to modern energy code standards. The actual savings depend very much on the baseline used for comparison with the current tool providing a conservative estimate that might significantly underestimate savings for some applications. Also, it should be noted, that depending upon soil depth, vegetative lushness, local climate, and building type, a green roof can actually INCREASE the energy cost for heating or cooling in a building. The tool can provide the necessary feedback to avoid such a situation, and then help you move toward an optimum design with respect to total energy performance.

GrID: Oftentimes, engineers modeling the energy use of a building find it difficult to accurately simulate the effects of green roofs on energy use. Can you tell our readers about the plug-in your have created for the Department of Energy’s (DOE) EnergyPlus modeling software? How has this enabled mechanical engineers to more accurately model the effects of green roofs? How widely used is it?

Dr. Sailor: We developed a physically-based model of the energy balance of a vegetated roof and integrated this model into EnergyPlus. This module is now a part of the standard release of EnergyPlus and allows the energy modeler to explore how variations in green roof design can impact whole building energy performance. It is hard for me to assess how widely used it is among practitioners in the field, but I have been contacted by multiple groups around the US who are now gearing up to use the model in their research and design work.

GrID: If the impact green roofs have on energy use in a building is as modest as you describe, why would you need to model the green roof? Are there cases where it can/has make/made a significant difference?

Dr. Sailor: As I mentioned previously, if one does not pay attention to the green roof design from an energy standpoint, the roof may perform WORSE than a conventional roof. The tool can help the user avoid such potentially undesirable outcomes and then be used to optimize the design for improving energy performance beyond a conventional design. In the case of a retrofit the existing roof insulation may be significantly lower than current code or the current membrane may be much darker than the 30% reflective baseline that I use in the modeling. In such cases, the actual energy savings of the retrofit may be much larger than that reported directly in the current version of the calculator. Nevertheless, the calculator can be used to optimize the energy performance of the new roof.

GrID: What do you see as the future of green infrastructure?

Dr. Sailor: I think that historically there has been a bit of inertia within the building industry that tends to limit the pace of innovation and application of new concepts. From the perspective of an academic researcher I see great opportunities for applied research to develop new technologies and the data and modeling tools necessary to understand the building performance implications of these technologies. Green roofs and walls are technologies that are both promising, and receiving increased interest in recent years. In order for green infrastructure to reach its full potential, however, it is important to develop the tools and data needed to fully evaluate their many co-benefits.

-Brian Phelps


-Green Roof Energy Calculator

-Mitigation Impact Screening Tool

How much water can you harvest from fog?

21 12 2009

Photo Credit: istockphoto.com/JeanUrsula

How much water can you harvest from fog? I hadn’t really thought about it until, I recently came across the work of FogQuest. FogQuest is a small Canadian all-volunteer organization founded in 2000 that constructs fog collection systems in areas where conventional sources such as wells, rivers and pipelines are not available.

While not as applicable in most of the United States as a primary source of water harvesting (where we use approximately 100gals of water per person per day), the technology is still fascinating and has been effective in developing countries. The system is comprised of a series of screens made of polyethylene or polypropylene erected on poles in areas that frequently experience fog events. According to FogQuest’s website, a 40m2 system can on average collect approximately 200L per day (53 gallons). Like rain harvesting, there are days where no water is harvested, but on some days the system has been reported to collect up to 1000L (264 gallons). FogQuest estimates that a 40m2 system cost between $1,000-$1,500. They have a number of videos on their site that describe the system in more detail (Link to Videos). Andrew R. Parker, a zoologist at the University of Oxford, and Chris R. Lawrence, an investigator at QinetiQ, have developed another fog collection technology based on the Namib Desert Beetle’s wings. They have been able to mimic the beetle’s process for collecting water. It is an interesting application of biomimicry. As the name suggest, the Namib Desert Beetle (see photo) lives in the Namib Desert where only a half-inch of rain falls annually. In response, the beetle has developed a unique survival mechanism. It is able to use its wings to collect water from fog that forms in the early morning and blows across the desert. The researchers discovered that this is accomplished through a series of small bumps on the surface of the beetle’s wings. When the beetle positions its body at 45 degrees the fog collects on its back and runs down the wings to its mouth. Here is a link to a website with more information about the process (link).

