The Sierra Tract Water Quality Improvement Project: A Long, Bumpy, and Collaborative Path to Effective Stormwater Management in South Lake Tahoe
After more than ten years in the planning process, the Sierra Tract Phase 3 & 4 Water Quality Improvement Project (Sierra Tract Project) was successfully completed by the City of South Lake Tahoe (City) during the summer of 2016. The project was planned in accordance with the Lake Tahoe Stormwater Quality Improvement Committee’s (SWQIC) guidance, which requires close collaboration and coordination with multiple funding, regulatory, and other stakeholder agencies. A project specific technical advisory committee (TAC) included representatives from the City, California Department of Transportation, United States Forest Service, California Tahoe Conservancy, Tahoe Regional Planning Agency, and the Lahontan Regional Water Quality Control Board. CDM Smith worked closely with the TAC to develop and evaluate multiple complex project alternatives and then select a preferred alternative through a consensus-based decision making process. Work was stopped on multiple occasions due to bond funding issues and modifications to the project area, and a changing regulatory environment further confounded the planning process.
The Sierra Tract subdivision is located within a 350 acre, densely developed commercial and residential community in South Lake Tahoe, California. The area was originally developed in the 1950’s with minimal drainage infrastructure and no consideration of water quality. At an elevation of 6,250 feet above sea level, the area has historically received about 80 percent of its precipitation as snowfall during the winter months. Although large snowfalls and sub-freezing temperatures are still common, climate change is now increasing the frequency of large winter rain storms and intense summer thunderstorms. The changing weather patterns, extreme conditions, and highly sensitive downstream water bodies combine to create a highly challenging environment for implementation of water quality improvements. The 2016-17 winter season produced over twice the average precipitation and provided a demanding test for the new stormwater improvements during their first year of operation.
The project area drains to the Upper Truckee River, which is the largest tributary, and carries the largest sediment load, to Lake Tahoe. Prior to the project, several directly connected stormwater systems efficiently conveyed large volumes of untreated stormwater to the Upper Truckee River and to Lake Tahoe. The large size of the catchments and the dense commercial, residential, and primary roadway land uses, combined to create significant pollutant sources and a high priority for effective mitigation.
The Sierra Tract Project provides an example of how older and densely developed communities, with challenging environmental conditions can be successfully retrofitted with green stormwater improvements. Green infrastructure elements include dispersed infiltration, disconnection of hard conveyances, large and small-scale subsurface infiltration galleries, bioretention basins and bioswales. Together, these improvements reduce erosion, hydromodification, recharge the groundwater table, and improve water quality in downstream surface waters. The project represents a key component of the City’s compliance strategy with their MS4 permit and the associated Lake Tahoe TMDL implementation requirements. An engaging and interactive presentation will provide an overview of the collaborative planning process, the key project components, the adaptations for cold-climate conditions, and how the project was used for TMDL compliance through load reduction modeling and ongoing condition assessments. Unique aspects and challenges of the Lake Tahoe TMDL are also discussed, along with specific solutions that were implemented in the Sierra Tract Project.
Stefan Schuster is a Senior Water Resources Enginner and Project Manager with CDM Smith in Truckee, California. Stefan has a Bachelor’s Degree in Environmental Biology from U.C. Santa Barbara and a Master’s in Civil Engineering from the University of Nevada at Reno. He is registered as a Professional Engineer in California and Nevada, holds multiple stormwater certifications and is an Envision Sustainability Professional (ENV SP). Stefan manages the CDM Smith offices in Truckee, California and has overseen many projects involving water quality, stormwater management and monitoring, erosion and sediment control, low impact development strategies, and CEQA/NEPA environmental analyses.
Stan Hill is a civil engineer with the City of South Lake Tahoe where he has worked on a variety of public works and stormwater quality projects for the past 15 years. Mr. Hill has over 20 years of experience as a professional civil engineer in the States of Nevada and California, in both the private and public sector.