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HomeMy Public PortalAboutHDSU - Vortechs Maintenance GuideENGINEERED SOLUTIONS Vortechs® Guide Operation, Design, Performance and Maintenance 2 3 Vortechs® The Vortechs system is a high-performance hydrodynamic separator that effectively removes finer sediment (e.g. 50-microns (µm), oil, and floating and sinking debris. The swirl concentration operation and flow controls work together to minimize turbulence and provide stable storage of captured pollutants. Precast models can treat peak design flows up to 30-cfs (850-L/s); cast-in-place models handle even greater flows. A typical system is sized to provide a specific removal efficiency of a predefined particle size distribution (PSD). Operation Overview Stormwater enters the swirl chamber inducing a gentle swirling flow pattern and enhancing gravitational separation. Sinking pollutants stay in the swirl chamber while floatables are stopped at the baffle wall. Vortechs systems are usually sized to efficiently treat the frequently occurring runoff events and are primarily controlled by the low flow control orifice. This orifice effectively reduces inflow velocity and turbulence by inducing a slight backwater that is appropriate to the site. During larger storms, the water level rises above the low flow control orifice and begins to flow through the high flow control. Any layer of floating pollutants is elevated above the invert of the Floatables Baffle Wall, preventing release. Swirling action increases in relation to the storm intensity, while sediment pile remains stable. When the storm drain is flowing at peak capacity, the water surface in the system approaches the top of the high flow control. The Vortechs system will be sized large enough so that previously captured pollutants are retained in the system, even during these infrequent events. As a storm subsides, treated runoff decants out of the Vortechs system at a controlled rate, restoring the water level to a dry- weather level equal to the invert of the inlet pipe. The low water level facilitates easier inspection and cleaning, and significantly reduces maintenance costs by reducing pump-out volume. Design Basics Each Vortechs system is custom designed based on site size, site runoff coefficient, regional precipitation intensity distribution, and anticipated pollutant characteristics. There are two primary methods of sizing a Vortechs system. The first is to determine which model size provides the desired removal efficiency at a given flow for a defined particle size or PSD. The second and more in depth method is the summation of Rational Rainfall Method™ which uses a summation process described below in detail and is used when a specific removal efficiency of the net annual sediment load is required. Typically Vortechs systems are designed to achieve an 80% annual solids load reduction based on lab generated performance curves for either 50-µm particles, or a particle gradation found in typical urban runoff (see performance section of this manual for more information). The Rational Rainfall Method™ Differences in local climate, topography and scale make every site hydraulically unique. It is important to take these factors into consideration when estimating the long-term performance of any stormwater treatment system. The Rational Rainfall Method combines site-specific information with laboratory generated performance data, and local historical precipitation records to estimate removal efficiencies as accurately as possible. 2 3 High Flow Control The high flow control, or weir, is sized to pass the peak system capacity minus the peak orifice flow when the water surface elevation is at the top of the weir. This flow control is also a Cippoletti type weir. The weir flow control is sized by solving for the crest length and head in the following equation: Qweir = Cd •L• (h)3/2 Where: Qweir = flow through weir, cfs (L/s) Cd = Cippoletti weir coefficient = 3.37 (based on lab testing) h = available head, ft (m) (height of weir) L = design weir crest length, ft (m) Bypass Calculations In most all cases, pollutant removal goals can be met without treating peak flow rates and it is most feasible to use a smaller Vortechs system configured with an external bypass. In such cases, a bypass design is recommended by Contech Engineered Solutions for each off-line system. To calculate the bypass capacity, first subtract the system’s treatment capacity from the peak conveyance capacity of the collection system (minimum of 10-year recurrence interval). The result is the flow rate that must be