Background

Descanso Gardens (Gardens) is a world-renowned botanical and horticultural garden located just north of Los Angeles in the City of La Canada Flintridge, CA. The Gardens are host to tens of thousands of visitors a year who flock to the location to see its famous collection of local and exotic flora and historical landmarks.

Challenge

In 2012, a new treatment system was designed and installed by the County of Los Angeles Department of Public Works to replace the existing septic tank and leach field. The new system consisted of two new biofilters, three underground collection tanks, a tab chlorination system, a UV disinfection system, an ozone de-chlorination system, and three 35-foot deep seepage pits. In 2015 and 2016, the system experienced capacity issues and seepage pit structure failures that resulted in untreated wastewater inundating the seepage pits.

From these failures going forward, the Gardens were forced to collect and haul approximately 6,000 gallons per day of wastewater, incurring huge ongoing costs and negatively impacting visitors’ experiences. In Q3 2018, the Guild performed an evaluation of the system and determined that the 2012 system had structural failure in the seepage pits and was undersized for the Gardens’ peak flows and made a recommendation to replace the 2012 system.

Solutions

1. Membrane Bioreactor Technology

The installation of a new, state of the art packaged Membrane Bioreactor (MBR) system provides a long-term solution for the Gardens. In addition to restoring on-site treatment capacity, the new package MBR system provides the opportunity to utilize the recycled water to irrigate the facility.

In January 2019, LEE + RO joined the design build team, which was led by John Robinson Consulting (JRC), to provide engineering design and construction phase engineering services. Fluid Resource Management (FRM) was the construction contractor, and JRC provided project management and onsite construction management.

2. The System

LEE + RO’s design centered around the MBR technology, which produces Title 22-compliant tertiary (recycled water) effluent within a compact, modular footprint. The improvements designed by LEE + RO included:

• A new Cloacina Mempac-M MBR unit
• Rehabilitation of two existing underground collections tanks
• Four new 10,000 gallon above-ground recycled water storage tanks
• A new recycled water booster pump
• A new electrical switchgear for the Gardens’ new water recycling facility and existing electrical equipment.
• A new emergency generator for the Gardens new water recycling facility.
  
  

3. Location, Location, Location

The final location of the MBR unit was determined by evaluating the available space within the picturesque facility while maximizing the benefits of the existing elevations and hydraulic conditions of the site. The design team worked with Garden staff and RCH Studios (landscape architect and Facilities Master Planner) to provide a location that would take into consideration future expansion of the facility. LEE + RO determined that the southeast corner of the parking lot was the ideal location based on the available space, its proximity to existing electrical and plumbing infrastructure, and because the site elevations allow for use of a smaller recycled water booster pump. This position reduced the recycled water pump size requirement resulting in a reduction in the Garden’s operating costs and the facility’s carbon footprint.

LEE + RO coordinated with RCH Studios and Sweeney + Associates (irrigation design consultant), who were contracted by the Guild for design of the landscaping and irrigation system, respectively to provide landscaping and architectural features to integrate the industrial looking treatment works with its carefully curated surroundings—a textural and visual contrast that not only pays homage to the Gardens’ history, but to lay bold claim to its future, too.