Low Impact Development Technology: Implementation and Economics

Since 2001, the Puget Sound Partnership (Partnership), and its predecessor, the Puget Sound Action Team have provided technical assistance on low impact development (LID) to numerous audiences in the Puget Sound region. The intent of the assistance is to help transition the region to the LID approach as the preferred method for developing land and managing stormwater. During 2001–2009, the Partnership, with numerous regional partners, convened the first national conference on LID; held regional workshops; developed educational and technical publications; co-produced the region’s technical guidance manual; and provided technical assistance to help 36 local governments in the region integrate LID into their codes and standards. This paper provides a brief overview of the technical assistance provided to the region both during this time period (2001–2009) and immediately afterwards (during the 2009–2011 state biennium). Assistance evolved significantly during this latter time frame due to dramatic changes at the state level regarding LID: LID was rapidly transitioning from a voluntary to a required approach. This paper will briefly describe these changes, and describe how the products and services evolved to meet these changing needs.

Planners and engineers face many barriers when implementing green infrastructure and Low Impact Development (LID) practices. Some of these barriers are physical and require regulations and/or specialized designs to overcome, while other barriers are caused by perceptions and can be removed through education, outreach, and coordination. Four of the most common barriers are the misperception of how LID works, cost, maintenance, and delayed permit approval. This paper describes these barriers to the implementation of green infrastructure/LID practices and provides approaches to overcome them. The approaches are based on lessons learned while implementing LID practices in municipal projects and military facilities. Practitioners need to continue to share lessons they have learned, to facilitate future implementation and demonstrate the success of green infrastructure and LID practices.

This paper describes the development of a Low Impact Development (LID) Model Ordinance and Guidance documents developed to assist communities which are in the process of adopting LID technology to develop and ordinance that helps them to overcome many of the traditional impediments to the application of this technology. Many communities throughout the US are interested in implementing LID technology because it offers a sustainable “green” approach to site design and stormwater management. However, in many instance they are faced with a patchwork of local codes (zoning, subdivision, inland wetland regulations, board of health regulations, and safety regulations (Fire Marshall, Department of Transportations, State Environmental Protection Departments)) which may provide overlapping and sometime conflicting regulations which may create impediments to the implementation of LID technology. The model LID ordinance and guidance documents are being developed as a resource document which accomplishes the following objectives: 1) first, identify the elements of a model LID ordinance and 2) identify the potential impediments to the implementation of LID technology and offers some approaches to address these issues.

This paper describes the process the towns of Harwinton, Plainville, and East Granby Connecticut used to adopt Low Impact Development (LID) strategies into their existing land use regulations under the Farmington River Enhancement Grants, which were administered by the Connecticut Department of Environmental protection (CT DEP). The CT DEP offered grants to communities located within the Farmington River Watershed to retain qualified consultants to review existing land use regulations in order to encourage the implementation of the LID. This paper discusses and contrasts the approach of the three communities. The Town of Harwinton, CT is a predominately rural community in northwest Connecticut having an approximate population of 5,000 residents. Most of the development in town consists of single family residential units on the typical twoacre building lot. There are several public drinking water supply reservoirs in Harwinton, which are owned by the City of Bristol so maintain the high quality of runoff going into them was a concern to Harwinton. The Town of Plainville is predominately an urban environment, located near the southwest corner of the Farmington River watershed. Over 90% of the community has been developed as either medium/high density residential and/or commercial/industrial. This has led to large, interconnected impervious areas in many areas. The Town of East Granby is mostly rural community with scattered agricultural uses in the western portion of the community and commercial/industrial uses clustered around Bradley International Airport. The paper describes the land use issues in each community which drove the process to consider LID. It also shows how LID development strategies were presented for consideration and adopted to address these issues. Lastly, the paper shows how public outreach was conducted to facilitate the adoption of LID.

