Infiltration Sump System

Transcription

1 Stormwater Management Goals Achieved Acceptable Sizing Methodologies Pollution Reduction.... NA Flow Control. PRES Destination PRES This facility is classified as an Underground Injection Control structure (UIC). SIM=Simplified Approach, PRES= Presumptive Approach, PERF= Performance Approach Notes: 1) Infiltration sump systems are used to manage stormwater from street surfaces. Description: Infiltration sump systems can be used to provide street drainage by collecting and recharging stormwater runoff into the ground. The use of sumps is highly dependent on soil type and height of the groundwater table. Note: The Oregon Department of Environmental Quality (DEQ) has identified sumps as Class V Injection Wells" under the federal Underground Injection Control (UIC) Program. These facilities must be either authorized by rule or authorized by permit by DEQ. Since the UIC Program states that these types of wells can have a direct impact on groundwater, site controls and pollution reduction facilities are required prior to disposing stormwater into them. Designers shall design all underground injection systems to quality for DEQ Rule Authorization. More information about the UIC Program can be found in Section or at DEQ's website at: For technical questions call DEQ- UIC Program at City staff will file all registration forms with DEQ. Stormwater Management Manual Page 2-127

2 Sumps are recognized as a destination and flow control facilities for managing stormwater runoff, but are not intended to be used to meet pollution reduction requirements. Sump systems are excluded from use within the following specific areas and land-use types within the City: Neighborhood collectors in commercially zoned areas (Refer to Arterial & Collector Street Plan, City of Eugene, November 1999) Within 500 feet of municipal or domestic drinking water wells, or a two-year time of travel zone, whichever is greater. In areas with permanent or seasonally-shallow groundwater (< 10 feet below the ground surface). A sump system (see Exhibit 2-28) is the total of all sump components at a single location (e.g., an intersection) and consists of inlets, piping, a sedimentation manhole, and one or more sumps. If one sump lacks adequate capacity to handle the design flow, a second sump may be placed in series with the first to provide additional capacity. Sedimentation manholes with oil traps receive runoff from inlets before stormwater enters the sumps. The sedimentation manholes settle out most of the large particulate material that can clog sumps drainage holes, decreasing maintenance needs and increasing long-term effectiveness. Detailed drawings of a standard sump and standard sedimentation manhole can be found as Exhibits 2-29 and Construction Considerations: When constructed according to the standard design procedures, the sump system achieves both flow control and destination benefits. A sedimentation manhole reduces pollution through removal of sediment, oils, and grease. Additional pollution reduction facilities, such as street swales, planters or filters, must be used in non-residential streets, or streets with over 1,000 average daily trips. Sump System Design and Sizing: Hydraulic calculations for public sumps shall be performed using the Rational Method. The required storage capacity of the facility shall be determined by subtracting the volume of water that can exfiltrate out of the facility with the required drawdown period from the volume runoff from the contributing basin for each facility design. Stormwater Management Manual Page 2-128

3 Sumps shall be designed for the Flood Control Design Storm, with a safety factor of 2. The drawdown time for sump design when full shall not exceed 12 hours. Example: What is the design percolation rate that a sump system must achieve to adequately dispose of runoff from 10,000 square-feet of paved street area? Rational Formula: Assume: Where: Q=C*I*A Time of concentration = 5 minutes for the street area Q= Flow in cubic feet per second C= Runoff Coefficient (0.9 for paved surfaces) I= Intensity (3.1 inches per hour for a 10-year storm event and a time of concentration of 5 minutes) A= Area in acres (10,000 square-feet = 0.23 acres) Q= (0.9) * (3.1) * (0.23) = 0.64 cfs Apply safety factor of 2: Q= 2 * 0.64 cfs = 1.28 cfs or gallons per minute Stormwater Management Manual Page 2-129

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7 Sump System Design and Construction Requirements A maximum of two sumps shall be used in series, unless approved by PW. The minimum distance between sumps shall be 25 feet. The desired distance between the sump and sedimentation manhole is 25 feet. This figure is a guideline and depends on site conditions. If no dispersion pipe is constructed as part of the system, the maximum drainage medium area width around the sump shall be 50 feet on each side of the sump. The maximum velocity out of the holes is 5 fps. All design calculations and/or manufacturer s recommendations shall be submitted with the design application. Sumps shall not be located within 200 feet from the tops of slopes more than 10 feet high and steeper than 2h: 1v. The diameter of pipe between the sump and sedimentation manhole shall be 12 inches. Sumps shall not be located in areas with a constant or seasonally high groundwater table, or shallow bedrock. The bottom of the sump shall be at least 10 feet above the seasonal high water table, and at least 3 feet above bedrock. Drainage Medium shall be a minimum of 12 of 1 ½ inch to ¾ inch coarse aggregate for concrete. As part of the Project Acceptance Inspection and the Warranty Inspection of citymaintained sumps, the contractor shall verify the design capacity of the sump using the Sump Testing procedures. City-maintained sedimentation manholes shall be cleaned prior to City acceptance of ownership and maintenance. Checklist of minimal information to be shown on the permit drawings: 1) Sump and sedimentation manhole location with setbacks to curb, right-of-way lines, and other existing and proposed utilities. 2) Rim and bottom elevation. 3) All stormwater piping associated with the facility, including pipe materials, sizes, slopes, and invert elevations at every bend or connection. 4) Groundwater and bedrock elevations. 5) Soil units encountered. 6) The longitude and latitude for each facility. 7) The total impervious surface drained for each facility. Stormwater Management Manual Page 2-133

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