Green Building: Essential Design Strategies for a Sustainable Future  

Stormwater management has been an integral component of human civilization for thousands of years. Over 4,000 years ago, early inhabitants of the Greek island of Crete designed storm drains and channels, which are still intact today. Unfortunately, as civilizations grew and became increasingly urbanized, stormwater came to be seen as a hazard and nuisance rather than a resource worthy of treatment and conservation. This resulted in urban areas plagued with polluted rivers and undrinkable water.

Irresponsible dumping combined with uncontained overland runoff led to the Cuyahoga River in Ohio catching fire at least 13 times between 1868 and 1969. The largest fire, in 1952, caused over $1 million in damage.

These fires, as well as other environmental impacts, resulted in the formation of the Environmental Protection Agency (EPA) in 1970 and significant expansion and amendment of the Clean Water Act (CWA) in 1972 to establish the National Pollutant Discharge Elimination System (NPDES), a framework for regulating the discharge of pollutants into waters of the United States. Since 1972 the NDPES permit program has evolved into a multi-tiered framework of regulations at the federal, state and local levels addressing wastewater, stormwater and other discharges of pollutants.

The Need For Regulations

Originally enacted in 1948 as the Federal Water Pollution Control Act, and later passed as the Federal Water Pollution Control Amendments of 1972, the Clean Water Act (CWA) established the framework for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters.

Plastic arch system failure beneath parking lot Photo courtesy of Zallen Engineering

As authorized by the CWA, the Environmental Protection Agency (EPA) developed the National Pollutant Discharge Elimination System (NPDES) Permit Program to regulate point source water pollution from municipal and industrial wastewater discharges and stormwater discharges from an array of industrial sectors, including construction, mining, transportation, manufacturing and other similar activities. The CWA also established technology-based and water-based water pollution control strategies, in the form of effluent limitations and water quality standards, respectively.

Water Management Options

Through federal rulemaking (Phase I in 1990, Phase II in 2003 and Phase III currently ongoing), the NPDES permit program has expanded significantly since it was originally established and today, most development projects in urban and suburban areas are required by federal, state and/or local regulations to provide treatment of stormwater runoff though the use of best management practices (BMPs).

Above-Ground BMPs

Above-ground BMPs include stormwater treatment practices such as swales, extended detention and retention ponds, and bioretention facilities.

Swales refer to the use of land or other landscaped feature to collect and convey water runoff. Swales range from very simple open-chanel depressions in the soil that follow the contour of the land, to very complex engineered bioswales designed specifically to attenuate and treat stormwater runoff.

Failed plastic stormwater module system at a landfill in Long Island, N.Y. Photo courtesy of A. L. Filshill

Ponds. A stormwater management pond refers to an excavated area that is typically constructed to collect and treat stormwater runoff. The most common types of ponds are retention and detention.

Corrugated pipe culvert collapse Photo courtesy of Newnham Farms

Retention ponds, also called “wet ponds” or “retention basins,” are permanent pools of standing water designed to hold stormwater runoff for long periods of time and treat the water primarily through sedimentation, biological uptake, and chemical and biological processes that occur between events in the permanent pool.

Detention ponds, typically referred to as “dry extended detention basins” or simply “dry ponds” when used for water quality purposes, are designed to temporarily detain stormwater runoff and promote the settlement of pollutants. Typically dry ponds are designed to fully empty in a time ranging from 12 to 24 hours depending on the characteristics of stormwater solids (smaller particles require longer detention times for removal). Unlike retention ponds, which always have some water present, detention ponds are designed to empty between rain events.

Bioretention ponds, also called “rain gardens” or “bioretention filters or cells,” are designed and engineered to capture, temporarily store and remove pollutants from stormwater runoff. A bioretention facility provides temporary storage of runoff on the surface of the facility (sized similarly to wet or dry ponds); however, bioretention facilities are designed to infiltrate the captured water, providing filtration in the process. The depth of ponding in a bioretention facility is typically far less than in a wet or dry pond. Bioretention gardens are often designed with underdrains if subsoils or presence of other nearby infrastructure make infiltration difficult or undesirable. Bioretention facilities also include vegetative components that aid in evapotranspiration and nutrient cycling.

