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 Kevin D. Blayton, PE City Engineer - Public Works Director December 8, 2016
Main Street Design/Permitting
Main Street Project Design Goals!! 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 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)
Drainage Basin Map 2 nd Ave. North Beach Outfall Proposed Outfall 3 rd Ave. South 1 st Ave. South 2 rd Ave. South Existing 6 th Ave. South Outfall 72 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
Outfall Plan View Landside Off-Shore Side Overall Project
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
Storm Drainage Plume Atlantic Ocean Beach 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.
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
Structure #2 & 2A Structure #3 Structure #8 Structure #1 Structure #5 Structure #9 Structure #6 Main Street (Street-End) Land Side
Off Shore Side Landside 60 Check Valve Outfall Pipe Structure #1
Structure #3 Structure #2A Structure #2 Example of Sediment Box Design
96 Snout BENEFITS!! Removal of Oil and Sediments!! Reduction of Coliforms!! Removal of Floatables!! Bacteria Kill (Bio-Skirt) Structures #2 & 2A Example of Sediment Box Design
BENEFITS!! Trap of Oil and Sediments!! Traps of Floatables!! Settlement of Solids and Grit!! Bacteria Kills (Bio-Skirt)!! Low Head Loss Example of The Snout
Catch Basin with Deep Sumps and Hoods
Sediment Boxes
WQ Sampling Protocol Dr. Susan Libes Director, Waccamaw Watershed Academy Professor of Marine Science and Chemistry Burroughs & Chapin Center for Marine & Wetland Studies Coastal Carolina University
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Sampling Site Map 1 st Ave S Phase I only 2 nd Ave N Main St OuFall Pipe Phase II only
Pollutants of concern Ambient Water Quality Criteria R.61-68 Fecal Indicator Bacteria Enterococcus (recrea2onal saltwater indicator) E. coli (recrea2onal freshwater indicator) Sediment Turbidity Total suspended solids and vola2le solids Poten2al contributors to low oxygen (hypoxia) Vola2le solids Biochemical Oxygen Demand (5-day) Nutrients (Total Nitrogen & Total Phosphorus (par2culate and dissolved), nitrate + nitrite, orthophosphate)
Equipment deployment In-situ measurements Measured in one-minute intervals Parameters: Water level Water velocity Water discharge Temperature Conduc2vity Dissolved oxygen
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&$#0*4%& A#8/&N+& _ /3 &M.%& V&
Pollutant behavior in untreated flows NSQD = EPA s Na,onal Stormwater Quality Database Fecal bacteria: consistently contravene water quality criteria, especially at Main Street. All E. coli above NSQD median. Total suspended solids: maximum loads of 30 to 35 lbs per event. Concentra2ons above NSQD median at Main Street. VolaLle solids: 30 to 100% of TSS, averaging 50% => organic rich! BOD: mostly > 5 mg/l with max of 25 mg/l. Above NSQD median at Main Street. Nutrients: 20% of nitrogen and 40 to 60% of phosphorus is par2culate and should be sehable. Levels generally above US EPA eutrophica2on criteria. TP and Orthophosphate above NSQD median. One site was a pond that had no ou<low during Phase I. Elevated bacteria and nutrients. Perfect BMP!
Outfall pipe results Sensors have been in place since Dec 2015 with some interrup2ons for comple2on of overland construc2on. Preliminary observa2ons Tidal behavior which complicates load reduc2on assessments Resulted in some upstream flow adjustments Current configura2on Maximum velocity = 2.8 j/s Tidal range = 10 to 15 inches Conduc2vity is similar to untreated flows, but shows some brief increases on the start of the ebb 2de that might be backflow. Oxygen levels are very low prior to ini2a2on of flows.
Outfall pipe hydrograph Sensors located between sediment and mixing boxes. Depending on when the rain hits on a 2dal cycle, runoff flushes through in one to two cycles. Other perspec2ve on load calcula2ons. 60 50 40 30 20 10 0-10 1:12 August 18, 2016 Ou<all Pipe Storm Event Q max = 3.6 cfs 93,407 gallons 6:00 10:48 15:36 20:24 Water Level (in) Velocity x 10 (X/s) Rainfall (in) 1:12 6:00 10:48 15:36 0.00 0.05 0.10 0.15 0.20 0.25 0.30
Current status! V17&1/&$+#/39J&+1& )#*+,-%&a,#485j8/c&-#8/& %.%/+$>&!!,44%3&#/3&-%*4#)%3&C%#-& 8/&S)+19%-&+1& #))10013#+%&n,--8)#/%& A#h"%7>& n,--8)#/%&q1#a,8/&s)+19%-&_^dt&! @%417U0%38#/&*-%)8*8+#21/& *-%38)+%3&51-&+"8$&78/+%-&3,%& +1&g#&V8o#&)1/3821/$>&! H=*%)+%3&+1&9%&$"1-+&48.%3p&
Construction
INSTALLED SMALLER SNOUT WITH BIO-SKIRT
Typical Sheeting Wall Trestle Typical Pipe Laying (Surf Zone) (Trench Sheeting)
Vacuum -10.0 psi to -11.0 psi Equals 55,471 lbs Force
Pipe Sleepers
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