Low-Impact Development

By 2030, almost 70% of the world’s human population is predicted to live in rapidly urbanizing metropolitan areas. Human induced pressures on water quality and other natural resources throughout the United States and most of the rest of the world continues to increase in concert with urban development. To accommodate increasing human population developmental pressures and mitigate continued environmental impacts, innovative development techniques are being designed low-impact development, or LID). LID is a general term used to describe innovative engineering for residential or commercial sites. It attempts to develop a site with minimal disruption to the local environment and hydrology. The intent is to maintain an area’s predevelopment flow regime by encouraging infiltration and shallow surface storage of precipitation in order to avoid concentrated flow.

Few articles are written illustrating the complexities of LID implementation policy. Increased capital construction costs of LID compared with traditional gray infrastructure make it difficult to garner stakeholder acceptance. This article presents an LID case study plan proposed in one of the most rapidly developing counties in the Midwest: St. Charles County, MO.

St Charles is in the top 2% for population growth of all US counties. In rapidly developing counties of the Midwest, cultural perceptions prohibitive to LID advancements are slowly giving way to environmentally conscious LID strategies essential to better managing stormwater runoff, storm-induced flooding, and water quality. In this article, we propose an organizational structure for implementation from a lessons-learned perspective, thus providing basic organizational criteria of LID implementation.

LID strategies are designed to achieve hydrologic stability in post-developed environments, thereby modulating stormwater and transported water-quality constituents (e.g., sediment). LID strategies encourage the following:

• Use of structures that mitigate impervious surface loss, including preserving, and restoring native vegetation to approach predevelopment drainage
• Minimal clearing and grading of surface soils
• A variety of detention, retention, and runoff practices to store precipitation and runoff
• Use of engineered hydrologic controls and use of onsite natural features to protect water quality by preventing or reducing pollutant loads
• Directing runoff to natural areas (encouraging infiltration and recharge of streams, wetlands, and aquifers)
• Education, to actively involve all stakeholders (US EPA 1999)
• Theoretically, if properly implemented, LID practices could mitigate many contemporary environmental problems plaguing urban development.

St. Charles County, located west of St. Louis, MO, has undergone conventional urban expansion for more than 100 years. Development was “conventional” in the sense that construction required few or no practices to mitigate soil loss and concentrated runoff. Since approximately 1990, population growth and urban development have increased rapidly, demanding mitigation for runoff and water quality. LID practices generally include additional upfront costs, the benefits of which are only realized over time. Experiences gleaned from a planned development in St. Charles County indicate growing acceptance of upfront costs for long-term sustainability of water resources.

Methods: LID Implementation
Project Site-The project setting is located at latitude 38.7946198, longitude -90.8711885, within the Peruque Piasa Watershed (Figure 1). Property characteristics, including hydrology, soil type, elevation/relief, and proximity to residential and commercial areas (restaurants, grocery, entertainment, etc.) with increasing amounts of impervious surfaces, provide an optimal setting to demonstrate the benefits of LID housing development in Missouri. Soil types include Keswick silt loam (3% of the project area), Crider silt loam (62% of the project area), and Haymond silt loam (35% of the project area). Average elevation is approximately 560 feet, with a 3.4% average slope (40-foot rise/1,180-foot run) and a total area of about 9 acres (CARES 2010). The property (zoned for agriculture) was purchased in unincorporated St. Charles County in March 2006 for the explicit purpose of designing and constructing a 29-lot LID residential development, known as The Village at Peruque Bend. A number of LID structures were planned for construction along with development landscape techniques to best manage stormwater runoff. The plan included a membrane treatment plant, a constructed wetland, cisterns and rain barrels (one for each home), green roofs (29 total, one for each home), permeable pavement on all streets, gravel pathways, and six bioswales for each alley or driveway. The housing layout was designed as a variation of cluster development (Figure 2).

Bioswales are generally very easily maintained once established. Bioswales are multifunctional open drainage systems designed to encourage infiltration and remove silt and pollution from surface runoff water. The drainage routes are filled with vegetation, compost, and/or riprap. Vegetated (often grassy) open drainage systems alleviate flooding problems and reduce the need for conventional storm-drain systems. Grading of lots is recommended to minimize the velocity and volume of surface runoff within the bioswale open drainage systems (US EPA 1999). To be most effective, bioswales are planned to be centrally located in each driveway in the proposed development.

