Section: The following Sediment Control practicesare presented inthis 4-2. Sediment Control Practices • • • • • • • • • • Flocculants dewatering Construction Temporary sedimentbasin Temporary sedimenttrap Temporary exit construction Temporary stormdraininletprotection Temporary checkdam Erosion control mixberms Straw orhaybalebarrier Silt fence

4-2. Sediment Control Practices 4-2. Sediment Control Practices fence. severe erosion of the channelbothupstream anddownstream ofthe sediment accumulatedontheupgradientsideoffence, and complete failure ofthefence.Such failures typicallyrelease the only results inthebypass ofsedimentladen-water, butalsointhe undercutting, endcutting,andovertopping. This frequently not fences installedacross aconcentratedflow pathare subjectto impound sedimentorwatermore than18incheshigh.Silt with channelized flow. Silt fencesshouldnotbedesignedto effectively filteringthehighratesand volumesofwaterassociated ditches orotherdrainage ways. Silt fencesshouldnotbeusedacross streams, channels,swales, installed siltfencewillincrease erosion. practices thatdoprevent orcontrol erosion. Improperly appliedor practice. It isintendedtobeusedinconjunctionwithother Silt fenceisasedimentcontrol practice,notanerosion control expected. form. Theiruseislimitedtoareas where overland sheetflows are and therefore shouldbelocatedwhere onlyshallow poolscan Silt fencesare notdesignedtowithstandhighheadsofwater, to slow andpondthewaterallow tosettle. soilparticles Silt fenceshave ausefullifeof oneseason.Theyfunctionprimarily areas. retain smallamountsofsedimentfrom disturbedorunprotected barrier isinstalledacross oratthetoeofaslope,tointercept and posts andentrenchedattached tosupporting intothesoil.This sedimentbarrierconsistingoffilterfabric Silt fenceisatemporary G l a r e n e D n o i t p i r c s e Silt Fence Silt fencesare notcapableof • C • • • i s n o o o o o o Potential causesofsiltfencefailure include: Silt fencinggenerallyisabetterbarrierthanhaybalebarriers. projects. longer durationconstruction life ofoneseason,andshouldbeperiodicallyreplaced on recommendations. However, siltfencesgenerallyhave auseful longer dependingonultravioletstabilityandmanufacturer’s Silt fences(syntheticfilter)canbeusedfor60daysor o o o o o Silt fencebarriersare usedwhere: o o o o o o o o o o d Inadequate maintenanceofthesiltfenceafterinstallation; Improper attachmenttoposts; compaction ofthebottom thesiltfencefabric; Inadequate trenching depthandimproper backfilland Allowing excessive drainagearea tothesiltfence structure; Improper placementonthesite; the possibilityofawashout. in streamsfences beconstructed orinswaleswhere there is concentrated flows. Under nocircumstances shouldsilt Sediment barriersshouldnotbeusedinareas of erosion and tointercept andtreat thesedimentload. are exceeded, tocontrol othermeasures maybenecessary the barrieris50percent (2:1).If anyoftheseconditions the barrieris100feet,andmaximumgradientbehind feet ofbarrierlength,themaximumlengthslopeabove The contributingdrainagearea islessthan1/4acre per100 systems oradversely affectadjacentareas. Sedimentation willreduce thecapacityofstormdrainage watercourses. Sedimentation canpolluteordegradeadjacentwetlands or overland sheetflow. Flow tothesiltfencefrom adisturbedarea occursas s n o i t a r e

4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • • • • • M e c n a n e t n i a as required tomaintain effectiveness. projects, siltfenceshouldbereplacedconstruction periodically Silt fenceshave ausefullifeofoneseason.On longer diversions andsedimenttraps. measures, suchastemporary extend barriersuphillorconsiderreplacing themwithother If there is evidenceofendflow onproperly installedbarriers, grade, prepared andseeded. no longerrequired shouldbedressed toconformtheexisting Any sedimentdepositsremaining inplaceafterthesiltfenceis barrier stillisnecessary, thefabric should bereplaced promptly. ineffective priortotheendofexpectedusablelifeand Should thefabriconasiltfencedecomposeorbecome checkdam. barriers shouldbereplaced withatemporary impounding oflargevolumes ofwaterbehindthem,sediment of undercutting atthecenteroredgesofbarrier, or signs oferosion orsedimentationbelow them.If there are signs Silt fencesshouldberepaired immediatelyifthere are any backtowardtransported thesilt fence. moved toanappropriate locationsothesedimentisnotreadily deposition accumulatestoone-halftheheightoffence,and Sediment depositionshouldberemoved, ataminimum,when each rainfallandatleastdailyduringprolonged rainfall; Fences shouldbeinspectedandmaintainedimmediatelyafter o o o o concentration offlows. allow forthisfunction,andtoavoid potentialdiversion or water, itshouldbeplacedatthetoeofsuchslopes,to embankment. Because asiltfenceworks by impounding Placement offenceatmid-slopeacutorfill runoff. alignment, resulting inthediversion orconcentrationof Installing siltfence with adescendinggradealongthefence R e r i u q e m s t n e in achannelordrainagewayabove thefence.Sediment barriers the formofsheeterosion andthere isnoconcentrationofwater Fences shouldbeusedinareas where erosion willoccuronlyin S • • • • • • drainage area above them. should beinstalledpriortoanysoildisturbanceofthecontributing s n o i t a c i f i c e p manufacturer orsupplier. nylon, polyesterby the orethyleneyarnand shouldbecertified sheetof propylene, The filterfabricshouldbe apervious Silt fencingshouldnotbestapledornailedtotrees. o o o o o closely aspossible,and Fences shouldbeinstalledfollowing thecontouroflandas The maximumslopeabove thefenceshouldbe2:1; feet; The maximumlengthofslopeabove thefenceshouldbe100 should belessthan¼acre per100linearfeetoffence; The maximumcontributingdrainagearea above thefence o o o o o diagonal ties. fabric shouldbewire-tied directly tothepostswith three post.If metalpostsareand stapledtoasupport used, a minimumof6inches(24ispreferred), folded Adjoining sectionsofthefenceshouldbeoverlapped by spacing of6feet; to themanufacturer’s withmaximumpost instructions Support postsshouldbesized andanchored according The soilshouldbecompacted over theembeddedfabric; ¾-inch stone; be embeddedwithaminimumthicknessof8inches or thepresence ofheavyroots, thebaseoffabricshould ground, or ifsiteconditionsincludefrozen ground, ledge, depth and4inchesinwidthatrench excavated intothe The fabricshouldbeembeddedaminimumof4inchesin The endsofthefenceshouldbeflared upslope;

