Large Trash Capture City of Richmond, CA

In 2015 the California State Water Resources Control Board (State Water Board) adopted statewide Trash Provisions to address the impacts of trash on the States surface waters. The Trash provisions established a statewide water quality objective for the prohibition of trash discharge to surface waters of the state. The Trash Amendments apply to all Phase I and II permittees under the NPDES municipal separate storm sewer systems (MS4) permits and Transportation MS4s. At the heart of these efforts are requirements to reduce environmental issues associated with trash in waters by installing, monitoring, and maintaining stormwater BMPs that collect and retain trash and total suspended solids (TSS) from drains serving high-priority trash areas.

Full trash capture systems are defined as systems (either a single device or a series of devices) that trap 100% of particles that are 5 mm or greater and are sized to treat the peak flowrate resulting from a 1-year, 1-hour storm event (design storm) before bypass.  

Richmond, CA, located in the San Francisco Bay Area's East Bay region, is an excellent example of how one community addressed the new requirement. Running through Richmond is Interstate 580, an east-west auxiliary Interstate Highway in Northern California with its own MS4 permit managed by the California Department of Transportation (Caltrans).

Since Caltrans and Richmond both needed to comply with the new regulations, it made sense to combine efforts. Since Caltrans lacks the resources to maintain and operate stormwater BMPs, they created a mechanism that enables them to provide funding for capital construction costs of stormwater treatment projects in exchange for transferring the responsibility of the maintenance and operation over to the local MS4. It's a win-win for Caltrans and the City. Caltrans provides funding for the treatment system, Caltrans and the City get a portion of their runoff treated to meet the new regulation, and the City pays for the long-term operation and maintenance of the system.

Engineering full trash capture systems can be challenging, as they often treat large drainage areas, accommodate large flows, are adjacent to receiving waters, and must include uninhibited access for maintenance. The drainage area was 129 acres, with roughly 100 acres covered on the City's permit and the remainder covered by the Interstate 580 permit.

The site selected for the trash capture device was on Cutting Blvd. The primary challenge at this location was high flows, shallow depth, tidal influence and a nearby sewer line. 

A 12-foot diameter CDS hydrodynamic separator was selected for this site. The CDS is a California Statewide Trash Amendments Full Capture System Certified device that uses continuous deflective separation – a combination of swirl concentration and indirect screening to screen, separate and trap debris, sediment, and hydrocarbons from stormwater runoff. A Contech Stormwater Design Engineer designed the CDS to handle a treatment flow rate of 44 cfs within the CDS and divert the peak flows from the design storm of 96 cfs over a custom 12’ x 30’ diversion structure, which is an integral part of the CDS unit, directing the treatment flows to the unit before going into bypass. Because the system was installed about 100 yards from the Bay, the long weir takes into consideration the mean high tide elevation and prevents overtopping prior to the 1-year, 1-hour. The top slab of the weir was custom designed to be thinner and allowed asphalt to be added without causing a bump in the road. 

After all the work to find a suitable location and design the system, the team had approximately ten weeks to complete the project or the Caltrans funding would expire. The majority of the manhole and weir components were pre-cast. Careful coordination was needed to ensure all system components were manufactured and delivered on time. A Contech Feld Consultant was on site to assist the contractor and ensure a proper installation.

In October 2021, the region experienced an "atmospheric river," bringing much-needed rain to the region. The storm intensity was more than a 100-year storm which put the system and the overall design to the test. The system performed as expected, with no flooding during the unprecedented storm event.