Below-Ground BMPs

Below-ground BMPs typically employ pollutant removal processes including sedimentation, filtration, straining and other forms of treatment incorporated into underground vault, pipe and manhole systems. Underground systems can be designed to include many of the same processes as surface systems including straining, sedimentation, filtration and others; although, biological processes are generally absent or less significant due to the fact the facilities are underground and do not receive sunlight. Extended detention and sand or media filtration are common processes used by subsurface BMPs. Primary below-ground solutions include metal systems using corrugated metal pipes, plastic systems such as chambers, arches and corrugated pipe, and concrete systems such as vaults, culverts, chambers or pipes.

Metal solutions. Corrugated metal pipes come in a wide variety of sizes with multiple end fittings and are designed for relatively fast installation in a variety of configuration layouts and project applications.

Plastic solutions. Plastic chambers, arches and corrugated pipe solutions are made from lightweight HDPE plastic material and are also available in a wide variety of sizes designed for easy handling as well as fast installation in a variety of configurations. Plastic solutions can range from small low-profile pipe systems to larger-capacity plastic chamber systems.

Concrete solutions offer exceptional strength and durability, and can be designed and engineered to meet a wide range of project needs. From standard reinforced concrete pipe (RCP) to high-challenge projects requiring extensive planning and engineering, the versatility and strength of engineered concrete make it the most durable material of choice for stormwater management systems whether poured-in-place or precast.

Poured-in-place concrete offers increased jobsite flexibility with forming that can be designed, changed or customized on the jobsite as needed to create unique stormwater management solutions.

Precast concrete solutions for managing stormwater include prefabricated engineered vaults, chambers and pipe products that can be manufactured in a variety of shapes and sizes and can be assembled into systems having a multitude of configurations. Modular sized vaults allow for rapid installation of multiple vaults into a complete system. The durability and strength of precast concrete also make it ideal for use beneath areas requiring traffic loading.

In addition to managing the quantity of stormwater runoff, concrete solutions for improving the quality of the stormwater can also be incorporated into the system. Treatment options, such as pre-treatment vaults, integrated treatment and post-treatment vaults, can vastly improve the quality of captured stormwater.

When Systems Fail

When a system fails, it can result in significant damage to buildings, property and utility infrastructure. This will also have a direct impact on the project schedule for removal and replacement of all or part of the failed system as well as to repair any resulting damage. These costs can quickly escalate, even reaching into millions of dollars on large-scale commercial or residential development projects.

Failures can occur in all types of stormwater management systems for a wide variety of reasons; however most of the failures can be assigned to one of the following failure categories:

• Maintenance, environmental, installation, related failures
• Functional or process failures related to capacity and volume
• Structural/material failures

Having a stronger understanding of the contributing factors that can lead to stormwater management system failures will lead to better system designs that are less likely to fail.

Swale/Bioswale Failures

Sink hole caused by failed stormwater system in Dalton, Ga. Photo courtesy of Dalton Utilities

Maintenance failure. Growth and maintenance of vegetation play an important role in the ongoing function of a bioswale system. Failure to properly maintain bioswales can result in failed vegetation growth and poor water conveyance, permeation, and failed treatment.

Functional failure. As with all types of stormwater management systems, swale and bioswale systems are dependent on proper planning, design and execution during all phases to ensure success. Miscalculations in any of these phases can result in the swale not functioning as intended. If the required volume or capacity is underestimated, the results would be a failure of the swale to properly manage or treat stormwater runoff.

Structural failure. Over time, erosion can strip away vital vegetation and soils of a bioswale and result in an overall breakdown of the swale itself. Ground saturation during extreme rain events can result in reduced ground permeability and increased surface water that can result in erosion as well as flooding onto roadways, walkways or other surrounding ground surfaces.

Pond System Failures

Maintenance failure. Poor ongoing maintenance is the primary cause of pond failure. Retention/detention ponds that are poorly maintained can result in unwanted algae blooms, foul odors and a build-up of trash or debris resulting in the clogging of inlet or outflow pipes as well as clogged permeable base material.