To offset increased stormwater runoff from roofs, green roofs are planned for installation on the garage roof of every home site of The Village at Peruque Bend. Other LID implements are designed to compensate for additional roof area to balance cost effectiveness. Green or vegetated roofs absorb and filter pollution, store precipitation, and reduce pressure on sewer systems. They improve energy efficiency by providing insulation to balance temperature variations (buildings stay cooler in the summer and warmer in the winter). The majority of research pertaining to green roof thermal performance has focused on the ability to buffer extreme temperatures during summer months, but data from a recent study suggest that in sub-zero temperatures (0°C to -25°C) a vegetated roof (100- or 150-millimeter-thick growing medium) can have a 37% higher R-value (measure of thermal resistance or insulation) than a conventional roof (Pierre et al. 2010). Green roofs provide wildlife habitat (US EPA 2010a) and have high aesthetic value (Montalto et al. 2007). Green roofs are also relatively low maintenance and can extend the life of the roof membrane substantially relative to conventional roofs. In the proposed design project, the unvegetated portion of each home’s roof will also be facing from south to west in anticipation of future solar panel installation. Precipitation that exceeds the water-holding capacity of the green roofs will be routed to rain barrels or cisterns.

Precipitation and runoff that isn’t captured and stored will be largely infiltrated. Roads are planned using permeable pavement to encourage infiltration and groundwater recharge and to moderate surface runoff. This includes minimal grading to reduce soil disturbance and impermeable surfaces (i.e., compacted, dense subsoil lacking in significant macropores). Conventional developments would most likely regrade the entire site, thereby heavily compacting a large area of the soil and increasing soil impermeability. The LID approach requires a change in the current paradigm of construction methodologies, including educating developers about long-term benefits of LID systems.

Approximate LID Expense-Montalto et al. (2007) conducted a study assessing the investment of LID cost-effectiveness for reducing combined sewer overflows (CSOs) in urban watersheds. Varying costs by location, rain gardens ranged from $89 to $108 per square yard, porous concrete ranged from $24 to $76 per square yard, new green roofs ranged from $58 to $139 per square yard, retrofit green roofs ranged from $80 to $232 per square yard, and constructed treatment wetlands ranged from $5,680 to $6,680 per acre (US dollars). Despite upfront costs, long-term gains from LID systems are increasingly shown (largely a function of time of use) to result in monetary and sustainability gains relative to conventional practices (US EPA 2010a).

LID Implementation in St. Charles County
Community LID Acceptance-Not unlike many counties of the Midwest, St. Charles County has a development community with relatively limited LID experience compared with conventional development practices. After research on site characteristics and existing LID implementation study outcomes, a preliminary site plan was developed (Figure 2). The developer approached the adjacent city of Wentzville regarding annexation and availability of sewer and water service. The city indicated that an adjacent development was in the planning stages and that their sewer line could potentially terminate within 100 yards of the project site. After six months, it was determined that the sewer line would run in an alternate direction and that a connection was not cost effective, and that the project property was not contiguous to the existing city boundaries and therefore not annexable (Smith 2010).

Lessons in LID Planning-Efforts to implement the Village at Peruque Bend demonstration community LID project are ongoing in St. Charles County. While interim results and experiences could result in a polarized development and environmental community, they are instead being utilized to provide experience-based criteria for LID developers (Figure 4). To navigate the process in the future, it is recommended that developers meet personally with any neighboring landowners who may be affected by a residential or commercial LID. Educating property owners of the benefits of LID systems with regard to nearby water supplies and providing multiple perspectives and contrasts to conventional practices can build a formidable support base for development decisions. This illustrates the importance of creating a community support network, primarily through education.

The St. Charles County council and rezoning committee provided a significant obstacle for this project. When a rezoning application is submitted and in question, landowners within a quarter-mile radius of the property are made aware of the proposed development and the council meeting time to provide an opportunity to voice their concerns (standard practice in most states). Notably, both the rezoning committee and county council had misconceptions of LID development, particularly in terms of the method of sewage/wastewater treatment (i.e., private membrane treatment plant). Though a 29-lot development is within the capacity of the device, concerns about flooding/overflowing of concealed effluent persisted. In their defense, however, St. Charles County is geographically wedged between the Missouri (south) and Mississippi Rivers (north and east). It is therefore not surprising that potential water-quality issues are a sensitive topic.

Not unlike other regions in America, Missouri’s Natural Watercourse Protection Ordinance, applying also to St. Charles County (St. Charles Ordinance 2010), emphasizes the intent to protect natural waterways. The purpose of the ordinance is

• to establish requirements for the design of vegetated buffers for the protection of natural watercourses of all watersheds within unincorporated St. Charles County;
• to protect the water quality of all water bodies and riparian and aquatic ecosystems within those watersheds; and
• to provide for the environmentally sound use of land and aquatic resources.

While St. Charles County clearly supports riparian or vegetated buffers (which are designed with very similar principles to LID), LID techniques for urban developments have yet to be fully embraced, despite validation through field-based and modeling exercises (Montalto et al. 2007, Geosyntec 2009, Houdeshel et al. 2009).

