Monday, March 29, 2010

A Primer on Post-Construction Storm Water Regulations

The Clean Water Act, passed in 1972, and amended in 1977 and 1987, is a Federal law regulating the discharge of pollutants into receiving waters of the US. Its enforcement is broadly overseen by the Environmental Protection Agency (EPA), but more directly controlled and interpreted by the Regional Storm Water Quality Control Board (RWQCB). The San Diego RWQCB is the 9th (out of 9) boards in California. The regulations require that local municipalities oversee, mitigate, or control storm water exiting from a site when reviewing or approving local development projects.

The Board regulates the water runoff from sites both (1) during construction and (2) post-construction. Although the ‘during construction’ requirements can be onerous and difficult in themselves, this discussion covers only the post-construction or permanent conditions.

Controlling Factors

The level of detail for water quality design solutions varies depending on a number of factors, but the 3 main controlling features are:

  • Location of the site: The proximity of your project to a sensitive water body (i.e. a major river, stream, or the Pacific Ocean) may affect what category of design solutions you need to have studied and mitigated.
  • Type of project proposed: A single-family residence will be much less likely to trigger a full water quality report than say, a manufacturing operation, large restaurant, or a 50-lot subdivision.
  • Existing terrain of project: Most municipalities have a special category for sites that lie on or adjacent to a steep natural slope.

Different Requirement Categories

Depending on the factors listed above, your site generally falls into 3 different categories of study and enforcement:

  1. Basic: If you’re fortunate, your site will trigger only an elementary level of study. May times, this consists only of a signed statement from the owner or developer and simple information on the site or drainage plan which demonstrates an effort to reduce storm water pollutants as much as practicable. In addition, the municipality may require that a standard checklist-based form be filled out describing the water quality-based design implementations for the project. More recently, the City of San Diego has been mandating a Water Quality Study (WQS) for this level, which requires a basic analysis of polluted waters downstream, a summary of potential pollutants to be generated from the site, and a description of mitigating design solutions (including scheduling and costs to maintain).

  2. Intermediate: If your project triggers one of the pollutant risks described in the ‘controlling factors’ above, a more advanced analysis will be required. This takes the form of a Water Quality Technical Report (WQTR), or a Storm Water Mitigation [Management] Plan (SWMP). This is a more advanced study that requires a more detailed analysis of downstream impacts. It requires that list of possible pollutants be matched to the found pollutants in a downstream water body, and a solution be specifically designed for any correlations. For example, if a downstream river has tested positive for bacteria, and your site use has been known to generate bacteria and send it downstream in storm water, then a specific solution must be designed to limit or eliminate bacteria from heading downstream.

  3. Advanced: This category is reserved for sites that are expected to generate specific levels of harmful pollutants. A WQTR or SWMP is needed, but in addition, a specific monitoring and testing program must be outlined to assure the municipality that the implemented solution is adequate to limit the pollutant. Monitoring is generally conducted at certain intervals, and the results of such testing are submitted to the municipality for their review over time, or in perpetuity.

Types of Solutions

Since the onset of more rigorous enforcement of the regulations, literally hundreds of methods, solutions, and products have been implemented to mitigate the effects of storm water pollutants from leaving the project site. But a few of the most popular solutions for the majority of projects include the use of one or more of the following:

  • Flow over planted surfaces (vegetated swales, strips, buffers)

  • Pervious Paving (open aggregate surfaces, ‘turf block’, ‘grasscrete’, open pavers)

  • Reinfiltration Pits or Trenches

  • Sediment or Retention Basins

  • No ‘directly-connected’ systems (downspouts dump to surface, paved surfaces lead first to vegetated areas before employing catch basins)

  • Filter systems (Manufactured, pre-fabricated systems designed to treat different pollutants).

Monitoring Enforcement

Although the responsibility to maintain the implemented systems lies with the land owner, most municipalities have not yet installed a specific inspection and enforcement program to track completed projects. But in recent years they have been collecting detailed information about treatment implementations, and have required storm water maintenance agreements, recorded with the County Recorder’s office. Word has it that regular inspections, long after the project has been completed, are not far behind. Stay tuned.

John S. Coffey, PE, is founder and President of Coffey Engineering, Inc. in San Diego. He’s contributed to over a thousand civil engineering, surveying, and planning projects in San Diego and surrounding communities over the past 15 years. 858-831-0111