TMDL? What is it and what does it mean to the lake?

Total Maximum Daily Load (TMDL) is a regulatory term in the U.S. Clean Water Act (CWA), ascribing a value to the maximum amount of pollutant a body of water can receive while still meeting water quality standards. While Lake Tahoe is famous for its water clarity, exceeding its TMDL is causing a significant decline.

A 2007 report by the California Regional Water Quality Control Board Lahontan Region and the Nevada Division of Environmental Protection indicates that fine sediment particles are the primary pollutant. The November 2010 Lake Tahoe Total Maximum Daily Load (TMDL) Report attributes 72% of these fine sediments to urban upland run-off (page 50, figure 7-3 and below).

Disturbances due to the transportation system – cars, mass transit, parking lots, bus stops, etc. – are, directly and indirectly, the primary source. Atmospheric deposition contributes 15 percent, non-urban runoff 9 percent, stream channel erosion 4 percent and shoreline erosion less than 1 percent.

TMDL reductions have been proposed and are likely to be part of the regional plans for TRPA to require all Tahoe Basin jurisdictions to reduce fine particle loads by 34 percent by 2026.  The Army Corps of Engineers has been assigned to assist Basin jurisdictions in re-prioritizing so they can meet the TMDL requirements.

In July 2011, the Army Corps released a study, “Placer County Storm Water TMDL Strategy,” to aid in assessing the science and economics to pinpoint the most cost-effective ways of reducing pollutant loads into Lake Tahoe. The conclusions compared cost and reduction of fine sediments for each of three concepts: the current area-wide Environmental Improvement Program (EIP), street sweeping and abrasive control, and current BMP practices on individual parcels.

  • Current EIP’s  may reduce loads of fine sediment particles (FSP) between 18 to 26 percent at a cost of $70-$88 per lb/year.
  • Frequent sweeping plus abrasive controls will reduce FSP between 27 percent and 38 percent at a cost of $3.50 to $4.25 per lb/year.
  • Parcel BMP’s will reduce FSP between 20% and 23% at a cost of $26 to $41 per lb/year.

According to the report, Tahoe jurisdictions can take the following measures to reduce TMDL:

  • Water Quality Improvement Projects
  • Improve road maintenance practices for water quality – Increase and target private parcel best management practice implementation

What measures have you taken to help reduce TMDL?

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