bypassed to avoid surcharging the Vortechs system. Then use the following arrangement of the Francis formula to calculate the depth of flow over the bypass weir. H = (Qbypass /(Cd • L))2/3 Where: H = depth of flow over bypass weir crest, ft (m) Qbypass = required bypass flow, cfs (L/s) Cd = discharge coefficient = 3.3 for rectangular weir L = length of bypass weir crest, ft The bypass weir crest elevation is then calculated to be the elevation at the top of the Cippoletti weir minus the depth of flow. Hydraulic Capacity In the event that the peak design flow from the site is exceeded, it is important that the Vortechs system is not a constriction to runoff leaving the site. Therefore, each system is designed with enough hydraulic capacity to pass the 100-year flow rate. It is important to note that at operating rates above 100-gpm/ft2 (68-Lps/m2) of the swirl chamber area (peak treatment capacity), captured pollutants may be lost. When the system is operating at peak hydraulic capacity, water will be flowing through the gap over the top of the flow control wall as well as the orifice and the weir. Short duration rain gauge records from across the United States and Canada were analyzed to determine the percent of the total annual rainfall that fell at a range of intensities. US stations’ depths were totaled every 15 minutes or hourly and recorded in 0.01-inch increments. Depths were recorded hourly with 1-mm resolution at Canadian stations. One trend was consistent at all sites; the vast majority of precipitation fell at low intensities and high intensity storms contributed relatively little to the total annual depth. These intensities, along with the total drainage area and runoff coefficient for each specific site, are translated into flow rates using the Rational Rainfall Method. Since most sites are relatively small and highly impervious, the Rational Rainfall Method is appropriate. Based on the runoff flow rates calculated for each intensity, operating rates within a proposed Vortechs system are determined. Performance efficiency curve determined from full scale laboratory tests on defined sediment PSDs is applied to calculate solids removal efficiency. The relative removal efficiency at each operating rate is added to produce a net annual pollutant removal efficiency estimate. Once a system size is established, the internal elements of the system are designed based on information provided by the site engineer. Flow control sizes and shapes, sump depth, oil spill storage capacity, sediment storage volume and inlet and outlet orientation are determined for each system. In addition, bypass weir calculations are made for off-line systems. Flow Control Calculations Low Flow Control The low flow control, or orifice, is typically sized to submerge the inlet pipe when the Vortechs system is operating at 20% of its treatment capacity. The orifice is typically a Cippoletti shaped aperture defined by its flat crest and sides which incline outwardly at a slope of 1 horizontal to 4 vertical. Qorfice = Cd • A • 2gh Where: Qorifice = flow through orifice, cfs (L/s) Cd = orifice coefficient of discharge = 0.56 (based on lab tests) A = orifice flow area, ft2 (m2) (calculated by orifice geometry) h = design head, ft (m) (equal to the inlet pipe diameter) g = acceleration due to gravity (32.2-ft/s2 (9.81-m/s2) The minimum orifice crest length is 3-in (76-mm) and the minimum orifice height is 4-in (102-mm). If flow must be restricted beyond what can be provided by this size aperture, a Fluidic-Amp™ HydroBrake flow control will be used. The HydroBrake allows the minimum flow constriction to remain at 3-in (76-mm) or greater while further reducing flow due to its unique throttling action. 4 5 Performance Full Scale Laboratory Test Results Laboratory testing was conducted on a full scale Vortechs model 2000. The 150-µm curve demonstrates the results of tests using particles that passed through a 60-mesh sieve and were retained on a 100-mesh sieve. The 50-µm curve is based on tests of particles passing through a 200-mesh sieve and retained on a 400-mesh sieve (38-µm). A gradation with an average particle size (d50) of 80-µm, containing particles ranging from 38–500-µm in diameter was used to represent typical stormwater solids. (Table 1) As shown, the Vortechs system maintains positive total suspended solids (TSS), defined by the tested gradations, removal efficiencies over the full range of operating rates. This allows the system to effectively treat all runoff from large, infrequent design storms, as well as runoff from more frequent low-intensity