Long-Term Assessment of the Low Impact Development Strategies Used for the Lorton Road Widening Project, Fairfax County, VA Phase V

Non-point source pollution, such as stormwater runoff, is a leading threat to the quality of water resources and aquatic ecosystems near highly developed watersheds. Sudden discharges of stormwater from paved surfaces can result in flooding, erosion, sewer overflows, and pollution into receiving waters. These concerns have increased in recent years as more roads are built or widened, increasing impervious surface areas, and more vehicle miles are traveled annually, increasing the sources of pollutants. To mitigate the potential effects of road runoff on receiving waters, low impact development (LID) stormwater management systems are being used as a decentralized, hydraulic and non-point source control alternative to centralized best management practices (BMPs). Although LID practices for stormwater management are becoming more common, a number of knowledge gaps related to the long-term performance and maintenance of LIDs still exist, particularly in regard to linear transportation systems. The objective of this study is to continue to collect long-term data on the effectiveness of multiple LID systems for mitigating adverse impacts of highway stormwater runoff to achieve a total monitoring time of 4 to 5 years for each system. Field sampling of these LIDs began in Spring of 2018. The Lorton Road Widening Project, the selected study site provides an ideal opportunity to evaluate a variety of LID systems which receive essentially identical rainfall, climate, daily traffic, and maintenance. LID performance has been previously difficult to quantify due to the large variability of these factors observed in previous studies. The primary objectives of this study are to (1) determine the long-term effectiveness of multiple LID systems on water quality for mitigating adverse impacts of highway stormwater runoff, and (2) determine the maintenance requirements, procedures, and operating costs associated with LIDs used in the highway setting.