Stormwater step pool materials specifications

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