A Comparison of Maintenance Costs, Labor Demands, and System Performance for LID and Conventional Stormwater Management

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.