In 1989, design plans were approved for a large underground detention facility to manage the stormwater runoff for a commercial shopping center in Loudoun County.  That facility was designed as a 96-inch diameter, 300-foot long triple Corrugated Metal Pipe (CMP) underground detention BMP located about 20 feet below ground surface. As with most CMPs, it lasted for several decades, but in the mid-2010’s signs of age began to show.

The main challenge with the facility is its location 20 feet under a main cut-through drive aisle for a neighborhood and is also underneath a parking lot of a heavily used shopping plaza with local businesses.  Portions of the facility were located very close to the loading plane of the adjacent two story commercial buildings.

This presentation will go through the many repair strategies employed from digging up and replacing a 175 foot section to ultimately using a geopolymer material to line the BMP.  Procurement, inspection and repair activities were additionally hampered by COVID emergency restrictions.  The presentation will discuss engineering, construction and public outreach strategies employed as well as challenges the project faced along the way.