Namib Desert Beetle
Photo Credit: asknature.org

In places with high winds, it is thought that this new fog collecting material may be more efficient than the open polyethylene mesh used by FogQuest because the water cannot be blown through it. Other applications being considered for the material include using it to reclaim water vapor from cooling towers to developing tents that would capture fog for drinking water. This material has even been envisioned to reduce or eliminate fog that can disrupt transportation systems (i.e. airports, roads).


18 12 2009

Green Roof Dashboard
from Davis Center at University of Vermont

With a son who is a sophomore in college and a daughter as a high school senior, I have managed to spend a lot of time visiting college campuses over the past few years. One of the things that I have paid particular attention to (and seen an huge increase in during the past two years) is the focus on sustainability. My strong hunch is that schools are incorporating sustainable technologies because this generation of smart, college age youth demand it.

Many college campuses now sport LEED certification on at least one building – my son’s dorm at the University of Richmond (Lakeview Hall) is LEED registered and undergoing certification. It is one of nine buildings at the University which is either certified, or in process of being certified as LEED with the USGBC. Locally, Vanderbilt University completed the LEED certified The Commons at Vanderbilt residential housing complex in 2008. As I have traversed the country and seen what must be dozens of (mostly) smaller liberal arts colleges, I have seen organic gardens and solar panels at Whitman College, windmills and biomass generators at Middlebury, local and organic foods at Skidmore, a unique “homestead” intentional environmental community at Denison, beautiful rain gardens at Emory and the list goes on.

I also found a interesting resource online called the College Sustainability Report Card for 2010 (www.greenreportcard.org), This report card basically looks at environmental sustainability at over 325 colleges and universities in the United States and Canada based on 48 indicators used to evaluate performance within four categories.

One of those categories is “green building”. It was heartening to see that 44% of the schools have had at least one LEED-certified green building or are in process of constructing one and a whopping three-quarters of all of the schools have adopted green building policies that specify minimum performance levels such as LEED certification for new construction.

I was particularly interested in taking a closer look at some of the successes that I have witnessed at several of the schools that I have visited especially as they relate to green infrastructure. I found some additional information on Emory, Allegheny, Middlebury, University of Vermont and Macalester.


As a part of Emory University in Atlanta’s overall commitment to sustainability (with over 1 million square feet in LEED certified buildings), Emory has incorporated many innovative water-conservation technologies.. Particularly impressive to me was their implementation of rainwater harvesting and condensate recovery, especially in light of the fact that Atlanta suffered an historic drought event in the summer of 2007. On Emory’s whole campus they have to date included 6 cisterns with a collective size of over 350,000 gallons for both toilet flushing and for irrigation as well as a condensate recovery technology for over 4 million gallons of water per year.

In their new freshman residence complex including Ignatius Few Hall and Lettie Pate Whitehead Evans Hall, rainwater and condensate collection is diverted to an 89,000 gallon reservoir underground which can provide adequate volume to provide 2170 gallons per day needed to flush all toilets int eh buildings. The rainwater is collected form the roof, then filtered and slowed through a bioswale system outsde of the building and then into the below grade cistern. The condensate harvest provides a reliable source of water to supplement rainfall during those months from May through September. It is estimated that the condensate harvests is adding 300,000 gallons per year to the system.

At the nearby Whitehead Biomedical Research Facility Building, completed in 2001, the engineers devised a system of piping condensate back into nearby cooling towers to use as make-up water. This system conserves water AND diverts 2.5 million (that’s 2,500,000) gallons a year from the sanitary sewer system.

Video About Emory University’s Sustainability Efforts


It seems to me that many, many schools are incorporating green roofs as that technology provides one of the most visible elements to show-off sustainable design. In every school we visited, if there WAS a green roof, it was highlighted on the student led campus tours. The green roof were touted for their well-documented benefits such as longer roof life, reduced cost of heating and cooling, stormwater runoff reduction and habitat.

Allegheny College in Meadville, Pennsylvania impressed me with the well designed green roof on the Vukovich Center for Communication Arts. It is located within the topography of the campus site allowing for a fully accessible roof (entering the building at the green roof on the high side and entering on a lower level to the main campus commons or quad –type area. The roof includes extensive and semi-intensive depths and features lawn space as well as sedums and native grasses with an interesting incorporation of stones and cedar decking through the rooftop.

University of Vermont, just on the edge of downtown Burlington, Vermont, recently completed the 186,000 s.f. Dudley H. Davis Center. The Center features a 19,000 s.f. green roof.