storms. Typical Vortechs systems are designed to treat peak flows from 1.6-cfs (45-L/s) up to 30-cfs (850-L/s) online without the need for bypass. However, external bypasses can be configured to convey peak flows around the system if treatment capacity is exceeded. The system can also be configured to direct low flows from the last chamber of the system to polishing treatment when more stringent water quality standards are imposed. In all configurations, high removal efficiencies are achieved during the lower intensity storms, which constitute the majority of annual rainfall volume. Full report available at www.conteches.com/vortechs. Particle Size Percentage of Sample Distribution (µm) Make-Up <63 42% 63 - 75 4% 75 - 100 9% 100 - 150 7% 150 - 250 11% >250 27% Table 1: Particle gradation of typical urban runoff used for efficiency curve 0 (0)10 (7)20 (14)30 (20)40 (27)50 (34)60 (41)70 (48)80 (54)90 (61)100 (68) 20% 0% 40% 60% 80% 100% Operating Rate gpm/ft2 (L/s/m2)Removal Efficiency50-micron 150-microntypical gradation Figure 1: Vortechs model 2000 Removal Efficiencies Laboratory Testing Full reports available at www.conteches.com/vortechs Technical Bulletin 1: Removal Efficiencies for Selected Particle Gradations Technical Bulletin 2: Particle Distribution of Sediments and the Effect on Heavy Metal Removal Technical Bulletin 3: Sizing for Net Annual Sediment Removal Technical Bulletin 3a: Determining Bypass Weir Elevation for Off- Line Systems Technical Bulletin 4: Modeling Long Term Load Reduction: The Rational Rainfall Method Technical Bulletin 5: Oil Removal Efficiency Field Monitoring Following are brief summaries of the field tests completed to date. Full reports available at www.conteches.com/vortechs DeLorme Mapping Company Yarmouth, ME Contech Engineered Solutions Prior to this premier field test of the Vortechs system, Contech developed an extensive body of laboratory data to document total suspended solids (TSS) removal efficiency. Contech performed this field study in order to compare the performance predicted using laboratory data to the performance of a correctly sized system in the field. The study site was the headquarters of DeLorme Mapping in Yarmouth, Maine. The building, driveway, parking lot and ancillary facilities were constructed in 1996. A Vortechs model 11000 was installed to treat runoff from the 300-space, 4-acre (1.62-ha) parking lot. The main purpose of the DeLorme study was to verify that the sizing methodology developed from our full-scale laboratory testing was valid and an accurate means of predicting field performance. The results of the study confirmed our sizing methodology. Village Marine Drainage Lake George, NY New York State Department of Environmental Conservation, Division of Water The New York State DEC used funds obtained in a Section 319 grant to initiate a study of the effectiveness of the Vortechs system to remove sediment and other pollutants transported Testing Period May 1999 to Dec 1999 # of Storms Sampled 20 Mean Influent Concentration 328-mg/L Mean Effluent Concentration 60-mg/L Removal Efficiency 82% Timothy Edwards Middle School South Windsor, CT UCONN Department of Civil & Environmental Engineering This study of the Vortechs system was published as a thesis by Susan Mary Board, as part of the requirements for a Master of Science degree from the University of Connecticut. Her objective was to determine how well the Vortechs system retained pollutants from parking lot runoff, including total suspended solids (TSS), nutrients, metals, and petroleum hydrocarbons. A Vortechs model 5000 was installed in 1998 to treat runoff from the 82-space parking lot of Timothy Edwards Middle School. The entire watershed was approximately 2 acres (0.81 ha), and was 80% impervious. Additionally, the Vortechs system was particularly effective in removing zinc (85%), lead (46%), copper (56%), phosphorus (67%) and nitrate (54%). The study concluded that the Vortechs system significantly reduced effluent concentrations of many pollutants in stormwater runoff. 