Functional failure. Treatment of stormwater primarily occurs by allowing particles to settle to the pond bottom and facilitating the uptake of pollutants, including nutrients, through the biological processes of the pond. When a pond stops functioning as designed, it can result in an overloading of the biological process within the pond. Additional treatment solutions such as aeration may then be required.

Structural failure. In addition to reduced water quality, each new rain event brings the potential for flooding and destructive erosion of surface areas surrounding the pond, creating the potential for a washout to occur. Erosion is often prevalent at concentrated inflows to ponds. Ponds that are poorly maintained or neglected also pose serious health and safety risks, particularly to children. Unfenced ponds are often mistaken for recreational water areas and result in countless unfortunate child deaths each year. Several states including Indiana and Hawaii have proposed legislation that would require perimeter barriers or fencing around retention and detention ponds in an attempt to reduce the number of injuries or deaths associated with ponds.

Metal Pipe System Failures

Maintenance-related failure. In low-profile applications where no access is provided to maintain or clean out the system, failure of a corrugated metal pipe system can often occur as a result of clogging from debris that enter and build up in the system.

Functional failure. As with all other stormwater management systems, corrugated metal pipe systems depend on proper design at the beginning of a project to accurately calculate the required storage volume and ensure optimal function of the system before, during and after any storm event.

Structural failure. Metal pipe relies on accurate placement and compaction of structural backfill, especially under the haunches of the pipe. Uncompacted fills such as “pea gravel” are not recommended as they can result in pipe deflection and failure. Failure to properly install connecting bands with gaskets can result in exfiltration of water and a compromise of the backfill envelope and also ensure that backfill does not infiltrate into the pipe. Application of ASTM 798 “Standard Practice for Installing Corrugated Metal Pipe in Sewers” is recommended. Traffic loads without proper minimum cover over the top of corrugated metal pipe is the most common cause of failure. ASTM A796 “Standard Practice for Structural Design of Corrugated Steel Pipe, Pipe-Arches, and Arches for Storm and Sanitary Sewers and Other Buried Applications” prescribes the method for determination of pipe metal gages and the allowable minimum cover for traffic loading.

Plastic System Failures

Maintenance-related failure. Ongoing maintenance is crucial to any system. Plastic pipe and chamber systems that do not have access for maintenance can accumulate debris build-up and result in clogging of the system.

Functional failure. Plastic pipe stormwater management systems often incorporate the void space within surrounding stone backfill as storage capacity for the overall system. In these applications, accurate compaction of stone fill material is critical to the function of the system to prevent wash outs and surface settling.

Structural failure. Plastic products can fail from exposure to extreme temperatures, thermal expansion and improper installation such as incomplete or improper fill and compaction around the system. Stackable modular plastic units have been involved in high-profile structural failures that resulted in Fairfax County, Va. issuing a moratorium on the use of five specific plastic modular products. As with corrugated metal pipe, plastic pipe, plastic chambers and plastic modules are quite flexible and their long-term performance is a function of well-placed granular, select structural backfill. In addition, if deflected, gaps in joints and connections can open, allowing backfill to infiltrate; loss of structural support will occur so deflection control during backfilling is of paramount importance. Exfiltration of captured stormwater can also be a concern as this can saturate the surrounding backfill envelope.

Plastic arch collapse Photo courtesy of Zallen Engineering, Oldcastle Precast

ASTM 2321 “Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity Flow Applications” should be followed to ensure the proper installation of plastic pipe systems. ASTM 2787 “Standard Practice for Structural Design of Thermoplastic Corrugated Wall Stormwater Collection Chambers” governs the design of plastic chambers and provides guidance for installation.

Concrete System Failures

Structural concrete failure Photo courtesy of Zallen Engineering, Oldcastle Precast

Maintenance-related failure. Concrete stormwater management systems, while structurally superior to other material options, require the same ongoing maintenance as other systems. Concrete systems require periodic clean out and removal of debris that build up during use and can restrict water flow through the system. Smaller diameter pipe systems have limited access and are difficult to maintain. Larger vault systems with manhole access will allow easy access for ongoing maintenance.

Functional failure. Proper site-specific hydraulic design is critical to the success or failure of all stormwater management systems. Improper design can result in inadequate flow through the system, insufficient treatment and inability to handle runoff volume. Improper site preparation can lead to differential settlement of the components.