4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • • • • • • • • minimally disrupts thesoilupwardminimally disrupts andslightly displacesthe or slicethesiltfencematerial intothesoil.Theslicingmethod method usesanimplement towed behindatractorto“plow” equipment specificallydesigned forthisprocedure. Theslicing Silt fencemaybeinstalledby “slicing” usingmechanical the filterfabric. The trench shouldbebackfilledandthesoilcompacted over above theoriginal ground surface. the trench. Thefabricshouldnotextendmore than 36inches to thepost,and8inchesoffabricshouldbeextended into The standard strength offilterfabricshouldbestapledorwired barrier. 4 inchesdeepalongthelineofpostsandupgradientfrom the A trench shouldbeexcavated approximately 4incheswideand Post spacingshouldnotexceed 6feet. used. A manufactured siltfencesystemwithintegralpostsmaybe sealed. post,withaminimum 6-inchoverlap,at support andsecurely joints are necessary, filterclothshould besplicedtogetheronly to thelengthofbarrieravoid theuseofjoints. When The filterfabricshouldbepurchased inacontinuous rollcut failure ofthestructure. fences mayimpoundvolumes ofwatersufficienttocause The heightofasiltfenceshouldnotexceed 36inchesashigher fabric. to them.Posts shouldbeplacedonthedownslope sideofthe 5 feet.Steel postsshouldhave projections forfasteningwire 1.33 poundsperlinearfootsteelwithaminimumlengthof Posts forsiltfencesshouldbeeither4-inchdiameterwoodor Fahrenheit to120degrees Fahrenheit. lifeatatemperatureusable construction rangeof0degrees stabilizers toprovide aminimumof6monthsexpected The filterfabricshouldcontainultravioletrayinhibitorsand • • • • permanently stabilized. useful purpose,butnotbefore theupslopeareas have been Silt fencesshouldberemoved their when theyhave served allow formaintenanceaccesswithoutdisturbingtheslope. feet from the toetoallow space forshallow ponding andto Silt fencesplacedatthetoeofaslopeshouldbesetleast6 The endsofthefenceshouldbeturneduphill. diagrams). reduce thedrainagearea thatanysegmentwillimpound(see Silt fencesshouldbe installedwith“smiles” or“J-hooks” to condition forsubsequentmechanicalcompaction. soil, maintainingthesoil’s profile andcreating anoptimal

4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices device. severe erosion ofthechannelbothupstream anddownstream ofthe sediment accumulatedonthe upgradientsideofthebarrier, and complete failure ofthebarrier. Such failures typicallyrelease the only results inthebypass ofsedimentladen-water, butalsointhe to undercutting, endcutting,andovertopping. This frequently not bale barriersinstalledacross aconcentratedflow pathare subject and provide forfrequent monitoringofthebarrier. Straw orhay bale barrier, limitcontributingdrainagearea tolessthananacre, installation mustprovide proper embedmentofthestraworhay prevent the useofpreferred materialssuchasstone;incases, dams inapplicationswhere installationaccessorotherconditions with channelized flow. However, theymaybeusedforcheck effectively filteringthehighratesand volumesofwaterassociated areas withconcentrated flows. streams, channels,swales,ditchesorotherdrainage waysor Straw orhaybalebarriersshouldgenerally notbeusedacross applied orinstalledsedimentbarrierswillincrease erosion. with otherpracticesthatdoprevent orcontrol erosion. Improperly not anerosion control practice.Themustbeusedinconjunction Straw orhaybalebarriersconstituteasedimentcontrol practice, the device. form. Theiruseislimitedtoareas thatonlycontributesheetflow to water, andtherefore shouldbelocatedwhere onlyshallow poolscan tosettle.They areparticles notdesignedtowithstandhighheadsof They functionprimarilytoslow andpondthewaterallow soil Straw orhaybalebarriershave ausefullifeofless thansixmonths. amounts ofsedimentfrom disturbedorunprotected areas. installed across oratthetoeofaslope,tointercept andretain small Straw sedimentbarrier andhaybalebarriersare atypeoftemporary G l a r e n e Straw D n o i t p i r c s e

or Hay Such barriersare notcapableof Bale Barrier • C • • i s n o o Potential causesofstraworhaybalebarrierfailure include: for nolongerthan60days. Straw barrier orhay balesshouldonlybeusedasatemporary o o o o o form. Straw orhaybalebarriersare usedwhere: therefore theyshouldbelocatedwhere onlyshallow poolscan barriers are notdesignedtowithstandhighheadsofwater; temporarily pondingwater, allowing tosettle.These particles Straw orhaybalebarriersprincipallytrapsedimentby o o o o o o d Improper placementonthesite; washout. live streams orinswaleswhere there isthepossibilityofa in circumstances shouldsedimentbarriersbeconstructed provide forfrequent monitoringofthebarrier. Under no contributing drainagearea tolessthanoneacre, and proper embedmentofthestraworhaybalebarrier, limit such asstone;incases,installationmustprovide other conditionsprevent theuseofpreferred materials check damsinapplicationswhere installationaccessor concentrated flows. However, theymaybeusedfor Sediment barriersshouldnotbeusedinareas of erosion and tointercept andtreat thesedimentload. are exceeded, tocontrol othermeasures maybenecessary the barrieris50percent (2:1).If anyoftheseconditions the barrieris100feet,andmaximumgradientbehind feet ofbarrierlength,themaximumlengthslopeabove The contributingdrainagearea islessthan1/4acre per100 systems oradversely affectadjacentareas. Sedimentation willreduce thecapacityofstormdrainage watercourses. Sedimentation canpolluteordegradeadjacentwetlands or sheet flow. Flow to the barrier from a disturbed area occurs as overland s n o i t a r e

4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • • S • • • • • M s n o i t a c i f i c e p e c n a n e t n i a should beinstalledsothatbindings are orientedaround the All balesshouldbeeitherwire-bound orstring-tied.Bales Barriers more shouldnotbeconstructed thanonebalehigh. another. Theendsofthebarriershouldbe flared upslope. contour, withendsofadjacentbalestightly abuttingone Bales shouldbeplacedinasinglerow, lengthwiseonthe disturbance ofthecontributingdrainagearea above them. Sediment barriersshouldbeinstalledpriortoanysoil existing grade,prepared andseeded. is nolongerrequired shouldbedressed toconform tothe Any sedimentdepositsremaining inplaceafterthefilterbarrier half theheightofbarrier. They mustbe removed whendeposits reach approximately one- Sediment depositsshouldberemoved aftereachstormevent. Damaged ordecomposedbalesshouldbereplaced promptly. directing toasedimenttraporbasin). sediment-ladenrunoff intercept and capture sediment(forexample,adiversion berm the barriershouldbereplaced withanalternative measure to impounding oflargevolumes ofwaterbehindthebarrier, of undercutting atthecenteroredgesofbarrier, or of erosion orsedimentationbelow them.If there are signs Barriers shouldberepaired immediatelyifthere are anysigns rainfall andatleastdailyduringprolonged rainfall. Hay balebarriers shouldbeinspectedimmediatelyaftereach o o o o o o Inadequate maintenance afterinstallation; Inadequate keyingof thebalesintoground surface; Allowing excessive drainagearea tothebarrier; R e r i u q e m s t n e • • • • • upslope areas have beenpermanentlystabilized. theirusefulness,butnotbeforewhen theyhave the served be madepromptly asneeded.Bale barriersshouldberemoved Inspection shouldbefrequent andrepair orreplacement should with haytoprevent waterfrom escapingbetween thebales. The gapsbetween balesshouldbechinked(filled by wedging) bales. be driven deep enoughintotheground tosecurely anchorthe previously laidbaletoforce thebalestogether. Stakes should bale. Thefirststakeineachbaleshouldbedriven toward the least 18inchesintotheground, shouldsecurely anchoreach At leasttwo stakesdriven through thebaleandpenetratingat slope. Ideally, balesshouldbeplaced10feet awayfrom thetoeof be builtup4inchesagainsttheuphillsideofbarrier. conform totheground level onthedownhill sideandshould should bebackfilledagainstthebarrier. Backfill soilshould After thebalesare stakedandchinked,theexcavated soil proposed barrier toaminimumdepthof4inches. should beexcavated thewidthofabaleandlength The barriershouldbeentrenched andbackfilled.A trench the bindings. topreventsides, paralleltotheground surface deteriorationof