Middlebury College, also in Vermont, provided a sloped green roof above the Atwater Dining Hall. I was interested in seeing their notation that in addition to the traditional green roof benefits that I have seen listed in may locations, Middlebury includes improved acoustical insulation, noting that green roof systems can reduce airborne sound levels by 40 to 50 decibels.

Macalester College in St. Paul, Minnesota impressed me, not in size but in determination. The two green roofs on campus were the result of student designs and even some student labor! The first green roof at Macalester was a 300 s.f. tray system installed above a walkway between tow residence halls and the newer 1350 s.f. green roof on Kagin Commons. I happened to be on campus the day the Kagin Commons green roof was unveiled.

I believe the influence of these campuses and so many others will influence the bright minds of our next generation of decision makers and leaders.

Green Infrastructure for Clean Water Act of 2009

16 12 2009

Photo Credit: istockphoto/ericfoltz

On December 4th, Representatives Donna F. Edwards (D-MD), Russ Carnahan (D-MO), and Steve Driehaus (D-OH) introduced the Green Infrastructure for Clean Water Act of 2009 to Congress. The legislation is expected to be referred to the House Transportation and Infrastructure Water Resources & Environment Subcommittee, as well as the House Science and Technology Committee on which Edwards and Carnahan serve. The bill seeks to establish five research centers across the country. One of the centers will be designated as the national electronic clearinghouse that would develop, operate, and maintain an on-line resource for green infrastructure information. Each of center would be required to do the following (excerpt from bill):

(A) conduct research on green infrastructure that is relevant to the geographic region in which the center is located, including stormwater and sewer overflow reduction, other approaches to water resource enhancement, and other environmental, economic, and social benefits;

(B) develop manuals and set industry standards on best management practices relating to State, local, and commercial green infrastructure for use by State and local governments and the private sector;

(C) provide information about research conducted under subparagraph (A) and manuals produced under subparagraph (B) to the national electronic clearinghouse center for publication on the Web site created pursuant to subsection (C) to inform the Federal Government and State and local governments and the private sector about green infrastructure;

(D) provide technical assistance to State and local governments to assist with green infrastructure projects;

(E) collaborate with institutions of higher education and private and public organizations in the geographic region in which the center is located on green infrastructure research and technical assistance projects;

(F) assist institutions of higher education, secondary schools, and vocational schools to develop green infrastructure curricula;

(G) provide training about green infrastructure to institutions of higher education and professional schools;

(H) evaluate regulatory and policy issues about green infrastructure; and

(I) coordinate with the other centers to avoid duplication of efforts.

In addition, the bill would create a $300 million grant program that could be used for planning, development, and implementation. As much as $100 million could be given to selected planning and development initiatives and a total of $200 million would be designated for implementation projects. The cap for individual projects would be $200,000 for planning and development projects and $3 million for implementation.

As this bill progresses, we will keep you up-to-date.

-Brian Phelps

Sustainability Resource Guides from ASLA

14 12 2009

The website for ASLA (American Society of Landscape Architects) has a fairly new section devoted to resources for sustainable design and planning. If you haven’t wandered across it already you should take a minute to see what it has to offer. It is aimed at national and local policymakers, government agencies, design professionals, planners and students. Resources include hundreds of project case studies, research papers, organizations and other government resources on sustainable design.

The following description of the five resource categories is taken from an announcement by ASLA, they include:

  • Green Infrastructure (www.asla.org/greeninfrastructure) covers park systems, wildlife habitat and corridors, urban forestry and green roofs.
  • Sustainable Transportation (www.asla.org/sustainabletransport) covers sustainable transportation planning, siting sustainable transportation infrastructure, designing safe and visually appealing transportation infrastructure, green streets and reducing the urban heat island effect.
  • Sustainable Urban Development (www.asla.org/sustainableurban) covers fighting sprawl, sustainable zoning, reusing brownfields, investing in downtowns, open spaces and sustainable urban design.
  • Livable Communities (www.asla.org/livable) covers sustainable land use, place making, green schools, sustainable housing, sustainable employment growth and health, safety and security.
  • Combating Climate Change with Landscape Architecture (www.asla.org/climatechange) covers site planning, open spaces, plant selection, stormwater management and other areas.