Structural failure. While the controls of factory-produced precast are typically superior to poured-in-place concrete, there are a number of factors that can contribute to precast structural failures that must be considered. Improper structural design and designs that do not consider site-specific conditions can lead to reduced service life of the system.

Forming and pouring. Inadequate reinforcing within the concrete can also cause both poured-in-place and precast concrete to fail.

Inherent to poured-in-place concrete is the large number of variables that can impact the final product quality. These variables, mostly weather related, can impact concrete mix quality, forming and placement, and concrete curing. Concrete that is poured-in-place will require approximately 28 days to fully cure. During that time it is susceptible to adverse weather conditions that can affect the moisture content of the mix and cause physical or structural failure of the concrete. The risk of failure of poured-in-place concrete is compounded by premature backfilling of the structure.

Engineered For Success

Stormwater management solutions, whether above ground or below ground, are subject to failure from a variety of potential reasons if not designed, installed and maintained properly. Taking the time to understand those potential reasons and taking the necessary steps to prepare for, and avoid them, will lead to safer, better-engineered and structurally sound stormwater management systems that will last for years to come.

Reference: Collapse of Underground Stormwater Detention System www.zallenengineering.com/On-Line_Issues/OL-16.pdf

Case Studies

Horizon Bay Congregate Living Facility Uses Green StormWater Detention Infrastructure

A unique precast concrete subsurface stormwater detention infrastructure was specifically engineered and designed to accommodate both the stormwater storage capacity demands and the load-bearing needs of the land use above them, at the new Horizon Bay Congregate Living Facility located in Tampa, Fla. The Horizon Bay project needed to be able to capture stormwater and pipe it to 6,572 CF of stormwater detention under the parking area to absorb and detain the stormwater and allow water to slowly infiltrate into the ground, assisting in recharging the groundwater. Limited available site space necessitated the use of an underground stormwater detention structure beneath the facility parking lot. Underground detention was the only practical choice according to design engineer Fuxan Engineering of Odessa, Fla. An overflow pipe led to storm sewers, but the majority of the stormwater would be infiltrated back into the ground; a common low-impact development (LID) practice in Florida that serves to help recharge the aquifer. The “green” precast concrete module detention system provided a much better value proposition to the owner and engineer in place of the plastic underground storage chambers originally proposed for the site. The module system is ideally suited for this type of underground detention application due to its stand-alone, traffic-bearing design which does not rely on final paving and associated stone underlayment for structural capacity. The precast modules are constructed of high-strength structural concrete. Their ability to support traffic on the parking lot allowed for a 50% reduction in thickness of base rock required between the pavement and modules, as well as a 20% reduction under the modules, as compared to the originally planned plastic chambers. The completed system design for Horizon Bay included 37 modules. Each module is constructed of precast reinforced concrete with interior dimensions of 6 ft x 12 ft x 2.5 ft tall, with open bottom for infiltration. Four of the modules incorporated standard inlet grates to allow stormwater direct entry from the parking lot into the system. This eliminated the need for the four separate inlet structures originally designed into the project. A precast splash pad was installed below each inlet grate to prevent scour of the bedding material. In addition, the inlet grates are used for direct access to the modules for inspection and cleaning as needed. Each module has large conveyance windows into adjacent modules to allow flow equalization, as well as access for maintenance. This was the first project where Ripa Construction used this precast stormwater detention module system. Ripa Construction’s project managers stated that the modules were a key component to providing access for a very limited site and did not require ongoing maintenance or cleanout during construction. The initial savings experienced from the reduction of aggregates in the foundation, backfill and under the pavement are hard, tangible costs. Ripa believes that coupling those savings with the experience they gained in the ease and speed of installation and lack of construction maintenance will make this system very useful in future projects.