4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices are activity. disturbedinthecourseofconstruction Erosion control mixbermscanbeeasilyandquicklyfixed, ifthey sites. be disposedofasasolidwaste,andisoftenleftabandoned onjob synthetic barriercancauseadditionaldisturbance.Silt fencehasto embankments nearstreams, toremove asre-entry ormaintaina below important and canbeleftonsite.Thisisparticularly The erosion control mixisorganic,biodegradable, renewable, cost-effective. This makesthetechnique very orremoval,construction, unlikestrawbales,siltfenceorcoirrolls. because theorganicmaterialdoesnotrequire anyspecialtrenching, solution thansiltfenceandothersedimentcontrol methods, Erosion control mixbermsand sockssometimesofferabetter unprotected areas. and retain smallamountsofsedimentfrom disturbedor This barrierisinstalledacross oratthetoeofaslope,tointercept fabric (or“filtersock”). consisting oferosion control mixcompostencapsulatedinamesh simple erosion control mixbermisa“continuous containedberm”, and cost-effective alternative tosiltfence.Analternative toa filtering sedimentas well. They are anenvironmentally sensitive sheet flowrunoff, allowing andponds sedimenttosettle,and An erosion control mixbermisatrapezoidal bermthatintercepts G Erosion l a r e n e D n o i t p i r c s e C ontrol Mix B erms • The bermisusedwhere: C • • • • • • • i s n o slopes. closed stormsystems,andatthebottomofsteepperimeter belowrunoff, outletaprons, culvert around catchbasinsand Other BMPs shouldbeusedatlow pointsofconcentrated practical andeffective. areas are locationswhere bermsoferosion control mixare most Frozen ground, outcropsrooted ofbedrockforested andvery disturbance ofthecontributingdrainagearea above them. Sediment barriersshouldbeinstalledpriortoanysoil properly. Sediment barriersare effective onlyifinstalledandmaintained is thepossibilityofawashout. in live streamsbarriers beconstructed orinswaleswhere there flows. Under nocircumstances shoulderosion control mix Sediment barriersshouldnotbeusedinareas ofconcentrated slope length. toreducemeasures the suchasdiversions maybenecessary the barrieris5percent. If theslopelengthisgreater, other the barrieris100feet,andmaximumgradientbehind feet ofbarrierlength,themaximumlengthslopeabove The contributingdrainagearea islessthan1/4acre per100 systems oradversely affectadjacentareas. Sedimentation willreduce thecapacityofstormdrainage watercourses. Sedimentation can pollute ordegradeadjacentwetland and/or d s n o i t a r e

4-2. Sediment Control Practices 4-2. Sediment Control Practices • M • mix. products willnotbeacceptableastheorganiccomponentof and bark debrisorreprocessed chips,ground construction wood composted bark, oracceptablemanufactured products. Wood of generation,andmayincludeshredded bark, stumpgrindings, It mustconsistprimarilyoforganicmaterial,separatedatthepoint Erosion control mixcanbemanufactured onorofftheproject site. S • • • s n o i t a c i f i c e p e c n a n e t n i a o o Composition oftheerosion control mixshouldbeasfollows: grade, prepared andseeded. longer required shouldbedressed toconform the existing Any sedimentdepositsremaining inplaceafterthebarrierisno Filter bermsshouldbereshaped or reapplied asneeded. third oftheheightbarrier. They mustbe removed whendeposits reach approximately one- Sediment depositsshouldberemoved aftereachstormevent. toasedimenttrap orbasin). runoff intercept and trapsediment(suchasadiversion bermdirecting them, thentheyshouldbereplaced withothermeasures to the barrier, orimpoundingoflargevolumes ofwaterbehind sedimentation below them.If there are signsofbreaching of be repaired immediatelyifthere are anysignsoferosion or and atleastdailyduringprolonged rainfall.Theyshould Filter bermsshouldbeinspectedimmediatelyaftereachrainfall o o 65%, dry weight basis. 65%, dry The organicmattercontent shouldbebetween 25and The mixcompositionshould meetthefollowing standards: physical contaminants,andmaterialtoxic toplantgrowth. diameter. Erosion control mixmustbefree ofrefuse, sizes andmaycontainrocksof particle lessthan4”in Erosion control mixshouldcontainawell-graded mixture R e r i u q e m s t n e through thenetting. containment willprovide stabilitywhilevegetation isrooting material andcanpermanentlystabilize ashallow slope.The contained berms.Seeds maybeaddedtotheorganicfiller drawing inthissectionfortheinstallationofcontinuous such asover frozen ground orover pavement. See thedetail especially works well inareas where trenching isnotfeasible asasturdyperforms sedimentbarrierthatishighlydurable.It The organicmixisplacedinthesynthetictubularnetting and containment andstabilitytoabermoferosion control mix. “filter sock”), canbeaneffective sedimentbarrierasitadds An alternative product, thecontinuouscontainedberm(or C • • s u o u n i t n o feet wide. on theuphillsideofbarrier, andaminimumoftwo The barriermustbeaminimumof12”high,asmeasured stems. to washunderthebarrierthrough thegrassbladesorplant to avoid creating voids andbridgesthatwouldenablefines It tocuttallgrassesorwoodyvegetation maybenecessary The barriermustbeplacedalonga relatively level contour. o o o o o o o o o o The pHshouldbebetween 5.0and8.0. Soluble saltscontentshouldbe<4.0mmhos/cm. The mixshouldnotcontainsilts,claysorfinesands. needs tobefibrous andelongated. The organicportion 30% to75%,passinga0.25-inchscreen. 100% passinga0.75-inchscreen, andamaximumof screen, 90%to100%passinga1-inchscreen, 70%to Particle size by weight shouldbe100%passinga3“ C e n i a t n o d B r e m s