4 5 by stormwater to Lake George, Lake George Village, New York. “Since the 1970s, when there was a rapid increase in the rate and concentration of development along the southwestern shores of Lake George, we have been concerned about the impact of stormwater discharges into the lake,” said Tracy West, co-author of the study. The study concluded that the Village and Town of Lake George should consider installing additional Vortechs systems in areas where sedimentation and erosion have been identified as non- point source pollution problems. Harding Township Rest Area Harding Township, NJ RTP Environmental Associates This third party evaluation was performed under a U.S. Environmental Protection Agency grant, administered by the New Jersey Department of Environmental Protection. A. Roger Greenway, principal of RTP Environmental Associates, Inc., conducted the study in conjunction with Thonet Associates, which assisted with data analysis and helped develop best management practices (BMP) recommendations. The Vortechs model 4000 was sized to handle a 100-year storm from the 3 acre (1.21 ha) paved parking area at the Harding Rest Stop, located off the northbound lane of I-287 in Harding Township, New Jersey. The study concluded that truck rest stops and similar parking areas would benefit from installing stormwater treatment systems to mitigate the water quality impacts associated with stormwater runoff from these sites. Testing Period Feb 2000 to Dec 2000 # of Storms Sampled 13 Mean Influent Concentration 801-mg/L Mean Effluent Concentration 105-mg/L Removal Efficiency 88% Testing Period May 1999 to Nov 2000 # of Storms Sampled 5 Mean Influent Concentration (TSS) 493-mg/L Mean Effluent Concentration (TSS) 35-mg/L Removal Efficiency (TSS) 93% Mean Influent Concentration (TPH) 16-mg/L Mean Effluent Concentration (TPH) 5-mg/L Removal Efficienty (TPH) 67% Testing Period Jul 2000 to Apr 2001 # of Storms Sampled weekly composite samples taken Mean Influent Concentration 324-mg/L Mean Effluent Concentration 73-mg/L Removal Efficiency 77% 6 7 Maintenance The Vortechs system should be inspected at regular intervals and maintained when necessary to ensure optimum performance. The rate at which the system collects pollutants will depend more heavily on site activities than the size of the unit, e.g., unstable soils or heavy winter sanding will cause the swirl chamber to fill more quickly but regular sweeping will slow accumulation. Inspection Inspection is the key to effective maintenance and is easily performed. Pollutant deposition and transport may vary from year to year and regular inspections will help ensure that the system is cleaned out at the appropriate time. Inspections should be performed twice per year (i.e. spring and fall) however more frequent inspections may be necessary in equipment washdown areas and in climates where winter sanding operations may lead to rapid accumulations. It is useful and often required as part of a permit to keep a record of each inspection. A simple inspection and maintenance log form for doing so is provided on the following page, and is also available on conteches.com. The Vortechs system should be cleaned when inspection reveals that the sediment depth has accumulated to within 12 to 18 inches (300 to 450 mm) of the dry-weather water surface elevation. This determination can be made by taking two measurements with a stadia rod or similar measuring device; one measurement from the manhole opening to the top of the sediment pile and the other from the manhole opening to the water surface. Note: To avoid underestimating the volume of sediment in the chamber, the measuring device must be carefully lowered to the top of the sediment pile. Finer, silty particles at the top of the pile typically offer less resistance to the end of the rod than larger particles toward the bottom of the pile. Cleaning Cleaning of the Vortechs system should be done during dry weather conditions when no flow is entering the system. Clean- out of the Vortechs system with a vacuum truck is generally the most effective and convenient method of excavating pollutants from the system. If such a truck is not available, a “clamshell” grab may be used, but it is difficult to remove all accumulated pollutants using a “clamshell”. In installations where the risk of petroleum spills is small, liquid contaminants may not accumulate as quickly as sediment. However, an oil or gasoline spill should be cleaned out immediately. Motor oil and other hydrocarbons that accumulate on a more routine basis should be removed when an appreciable layer has been captured. To remove these pollutants, it may be preferable to use adsorbent pads to solidify the oil since these pads are usually much easier to remove from the unit individually and less expensive to dispose of than the oil/water emulsion that may be created by vacuuming the oily layer. Floating trash can be netted out if you wish to separate it from the other pollutants. Cleaning of a Vortechs system is typically done by inserting a vacuum hose into the swirl chamber and evacuating this chamber of water and pollutants. As water is evacuated, the