While the site is a little hard to navigate, (if you like what you see, I suggest you bookmark the above links to be able to find them again) this is a good resource that pulls a lot of varied information together into one area. It has potential to be not only helpful for designers, planners and people who speak the sustainability language, but also to be useful to vastly wider audience. I understand they are also always looking for new projects, research, case studies, etc. to highlight, if you want to contribute you can contact ASLA @ info@alsa.org

-Sara Putney

Trees Please

11 12 2009

Street Trees at Hill Center Green Hills

This year many cities in the Southeast have already exceeded their average rainfall by over 20%. As a result, we’ve heard many stories about flooding and 500 year flood events in the Atlanta area and elsewhere. I wondered about the ability of tree planting to affect stormwater. I have seen various reports referring to the benefits of trees based on their ability to reduce stormwater through evaporation of rainwater which lands on its leaves and branches back into the atmosphere, and through the infiltration of rainwater into the ground reducing the total amount of runoff and also affecting the peak flows by making slight reductions to the volume of stormwater runoff.

Over the past few decades, American Forests has developed an analysis that they refer to as an Urban Ecosystem Analysis (UEA) in over 40 metro areas in the U.S. These reports quantify a number of benefits provided by trees especially relating to stormwater benefits , air pollution reduction and carbon sequestration. The assessment is based on specific GIS modeling of tree canopy for regional and site specific areas within each municipality it studies. The GIS studies also show that impervious surfaces have increased by 20% over the past 2 decades in urban areas. American Forests has developed tree canopy goals for various areas in the United States, with the following recommended generally for cities east of the Mississippi.

AMERICAN FORESTS’ General Tree Canopy Goals
40% tree canopy overall
50% tree canopy in suburban residential
25% tree canopy in urban residential
15% tree canopy in central business districts

I noted that several southeastern cities had had an Urban Ecosystem Analysis including nearby Chattanooga and Knoxville. I also found some data for Charlotte/Mecklenburg County. One of the critical items that the UEA measures is loss of tree canopy. Some of the losses noted are staggering.

Between 1984 and 2001, Mecklenburg County (Charlotte, NC) lost over 22% of its tree cover and 22% of its open space. Over that same time period, the county’s impervious surfaces increased by 127%. By comparison between 1974 to 1996 Chattanooga and its nearby neighbor, Atlanta, both lost 17% of its regional tree cover.

Even with the dramatic percentage of loss noted in Mecklenburg Co, the 2002 UEA still noted that Charlotte, whose city limits are within Mecklenburg County, still exceeds the Tree Canopy Goals mentioned above at 49% Tree Canopy. The city’s tree canopy is valued of $398 million dollars based on a total stormwater retention capacity of Charlotte’s existing urban forest of more than 199 million cubic feet. This translates into a value of approximately $398 million dollars (based on construction costs estimated at $2 per cubic foot to build equivalent retention facilities). Chattanooga comparatively achieved a Tree Canopy Goal of 22.5%.

In a ten year period from 1989 to 1999, Knox County (Knoxville, TN) lost a less dramatic 2.2% of its regional tree cover. Knoxville’s tree canopy measured at 40% of the total land area just met the 40% American Forest Tree Canopy Goal. This was assessed by the UEA to have a value equal to $280 million dollars.. This value is based on a total stormwater retention capacity and related construction costs to build equivalent retention facilities noted in the above Charlotte example. UEA also quantified that the tree cover in Knoxville sequesters more than 2.3 million pounds of pollutants from the air, with a value of more than $5.9 million.

As we consider the goal of increasing our Tree Canopy cover and, especially, the American Forests recommendation of 15% Tree Canopy cover for central business districts, consider that the Knoxville UEA study and The Green Build-out Model: Quantifying the Stormwater Benefits of Trees and Green Roofs in Washington, D.C . completed in 2007, noted a difference in a tree’s stormwater benefit based on whether it was over a pervious or impervious surface. The D.C. report modeled that trees over impervious areas, such as a sidewalk or parking lot, provided a stormwater benefit that was over 5 times that of a tree over a pervious surface such as grass or planting beds. The Knoxville report further noted that it requires ten or more newly planted trees to equal a single large mature tree’s ecological value.