4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices monitoring ofthebarrier. drainage area tolessthanoneacre, andprovide forfrequent embedment ofthestraworhaybalebarrier, limitcontributing such asstone;incases,installationmustprovide proper access orotherconditionsprevent theuseofpreferred materials may beusedforcheckdamsinapplicationswhere installation in anylocationwhere there isconcentratedflow. However, they Hay orstraw balesshouldgenerallynotbeusedascheckdams,or which needprotection duringtheestablishmentofgrasslinings. orpermanentditchesswales, applications includetemporary is notavailable, timbercheckdamsmaybeconsidered. Typical ofstone.InCheck damscanbeconstructed locationswhere stone streams orintermittentstream channels. one acre orless.It should The practiceislimitedtouseinsmallopenchannelsthatdrain practice andshouldnotbeusedassuch. the ditchitself. However, thecheckdamisnotasedimenttrapping Check damsmayalsotrapsmallamountsofsedimentgeneratedin of theswaleorditch. velocity of concentratedstormwaterflows, thereby reducing erosion across aswale ordrainageditch.Checkdamsare usedtoreduce the Temporary damsconstructed checkdamsare smalltemporary G l a r e n e Temporary D n o i t p i r c s e not beusedineitherperennially flowing Check D ams • C • • • • • M • • i s n o e c n a n e t n i a when itreaches onehalfoftheoriginalheightorbefore. after eachsignificantrainfall. Sediment shouldbe removed Check damsshouldbecheckedforsedimentaccumulation adjusted immediately. from thecheckdam,damshouldbeinspectedand If evidenceofsiltationinthewaterisapparent downstream must becorrected immediately. Erosion causedby highflows around theedgesofdam than theedges. Inspections shouldverify that thecenterofdamislower made immediately. repairs shouldbe daily duringprolonged rainfallandnecessary Check damsshouldbeinspectedaftereachrainfallandatleast washed downstream. ensure thatallstonesare removed. Thisincludesstonethathas lined channelthatwillbemowed, care shouldbetakento toremoveIf itisnecessary astonecheckdamfrom agrass- planscall forthemtoberetained.and construction project design hasaccountedfortheirhydraulic performance disturbanceofthesoilonremoval,unnecessary butonlyifthe The checkdammaybeleftinplacepermanentlytoavoid intermittent). but mustnotbeusedinstream channels(whetherperennial or This practiceisintendedforuseinareas ofconcentratedflow, d s n o i t a r e R e r i u q e m s t n e

4-2. Sediment Control Practices 4-2. Sediment Control Practices requirements: Temporary checkdamsshouldconformtothefollowing S • • • • • • • • • • s n o i t a c i f i c e p o o ditch hasbeenstabilized: Temporary structures shouldberemoved oncetheswaleor place permanently. If provided plans,leave by thedamin designandconstruction downstream ofthe devices. stone checkdamslesssusceptibletoscouraround theendsand to conformthechannelandsettleifscouroccurs,rendering check damsare generallypreferred. Thestonehastheability embedded atleast18inchesdeepintothesoil.However, stone of4-inchto6-inchlogs be used,andshouldconstructed If carefully installedandmonitored, timbercheckdamsmay face isrecommended forbetterfiltering. angular 2-inchto3-inchstone.¾-inchstoneontheupgradient Stone ofawell-graded checkdamsshouldbeconstructed The checkdamshouldnotbeusedinaflowing stream. overflow elevation ofthedownstream dam. the toeofupstream damisatthesameelevation asthe The maximumspacingbetween thedamsshouldbesuchthat the outeredges. The centerofthedamshouldbeatleast6incheslower than The maximumheightofthedamshouldbe2feet. less thanoneacre. The maximumcontributingdrainagearea tothedamshouldbe swale ordrainageditch. Check damsshouldbeinstalledbefore isdirected runoff tothe o o when apermanentlininghas beenestablished.If the In permanentstructures, checkdamsshouldberemoved needed. be removed andtheditchfilledinwhenit isnolonger ditches andswales,checkdamsshould In temporary removal. dam mustbeseededandmulchedimmediatelyafter protect theditchorswale.Thearea beneaththecheck should beretained untilthegrasshasmatured to permanent liningisvegetation, thenthecheckdam

4-2. Sediment Control Practices 4-2. Sediment Control Practices prevent sediment from enteringthesystematinlets. its conveyance capacity. To to avoid theseproblems, itisnecessary accumulate sufficientsedimenttosignificantly reduceoreliminate natural drainageways.In somecases,thestormdrainitselfmay convey large amountsofsedimenttostormsewersystemsor made operationalbefore theirdrainageareas are stabilized can stabilization ofthecontributingdisturbedarea. Storm drains from entering astormdrainagesystempriortopermanent The purposeofstormdraininletprotection istoprevent sediment evaluated upslope ofthecatchbasin. trap orbasin,alternative solutionsfortreating thewatershould be to thisstructure andthatwaterdoesnotcontinuetoasediment If turbidwaterisbeingdirectedwill onlytrapthecoarserparticles. sedimentarea asit drain. Thistechniqueisintendedasasecondary stone andwire willnotprevent finesedimentfrom enteringastorm sediment particles. Temporary stormdraininletprotection using shallow pondingadjacenttothebarrierandresulting settlingofthe or concrete blocksandgravel. Sediment removal isaccomplishedby ofgravel andwireThe sedimentbarriermaybeconstructed mesh, a storm Drain drop inlet or curb inlet to reduce sediment discharge. A stormdraininletprotection isasedimentbarrierinstalledaround G l a r e n e Temporary D Inlet n o i t p i r c s e Protection Storm Drain

• • C • • • • M • • • i s n o e c n a n e t n i a end of construction andafterthesitehasbeenfully stabilized. end ofconstruction All catchbasinsandstormdrain inletsmustbecleanedatthe the contributingdrainagearea hasbeenproperly stabilized. The barriersshouldbe removed andthearea stabilized when in suchamannerthatitwillnoterode. Removed sedimentshouldbedeposited inasuitablearea and has accumulatedto1/2thedesigndepthofbarrier. barrier restored toitsoriginaldimensionswhenthe sediment Sediment shouldberemoved andthestormdrainsediment event andrepaired asneeded. Inlet barriersshouldbeinspectedbefore andaftereachrain preventing erosion andstoppingsedimentatitssource. sewer systemistostabilize thesiteasquicklypossible, The bestwaytoprevent sedimentfrom enteringthestorm through a sedimenttraporbasin. one acre The inletprotection practicesare fordrainageareas of protection. from will runoff. particles bypass theinlet Silt andclayparticles This practiceiseffective in reducingcoarsegrainsuspended their effectiveness. used, buttheyshouldbeinstalledonlyaftercareful studyof Other techniques foraccomplishingthesamepurposemaybe which maydependonsiteconditionsandthetypeofinlet. This practiceincludesseveral typesofinletbarriers,theuse This practiceappliesprimarilytoencloseddrainagesystems. d s n o i t a r e . Runoff from largedisturbed areas shouldbe routed R e r i u q e m s t n e less than

