The document discusses a case study of an underground detention facility in Fairfax County, Virginia. It was constructed in 1979 using 300 linear feet of 72-inch corrugated metal pipe. Over time, a lack of adequate access, low flow, and no trash rack led to significant sediment deposition that impacted the functioning of the facility. Routine maintenance through jetting and vacuuming was needed to restore capacity. The presentation emphasizes the importance of considering long-term maintenance needs in the design of underground detention facilities.

1. 128 Cockeysville Road, Suite 200 Hunt Valley, Maryland 21030 410.785.0875 UNDERGROUND DETENTION: OUT OF SIGHT AND OUT OF MIND, UNTIL... August 5, 2008 Theodore E. Scott, CPESC, PE T.E. Scott & Associates, Inc. Stormwater Maintenance, LLC tes@MdSWM.com www.SWMaintenance.com www.AppliedStormwater.com PRESENTATION BMP B31

2. UNDERGROUND DETENTION BMP CASE STUDY INTRODUCTION Facility Fairfax County, Va One of Three Underground 72” CMP Detention 300 LF Constructed 1979 PRESENTATION BMP B31

3. UNDERGROUND DETENTION BMP CASE STUDY DESIGN & CONSTRUCTION AFFECTS ON MAINTENANCE Control Structure Access PRESENTATION BMP B31

4. UNDERGROUND DETENTION BMP CASE STUDY DESIGN & CONSTRUCTION AFFECTS ON MAINTENANCE Upstream Access PRESENTATION BMP B31

5. UNDERGROUND DETENTION BMP CASE STUDY DESIGN & CONSTRUCTION AFFECTS ON MAINTENANCE Low Flow No Trash Rack PRESENTATION BMP B31

6. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE INSPECTION Low Flow PRESENTATION BMP B31

7. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE INSPECTION Dewatering PRESENTATION BMP B31

8. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE INSPECTION Deposition Granular Sediments PRESENTATION BMP B31

9. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE INSPECTION Deposition Fine Sediments PRESENTATION BMP B31

10. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE INSPECTION Deposition Floatables PRESENTATION BMP B31

11. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE OPERATION Access Slab cut for New access PRESENTATION BMP B31

12. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE OPERATION Jetting & Vacuuming PRESENTATION BMP B31

13. UNDERGROUND DETENTION BMP CASE STUDY MAINTENANCE OPERATION Completion PRESENTATION BMP B31

14. Thoughts for Owners Annual Inspection Programs Routine Maintenance Programs Thoughts for Regulators Detention approach allows significant pollutant conveyance UNDERGROUND DETENTION BMP CASE STUDY CONCLUSION Thoughts for Designers Consider Maintenance in Designs Vehicular Access Equipment Access Personnel Access Trash and Debris Racks Non-clogging devices PRESENTATION BMP B31

15. Main Office: 128 Cockeysville Road, Suite 200 Hunt Valley, Maryland 21030 410.785.0875 Northeast Office: 31 Gardiners Lane Hampton Bays, NY 11946 410.703.4936 THANK YOU UNDERGROUND DETENTION: OUT OF SIGHT AND OUT OF MIND, UNTIL... August 5, 2008 Theodore E. Scott, CPESC, PE T.E. Scott & Associates, Inc. Stormwater Maintenance, LLC tes@MdSWM.com www.SWMaintenance.com www.AppliedStormwater.com PRESENTATION BMP B31