-Kim Hawkins

EPA Releases Technical Guidance for Implementing EISA Section 438

9 12 2009

Just in case you missed it last week among all of the other pressing news stories, the EPA released a report outlining technical guidelines for implementing the stormwater runoff requirements for federal projects under Section 438 of the Energy and Independence and Security Act (EISA). In effort to afford designers maximum flexibility, the guidance provided is performance-based. The Section 438 of the EISA established the following requirements:

“Storm water runoff requirements for federal development projects. The sponsor of any development or redevelopment project involving a Federal facility with a footprint that exceeds 5,000 square feet shall use site planning, design, construction, and maintenance strategies for the property to maintain or restore, to the maximum extent technically feasible, the predevelopment hydrology of the property with regard to the temperature, rate, volume, and duration of flow.”

On October 5th, the White House issued a Presidential Executive Order addressing this requirement. The Executive Order titled “Federal Leadership in Environmental, Energy, and Economic Performance.” It required the EPA in coordination with other agencies to develop guidelines for implementing Section 438 of the EISA within 60 days. The current publication meets these guidelines.

The guidelines establish two options for meeting Section 438. The first option is to retain 100% of a rainfall event on site that is less than or equal to a 95th percentile. A 95th percentile rainfall event is an event with a volume over a 24-hr period that is equal to or less than the volume of 95% of all rain events for a period of record (i.e. 20 to 30 years). The table from the report provided below shows the size of the 95th percentile events for various cities across the Country. The events range between 0.7 to 1.8 inches of rainfall. These events commonly known as a “first flush” event were identified because they often contain the highest level of pollutants. Option 2 allows designers to conduct their own hydrological analysis and determine the site specific pre-development hydrological conditions. This options states that “temperature of runoff should not exceed the pre-development rates and the predevelopment hydrology should be replicated.”

For both of these options, the guidelines encourage the use of green infrastructure stategies. The guidelines recognize that “runoff event frequency, volume and rate can be diminished or eliminated through the use of green infrastructure (GI)/Low Impact Design (LID) designs and practices, which infiltrate, evapotranspire and capture and use stormwater”. The guidelines provide a number of studies that illustrate how green infrastructure can meet the established criteria. It is exciting to see the continued momentum green infrastructure is experiencing. If your considering working on federal projects, you will need to take a serious look at green infrastructure as an integral part of your site strategy.

Liquid Assets: A Review

7 12 2009

Trailer for Liquid Assets (Click Here if you don’t see it above)

Last week I ordered a copy of Liquid Assets from the WPSU media store and had a chance to watch it over the weekend. The documentary debuted Fall 2008 on public television stations across the country. It provides an informative overview of the issues facing our Nation’s water infrastructure and the need to address it. Through a series of interviews and helpful computer animations, the video examines the infrastructure for our drinking water, wastewater, and stormwater, primarily concentrating on the public health and economic development issues. The documentary is a sobering look at the great need to maintain or replace our aging water systems. It was able to capture the magnitude of the problems while offering hope by showing how cities are addressing the problem. Boston, Philadelphia, Milwaukee, Washington D.C., New York City, Pittsburgh, Herminie,PA, Los Angeles, Las Vegas, and Atlanta are profiled.

The audience for the documentary is not design and engineering professionals who are steeped in these issues and have a firm grasp on them. The video is intended for a general audience that may not have a thorough understanding of water issues. My seven year old daughter sat with me to watch it and surprisingly she lasted over an hour before getting bored. She seemed to take a lot of way from the portions she did watch. Some of the basics the video teaches people is what watersheds are, how we get our water, and what a combined sewer overflow is. As an entertaining tool for bringing the general public up to speed with the issues, the documentary is excellent. A complementary community outreach toolkit is provided on-line. This toolkit provides information on how to conduct public workshops in your city and facilitate discussions about water issues. In addition, the documentary is broken into chapters that address specific topics, allowing for groups to tailor it to specific needs within their community. However, I would highly recommended watching the entire 86 minutes. In context of the whole, the chapters are much stronger.

My only major disappointment was that green infrastructure was not addressed to any great depth. The Pittsburgh segment touched on it. The work of the Nine Mile Run Watershed Association was highlighted and concentrated on the Nine Mile Run Restoration. During this segment, there was some mention about street planting and rain barrels. Liquid Assets does however illustrate the issues green infrastructure can address within these troubled systems. This includes combined sewer overflows, protection of water sources, and non-point source water pollution.

Overall the video is a high quality documentary that can spur great discussions about the past, present, and future of our water system.

-Brian Phelps