4-2. Sediment Control Practices 4-2. Sediment Control Practices • S • • • • s n o i t a c i f i c e p following additionalrequirements: Concrete blockandgravel inletbarriers shouldmeetthe o o o o o o o additional requirements: Gravel andwire meshinletbarriersshouldmeetthefollowing inconvenience ordamagetoadjacentareas orstructures. Any resultant pondingofstormwatermustnotcauseexcessive and minimizeactivities. interference withconstruction that willfacilitateClean-outanddisposaloftrappedsediments inamanner The inletprotection deviceshouldbeconstructed less thanoneacre; The maximumcontributingdrainagearea tothetrapshouldbe o o o o o o o must bepulledawayfrom theinlet,cleaned andreplaced. itsfunction,thestones it nolongeradequatelyperforms If thestonefilterbecomescloggedwithsedimentsothat The gravel shouldbeatleast12inchesindepth. drain opening;and The gravel shouldbeatleast18inchesonallsidesofthe The gravel filtershouldbecleancoarseaggregate; openings uptoonehalfinch; The wire meshshouldbehardware cloth orwire with the openingare covered by themesh; the entire openingandaminimumof12inchesaround The wire meshshouldbeplaced over thedrop inletsothat working areas, andadjacentproperty. of pondingontraffic movement, nearby structures, Consideration shouldalsobegiven tothepossibleeffects used where overflow mayendanger anexposedfillslope. removed regularly. Thistypeofbarriershouldnotbe than withotherbarriers,especiallyifsedimentisnot ponding attheinletmaybesignificantlygreater indepth This typeofbarrierhasno overflow provision; therefore, removed andreplaced withaneffective alternative barrier. therequiredperform sedimenttrappingfunction,theyshouldbe from enteringthestormdrainsystem.If suchproducts failto as specified by the vendor ormanufacturer, andprevent sediment are acceptableaslongtheyare installed,used,and maintained functionally equivalent tothebarrierslistedabove. Thesemeasures Manufactured sediment barriersare now available thatcouldbe M e r u t c a f u n a o o o o o o o o o o o o o o be pulledawayfrom theblocks,cleanedandreplaced. itsfunction,thestonemust no longeradequatelyperforms If thestone filterbecomescloggedwithsedimentsothatit outside edgesoftheblockstotopblockbarrier. The gravel shouldbeplacedagainstthewire andalongthe The gravel filtershouldbecleancoarseaggregate; should beused. cloth orcomparablewire meshwith1/2-inchopenings through theopeningsinblocks.Hardwaretransported inches around theopeningtoprevent aggregate from being openings oftheconcrete blocksandextendatleast12 A hardware clothorwire meshshouldbeplacedover the than 24incheshigh. filter shouldbeaminimumof12incheshighandnomore and 12-inchwideblocks.Thebarrierofblocksgravel design needs,by stackingcombinationsof4-inch,8-inch The heightofthebarriercanbe varied, dependingon The blockendsshouldabutoneanother; around theperimeterofinlet; The blocksshouldbeplacedlengthwiseinasingle row d S e d i m t n e B s r e i r r a

4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • C from public stormwater runoff roads. This helpsprotect receiving watersfrom sedimentcarried by tracking ofsedimentontopublicroads vehicles. by construction Itsor otherpaved surface. purposeistoreduce oreliminatethe sitetoanexistingaccessroad way will beleavingaconstruction placed onageotextilefilterfabric,locatedatanypointwhere traffic exitconsistsofapadstoneaggregateA stabilized construction G i s n o l a r e n e any measures usedtotrap sediment. stone asconditionsdemand,andrepair and/ormaintenanceof way. Thismay require periodictopdressing withadditional prevent trackingorflowing ofsedimentontopublicrights-of- The entranceshouldbemaintainedinaconditionthat will inpublicroads. and entrancesatcurves vehicles. Avoidconstruction entrancesthathave steepgrades leaving thesiteandtoprovide formaximumutilityby all entrancesandexitstolimitsediment Locate construction device. loads enteringthesiteandreducing thetotaltraffic over the increase thelongevityofstabilized exitby eliminatingheavy unprotected, entrancefortrafficenteringthesite.Thiswill stabilized exit.Considerprovidingthe temporary aseparate, traffic Only construction d s n o i t a r e D C onstruction n o i t p i r c s e Temporary leaving thesiteisrequired touse Exit

The exitshouldbemaintainedinaconditionthatwillprevent M • • • • • • requirements: Temporary exitsshouldmeetthefollowing construction S • • • tracking ofsedimentontopublicrights-of-way. s n o i t a c i f i c e p e c n a n e t n i a pad and the earth surface below surface thepad. pad andtheearth A geotextilefilterfabricshould beplacedbetween thestone The padshouldbeatleast 6 inchesthick. The padshouldslopeawayfrom theexisting roadway. road or10feet,whichever isgreater. access The padshouldextendthefullwidthofconstruction 6-inch highbermisinstalledattheentranceofproject site. the minimumlengthmaybereduced to50feetifa3-inch The minimumlengthofthepadshouldbe75feet,except that stone. The minimumstoneusedshouldbe3-inchcrushed from entering stormdrains,ditches,orwaterways. sediment-trapping device.Allsedimentshouldbeprevented area stabilized withaggregate, whichdrainsintoanapproved When wheelwashingisrequired, itshouldbeconductedonan traveled way. soil materialsare trackedontotheadjacentpavement or The contractorshouldsweep thepavement atexitswhenever and stabilized. Theentranceshouldthenbe reconstructed. removed along with the collected soil material, regraded on site, When thecontrol padbecomesineffective, thestoneshouldbe R e r i u q e m s t n e

4-2. Sediment Control Practices 4-2. Sediment Control Practices • • with suitableoutletprotection. should beintercepted andpipedbeneaththepad,asnecessary, Natural drainagethatcrosses thelocationofstonepad areparticles trackedoff-site. clogthevoids inthestone suchthatmudandsoil particles The padshouldbemaintainedor replaced whenmudandsoil 4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • • C of dischargefrom adisturbedarea. inlet,orotherpoints swale orchannel,atastormdrainculvert Asediment trapisusuallyinstalledinadrainage sediment particles. is runoff retained longenoughtoallow forsettlingofthecoarser from smalldisturbedareas.sediment-laden runoff Intercepted pondingarea tointercept A sedimenttrapisasmall,temporary G i s n o l a r e n e accumulated sediment. from theterrain,aswell asforeaseofremoval anddisposalof Traps shouldbelocatedtoobtainmaximumstoragebenefit undisturbed areas canbeexcluded from thetrap. Sediment trapsshouldbeinstalledwhere from runoff used instead. larger contributingareas, engineered sedimentbasinsshouldbe watersheds (contributingdrainagearea lessthan5acres). For Sediment trapsshouldbeusedindrainagewayswithsmall disturbed area orsedimentsource. A sedimenttrapshouldbeinstalledasclosepossibletothe d s n o i t a r e D n o i t p i r c s e Sediment Temporary Trap

• M • • • • • Temporary sedimenttrapsshouldmeetthefollowing requirements: S • • • • s n o i t a c i f i c e p e c n a n e t n i a be stabilized immediatelyaftertheirconstruction. The sideslopesofthetrap should be3:1orflatter, andshould storage foreachacre ofdrainagearea. The minimum volume ofthetrapshouldbe3,600cubicfeet less than5acres. The maximumcontributingdrainagearea tothetrapshouldbe source ofsedimentaspossible. The trapshouldbeinstalledasclosetothedisturbedarea or prior todisturbingthearea theyare toprotect. Sediment trapsshouldbelocatedsothattheycaninstalled has becomecloggedwithsediment. should becheckedperiodicallyandreplaced whenthematerial Geotextile fabricorstoneusedaround apipe-outletriser such damageisobserved. inspection foranydamage,andrepaired immediatelyifany Sediment trapoutletsshouldbeexaminedatthetimeof disposed ofandstabilized. The materials removed from thetrapshouldbeproperly original volume. capacity whensedimenthasaccumulatedto50%ofthe Sediment shouldberemoved and the traprestored tooriginal and are notdamaged.Repairs shouldbemadeimmediately. rainfall periods),toinsure thattheyare functioningproperly storm(ordailyduringprolonged andafterevery construction Sediment trapsshould beinspectedatleastweekly during R e r i u q e m s t n e

