Stormwater step pool materials specifications
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Parameter Specification Size Note
Topsoil Topsoil per MNDOT 3877 n/a Characteristic of local site soils
Media sand ASTM C-33 fine aggregate concrete sand 0.02” to 0.04”
Check dam (pressure treated) AWPA Standard C6 6” by 6” or 8” by 8” Do not coat with creosote; embed at least 3’ into side slopes
Check Dam (natural wood) Black Locust, Red Mulberry, Cedars, Catalpa, White Oak, Chestnut Oak, Black Walnut 6” to 12” diameter; notch as necessary Do not use the following, as these species have a predisposition towards rot: Ash, Beech, Birch, Elm, Hackberry, Hemlock, Hickories, Maples, Red and Black Oak, Pines, Poplar, Spruce, Sweetgum, Willow
Check dam (rock, rip rap) Per local criteria Size per requirements based on 10-year design flow Cannot get water quality volume credit when using a permeable check dam
Check dam (earth) Per local criteria Size per requirements based on 10-year design flow Use clayey soils with low permeability
Check dam (precast concrete) Per pre-cast manufacturer Size per requirements based on 10-year design flow Testing of pre-cast concrete required: 28 day strength and slump test; all concrete design (cast-in-place or pre-cast) not using previously approved State or local standards requires design drawings sealed and approved by a licensed professional structural engineer.

Embed at least 3’ into side slopes

Filter Strip sand/gravel pervious berm sand: per dry swale sand gravel; AASHTO M-43 sand: 0.02” to 0.04” gravel: 1/2” to 1” Mix with approximately 25% loam soil to support grass cover crop; see Bioretention planting soil notes for more detail
Pea gravel diaphragm and curtain drain ASTM D 448 varies (No. 6) or (1/8” to 3/8”) Use clean bank-run gravel
Underdrain gravel per pre-cast manufacturer 1.5” to 3.5”
Underdrain ASTM D-1785 or AASHTO M-278 6” rigid Schedule 40 PVC 3/8” perf. @ 6” o.c.; 4 holes per row

This page was last modified on 29 March 2018, at 15:52.

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