water level outside of the swirl chamber will drop to a level roughly equal to the crest of the lower aperture of the swirl chamber. The water outside the swirl chamber should remain near this level throughout pumping as the bottom and sides of the swirl chamber are sealed to the tank floor and walls. This “water lock” feature prevents water from migrating into the swirl chamber, exposing the bottom of the baffle wall and creating excess pump-out volume. Floating pollutants will decant into the swirl chamber as the water level is drawn down. This allows most floating material to be withdrawn from the same access point above the swirl chamber. Floating material that does not decant into the swirl chamber during draw down should be skimmed from the baffle chamber. If maintenance is not performed as recommended, sediment may accumulate outside the swirl chamber. If this is the case, it may be necessary to pump out other chambers. It is advisable to check for sediment accumulation in all chambers during inspection and maintenance. These maintenance recommendations apply to all Vortechs systems with the following exceptions: 1. It is strongly recommended that when cleaning systems larger than the Model 16000 the baffle chamber be drawn down to depth of three feet prior to beginning clean-out of the swirl chamber. Drawing down this chamber prior to the swirl chamber reduces adverse structural forces pushing upstream on the swirl chamber once that chamber is empty. 2. Entry into a Vortechs system is generally not required as cleaning can be done from the ground surface. However, if manned entry into a system is required the entire system should be evacuated of water prior to entry regardless of the system size. Manhole covers should be securely seated following cleaning activities to prevent leakage of runoff into the system from above and also to ensure proper safety precautions. If anyone physically enters the unit, Confined Space Entry procedures need to be followed. Disposal of all material removed from the Vortechs system should be done in accordance with local regulations. In many locations, disposal of evacuated sediments may be handled in the same manner as disposal of sediments removed from catch basins or deep sump manholes. Check your local regulations for specific requirements on disposal. Contech has created a network of Certified Maintenance Providers (CCMP’s) to provide maintenance on Vortechs systems. To find a CCMP in your area please visit www.conteches.com/ maintenance. Vortechs Inspection & Maintenance Log 6 7 1. The water depth to sediment is determined by taking two measurements with a stadia rod: one measurement from the manhole opening to the top of the sediment pile and the other from the manhole opening to the water surface. If the difference between these measurements is less than eighteen inches the system should be cleaned out. Note: To avoid underestimating the volume of sediment in the chamber, the measuring device must be carefully lowered to the top of the sediment pile. 2. For optimum performance, the system should be cleaned out when the floating hydrocarbon layer accumulates to an appreciable thickness. In the event of an oil spill, the system should be cleaned immediately. Date Water depth to sediment Floatable layer thickness Describe maintenance performed Maintenance personnel Comments Vortech Model: ________________________________Location: _______________________________________________________ 800-338-1122 www.conteches.com ENGINEERED SOLUTIONS Support • Drawings and specifications are available at www.conteches.com. • Site-specific design support is available from our engineers. © 2015 Contech Engineered Solutions LLC Contech Engineered Solutions LLC provides site solutions for the civil engineering industry. Contech’s portfolio includes bridges, drainage, sanitary sewer, stormwater, earth stabilization and wastewater treatment products. For information on other Contech division offerings, visit conteches.com or call 800.338.1122 NOTHING IN THIS CATALOG SHOULD BE CONSTRUED AS AN EXPRESSED WARRANTY OR AN IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. SEE THE CONTECH STANDARD CONDITION OF SALES (VIEWABLE AT WWW.CONTECHES.COM/COS) FOR MORE INFORMATION. The product(s) described may be protected by one or more of the following US patents: 5,322,629; 5,624,576; 5,707,527; 5,759,415; 5,788,848; 5,985,157; 6,027,639; 6,350,374; 6,406,218; 6,641,720; 6,511,595; 6,649,048; 6,991,114; 6,998,038; 7,186,058; 7,296,692; 7,297,266; related foreign patents or other patents pending. vx_manual 04/15 PDF Revision