4-2. Sediment Control Practices 4-2. Sediment Control Practices • Embankments: • Stone Outlets: • • • Earth Outlets: • • • • Outlets (General Requirements): • crushed stonesectionintheembankment. crushed A stoneoutletsedimenttrap hasanoutletconsistingofa of construction. The embankmentandoutletshouldbe vegetated within3days in acres. The outletwidthshouldbeequalto6timesthedrainage area either over natural ground or cutintonaturalground. outletsedimenttraphasadischargepointthatis An earth pipe outlets. spillways,stoneoutlets, or asearth Outlets may beconstructed stabilized channel orastormsewersystem. must emptyontoundisturbedground, intoawatercourse, The outletshoulddischargetoastabilized area. Theoutlets the crest ofthetrap The outletofthetrapshouldbeaminimumonefootbelow is aminimumof1footabove thecrest elevation oftheoutlet. Outlets should bedesignedsothatthetopofembankment erosion at orbelow theoutlet doesnotoccur. such amannerthatsedimentdoesnotleave thetrapandthat andmaintainedin The outletshouldbedesigned,constructed The minimumtopwidthoftheembankmentshouldbe6feet. natural ground onthedownstream sideoftheembankment. should be4feetwhenmeasured from thelowest pointof The maximumheightofthesedimenttrapembankment • • • • • • • • Pipe Outlet: efficiency. stonecanalsobeusedaroundCrushed therisertoincrease trap covered withfiltercloth. below thelowest hole. Thetopoftheriserpipeshouldnotbe least six(6)inchesabove thehighestholeandsix(6)inches and secured by strapping.Theclothshouldcover anarea at wrapped withageotextilefabricheldinplaceby woven wire In order toincrease theefficiencyoftrap, therisercanbe base measurement shouldbetheriserdiameterplus24inches. on ittoprevent flotation. In eithercase,eachsideofthesquare The plateshouldhave placed 2.5feetofstone,gravel, orearth the circumference connection. oftherisertoformawatertight steel plateattachedtotheriserby acontinuousweld around inches intotheconcrete base,or(2)1/4”minimumthickness (1) Aconcrete base12inchesthickwiththeriserembedded9 weight to prevent flotationoftheriser. Two approved basesare: Anchoring Weight: Therisershouldhave abasewithsufficient horizontally around thepipe. and10to12inches diameter holesspaced8inchesvertically with1-inch The top2/3oftherisershouldbeperforated conditions. be subjecttodamagefrom vehicle trafficor from iceand frost may beconsidered, ifthepipingislocatedwhere itwillnot Plastic pipe (polyvinylchlorideorhigh-densitypolyethylene) metal. ofcorrugated The pipeandrisershouldbeconstructed riser.embankment, withaninletconsistingofaperforated A pipeoutletsedimenttraphasathrough the stone. crushed ofminimumsize 1½” The outletshouldbeconstructed embankment. natural ground, asdeterminedatthedownstream sideofthe The stonesectionshouldbelocatedatthelow pointofthe

4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • • Vegetation: • Combination ofEarth, Stone, orPipe Outlets: Practice recommendations forPermanent Vegetation Best Management vegetative growing seasonshouldbevegetated usingthe Basins thatwillbecarriedover thewinter andintothenext Management Practice describedinthismanual. the recommendation ofthe Temporary Vegetation Best growing season,thestructure maybevegetated using If thestructure isnotplannedfor more thanonevegetative ofthestructure. completion oftheconstruction below thestructure shouldbevegetated within72 hours of spillways,anddisturbedareasAll embankments,earth maximum drainagearea of5acres. 24” CMPriser(adequatefor2acres) couldbeusedforthe 3 acres) andapipeoutletwithan18”CMPbarrel witha For spillwayoutlet(adequatefor instance,a16.5-footearth sedimenttrapmayhave acombinationofoutlets. A temporary the following table: The minimumpipesizes shouldbedeterminedasprovided in Drainage Area Maximum (acres) 5 4 3 2 1

Barrel Diameter Minimum (inches) 30 24 21 18 15 Minimum Riser Diameter (inches) 24 21 36 30 30 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices 4-2. Sediment Control Practices • C • • • The sedimentbasin’s is designedto: than sedimenttraps. engineered largerareas impoundmentstructures, andmayserve Sediment basinsdifferfrom sediment traps,inthatbasinsare embankment orby excavating adepression. Sediment adamor basinsmaybemadeby constructing Flocculants shouldonlybeused uponapproval by NHDES. description oftheFlocculants Best Management Practice). be enhancedby theintroduction offlocculants(seeseparate to settle.Inthe sedimentparticles someinstances, settlingmay allowingby temporarily storingsediment-ladenrunoff, timefor capture andstore sedimentand/ordebris.Sediment isremoved to A sedimentbasinisawaterimpoundmentconstructed G i s n o l a r e n e o conditions exist: Sediment basinsshouldonlybeusedwhere thefollowing Provide storageofthetrappedsedimentanddebris. subsequent depositionindownstream drainagewaterways; Trap siteandprevent sedimentoriginatingfrom construction downstream waterways; Detain stormwater volume andslowly release ittothe o d utilities. ofpublic oftheuseorservice or railroads; orinterruption homes, commercial orindustrialbuildings, mainhighways, Failure ofthedamwillnotresult inlossoflife; damageto s n o i t a r e D n o i t p i r c s e Sediment Temporary Basin

• • • • • • • minimize thenumberofsedimentbasins required. Overall planninganddesignshouldbe carefully considered to habitats. Theseconditionsmustbeconsidered inthedesign. downstream water quality, wetlands andwater-related wildlife Pond activitiesmayaffect locationsandconstruction cold-water streams. exercised tonotlocatedischargesfrom sedimentbasinsnearto water temperatures thanthenaturalcondition.Care mustbe Sediment basins,likedetentionponds,canresult inwarmer enhance settlingofthesematerials. measures (suchasuseofflocculants)are implemented to for anextendedperiodoftime,orunlessothertreatment in thewaterandwilltravel off-siteunlessthewaterisdetained grained sedimentssuchassiltsandclayswillremain suspended Sediment basinsmostlytrapcoarse-grainedsediments.Fine- undisturbed areas canbeexcluded from thestructure. Sediment basinsshouldbeinstalledwhere from runoff disturbed area orsedimentsource. A sedimentbasinshouldbeinstalledasclosepossibletothe infiltration function). (such aspotentialcloggingofsoilsintendedtoprovide future useasasedimentbasin be adversely affected by temporary In somecases,thelong-termoperatingintegrityofabasincan design oftheproject, andauthorized by thedesignengineer. unlessspecificallyprovidedshould notbeundertaken inthe project. facility forthefinalconstructed However, thispractice permanent useasadetentionbasinorwaterqualitytreatment It ispossibletouseabasinthatdesignedforeventual o o o o Volume 2oftheNew Hampshire Stormwater Manual. applicable toimpoundmentembankments,asidentifiedin The basinisdesignedinaccordance withthepractices New Hampshire. The basinisdesigned by a Professional Engineer licensedin

