December 8, 2016

CITY OF NORTH MYRTLE BEACH OCEAN OUTFALL PROGRAM

Reduction of Pollutant Load as a Stormwater Management Option

Strategies and Tools to Protect and Restore Coastal Water Quality

CITY OF NORTH MYRTLE BEACH

Kevin D. Blayton, PE

City Engineer - Public Works Director

Main Street Design/Permitting

!! Eliminate Five (5) Drainage Outfalls from the Beach

!! Improve Water Quality Using BMP’s

!! Reduce/Eliminate Beach Advisories

!! Improve Drainage Characteristics and Reduce Flooding

!! Establish Baseline for Future Projects

!! Monitor and Report Water Quality

!! BMP Performance

!! Pre and Post Construction Monitoring

Main Street Project Design Goals

Main Street Basin Characteristics

!! 100± Acre Drainage Basin - Combination of five (5) Drainage Basins into one (1)

!! Highly Impervious (70%)

!! Flooding between 2 and 10-Year Storm Events

!! Existing Topography (from elevation 25.0’ – 7.0’)

!! All Stormwater Ultimately Outfalls to the Beach

!! Poor Water Quality

!! Beach Advisories (after certain rainfall events)

Existing 6th Ave. South Outfall 72”

3rd Ave. South

2rd Ave. South

1st Ave. South Proposed Outfall

2nd Ave. North Beach Outfall

Drainage Basin Map

Existing Beach Outfalls

Existing Main Street Ocean Outfall (before project)

Existing Water Quality Issues

!! 70% or Greater of Drainage Basin is Impervious Area -! Pavement, Roads / Parking Lots -! Roof Tops -! Coquina Parking Lots

!! Limited Available/Existing BMP’s

- Older Developments Prior Stormwater Regulations

!! Debris, Floatables, and Sediment Oils/Greases - Sand -! Plastics -! Cigarette Butts, Etc.

!! Beach Advisories !! Public Health Impacts

!! Community Business Impacts

!! Beach Erosion

Landside

Overall Project

Off-Shore Side

Outfall Plan View

Development of the plume in the presence of a cross current, which flows from

left to right and is indicated by red dye.

Stormwater Plume

Ocean Currents

Far-field plume development. Contours mark the isolines of constant levels of single sample concentration of bacteria per 100ml. The regulatory contour is 104 bacteria per 100 ml of water. The two culverts are shown as black lines.

Storm Drainage Plume

Beach

Atlantic Ocean

Permitting

Federal •! Environmental Protection Agency (EPA) •! U.S. Fish & Wildlife Service •! National Oceanic and Atmospheric Administration (NOAA) •! United States Coast Guard •! U.S. Army Corp of Engineers

State •! S.C. Department of Health and Environmental Control (SCDHEC) •! S.C. Department of Natural Resources (SCDNR) •! S.C. Historic Preservation Office (SCHPO) •! SCDHEC Ocean and Coastal Resource Management (SCOCRM)

Over 2! Year Process

BMP Selection

Use of Best Management Practices (BMP’s)

!! Sediment Boxes Upstream and Downstream (debris and floatables)

!! “The Snout” Catch Basin with Deep Sumps and Screens (debris, floatables, oils / greases)

!! Catch Basin Inserts (debris and sediments)

!! Bioskirts (oil / greases and kill bacteria)

!! Street Sweeping

!! Vacuum Truck for Maintenance of System (vacuum sediments and debris from catch basins)

!! Pollution Prevention / Good Housekeeping

!! Public Education

!! Ocean Water / Plume Study

!! Use of Sea Water for Passive Treatment Within Outfall Pipe

Land Side

Structure #1

Structure #2 & 2A Structure #3

Structure #8

Structure #6 Structure #9 Structure #5

Main Street (Street-End)

Structure #1

60” Check Valve

Outfall Pipe

Off Shore Landside Side

Example of Sediment Box Design

Structure #2A

Structure #3

Structure #2

Example of Sediment Box Design

BENEFITS !! Removal of Oil and Sediments !! Reduction of Coliforms !! Removal of Floatables !! Bacteria Kill (Bio-Skirt)

96” Snout

Structures #2 & 2A

Example of “The Snout”

BENEFITS

!! Trap of Oil and Sediments

!! Traps of Floatables

!! Settlement of Solids and Grit

!! Bacteria Kills (Bio-Skirt)

!! Low Head Loss

Catch Basin with Deep Sumps and Hoods

Sediment Boxes

WQ Sampling Protocol

Dr.SusanLibesDirector,WaccamawWatershedAcademyProfessorofMarineScienceandChemistry

Burroughs&ChapinCenterforMarine&WetlandStudies

CoastalCarolinaUniversity

Water Quality Assessment: Objectives and Plan •!!"#$%&'(&)#*+,-%&%.%/+&0%#/&)1/)%/+-#21/$&#/3&*144,+#/+&41#3$&51-&,/+-%#+%3&617&#+&+"-%%&$8+%$&+"#+&-%*-%$%/+&#91,+&::;&15&+"%&617&8/+1&+"%&1,<#44&91=>&&?"-%%&%.%/+$&)10*4%+%3>&

