Categories: Environmental, Landscape
The Seattle Public Works required a lightweight soil that must perform like a premium turf grass rootzone but at only a fraction of the weight to be laid on the concrete cap of their 16 acre reservoir project.
Project Details – Maple Leaf Reservoir Capping

Seattle Public Utilities
Landscape Architect
MWH Global
Seattle, Washington
Veratec Products & Services Required
Custom Lightweight Media
Soil Testing



  • A massive 8 acre planted roof area covers this 60 million gallon drinking water reservoir
  • Total of 15,600 cubic yards of custom engineered lightweight growing media was required to ‘cap’ the concrete reservoir roof deck
  • The Custom Engineered lightweight media performs similar to a USGA golf green rootzone, but at only 50-55% of the loose bulk density.


Project Description

Seattle Public Utilities is nearing completion of the 60 million gallon Maple Leaf covered reservoir. Inside the two cells are 768 columns, each with a diameter of 2 feet. The walls of the reservoir are 22 inches thick and a total of 30,000 cubic yards of concrete went into the project. With the structure completed, the cap is to be covered with a specialty lightweight growing media and turf grass, encompassing 16 acres, to create a new park space. This $49 million dollar project completed Spring 2013.

Veratec’s engineered soil specialists collaborated in the development of the design specification for the project. The engineering, design and testing of the media took several months as the desired characteristics were unique; the soil must perform like a premium quality turf grass rootzone but only at a fraction of the weight, a feat that hadn’t been accomplished prior to this project. Veratec was able to meet the new level of soil requirements.

Veratec was contracted to manufacture and deliver the custom engineered media to the reservoir in North Seattle. During the production and placement of the custom lightweight soil, extensive testing was done to ensure the media continued to meet the stringent specifications for maximum media density, saturated hydraulic activity, particle size distribution and organic content.