 

New Modular Stormwater Management System

A new underground structural precast concrete system for stormwater management consisting of an array of modules can be used for infiltration, detention, or retention and reuse, as well as for treatment-train systems. This modular stormwater system features a stand-alone, traffic-bearing design which does not rely on final paving and associated stone underlayment, or on specific stone backfill for structural capacity and storage. Precast modules are constructed of high-strength concrete and are installed on a simple setting bed of stone that is up to 20% less than other systems. Their ability to support traffic allows for minimal cover with pavement options of asphalt, concrete or concrete pavers. Standard inlet grates allow stormwater direct entry from a roadway surface into the system, eliminating the need for separate inlet structures. The system incorporates direct access for inspection and cleaning through grates, manholes or removable slabs, as well as a maintenance module for sustainability. Overall, precast modules have a smaller footprint with more storage capacity, and allow for rapid installation due to no select backfill requirements. The system can be installed early in the development process without fear of damage during construction.

 

Heavy-Duty, Compact Stormwater Detention System for Nashville Fire Station

To detain stormwater runoff at the Metro Fire Station # 21, the Metropolitan Government of Nashville and Davidson County elected to remove an above-ground detention pond and construct an underground stormwater detention system to gain back valuable land for parking during the recent replacement of the facility. The first design of the new stormwater detention system specified 36-in. corrugated metal pipe but concerns regarding fire truck traffic loading on the system resulted in a change to 36-in. reinforced concrete pipe. This in turn could not be used as it would not fit in the required footprint under the facility’s driveway. In the final design, a modular concrete stormwater management system was chosen and subsequently constructed under the entrance road, since it reduced the detention system width and overall footprint by over 40%, and easily fit under the fire station roadway. The modules were manufactured and supplied at a nearby precast concrete plant. The final system contained (16) modules at 3 ft tall, installed on top of (16) base slabs, for a total of 3,700 cu ft of detention storage. In addition, (5) catch basins/storm structures, 15-in. and 18-in. reinforced concrete pipe, and (3) sanitary manholes were provided for the project. The installation of the entire drainage system was completed in (1) one day. The detention system was a portion of the overall project to construct a new 21,000-sq-ft fire station for Nashville’s Fire Department. Fire Station #21 is expected to achieve LEED Silver certification. Littlejohn Engineering designed the stormwater system and Summit Constructors performed the installation for Messer Construction, the general contractor on Fire Station # 21.

 

New LID Stormwater Management System

A new low-impact development (LID) stormwater management system has been developed as an all-inclusive stormwater run-off control system that manages water volume in addition to protecting water quality by providing integrated pretreatment. This system combines the advantages and versatility of structural precast concrete modules (vaults) with the aesthetics and performance of permeable interlocking concrete pavers to provide a stand-alone, low-maintenance, LID green solution for stormwater retention, detention, reuse, groundwater recharge and flood management. The success of this stormwater management system begins with the permeable paver system. Due to the highly permeable aggregates that surround the specially designed concrete pavers, large volumes of stormwater originating on the permeable paver area, or running on from adjacent impervious surfaces (e.g. roofs), are infiltrated into the underlying aggregate base and ultimately drain to the underground storage modules (vaults). Not only is surface water flow virtually eliminated, but the paver system also provides initial water quality treatment through filtration; total suspended solids and metals are captured in the joint material, which can in time be vacuumed out as part of the regular maintenance program. A major component of the total stormwater management system is the underground precast concrete module with permeable lid. After infiltration through the permeable pavers, the stormwater flows through the permeable lid and collects in the precast modules for controlled management. This allows maximum runoff collection over the entire system’s footprint without the need for grated inlets. The lid permeations and permeable base materials above are strategically sized to eliminate the need for a geotextile fabric that has the potential to clog the system. The modules store the water and allow for controlled infiltration into the underlying soils. In addition, cleanout and maintenance of the stormwater system is easy through maintenance access into the below-grade modules. A stand-alone solution, suitable for a large number of engineered applications including parking lots and roadways, this complete stormwater management system reduces or eliminates runoff, minimizes area disturbance, offers impervious cover and underground storage for filtering, treating, storing, evaporating, detaining and exfiltrating stormwater runoff close to its source and is accepted as best management practices (BMP) to control stormwater runoff.

 

Oldcastle Precast is the leading manufacturer of precast and polymer concrete products in the U.S., providing engineered product solutions nationwide to a variety of market sectors. Contact: 7921 Southpark Plaza, Suite 200, Littleton, CO 80120. Tel: 888-965-3227. Fax: 303-794-4297. E-mail: Jackson.bishop@oldcastle.com www.oldcastleprecast.com