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Artificial Playing Field Scenarios Aug2016Artificial Playing Field Scenarios, Performance and Design Criteria for Storm Water Management August 24, 2016 MSD Development Review Department 1) Turf fields with infiltration, no lime stabilized soil subgrade: • To satisfy this condition, design parameters will mimic current pervious pavement design requirements. The pervious surface will drain to a flat soil subgrade base through open graded aggregate. Infiltration will be promoted by perching the perforated underdrain piping system outlet a minimum of 6” to store runoff under the turf field section in aggregate voids. Water quality will be satisfied and the storage area may be designed over the full turf field area or at a 2:1 ratio as allowed for pervious pavement. The minimum open aggregate section thickness will be 12”. Any additional aggregate section required to store the 2yr/24hr event will be at the discretion of the turf manufacturer. • The following parameters shall be used for calculating differential runoff, detention and channel protection requirements and thresholds. These parameters will only apply to the surface area of the perched underdrain portion of the field: • CN=80 / 5% impervious / P.I.=1.70 • 20” to 24” total thickness of the rock section can be used to create more bridging strength if subgrade soil settlement is anticipated. 2) Turf section per manufacturer, no lime stabilized soil subgrade: • The field section may have the underdrain system not perched (i.e. underdrain close to bottom, near subgrade) and may have a sloped base. Open aggregate drainage depth may be 4-5” or as required by the turf field manufacturer. 2” clean open graded aggregate may be used for field subgrade soil remediation if needed. The 2” clean will still allow for infiltration to occur. • The following parameters shall be used for calculating water quality, differential runoff, detention and channel protection requirements and thresholds: • CN=84 / 26% impervious / P.I.=2.11 • Water quality may be met by storing the WQv below the perimeter drain within aggregate void space at a maximum depth of 6”. This volume would be 100% of the water quality volume calculated. Alternatively 75% of the WQv may be treated downstream of the collection system in an off-line volume reducing BMP such as bioretention. • If needed, channel protection and/or detention may be metered out of the underdrain pipe collection system and rock storage layer per standard MSD design routing of the 2yr/24hr and 100yr/24hr storm events. WQv below discharge outlet may be counted towards total storage volume needed for channel protection and detention 3) Turf section per manufacturer with lime stabilized soil subgrade: • The same turf sections described in option 2 may be used with the addition of lime to stabilize the field subgrade. • The following parameters shall be used for calculating water quality, differential runoff, detention and channel protection requirements and thresholds: • CN=98 / 100% impervious / P.I.=3.54 In all cases, stormwater conduit sizing for public storm sewers downstream of the collection and metering systems shall be designed using the P.I. factor for 100% impervious. Private sewers with an acceptable overland flow path identified may be evaluated with a lower PI factor as directed by the District. For scenarios 1 & 2 above, an as-built certification, signed by the design engineer and contractor, stating that no lime stabilization was used on the turf field soil subgrade will be required prior to MSD construction approval.