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SamplingSiteMap

1stAveSPhaseIonly

MainSt

OuFallPipePhaseIIonly

2ndAveN

Pollutants of concern

•  FecalIndicatorBacteria•  Enterococcus(recrea2onalsaltwaterindicator)•  E.coli(recrea2onalfreshwaterindicator)

•  Sediment•  Turbidity•  Totalsuspendedsolidsandvola2lesolids

• Poten2alcontributorstolowoxygen(hypoxia)•  Vola2lesolids•  BiochemicalOxygenDemand(5-day)•  Nutrients(TotalNitrogen&TotalPhosphorus(par2culateanddissolved),nitrate+nitrite,orthophosphate)

AmbientWaterQualityCriteriaR.61-68

In-situmeasurements•  Measuredinone-minuteintervals•  Parameters:

•  Waterlevel•  Watervelocity•  Waterdischarge•  Temperature•  Conduc2vity•  Dissolvedoxygen

Equipment deployment

Phase I hydrographs •!Z#+%-&4%.%4&$"17/&9%417&78+"&0#=80,0&38$)"#-C%&-#+%&P)5$Q&#/3&+1+#4&-,/1]&.14,0%>&&

•! R%-J&6#$"J>&&H.%/+&8$&31/%&78+"8/&#&5%7&"1,-$&$1&$#0*48/C&"#$&+1&9%&5#$+>&

•! V%%3&#+&4%#$+&^>_T`&-#8/&+1&C%/%-#+%&$,B)8%/+&617&+1&$#0*4%&

A#8/&N+& _/3&M.%&V&V&

Pollutant behavior in untreated flows NSQD=EPA’sNa,onalStormwaterQualityDatabase

• Fecalbacteria:consistentlycontravenewaterqualitycriteria,especiallyatMainStreet.AllE.coliaboveNSQDmedian.

• Totalsuspendedsolids:maximumloadsof30to35lbsperevent.Concentra2onsaboveNSQDmedianatMainStreet.

• VolaLlesolids:30to100%ofTSS,averaging50%=>organicrich!• BOD:mostly>5mg/Lwithmaxof25mg/L.AboveNSQDmedianatMainStreet.

• Nutrients:20%ofnitrogenand40to60%ofphosphorusispar2culateandshouldbesehable.LevelsgenerallyaboveUSEPAeutrophica2oncriteria.TPandOrthophosphateaboveNSQDmedian.

• Onesitewasapondthathadnoou<lowduringPhaseI.Elevatedbacteriaandnutrients.PerfectBMP!

Outfall pipe results •  SensorshavebeeninplacesinceDec2015withsomeinterrup2onsforcomple2onofoverlandconstruc2on.

• Preliminaryobserva2ons•  “Tidal”behaviorwhichcomplicatesloadreduc2onassessments•  Resultedinsomeupstreamflowadjustments

• Currentconfigura2on•  Maximumvelocity=2.8j/s•  “Tidal”range=10to15inches•  Conduc2vityissimilartountreatedflows,butshowssomebriefincreasesonthestartoftheebb2dethatmightbebackflow.

•  Oxygenlevelsareverylowpriortoini2a2onofflows.

0.00

0.05

0.10

0.15

0.20

0.25

0.30-10

0

10

20

30

40

50

60

1:12

6:00

10:48

15:36

20:24

1:12

6:00

10:48

15:36

WaterLevel(in)

Velocityx10(X/s)

Rainfall(in)

Outfall pipe hydrograph •  Sensorslocatedbetweensedimentandmixingboxes.

•  Dependingonwhentherainhitsona2dalcycle,runoffflushesthroughinonetotwocycles.

•  Otherperspec2veonloadcalcula2ons.

August18,2016Ou<allPipeStormEvent

Qmax=3.6cfs93,407gallons

Current status •! V17&1/&$+#/39J&+1&)#*+,-%&a,#485J8/C&-#8/&%.%/+$>&

•! !,44%3&#/3&-%*4#)%3&C%#-&8/&S)+19%-&+1&#))10013#+%&n,--8)#/%&A#h"%7>&

•! @%417U0%38#/&*-%)8*8+#21/&*-%38)+%3&51-&+"8$&78/+%-&3,%&+1&g#&V8o#&)1/3821/$>&

•! H=*%)+%3&+1&9%&$"1-+&48.%3p&

n,--8)#/%&q1#a,8/&S)+19%-&_^DT&

Construction

INSTALLED SMALLER SNOUT WITH BIO-SKIRT

Typical Pipe Laying (Surf Zone)

(Trench Sheeting)

Trestle

Typical Sheeting Wall

Vacuum -10.0 psi

to -11.0 psi Equals

55,471 lbs Force

Sleepers

Pipe

Completed Project – Facing Seaward

Completed Project – Facing Landward

QUESTIONS?

With the Assistance of DDC Engineering American Bridge

RH Moore CCU Center for Marine and Wetland Studies