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by Charlene Harper, PE, LEED AP
Monday Jun 7, 2010
The Energy Independence and Security Act of 2007 is an “omnibus energy policy law that consists mainly of provisions designed to increase energy efficiency and the availability of renewable energy.” Amid the provisions requiring a CAFE standard 35 mpg by model year 2020 and a 30% decrease in total energy use in federal buildings by 2015 is a small paragraph called Section 438. Section 438 simply states that federal facility development projects exceeding 5,000 sf must use site planning, design, construction and maintenance strategies to maintain or restore, “to the maximum extent technically feasible,” the predevelopment hydrology of the site. This is a far bigger deal than it might appear at first reading.
In December, 2009, the USEPA issued guidance on meeting Section 438 with two purposes: first, to define “maximum extent technically feasible;” and second, to adopt a process for restoring or maintaining the predevelopment site hydrology. The method is Low Impact Development (LID), a design technique in which treatment measures are integrated throughout the site layout to capture stormwater as close to where it falls as possible. These pockets of retention and treatment help recharge groundwater and mimic the natural site’s ability to absorb rainfall before runoff begins (a.k.a. initial abstraction).
The treatment measures, which infiltrate, evapotranspirate and/or harvest and reuse stormwater, are known as “green infrastructure” and a palette of these options are as follows:
- Conservation and/or reforestation of riparian buffers and floodplains
- Infiltration
- Rain gardens/bioretention
- Amended soils
- Tree box filters and flow through planters
- Vegetated swales
- Vegetated medians and islands
- Porous and permeable pavements
- Green roofs
- Rainwater harvesting/cisterns/rain barrels
Part 2 of this series will explore the sizing goals for these measures and how section 438 guidance dovetails with both LEED and the runoff reduction method…
Tags: bio-rentention, green roof, Low Impact Development (LID), Reforestation, renewable energy, runoff, Stormwater Management, Stormwater Regulations, swales
Posted in Stormwater Management, Sustainability
by Aislinn Creel, EIT, LEED AP
Friday May 28, 2010
A paradigm shift is occurring in the way in which we control pollutants generated by stormwater runoff. This shift is evident by examining the existing and proposed stormwater regulations and design standards. Stormwater runoff (non-point source) pollution is one of the most difficult to quantify and manage, yet critical when it comes to protecting our receiving waterways from harm.
Current standards for water quality criteria in the Commonwealth of Virginia (applicable to all state agency projects and every land-disturbing activity regulated under §10.1-603.8 of the Code of Virginia) target a reduction of total phosphorus and are based on a comparison of existing and post-developed pollutant loading or pollutant removal efficiencies. Percent impervious cover is used to determine pollutant loading in both the performance-based and the technology-based methods and various recognized BMPs are then selected based on assigned pollutant removal efficiencies. To date, BMPs are sized to treat peak discharge rates and rely heavily on the principals of detention time and sedimentation for treatment.
By contrast, the 2007 Energy Independence and Security Act mandates for all federally-owned project sites (>5,000 ft2) that design strategies to maintain or restore the pre-development hydrology of the property with regard to temperature, rate, volume and duration of flow be employed. This aforementioned maintenance or restoration of pre-development hydrology can be accomplished by either controlling the 95th percentile rainfall event, or by analyzing pre- and post-development hydrographs. Either way, the federal mandate requires that 100% of the excess runoff determined be either infiltrated, evapotranspired or captured and used.
Similarly, LEED® standards (Leadership in Energy and Environmental Design) for water quality treatment of stormwater runoff require that 90% of the average annual rainfall is treated using acceptable BMPs and that the BMPs used are capable of removing 80% of the average annual post-developed TSS loads. To obtain LEED® credit for stormwater design: quality control, a stormwater management plan that reduces impervious cover, promotes infiltration or captures and treats the runoff must be implemented.
