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TMDL Introduction

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Marina del Rey TMDL

Bacteria TMDLs

On March 19, 2003, the State Water Resources Control Board approved the Santa Monica Bay wet-weather Bacteria Total Maximum Daily Load (TMDL) for the Santa Monica Bay beaches.

This TMDL encompasses 27 areas (sub-watersheds) that drain into the Santa Monica Bay beaches. These 27 subwatersheds are then grouped into 7 responsible jurisdictions. Compliance with the Bacteria TMDL includes a coordinated shoreline-monitoring plan between all contributing agencies in the watershed. In addition, each responsible jurisdiction must develop an Implementation Plan to reduce the amount of bacteria that enters the bay in order to meet the numerical limits set for by the TMDL.

Other upcoming Bacteria TMDLs that will affect the City of Los Angeles are the Cabrillo Beach Bacteria TMDL and the LA River Metals TMDL.

The cost to implement a plan to comply with these TMDL standards is approximately $400 million. The City has already begun constructing projects to reduce the amount of urban runoff from entering the ocean through its several low flow diversion projects.


On July 15, 2003, the Santa Monica Bay Beaches Bacteria (SMBBB) Total Maximum Daily Load during dry and wet weather conditions became effective. This TMDL encompasses 27 areas (subwatersheds) that covers 44 beaches from as far north as Malibu to as far south as Palos Verdes. These beaches were listed on the California State’s 2002-303(d) list as impaired due to bacteria.

The SMBBB TMDL has been divided into dry weather and wet weather, each having their own compliance dates and limits.

This TMDL requires the submittal of a Coordinated Shoreline Monitoring Plan (CSMP) to the LARWQCB for approval within 120 days of the effective date of the TMDL. The City of Los Angeles, Bureau of Sanitation led the effort working with over twenty (20) other agencies in the Bay and LARWQCB, Heal the Bay, and Santa Monica BayKeeper and met the deadline to complete the CSMP. The Final CSMP was approved by the LARWQCB on April 7, 2004. The approved Final CSMP provided 67 sampling sites to be monitored on a weekly basis. The monitoring program will start by November 1, 2004.


There are 25 storm drains that discharge runoff from some portion of Los Angeles to Santa Monica Bay beaches.

The key dry-weather bacteria TMDL requirements to reduce bacteria levels at beach areas in dry-weather are divided into two phases:

  1. Phase I of the TMDL requires that within the first three years, bacterial indicators at beaches should not exceed acceptable levels (no more than zero (o) days of exceedance) during summer dry weather: April 1 through October 31.
  2. Phase II requires that within six years of the effective date of the TMDL, bacterial indicators at beaches should not exceed acceptable levels (no more than one (1) day of exceedance) during winter dry-weather: November 1 through March 31.

Bacterial indicators that are measured at public beaches include total coliform, fecal coliform, enterococcus, and a fecal-to-total coliform ratio.

The City of Los Angeles is well along in complying with this TMDL. In large part, this is because of the City’s proactive low-flow stormwater diversion construction program which was already underway at the time of the issuance of this regulatory action. The City began efforts to divert dry-weather (low) flows from several storm drains into the sewer system in the early 1990s in an effort to decrease the number of beach closures from stormwater pollution. The City of Los Angeles in conjunction with the County of Los Angeles are constructing Low Flow Diversions along Santa Monica Bay to divert all dry weather flow into the sanitary sewer for treatment at the Hyperion Treatment Plant.

The least costly solution is to divert dry weather low flows from selected storm drains, which typically contain significant levels of bacteria, into the wastewater collection system. Rather than contaminating Santa Monica Bay beaches, these captured flows are treated at the City’s Hyperion Treatment Plant. The illustration below shows one of multiple low-flow diversions that have already been completed (Thornton Avenue diversion, completed in June, 1999.)

The figure below shows a typical cross-section of how dry weather runoff is captured and diverted to the wastewater collection system.

Other possible compliance strategies for the dry-weather bacteria TMDL include: eliminating illicit discharges; controlling sources of bacteria (including groundwater sources); or implementing “end-of-pipe” treatment. These are all more costly than implementing the low-flow diversion construction program.

As already noted, the City’s Low Flow Diversion Program was well underway before the adoption of the Santa Monica Bay Beaches dry weather Bacteria TMDL. The City has determined that this existing Low Flow Diversion Program to construct the diversions will meet the requirements of the dry-weather bacteria TMDL. Working with the Los Angeles County and the City of Santa Monica, the City of Los Angeles led the way in planning and implementing twenty five (25) low flow diversion facilities.

Wet Weather

The SMBBB Wet Weather TMDL requires bacterial indicators at beaches not to exceed acceptable levels (no more than seventeen (17) days of exceedance) during winter we weather: November 1 through March 31. As discussed earlier, due to the large area, the identified 27 subwatersheds are grouped into seven (7) Jurisdictions, and each must comply with the TMDL requirements. The City of Los Angeles is the lead in Jurisdiction Group 2 and participates in Jurisdiction Groups 1, 3, and 7. However, Jurisdiction Groups 2 and 3 have joined efforts to meet the requirements.

In order to comply with the limits, the Jurisdiction Groups 2 and 3 have chosen to take an Integrated Water Resources (IWR) approach, which would allow the groups up to eighteen (18) years to meet the compliance limits. This approach will consider the beneficial reuses of stormwater runoff.

To meet the July 15, 2005 deadline of developing and submitting an implementation plan (“I-Plan”) to the LARWQCB, the City of Los Angeles (Jurisdiction 2 lead) and the City of Santa Monica (Jurisdiction 3 lead) have combined their efforts to develop a joint implementation plan. The City of Los Angeles is leading the effort to develop this joint implementation plan with the cities of Santa Monica and El Segundo, the Los Angeles County Department of Public Works, and Caltrans. The implementation plan will address multiple pollutants and achieve multiple benefits including the beneficial use of runoff. The implementation plan will be carried out in phases that will entail institutional solutions, local (on-site) solutions, and regional solutions.

Marina del Rey TMDL >