Benefits of LID Implementation-Construction and life-cycle costs for LID systems can be significantly different from those of traditional developments. For example, porous pavement is more expensive initially than regular pavement. However, streets can be designed to be narrower (about 20 feet wide in our case study, as opposed to 28 to 30 feet wide for conventional streets). Avoiding costs of curbs and storm sewers can provide a substantial savings, and many incentives (i.e., grants) are available. Green roofs can add considerable upfront costs, which over time can be recaptured by the benefits they provide. Vegetation may extend the life of a roof by 20 years or more, which reduces the total cost of the roof (US EPA 2000). Upfront costs are also offset by future summertime energy savings. Collectively, these benefits can make the cost of a green roof closer to that of a conventional roof (US EPA 2010a). Ultimately, EPA research indicates that while installation costs of LID technologies are often more expensive than those of conventional stormwater infrastructure, these technologies can be more cost-effective on a volumetric basis for storing stormwater in the landscape (Montalto et al. 2007).

As the use of LID technologies becomes more widespread and culturally acceptable to the development community, costs will likely decrease and benefits of LID systems will become more obvious (US EPA 1999). In the interim, there are many positive aspects to LID. Disruption to soil is minimal (streets may be constructed near the existing grade) and home foundation excavation is the only considerable disturbance. Runoff volume should be minimal or comparable to predevelopment volume. In comparison to traditional development, there could be significantly diminished runoff and sediment loading during and after construction. These observations are of particular importance given recent works indicating potential problems with conventional flow-reduction methodologies and increased fine sediments from urban development in Missouri (Hubbart et al. 2010, Hubbart and Freeman 2010). Considering the upfront costs and long-term benefits of LID development and the current conventional stormwater infrastructure investments, it is expected that LID technologies will eventually cost less than conventional construction practices (a significant incentive for the development community). Ultimately, it is expected that the proposed LID project Village at Peruque Bend and others like it around the nation will exist as models for future LID developments.

The example presented here may eventually be the first residential LID in St. Charles County. Recently, the neighboring St. Louis County adopted LID practices in numerous commercial developments. This progressive mindset has yet to diffuse to St. Charles County, though a small number of implements have been installed recently. For example, a model rain garden was recently constructed in Quail Ridge County Park in St. Charles County (Figure 3). A case study in Burnsville, MN, monitored volume and peak flow of runoff before and after a post-developed area was retrofitted with 17 rain gardens. It was reported that the cumulative effect of the rain gardens reduced runoff volumes by as much as 90% (Wright Water and Geosyntec Consultants 2009). In the New Town at St. Charles (in St. Charles County), developers implemented permeable interlocking concrete pavement (PICP) in the community’s streets, plazas, and parking lots for stormwater management and infiltration. These are victories for LID implementation engineers and speak to the growing acceptance of LID systems in older communities.

Lessons Learned: A Way Forward-Lessons learned in the central US, Missouri, and St. Charles County provide an opportunity to provide insights to better organize future LID implementation practices locally and in many other regions where LID practices are growing in practicality. Figure 4 illustrates a simple theoretical framework for LID implementation. It could be easily argued that the most critical stage of implementation includes involving stakeholders (e.g., citizenry and the development community) early to garner acceptance and support through the entire LID implementation processes.

While each LID project may require customization, a number of steps to LID implementation are recommended. Community stakeholders must collectively acknowledge that current practices are no longer sufficient for preserving their watershed in terms of managing stormwater and water quality. For example, in the case study presented here, St. Charles County acknowledged the need to preserve its watersheds and more effectively manage stormwater to minimize sediment loss (Peruque Creek is on the 303(d) list of impaired waters). There then needs to be a clear set of milestones or goals and techniques toward solving the stormwater problem. A plan is then required to determine which LID implements will be utilized. The site plan for the Village at Peruque Bend includes green roofs, bioswales, pervious paved streets, rainwater catchment systems, a membrane treatment plant, and constructed wetlands. Property owners were identified that could be affected by LID implementation. Stakeholders were educated about the importance and benefits of the LID plan to nearby water resources. Stakeholders should be provided multiple perspectives and contrasts to conventional practices, which are often not as effective as LID practices. Establishing a dialogue with local citizens and contractors should be undertaken early. The voice of local citizens can often be more influential than expected, and, as shown in the example provided here, omitting this step can be detrimental to immediate LID implementation. It should be established early what type of wastewater treatment conveyance will be used in an LID plan (i.e., local sewer system or onsite sewage management). If onsite, the cost of ongoing maintenance must be factored in; if connecting to the local sewer municipality, the cost of piping and connection to existing city infrastructure should be factored in and stakeholders should be notified. Whether onsite LID measures or local sewers are used for wastewater conveyance, approval for such measures must be obtained from the city or county.

