Lake Tahoe Water Quality Shorezone Monitoring

Science Center Objects

USGS Nevada Water Science Center (NVWSC) is sampling for Volitile Organic Compounds (VOCs) in 2019 in order to confirm previous data collection efforts at Lake Tahoe. The Tahoe Regional Planning Agency (TRPA) requested sampling in targeted locations and at times when petroleum constituents are most likely to be detected in the lake.  

Lake Tahoe, with its beautiful blue waters and numerous ski resorts in the surrounding mountains, is an extremely popular year-round tourist destination. In 2004, Lico found that distribution and concentration of gasoline-related contaminants was related to boat use in Lake Tahoe. Two-stroke engines were contributing detectable concentrations of gasoline-related components to Lake Tahoe.

The Tahoe Regional Planning Agency (TRPA) is a bi-state leader in planning and facilitating action programs to preserve the environment within the Lake Tahoe Basin. TRPA is seeking the reliable data necessary to manage the waters of Lake Tahoe to ensure heath and public safety. Three types of contaminants have been identified as potential contaminants of concern: 

  1. Gasoline and diesel fuels contain hydrocarbons and could enter the Lake from boats or by spills (during fueling and accidental spills). Commonly associated with this type of contamination is a group of volatile organic compounds including benzene, toluene, ethylbenzene, and xylene; together they are collectively known as BTEX.  
  2. Although found in raw fuel, another set of hydrocarbons known as polyaromatic hydrocarbons (PAHs), are found primarily in exhaust emissions from the combustion process.
  3. Recreation of humans and animals in the nearshore, as well as, unintentional point source inputs (leaking pipes) can input fecal bacteria into Lake Tahoe. Termed fecal indicator bacteria (FIB).
BTEX Sampler in Lake Tahoe. Photo taken from the side of a boat.

BTEX Sampler in Lake Tahoe. Photo taken from the side of a boat. (Public domain.)

BTEX and PAHs in Lake Tahoe are primarily a product of boat exhaust, therefore increased summertime boat traffic results in high potential for PAH spikes, especially near popular beaches.

NVWSC will be sampling for: 

Water samples will be collected at the ten specified sampling locations on Lake Tahoe and analyzed for BTEX concentrations.

Even with increased boat traffic, PAHs are often found in low concentrations and also have a rapid rate of degradation and have been found in previous data collection efforts to be found in low concentrations. Therefore, PAHs will be sampled at five locations using SPMDs (semi-permeable membrane device), which are specialized passive in-situ samplers that concentrate organics for subsequent chemical analysis. 

Samples will be collected at 10 shoreline samples on 5 separate occasions within a 30-day period for the analysis of fecal indicator bacteria.