Low Impact Development (LID) storm water management practices (BMPs) are preferred methods for the treatment of stormwater runoff to remove certain pollutants from the runoff before the storm water evapotranspires, enters our streams or recharges groundwater. These systems are preferred because LID BMPs can be retrofitted into the existing landscape to intercept runoff without installation of a large amount of additional infrastructure. The optimum conditions for LID BMP’s are where the runoff has low velocity and low volume. LID BMPs are not designed to remove trash and debris from stormwater runoff. Such pollutants are untreated, impair the functionality and in view of LID BMP’s. They remain as an unsightly reflection of urban living. Simply put, LID BMPs are only part of the solution for stormwater treatment. Without the use of other technologies in a treatment train configuration, removal of trash and debris will remain beyond the capability of urban LID BMP designs. Fresh Creek Technologies, Inc. recognizes this problem and directs its efforts on developing cost efficient ways to remove trash, debris and other pollutants from stormwater runoff. This approach is complimentary to and an enhancement to LID BMP designs. From their research and development several unique systems have been designed that meet the parameters of sound, scientifically based engineering; low initial installation costs and cost effective long term operation and maintenance.

This paper outlines a methodology to quantitatively measure the cost-effectiveness of stormwater management plans by linking runoff pollutant load removal and volume reduction performance rates to long term life cycle costs. A step by step approach to calculate cost-effectiveness is provided and one case study presented to demonstrate the methodology. The EPA has applied this methodology to four case studies, each of which compares a built low impact development (LID) project to an alternative conventional design approach. The conventional designs make heavy use of two land cover surfaces that have become dominant in many of today’s existing developments: surface parking lots and turf grass cover. The results are reported in units of annualized cost per pound of nutrient removal ($/lb/yr) and annualized cost per cubic foot of runoff volume reduced ($/cf/yr). Findings show that the LID plans analyzed were four to six times more cost-effective, on average, than the alternative conventional designs. A key finding was that LID stormwater systems exhibited higher performance rates at a lower cost, thereby realizing a ‘compounding effect’ when compared on a cost per performance basis. The results are compared to 43 additional projects identified in a literature review. In addition, a total of eight case studies found that the LID projects cost 19% less on an average capital construction cost basis, and could provide up to twenty additional benefits beyond water quality, than the conventional plans.

This paper presents a range of case studies illustrating the advantages of Low Impact Development (LID) in economic terms and metrics employed in municipal decisions making. The environmental and water quality benefits of LID are commonly known however, there are also considerable economic, infrastructure, and climate adaptation benefits being overlooked or ignored. Municipalities are faced with difficult economic choices from reduced capital budgets and increasing regulatory demands. As such, there is value in understanding the substantive economic benefits—for both construction budgets and project life-cycle costs—that are increasingly being realized by municipalities, commercial developers, and others when using Green Infrastructure (GI) for stormwater management. LID is often misperceived as only adding expense to a project; however, this perspective fails to acknowledge the broader benefits that can be observed in terms of whole project costs for new construction, and in some instances, increased life-cycle benefits. While individually GI elements may add upfront capital expense to a project, reductions can result from a decreased need for conventional drainage infrastructure. Cost benefits are not observed in comparison with projects with few to no stormwater controls, but rather for projects consistent with new state and federal permitting requirements that address volume and pollutant reduction. Studies examined reported cost reductions for LID designs when compared with typical designs that relied heavily upon the use of drainage infrastructure. Project cost reductions were observed from 6% in residential developments to as high as 26% in commercial projects. Municipal use of GI reported cost reductions of 21% to as high as 44%. Of significant importance is the shifting of monies from infrastructure to jobs associated with the maintenance activities. From a sustainability perspective, a range of benefits includes reductions in flood damage and increased resiliency of drainage infrastructure; as well as reductions of 33 to 50% in energy demands for heating and cooling. Additional benefits observed included a 50% reduction in time to sale, and increased property values of 12-16%. Other benefits were incentives in the form of rebates, cost-sharing, and tax credits. The use of LID planning and structural controls can contribute to building community resiliency in managing water resources and reducing the flood risk associated with current and projected changes in land use and climate. In one study, the implementation of LID practices reduced the number of culverts determined to be undersized by 29 to 100 percent for the 24 hr - 25 yr event. The marginal cost increase to replace such undersized culverts was also reduced by one-third. At the site scale, the use of LID as an adaptation measure can increase onsite storage of runoff compensating for increases in rainfall depths due to climate change. Onsite storage has additional benefits that increase resiliency such as increases in lag time and reducing and delaying the runoff peak discharge. Minimizing 2-year to 100-year floods with LID has the benefit to minimize stream instabilities that result from hydromodifications.

