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12 ‐ Construction Site Management
Mary Halley
Module Content
ImportanceofconstructionsitemanagementtoRunoffReduction
CommonConstructionMistakesAvoidingGIPfailure
Time to Wake Up!
Themostimportantfactor determiningthesuccessorfailureofinfiltrationGIPSis
ConstructionSiteManagement.
InfiltrationGIPS willfail iftheyarecompactedorsedimentdischargestothem.
Same Site, Different Stages, Very Different Runoff
StageofDevelopment TotalSuspected Sediment (TSS)Concentration(mg/L) DataSource
Open Land(Urban) 70 (median) NURP, 1983
During Construction 20,000to 160,000 McCaleb etal,2008
PostConstruction 69 to100(median) NURP, 1983
Post‐Construction BMP Mechanisms
Infiltration:Runoffreduction&pollutantremoval(allpollutants)Evapotranspiration:Runoffreduction&pollutantremoval(nutrients)Settling:Pollutantremoval(TSS,Phosphorus,Metals)Filtration:Pollutantremoval(TSS,P,N,Metals)
Evapotranspiration
Settling
Filtration
Underdrain to Surface
Infiltration Filtration
Filtration
Sediment Impacts to BMP Mechanisms
Infiltration:ClogsvoidspacesinporoussoilsandpermeablepavementsEvapotranspiration:Preventsinfiltrationandwateruptakethroughroots,killingthevegetationSettling:DestroysthesettlingcapabilityandcauseuncontrolledsedimentdischargesifleftunmaintainedFiltration:Coversforestlitterandvegetation,clogsvoidspacesinporoussoilsandinunderdrains
Approved GIP – Bioretention
From Design Approval to Operation
Actual GIP – Sediment Basin
Different Stages, Similar Goals
DuringConstruction•Minimizetheextentanddurationofdisturbance
• Nodischargeofsedimentandconstructionmaterials
• Protectstreams,wetlandsandothernaturalfeatures
• InspectandmaintainBMPs• Stabilizedisturbedareas
PostConstruction• AvoidsoildisturbanceandcompactioninGIPareas
• Nodischargeoffirst1‐inchofrainfall(nopollutants)
• Protectstreams,wetlandsandothernaturalfeatures
• InspectandmaintainBMPs• Keepopenspacestabilized
The transition from construction to post-construction is the most critical time to ensure Green Infrastructure success!
Montgomery County, MDBioretention
GIPs are typically installed in final phases
of construction, primarily to protect them from sediment
discharges
GIPs look different from traditional BMPs.
Subcontractors may not realize these are
stormwater controls!
Final stage subcontractors, (home subcontractors,
landscapers) need to have full knowledge of site GIPs too!
Vehicles, equipment or activities in the wrong area can
cause failure.
The Top 10 List of Poor Construction Site Practices1. Pooron‐sitecommunicationbetweencontractorand
subcontractors,vendors,landscapers2. Failingtofollowtheapprovedconstructionsequencing
andsitephasingpracticesshownonEPSCplans3. InstallingPermanentStormwaterBMPstooearly4. FailingtostabilizeareasupstreamofPermanent
StormwaterBMPsbeforeinstallation5. FailingtoprotectareaswhereBMPswillbeinstalled6. Failingtoprotectnativevegetationorsoilareas7. Failingtoclean‐outtemporaryBMPsbeforeinstallationof
GIPs8. Massgrading9. FailingtoinstallandmaintaintheproperEPSCBMPs10. Failingtorepairerosionareasquicklyafterexposure
Communication Modes
Signs,fencingandtape!! Morningtailgatemeetings Subcontractorcheck‐ins On‐siteplanupdates On‐siteplanbillboards Siteinspectiondocuments Tandeminspections
Communication Needs
PermitHolder
SiteDesigner
Contractor
CountyInspector
Subcontractor
Construction Phasing & Sequencing MostGIPsrelyonuncompacted soil and/orhealthyvegetation,so
consider:• AdjustmentstootherconstructionactivitiestoaccommodatetheGIP(parkingareas,equipmentstorage,materialsstockpiles,etc.)
• Performinginspectionsduringlandscapeinstallation• Thetimeofyear,anticipatedweather,andneedforwateringplants• Ashort‐termandlong‐termplantwateringplan
Construction Phasing & Sequencing
BeforeGIPinstallation:• ContributingdrainageareastoGIPsmustbestabilized• UnprotectedGIPareasmayrequiresoilamendments• ThepotentialforGIPcompactionmustbeeliminated• Post‐installationprotectionmustbeplannedandready
Clean GIP Installations
Source: www.lid-stormwater.net
Final Thoughts
Designplansshouldincludephasing,sequencing,protection,andvegetationplanningandmaintenance.
CountySitePlanReviewersandSiteInspectorswillbemorediligentabouttheseelements– soyoushouldtoo!
Correctiveactionswillberequiredifthereisevidenceofsoilcompaction,sedimentdischargestoGIPs,orunhealthyvegetation.
Module Topic Summary
ImportanceofconstructionsitemanagementtoRunoffReduction
CommonConstructionMistakesAvoidingGIPfailure
Questions?