Mount Olivet Cemetery in Washington, D.C. sits on a historic hill overlooking the monuments of the nation’s capital. The largest Catholic Cemetery in D.C., it consists of approximately 80 acres of total area, with 10 acres of impervious surface, mostly roads. Tetra Tech, The Nature Conservancy and the associated entity District Stormwater LLC, have implemented a first-of-it's kind urban conservation collaboration at Mount Olivet Cemetery that included a multi-phase approach to generate stormwater retention credits (SRC) for the cemetery.
This is a collaborative design-build project between EQR and Tetra Tech. EQR is the prime contractor on this project and has subcontracted out the design work to Tetra Tech. The original concept of the project was created by the Anacostia Watershed Society (AWS) and from that concept design our current project was formed. The cemetery is subject to substantial stormwater fees under the 2013 Stormwater Regulations of the District of Columbia mainly due to the large amount of impervious cover on the cemetery site. The age of the cemetery also played a part in how they were impacted by those regulatory fees. It’s old and much of the existing infrastructure is unable to adequately handle the stormwater volume on site.
Our goal is to install five areas of bioretention facilities that can provide 133,500 gallons of stormwater retention volume. Due to the soil conditions at the cemetery, the ground infiltration rate was extremely poor (good brick clay means mostly impermeable). Therefore, we are capturing stormwater via sheet flow based on the topographic data of the cemetery and retaining and treating that stormwater by way of conveyance rather than infiltration i.e., the water is not designed to infiltrate into the ground, but instead is piped through the BMP via an underdrain after being treated through soil media and washed gravel and discharged at defined points to drain into existing stormwater infrastructure.
Ultimately, the captured stormwater volume is going to be predicated on the as-built conditions. Due to the absence of infiltration, the volume of this BMP is all about ponding. Therefore, it is critical we install the block retaining wall and concrete curb to design parameters, as well as the extent of excavation. At Mount Olivet, the primary function of the bioretention facilities is to slow the velocity, treat and convey stormwater. To perform that function, the stormwater must first find its way into the facility. Stormwater enters the facility via sheet flow from grass areas and impervious asphalt cover. Once captured within a facility, the stormwater is treated and conveyed to a desired discharge location. Understanding how the bioretention facility treats and conveys stormwater requires a review of the facility components that allow it to effectively manage stormwater.
The cemetery has frequent visitors due to its age and historic value. This historic site will soon become a more environmentally friendly site for D.C. creating cleaner water for the surrounding communities.
UPDATE:
On May 7th the Mount Olivet Cemetery Rain Garden Dedication was held at the Cemetery hosted by Mark Tercek, CEO of The Nature Conservancy and His Eminence Cardinal Donald Wuerl, Archbishop of Washington.