Many tools are becoming available to LID planners. Current LID cost-analysis tools available through the Water Environment Research Federation (WERF) are being expanded to include vegetative roofs, rainwater catchment systems, and bioretention facilities. These tools provide a detailed framework for estimation of capital costs, operation and maintenance costs, and life cycle net present value. They can serve as a format for cost reporting for past, current, and future projects and can provide users with planning-level cost estimates (Houdeshel et al. 2009). There is a great need for improved, more versatile modeling tools for future LID cost validation and pre-implementation studies.

Conclusions
Through the experience of a proposed model LID community such as The Village at Peruque Bend, a better-prepared, communicative approach to proposing LID implementation may yield improved stakeholder acceptance of LID constructions. Through experience of case studies and future LID validation studies, LID developments will become more attractive to progressive homeowners, construction engineers, and developers wishing to reduce development impacts and improve or restore natural resources. For developers intending to implement residential or commercial LID in other older communities of the country, suggested steps to success include establishing an understanding of LID goals and benefits addressing case-specific problems and expected long-term outcomes with community involvement. Obtaining support by involving property owners and developers in LID processes-prior to implementation-is one of the most important planning strategies in most communities.

Developing with low environmental impact practices on undeveloped and historically urbanized lands (retrofitting) is likely to become common practice and no longer the exception in the very near future. Numerous cost-analysis models for LID are present, available, and continuously improving, and the validation of LID implements is becoming increasingly feasible. LID systems are likely to become convention rather than a form of environmental innovation in all development community cultures of the US.

Acknowledgments
The authors acknowledge the comments of multiple reviewers that improved the overall quality of this article.

References
CARES. 2010. Center for Applied Research and Environmental Systems. Missouri Interactive Maps. Available online at http://ims.missouri.edu/moims200/step1AOI.aspx.

GE Water and Process Technologies. 2010. Triple Membrane Treatment
System. Available online at www.gewater.com/products/equipment/spiral_membrane/tmt_system.jsp.

Houdeshel, C. D., C. A. Pomeroy, L. Hair, and R. Goo. 2009. Cost Estimating
Tools for Low-Impact Development Best Management Practices. Proceedings of World Environmental and Water Resources Congress: Great Rivers. 342(2009):991–1003.

Hubbart, J. A., and G.W. Freeman. 2010. “Sediment Laser Diffraction: A New Approach to an Old Problem in the Central United States.” Stormwater 11(7):36–44.

Hubbart, J. A., J. Holmes, and G. Bowman. 2010. “Integrating Science Based
Decision Making and TMDL Allocations in Urbanizing Watersheds.” The Watershed Science Bulletin 01:19–24.

Montalto, F., C.Behr, K, Alfredo, M, Wolf, M. Arye, and M. Walsh. 2007. “Rapid Assessment of the Cost-Effectiveness of Low Impact Development for CSO Control.” Landscape and Urban Planning 82(3):117–131.

Pierre, J., L. Bisby, B. Anderson, and C. MacDougall. 2010. “Thermal Performance of Green Roof Panels in Sub-Zero Temperatures.” Journal of Green Building 5(2):91–104.

Smith, C. 2010. EcoCrafters/CPS Custom Homes. Wentzville, MO. St. Charles Ordinance. 2010. Natural Watercourse Protection Ordinance. Available online at http://cd.sccmo.org/commdev/index.php?option=com_content&task=view&id=49&Itemid=102.

US EPA. 1993a. Subsurface Flow Constructed Wetlands for Wastewater Treatment: A Technology Assessment. Available online at www.epa.gov/owow/wetlands/pdf/sub.pdf.

US EPA. 1993b. Constructed Wetlands for Wastewater Treatment and Wildlife Habitat. Available online at www.epa.gov/owow/wetlands/pdf/Introduction.pdf.

US EPA. 1999. Low Impact Development Design Strategies An Integrated Design Approach. Available online at www.epa.gov/owow/NPS/lid/lidnatl.pdf.

US EPA. 2010a. Green Roofs | Heat Island Effect. Available online at www.epa.gov/heatisland/mitigation/greenroofs.htm.

US EPA. 2010b. Low Impact Development (LID) | Polluted Runoff (Nonpoint Source Pollution). Available online at http://www.epa.gov/nps/lid/.

Wright Water Engineers and Geosyntec Consultants. 2009. Urban Stormwater BMP Performance Monitoring Manual. Prepared for USEPA, WERF, FHA, and EWRI/ASCE. October 2009. Available online at www.bmpdatabase.org.