SUBSURFACE INFILTRATION VAULTS: PUTTIN’ WATER IN IT’S PLACE OBJECTIVES Water Flow In Vaults STRENGTH ANALYSIS SEDIMENTATION AND INFILTRATION SLOPE FUNCTION AND TESTING VAULT DESIGN AND COST  Reduce runoff in developments  Infiltrate stormwater underneath sidewalks and driveways  Maintain modular design  Infiltrate stormwater on a slope  Lower cost than common BMPs  Filter stormwater before it enters system  Easy to clean out ABSTRACT EPA regulations require the infiltration of the first inch of rainfall from a storm event. Subsurface infiltration vaults increase residential stormwater infiltration according to those regulations. These vaults are an alternative to common Best Management Practices (BMP) such as rain gardens and green roofs. The vaults are corrugated plastic arches and will be placed in a trench and covered with gravel and cement. This design improves upon existing designs by enhancing applicability on slopes and aiding in site construction. The surface cement will act as sidewalks and driveways to reduce overall construction costs. Individual aspects of this design were analytically and physically tested to ensure feasibility. INSTALLATION The inlet vault receives stormwater runoff from surface grates and downspouts. Its partitions facilitate sedimentation of large particles from the stormwater. From the inlet vault, stormwater feeds into the infiltration vaults through piping sized to accommodate a 10 year storm event. DESIGN INLET VAULT INFILTRATION Each infiltration vault has a 100 gallon infiltration capacity. The number of vaults is determined according to the contributing impervious area. To achieve timely exfiltration from the vaults, the underlying soil surface will be ripped. To inhibit flow on a slope, the vaults are placed in a trench end to end and surrounded on all sides with sodium bentonite. The maximum calculated slope for the vault system is 13%. The vault system was tested at the East Tennessee Research and Education Center – Plant Science Unit. After multiple tests, applying a sodium bentonite slurry to the gravel surrounding the vault inhibited stormwater flow from vault to vault via down slope flow. There were problems in applying the bentonite and sealing to the soil surface. A second generation design is to bury wall extensions between the vaults to stop flow. The stormwater infiltration vaults are placed in a 34 inch deep trench. A 6 inch layer of gravel is placed in the bottom, followed by the vault. The vault is then filled with gravel up to 6 inches above the arch. Finally a 4 inch layer of concrete is applied, forming the sidewalk. The vault structure is designed to support a tire load of 1250 pounds, representing a 5000 pound car. The corrugations add rigidity and strength to the vaults, reducing stress at the site of impact. The subsurface infiltration vault serves as a mold for concrete to form a sidewalk and driveway. This application is intended for residential sites. The infiltration vault system allows for a conventional aesthetic while keeping costs below that of comparable BMPs. Finite Element Analysis (FEA) was used in Inventor as an initial approach (right). Using a software called Cande (above), loads including tire weight, gravel and concrete, and the infill support of the soil were distributed across the vault. Water flow between vaults is achieved through the pipe orifice located on both sides of the vault mold. Shown above, water is flowing from one vault to another once the vault is filled. On slopes, water has a tendency to flow from vault to vault by under the wall (right). This flow bypasses the system and must be stopped. Team Members: Ryan Miles Matt Ellison Thomas Lakas Callie Jernigan