4-2. Sediment Control Practices 4-2. Sediment Control Practices of thebasin,corrective measures needtobeimplementedkeep their installation.If there isanyevidenceofsiltationdownstream Sediment basininstallations needtoberegularly inspectedduring M • • • • • • • sediment from enteringdownstream areas. e c n a n e t n i a disposed ofandstabilized. The materials removed from thebasinshouldbeproperly volume ofthebasin. ofthetotal storage volume istypicallyonlyasmallportion sediment storagevolume. Note thatthedesignsediment capacity whensedimenthasaccumulatedtotheoriginal design Sediment shouldberemoved andthetraprestored tooriginal has becomecloggedwithsediment. should becheckedperiodicallyandreplaced whenthematerial Geotextile fabricorstoneusedaround apipe-outletriser source of sedimentation. erosion control measures shouldbeappliedtoeliminatethe are functioningandifsedimentationisapparent, additional monitored duringstormevents todeterminehow well they The waterdischargedfrom sedimentbasinsshouldbe activities. of seepage,andare notdamagedby erosion orby construction ensure thattheyare sound,are structurally notshowing signs Embankments shouldbeexaminedatthetimeofinspectionto immediately ifanysuchdamageisobserved. at thetimeofinspectionforanydamage,andrepaired Outlet structures andemergencyspillwaysshouldbeexamined and are notdamaged.Repairs shouldbemadeimmediately. rainfall periods),toinsure thattheyare functioningproperly storm(ordailyduringprolonged andafterevery construction Sediment basinsshouldbeinspectedatleastweekly during R e r i u q e m s t n e • Sediment basinsmust meetthefollowing requirements: S • • • • • s n o i t a c i f i c e p be stabilized immediatelyaftertheirconstruction. The sideslopesofthebasin shouldbe3:1orflatter, andshould expected tobetrapped. stormwater volume tobedetainedplus thevolume ofsediment The capacityofthesedimentbasinshouldbeequalto the be 3,600cubicfeetofstorageforeachacre ofdrainagearea. The minimumsedimentstorage volume ofthebasinshould o o o erosion. the 10-year frequency dischargewithoutfailure orsignificant An outletstructure shouldbeprovided adequatetohandle tomaintainthepond’snecessary capacity. expected tobetrapped.Periodic removal ofsedimentwillbe stormwater volume tobedetainedplusthevolume ofsediment The capacityofthesedimentbasinshouldbeequalto disturbance requiredconstruction toinstallthisBMP. downstream waterbodiesfrom sedimentationduetothe ofthesedimentbasintoprotect during theconstruction Erosion andsedimentcontrol measures shouldbeemployed season. with vegetation, theymustbeinstalledearlyinthegrowing the watershedabove them.If sedimentpondswillbestabilized Basins andstabilized priortodisturbing mustbeconstructed o o o protection shouldbeprovided. stabilized channelorastormsewersystem.Outlet must emptyontoundisturbedground, intoawatercourse, The outletshoulddischargetoastabilized area. Theoutlets Volume 2oftheStormwater Manual. embankment provides theminimumfreeboard specified in Outlets should bedesignedsothatthetopof that erosion atorbelow theoutlet doesnotoccur. in suchamannerthatsedimentdoesnotleave thetrapand andmaintained The outletshouldbedesigned,constructed

4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • • • • gravel. be installedaround theriserpriortoplacementof material.Ageotextilefilter should tofilterfineparticulate serve risersurrounded bywith aperforated agravel cone.Thiswill A sedimentbasinwithapipeoutletstructure shouldbefitted measures.structural sediment basinuntiltheisstabilized withvegetative or time limitwillnotapply. Water shouldnotbedirected tothe measures suchasriprapwillbeusedforfinalstabilization,this approved long-termstabilizationmeasure. If structural sideslopesmustbestabilized withanalternativeOtherwise, 15th ifvegetative measures willbeusedforfinalstabilization. sediment basinsmustbecompletedandseededby September BMP, BMP. orotherappropriate structural of Allconstruction with thePermanent Vegetation BMP, Temporary Mulching within seven calendardaysofthatdisturbanceinaccordance All areas shouldbestabilized disturbedduringconstruction fill. of thestorm.Theemergencyspillwayshouldnotbeinstalledin assuming thatthebasinisfulltodesigndepthatbeginning 50-year design stormwithoutdamagetotheembankment, An emergencyspillwayshouldbeprovided tosafelypassthe Basins mustbedesignedtodrainedwithina3-dayperiod. planned effective lifeofthestructure. the erosion so thatexpectedsedimentationwillnotshorten The drainagearea above thepondmustbeprotected against construction. in Volume 2oftheNHStormwater Manual forembankment regulations, andshouldmeetthedesignrequirements identified Embankments shouldbedesignedtomeetapplicable 4-2. Sediment Control Practices 4-2. Sediment Control Practices • • • • activitiesmustbeconductedto: dewatering Construction of thosewaterbodies. such aslakes,wetlands, orstreams, withsubsequentsedimentation pumped watermaydischargetodowngradient naturalresources to selectthepointofdischargeandprovide adequatetreatment, the theseenclosedareas.use ditchpumpstodewater If care isnottaken ortokeepwork conditionssafe.Contractorstypically performed water needstoberemoved before operationscanbe certain collect rain,ground orseepagewaterwithinthework area. This existing gradetrapeitherrainwaterorgroundwater, andcofferdams operations.Excavationsdewatering thatdonot“daylight” to Construction sites in New Hampshire typically require construction areas thattrapstormwaterandgroundwater. from excavations,during construction cofferdams, andotherwork sedimentation associatedwiththemanagementofwaterremoved practiceisintendedtoprevent dewatering This construction G C l a r e n e above objectives. Choose thebestlocationfordischargeinorder tomeetthe Preserve downgradient naturalresources andproperty. Remove sedimentfrom thecollectedwater. Prevent thedischargedwaterfrom eroding soilonthesite. onstruction D n o i t p i r c s e Dewatering • C • • • M • • • i s n o e c n a n e t n i a sedimentation ofdownstream receiving waters. assess whetheradditionaltreatment canbeprovide toprevent The visualqualityoftheeffluent shouldbemonitored to buffer’s vegetation orunderlyingsoil. sign oferosion orconcentrationofflow thatmaydamagethe Special attentionshouldbepaidtothebufferarea forany conditions. more aswarrantedby site frequent orcontinuoussupervision facilityshouldberevieweddewatering atleastdaily, with During theactiveprocess, dewatering inspectionofthe area shows anysignofinstabilityorerosion. The dischargeshouldbestoppedimmediatelyifthe receiving wetlands, intermittent streams, waters. orothersurface waterto dewatering that propose todischargeconstruction Dewatering General permitforprojectsthe Construction local, state,andfederalagenciesmustbemet,including All requirements ofstatelawandpermitrequirements of in accordance withNHDESrequirements. mustbecontained, treated,runoff anddischargedor removed products, or toxic andhazardous materials.Contaminated withoil,grease, dewatering otherpetroleumconstruction Care mustbeexercised toprevent contact ofwaterfrom discharges. for filtrationandabsorptionofsuch the bestopportunity process. Wooded buffersandflattomoderateslopes provide landscape’s abilitytotreat waterflows from thedewatering to thedowngradient waterresources andtheexisting The dischargeareas shouldbechosenwithcareful consideration d s n o i t a r e R e r i u q e m s t n e

