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Construction of Facilities Dan Cloak Environmental Consulting Construction Workshop, May 2, 2012.

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Presentation on theme: "Construction of Facilities Dan Cloak Environmental Consulting Construction Workshop, May 2, 2012."— Presentation transcript:

1 Construction of Facilities Dan Cloak Environmental Consulting Construction Workshop, May 2, 2012

2  Low Impact Development: What it is, what it does  Runoff dispersal (“self-retaining areas”)  Pervious pavements  Bioretention  How facilities work and how they are sized  What to watch for during construction

3  Features Impervious surfaces: roofs and pavement Catch basins and piped drainage “Collect and convey” design objective

4 Site ScaleWatershed and Stream Scale Higher peak flowsFlooding and scouring of stream beds Lower time of concentrationFlash flows Runoff from small stormsDischarge when runoff did not previously occur Increased runoff durationsStream erosion at moderate stream flow rates Greater runoff volumesHigher pollutant loading Greater runoff energyConveys trash and gross pollutants to streams Decreased infiltrationLower and less frequent stream base flow Dry weather dischargesHigh pollutant concentrations during low flows

5 Watershed and Stream ScaleSite scale Reduce peak flowsDetain runoff on site Increase time of concentrationSlow runoff from leaving site No runoff from small stormsInfiltrate, evapotranspirate and reuse Reduce duration of moderate flowsLet runoff seep away very slowly Reduce runoff volumeInfiltrate and reuse where possible Reduce runoff energyDetain and slow flows Increase groundwater storage and stream base flows Facilitate infiltration Reduce pollutants in runoffDetain and filter runoff Protect against spills and dumpingDisconnect drainage and filter runoff

6  Instead of “collect and convey,” “slow it, spread it, sink it.” Avoid concentrating flows Keep drainage areas small Promote infiltration Detain Treat

7  Optimize the site layout

8  Use pervious surfaces and green roofs where possible

9  Optimize the site layout  Use pervious surfaces and green roofs where possible  Disperse runoff to landscaping

10  Optimize the site layout  Use pervious surfaces and green roofs where possible  Disperse runoff to landscaping  Direct drainage from impervious surfaces to bioretention facilities

11  Rationale  Produce no runoff from “small” storms  Also called “zero discharge” areas  Criteria  Bermed or graded concave  Slopes do not exceed 4%  Amended soils and vegetation to maintain soil stability and permeability  Inlets of area drains, if any, 3" minimum above surrounding grade

12  Rationale  Self-retaining areas are capable of ponding and infiltrating some additional runoff  Criteria  Ratio is not greater than 2:1 if treatment-only requirements apply  Ratio is not greater than 1:1 if flow-control requirements apply  Provide sufficient ponding/storage depth  Facilitate infiltration

13  Variations  Pervious concrete  Porous asphalt  Porous pavers  Gravel  Open pavers  Solid unit pavers set on sand/gravel  Artificial turf  Common Characteristics  Require a base course  Base course depth varies with soil type  More costly than conventional concrete or asphalt  Installation on slopes requires careful design

14  Minimal compaction of underlying soil  Check base course depth  4 to 12 inches or more, depending on competence of underlying soils  Base course underdrains  Consider omitting the underdrain and relying on infiltration and lateral flow  Perforated SDR 35 or equivalent  Outlet elevation minimum 3" above bottom of base course  Underdrain may be routed to storm drain

15  Pavers  Rigid edge required  Solid pavers require 3/8" minimum gap  Joints filled with open-graded aggregate free of fines  Permeable concrete and pervious asphalt  Installed by industry-certified professionals according to vendor’s recommendations.



18 Overflow Underdrain

19 Surface Loading Rate i = 0.2 inches/hour i = 5 inches/hour BMP Area/Impervious Area = 0.2/5 = 0.04


21 Soil Mix Gravel 12" 18" 4"4" 2"2" Overflow A V1V1 V2V2 Φ =

22 Facility DesignSoil Group Area A (ft 2 /ft 2 ) Volume V 1 (ft 3 /ft 2 ) Volume V 2 (ft 3 /ft 2 ) Rainfall Adjustment for Surface Area Rainfall Adjustment for Storage Volume Maximum Release Rate Bioretention Facility A No min.Eq. 4-6 No orifice B No min.Eq. 4-7 No orifice C Eq. 4-8 Eq D Eq. 4-9*Eq. 4-9Eq Flow- through Planter ANot permitted in “A” soils BNot permitted in “B” soils C Eq. 4-8 Eq D Eq. 4-9*Eq. 4-9Eq Dry Well A N/AEq. 4-6 No release B N/AEq. 4-7 No release CNot permitted in “C” soils DNot permitted in “D” soils Cistern + Bioretention A N/AEq. 4-13Eq. 4-6Eq B N/AEq. 4-14Eq. 4-7Eq C N/AEq. 4-15Eq. 4-8Eq D N/AEq. 4-16Eq. 4-9Eq Bioretention + Vault A0.04N/A0.096N/AEq. 4-6No release B0.04N/A0.220N/AEq. 4-7Eq C0.04N/A0.152N/AEq. 4-8Eq D0.04N/A0.064N/AEq. 4-9Eq. 4-11

23 Drainage area includes portions of roof and of parking lot





28  Runoff may enter by sheet flow or be piped.  Roof leaders can be piped directly or spill across pavement  Ensure is consistent with DMA delineation


30  Outlet structure  Top of overflow grate  Underdrain connection  Inlet  Flow line at inlet  Top of curb  Top of adjacent paving  Soil layers  Top of soil layer  Bottom of gravel layer  Bottom of soil layer

31 15"



34 Overflow elevation


36  Class 2 permeable  Caltrans spec  Typical to be slightly off gradation spec on delivery  No filter fabric  Underdrain  Near top of gravel layer  PVC SDR 35 or equivalent; holes facing down  Solid pipe for 2' closest to outlet structure  Cleanout

37  Now included in NPDES Permit  60-70% Sand  ASTM C33 for fine aggregate  30-40% Compost  Certified through US Composting Council Seal of Testing Assurance Program  Submittal per Guidebook  Option to accept test results for a “brand-name” mix if volume is less than 100 cubic yards  Install in 8"-12" lifts  Do not compact  Do not overfill  Leave room for mulch

38  Maintain design top of soil elevation  Trees  Incorporate into bioretention facility  Account for surface roots

39  Inspect each new facility within 45 days of installation  Inspect 20% of all facilities each year  Inspect every facility at least once every five years

40  Stormwater C.3 Guidebook, 6 th Edition   Or search “Contra Costa Stormwater”  See in particular:  Chapter 5, Construction Checklist  Design sheets at end of Chapter 4  Appendix B, Soils/Plantings/Irrigation for Bioretention Facilities

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