Maintenance of Low Impact Development (LID) systems represents a significant barrier to the acceptance of LID technologies. Despite the increasing use of LID over the past four decades, stormwater managers still have minimal documentation in regards to the frequency, intensity, and costs associated with LID operations and maintenance. Due to increasing requirements for more effective treatment of runoff and the proliferation of total maximum daily load (TMDL) requirements, there is greater need for more documented maintenance information for planning and implementation of stormwater management strategies. This study examined 7 different types of stormwater treatment systems for the first 2-4 years of operations and studied maintenance demands in the context of personnel hours, costs, and system pollutant removal. The systems were located at a field facility designed to distribute stormwater in parallel, with normalized watershed characteristics including pollutant loading, sizing, and rainfall. System maintenance demand was tracked for all systems and included labor, activities, maintenance type, and complexity. Annualized maintenance costs ranged from $2000/ha/yr for a vegetated swale to $7600/ha/yr for a retention pond. In terms of mass pollutant load reductions, marginal maintenance costs ranged from $4-$8 per kg/yr TSS removed for porous asphalt, a vegetated swale, bioretention, and a gravel wetland, to $11-$20 per kg/yr TSS removed for a retention pond, a detention pond, and a sand filter system. When nutrients such as nitrogen and phosphorus were considered, maintenance costs per kg/yr removed ranged from reasonable to cost prohibitive especially for systems with no nutrient removal mechanisms. As such, best management practices (BMPs) designed for targeting these pollutants should be selected carefully. The results of this study indicate that generally, LID systems, as compared to conventional systems, have lower marginal maintenance burdens (as measured by cost and personnel hours) and higher water quality treatment capabilities as a function of pollutant removal performance. Annual system maintenance expenditures equal total upfront capital costs after 4.5 years for retention ponds and after 20 years for the porous asphalt system. In general BMPs with higher percentages of periodic and predictive, or proactive maintenance activities have lower maintenance burdens than BMPs with incidences of reactive maintenance.

Rutgers University recently completed a Stormwater and Landscape Management Master Plan for their Busch and Livingston Campuses. This plan provides an ecological and hydrological foundation for the University's future planning and development efforts through a low impact development (LID) and green infrastructure approach to stormwater and landscape management. The approach considers stormwater management as part of the broader ecological system using a combination of bioengineering techniques and native landscape practices within the campus context. Creating more sustainable green infrastructure requires transitioning from practices that may contribute to the degradation of the environment toward creating working landscapes that perform important ecological functions. Examples of these functions include: receiving, retaining, and filtering stormwater in a way that may preserve or mimic natural hydrological patterns (treating water as a resource, not as a problem); creating natural habitat for diverse ecosystems; providing educational opportunities; contributing to overall campus sustainability initiatives; and reducing the overall operation and maintenance burden for campus staff. This plan provides a unique approach to integrating low impact development practices with landscape ecological improvements, thinking holistically about broader ecological connections and implications while treating the more specific primary needs of the campus as a social and educational setting. After assessing the campus needs and coming up with an approach that strives to improve the health and function of the landscape, current and future stormwater conditions were modeled to better understand the implications of suggested practices and their ability to meet regulatory requirements for stormwater management. The plan also includes planning principles and design guidelines that emphasize a commitment to sustainable landscape and water management design. The master plan is intended to be flexible in terms of identifying techniques and practices that can be applied throughout various Rutgers University settings, while still being specific enough to reflect the unique ecological characteristics and opportunities on the Busch and Livingston Campuses.