The focus has shifted from management of discharge rates to management practices focused on volume that better mimic natural systems, i.e., infiltration, evapotranspiration and capture and use. Rather than assuming that retention and sedimentation will primarily treat harmful pollutants liberated by stormwater runoff, regulators are now focusing on mandates to treat entirely on-site the “first flush”; that is, zero discharge of runoff from small (1”-2”) storm events is allowed. EPA is currently in development of a new stormwater rule which may address performance standards for new and re-development; expanding coverage of regulated stormwater discharges to areas with rapid development; provisions for existing discharges (retrofits); permitting and non-permitting alternatives; and special provisions for Chesapeake Bay and maybe other sensitive waters. Based on the already mandated standards for federal sites and similar philosophies used in LEED criteria, it seems likely that the EPA will use a similar philosophy in development of the new rule. We’ll be tracking the progress of this new rule and you can, too, at www.epa.gov/npdes/stormwater/rulemaking.
Tags: LEED, runoff, Stormwater Management, Stormwater Regulations, water quality
Posted in Stormwater Management
by Stuart Toraason, PE, LEED AP
Friday Feb 19, 2010
Urban infill and re-development projects require special means of minimizing increases in stormwater flow is to implement innovative sustainable design techniques to increase pervious area and improve rainwater retention. Projects like Timmons Group’s LEED® Gold certified 1050 K Street project in DC use green roofs, planter beds and rainwater harvesting to meet city code and minimize impact to the combined sewer system.
Projects that involve large-scale infrastructure updates are often required to separate the storm and sanitary sewers as the project progresses. Rocketts Landing in Richmond, Virginia, is a good example of this. In this case, the existing combined sewer system was designated solely for stormwater runoff, and a separate sanitary sewer system was created by constructing new sanitary mains and connections. Stormwater runoff was treated on site and discharged directly to the James River, while the sanitary sewage was directed to the treatment plant.
Combined sewer systems do have one benefit from a development standpoint, in that most local jurisdictions, as well as state and federal codes, do not require stormwater quality control since the stormwater runoff flows to a municipal treatment plant. In addition, for projects in localities that control stormwater quantity, previously mentioned sustainable design techniques may be implemented to eliminate any stormwater increases; thus, the end result can be that stormwater management is not required at all.
Tags: combined sewer, infill, land development, sanitary sewer, Stormwater Management
Posted in Urban Redevelopment
by Lu Gay Lanier, LA, FASLA, LEED AP
Wednesday Feb 10, 2010
The integration of stormwater treatment for quality and quantity is always challenging on an urban site where traditional treatments require acreage that is simply not available. To meet current regulations, the design team needs to look at creative options for removal of pollutants and detention of rainfall within a restricted area.
The flow through planter has become a regular tool utilized in conjunction with green roofs, cisterns, bio-retention and traditional basins. The close coordination between civil engineers, architects and landscape architects from inception of the project enables the team to:
- Correctly size the planter according to capture area and quantities,
- Incorporate design with architecture for optimum aesthetics,
- Utilize required buffer and foundation plantings for uptake of nutrients, and
- Specify plantings that are tolerant of wet feet for up to 24 hours.
In designing DASH, an infill maintenance facility in Alexandria, Virginia, Timmons Group was challenged by the minimal space available for stormwater treatment. To design an effective solution within this limited area, a flow through planter was used to capture the first inch of rainfall for pre-treatment and detention prior to entering a traditional basin. The basin was able to be greatly reduced in size due to the successful design and fit of the planter in a tight space between the sidewalk and building.
The typical detail was updated to obtain enhanced horizontal flow of water from the roof drains to ensure that all plantings were getting equal saturation. Emergency overflow measures were specifically designed to accommodate any additional precipitation.
Let us know your experiences both positive and lessons learned. Continue to follow this thread for more on flow through planters; future discussions will focus on specifying planter components, mid-Atlantic plantings for use with flow through planters and long term maintenance requirements.
Tags: bio-rentention, Landscape Architecture, planters, Stormwater Management
Posted in Landscape Architecture, Stormwater Management
