Progress of Implementation of Nitrate TMDL for the San Lorenzo River, Santa Cruz County, California

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A watershed-related issue examined by the ENVS 560/L Watershed Systems class at CSUMB.


The San Lorenzo River TMDL for nitrate was the first TMDL written for a water body in the central coast region. The TMDL was first initiated in 2000, when the Central Coast Water Quality Control Board (CCWQCB) approved an amendment to the original Central Coast Basin Plan (Basin Plan). The amendment changed the Basin Plan's unrealistic nitrate concentration goal (which was so low that is was below background concentrations), to the target concentration required by a TMDL for the San Lorenzo. The CCWQCB approved the nitrate TMDL for the San Lorenzo River in September of 2000, and it was finally approved by the EPA in 2003.


...Name the smallest watershed (or other applicable region) within which the issue occurs...

Resource/s at stake

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...Who are the stakeholders in the watershed? e.g. agencies, non-profits, associations...

Laws, policies, & regulations

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... What elements of the biophysical system are/were involved?...


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Action Taken Since TMDL Approval

Much of the implementation plan for the San Lorenzo nitrate TMDL was adopted from the existing Nitrate Management Plan (NMP), which was developed for the Basin Plan in 1995 [1]. It was required that Santa Cruz County submit a Report on Nitrate Management Plan Implementation to the CCRWQCB in 2005, 2010, and 2020 [2].

In 2008, the County of Santa Cruz submitted a program status report for the Wastewater Management Plan, which included a review of the Nitrate Management Plan's progress. Implementation of the NMP was expected to reduce nitrate levels by 15-20% over the next 10 years, followed by a reduction of 10% in the next 10 years. Observed nitrate trends show that reductions are occurring slower than desired, with an 11% decrease over the past 15 years. Cen Lomons and Boulder Creek sites has experienced significant reductions of up to 60%. The report suggested that "no significant adverse impacts resulting from nitrate loading at the current level have been identified".

The following nitrate reduction measures have been directly taken from the program status report:

  • Manage Wastewater Disposal for Nitrogen Reduction:

Future research

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  1. CCRWQCB. 2000. Staff report for regular meeting for September 15, 2000: San Lorenzo River nitrate Total Maximum Daily Load. State of California: 1-32.
  2. CCRWQCB. 2000. Nitrate Total Maximum Daily Load for San Lorenzo River, Carbonera Creek, Shingle Mill Creek, and Lompico Creek. State of California: 1-44.


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