Regional Board staff have reviewed San Francisco Public Utilities Commission (SFPUCs) and North San Mateo County Sanitation District (NSMCSDs) proposed Water Quality Preliminary Screening Plan (Plan) for Lake Merced.

The stormwater discharge from Vista Grande Canal to Lake Merced is proposed to be performed on a controlled only pilot basis. The subject discharge of stormwater is currently regulated under the MS4 NPDES municipal stormwater permit.

We appreciate SFPUCs and NSMCSDs partnership efforts towards improving the water quality at Lake Merced. However, we find the current Plan deficient in several key areas necessary to adequately characterize and safeguard water quality threats associated with the proposed Plan and discharge of stormwater from the Vista Grande Canal. We have the following comments and recommendations relative to the Plan that we request be addressed before any discharge occurs from the Vista Grande Canal to Lake Merced.

1) The proposed Plan appears to be generally directed at the human health threats of coliform and does not adequately address other priority stormwater pollutants of concern appropriate in a baseline study of this nature. Along with the proposed sampling analysis parameters, the following additional priority stormwater pollutants of concern should be included in the Plan: Petroleum hydrocarbons (normally EPA 8015 and/or 8020), 17 priority metals (CAM 17); Fecal coliform; and a limited screening for candidate pesticides/herbicides. Lastly, we strongly recommend use of ammonia and nitrate field kits which can indicate high coliform levels and provide immediate results.

2) The proposed Plan does not have adequate sampling station locations to monitor the priority stormwater pollutants of concern appropriate in a baseline study of this nature. At a minimum, monitoring locations should be located: a) Before entering the Continuous Deflection System (CDS) unit; b) After leaving the CDS unit; c) In Soil and water samples in the wetland treatment area; d) LM-1; e) LM-2; f) LM-3 and, g) LM-PR.

Sampling should also be performed at different lake water levels, not just at the surface, to evaluate pollutant stratification in the Lake water. Board staff feel that the additional monitoring locations are important in gathering appropriate and meaningful information about the overall fate and transport of stormwater pollutants in the Lake.

Additionally, Regional Board staff strongly support the use of dye test studies to calibrate detention times and identify optimum sampling locations, however we find insufficient details in the Plan. Please discuss the proposed dye test in a more detailed and strategic manner (dye type, application rates/locations, sampling, etc.).

3) During sampling, visual observations should also be noted for changes in appropriate wildlife conditions (particularly the number and type of flora and fauna) and other general conditions (e.g., weather, floating trash, water levels, recreational use, etc.). In addition, it would be an opportunity to conduct and maintain a photographic history of changes in key areas of the Lake.

4) The Plan does not contain adequate information regarding the Vista Grande Stormwater diversion volume flow rate limits and associated safeguards to cease and desist a diversion, should environmental or human health water quality threats occur. For example, should significant surface runnoff occur over the wetland treatment area, or, if high pollutant concentrations are found in the Lake, there should be a clear strategy and associated proceedures so that the stormwater diversion discharge will be immediately shut off.

Please describe this section in more detail and include an evaluation of the wetland areas bio-retention capacity and effectiveness. This evaluation should describe flow attenuation as well as pollutant removal. Specific flow rate limits should also be discussed and appropriate adaptive management safeguards that will be in place to prevent water quality threats. The Plan should clearly describe what would be considered an environmental or human health threat (i.e., coliform exceeds DHS limits, or other parameters exceed Basin Plan limits, etc.).

Lastly, we request additional efforts by Daly City and the San Mateo County Stormwater Program to further investigate priority stormwater pollutant source areas and to minimize runoff to the Vista Grande Canal to the maximum extent practicable. Please feel free to contact me directly at (510) 622-2438 to further discuss this matter or if any clarification of these comments are needed.

December 18, 2003
John West
Stormwater Project Manager
Regional Water Quality Control Board
San Francisco Region