4-2. Sediment Control Practices 4-2. Sediment Control Practices treatment ofthecollectedwater. the removal ofthecollectedwaterwithinexcavation andthe Dewatering excavated areas isconductedintwodistinctoperations: S • Sediment Removal: • • • • • • Water Removal: s n o i t a c i f i c e p sediment thatacontractormay use. Typical measures include There are anumberof methods forsettlingorfiltering avoided. Dewatering duringperiodsofintense,heavyrainshould be the basin. toprevent scouringofthesoilin geotextile maybenecessary sediment removal area. Asplashpadofriprapunderlainwith Bucketed watershouldbedischargedinastablemannertothe a stoneliningorotherstabilizingmeasure shouldbeused. channels, thenthechannelshouldbere-stabilized; ifnecessary, discharge tothem.If flow velocities causeerosion withinthese from theexcavated area shouldbestablepriortodirecting All channels,swales,andditchesdugfordischargingwater pumping ofwell points. be withdrawnfrom theground adjacenttoanexcavation by scoop anddumpwaterfrom theexcavation. Water mayalso equipmentto siphoning, andusingthebucketofconstruction to gravitydrainagethrough channels,mechanicalpumping, accomplished by numerous methods,includingbutnotlimited The removal of waterfrom theexcavated area canbe trench. place theexcavated materialon theupgradientsideof For trench excavation, limitthetrench lengthto500feetand allowedclean stormwaterrunoff intotheexcavated area. Install diversion ditchesorberms tominimize theamountof • • Manufactured Devices: • • • • • Temporary basindesignsincludebutare notlimitedto: Temporary Basin Designs: • product. removal, suchasamanufactured silt“bag” orothersimilar manufactured filterstructure specificallydesignedforsediment Water operationsmaybedischarged toa from construction description ofSEDIMENTBASINinthismanual. detention ponds),ifdesignedinaccordance withthe A sedimentbasin(includingtemporarilymodifiedstormwater SEDIMENT TRAP inthismanual. Excavated orbermedsedimentationtrap. See thedescriptionof designed forsedimentremoval. Chambered settlingsystemfabricatedofconcrete orsteeland from collapsing undertheweight ofimpoundedwater. fence orhaybales.Silt toprevent fencemustbesupported it or both.Erosion control mix also maybeincorporatedwithsilt enclosure withhaybales,siltfence, constructed A temporary An enclosure ofJersey Barriers linedwithgeotextilefabric. and minimizingtheslopeofbufferarea. should maximize thedistancetonearest waterresources possible toawell-vegetated bufferthrough sheetflow and Sediment removal structures shoulddischargewherever and filterflow. structure’s volume capacityorthestructure’s capacitytosettle Flow tothesedimentremoval structure mustnotexceed the bags designedforfilteringpumpeddischarges. basinsorsedimenttraps,andmanufactured fabric temporary

4-2. Sediment Control Practices 4-2. Sediment Control Practices • Discharges: • • area isshowing anysignofinstabilityorerosion. The dischargeshouldbestoppedimmediatelyifthe receiving Never dischargetoareas thatare bare vegetated. ornewly enters thebuffer. long asamethodisusedtospread flow intosheetflow asit into well-vegetated buffered areas withlessthan2%slope,as contact withothercontaminants,maybedirectly discharged Water thatisvisiblyclearofsediment,andhasnotcomeinto 4-2. Sediment Control Practices 4-2. Sediment Control Practices G • • The useofflocculantsmustconsiderthefollowing: (BOD) inthedownstream receiving waters. aquatic lifeandshouldnotincrease Biochemical OxygenDemand selected forusemustbenon-toxic andsafeforbothhuman There isa variety offlocculantmaterials available. Any product removing from suspension. fineandcolloidalparticles erosion ofthesesoilsinthefirstplace,becausedifficulty in criticaltopreventamounts offinesiltsandclays,itisparticularly siteischaracterizedIf by aconstruction soilswithsignificant need tobeconsidered toprevent impactstoreceiving waters. materials are present insignificantquantities,othermeasures will canremainparticular insuspensionindefinitely. Whenthesesoil in techniques suchassedimenttrapsorbasins.Colloidalparticles Fine siltsandclaysare difficultto remove withconventional settling C Flocculants shouldonlybeuseduponapproval by NHDES. fines removed during thedetentionperiod. would beremoved andcanincrease thepercentage of otherwise the abilityofthesesettlingfacilitiestoremove than finerparticles prior todischarge. stormwater runoff Use offlocculantsimproves sediment trapstoremove from suspendedclayandfinesiltparticles Flocculants canbeusedinconjunction withsedimentbasinsand stormwater. group togethertoformflocs,whichsettleoutofdetained particles (clay)tocoagulate.Thecoagulated that causecolloidalparticles Flocculants (orcoagulants)are naturalmaterialsorchemicals i s n o l a r e n e on asite-specificbasis. Flocculants require specificdosingratesthatmustbe developed typeandconcentration. the soilparticle Selection ofanappropriate flocculantishighlydependenton d s n o i t a r e D n o i t p i r c s e Flocculants • • • • • • S on aproject. staff atthetimethatflocculants are reviewedandapproved foruse flocculants shouldbedeterminedincoordination withNHDES Site-specific maintenance requirements applicabletotheuseof M professionals, andaccording toNHDESregulations. circumstances, andshouldbeusedunderthedirection ofqualified For thesereasons, flocculantsare typicallyonlyused in special • • s n o i t a c i f i c e p e c n a n e t n i a Alteration of Terrain regulations (AoT) (Env-Wq 1506.12). procedures andmaterialsspecifications outlinedintheNH Flocculants shouldonlybeusedinstrictaccordance withthe waters. Turbidity violationsare describedinEnv-Wq 1703.11. turbidity violationsandsedimentationindownstream receiving alone orincombination,willnotbesufficientto prevent othererosion controlon-site claycolloidalparticles, measures, approval ofsuchusedemonstrates thatduetothepresence of Flocculants shouldnotbeusedunlessthepersonrequesting NHDES inwriting. waterunlessspecificallyapprovedfeet ofanysurface by the Flocculants shouldnotbeapplieddirectly toorwithin100 measures tominimize theneedtouseflocculants. Sites shouldbestabilized assoon aspossibleusingconventional approvedotherwise by NHDES. system capacity, anduponcompletionoftheproject unless Flocculated materialmustbe periodically removed tomaintain by settling. monitored toensure thatthechemicalisadequatelyremoved When flocculantsare used,thedischargemustbecarefully to provide detentiontimeforsettling. thenecessary Settling basinsmust have sufficient volumeand flow capacity being treated. Flocculants mustbethoroughly mixed withthestormwater R e r i u q e m s t n e

4-2. Sediment Control Practices