The URL can be used to link to this page

Home My WebLink AboutDRAFT Tech Memo - Placement of GAC Contractor and Greensand Filter Pressure VesselsKennedy/Jenks Consultants Draft Technical Memorandum Prepared for: Prepared by: Reviewed by: J. D. Wilson, P.E. Ray Sled, P.E. City of Renton Water Utility Chris Kelsey, P.E. Milt Larsen, P.E., Kennedy/Jenks Consultants Greg Pierson, P.E., HDR Date: 27 February 2007 K/J No. 0697005.01 Subject: City of Renton, Washington Well 5A Treatment Facility Pre-Design Considerations Placement of GAC Contactor and Greensand Filter Pressure Vessels Overview and Purpose This techhical memorandum has been prepared as part of Task 2-300 of the Renton Well 5A Water Treatment Improvements Project. The purpose of this memorandum is to provide an overview and comparative evaluation for placement of the GAC contactors and greensand filter pressure vessels that will be incorporated within the design of the new treatment facility for Well 5A. The two general alternatives discussed involve the advantages/disadvantages associated with either interior or exterior placement of the vessels. The following assumptions are made as part of this memorandum: • The materials of construction for the pressure vessels, piping, and appurtenances would remain the same, regardless of interior or exterior placement, and differences in cost for the specified paint coating systems of each are inconsequential. Grated platforms, to provide operators access to the access hatches, piping, and equipment located on the upper portions of the vessels, are assumed to be desirable and equivalent with both alternatives. • Operation and maintenance (O&M) costs are considered to be equivalent between the two options, even though some subtle differences exist. Among these differences are exterior vessels might require slightly more frequent painting and maintenance due to exposure to weather, whereas interior vessels would necessitate more energy cost associated with HVAC (including increased dehumidifying for condensation control) and could also require additional capital cost for a larger sprinkler system that would be required under a building "H" occupancy rating. Though the O&M would likely be slightly higher for interior placement, estimating costs associated with these potential differences are felt to be unnecessary in making an overall decision on which way the City of Renton (City) proceeds. Therefore, a life cycle cost analysis is not considered, and cost comparisons will be based solely on conceptual level opinions of probable construction costs. • The filter face piping and electric motor actuated valves would be located inside the building for both options. W:\2006\0697005.01_HDR Renton Well\06-Corrspnd\6.03-Other\2007\02cwk1tm.Pressure Vessel Placement TM.doc Kennedy/Jenks Consultants J. D. Wilson, P.E. Ray Sled, P.E. City of Renton Water Utility 27 February 2007 Page 2 Pressure Vessel Sizing The Well 5A Pilot Test Report by HDR evaluated different hydraulic loading rates across the granular activated carbon media in the contactors and the greensand/anthracite cap media within the pressure filters. The loading rates were varied from 5 to 12 gallons per minute (gpm) per square foot (ft^^ for each of the two treatment processes, which were typically connected in series under varying chemical treatment techniques and in the presence of different varieties of greensand media (GS and GS+). The results of testing indicated that effective removal of manganese, the most difficult constituent to remove, was obtained at maximum loading rates of 12 gpm/ft^, though the efficacy and reliability were better at a rate of 10 gpm/ft^. For this reason, a design criteria target loading rate for filtration of 10 gpm/ft^ is recommended. Given the City's desire to attempt to fully utilize their maximum instantaneous water right (Qi) of 1500 gpm, a surface area of 150 ft^ is needed for both the GAG and greensand media beds. In order to furnish some level of production redundancy, but at the same time limit the number of vessels, two GAG contactors and two greensand pressure vessels are recommended. Each of the four vessels has an approximate square footage of 78.5 ft^. These sizes were endorsed by three locally represented pressure vessel/greensand filter suppliers. Note with the flow split between two vessels in a unit process, it will be necessary to shut down the well while the backwash sequence as it is not desirable to double the flow rate through one vessel to approximately 20 gpm/ft^ while the other is being backwashed. The vessel heights are determined through manufacturer recommended media depths necessary to achieve adequate empty bed contact times (EBGT) that will adequately reduce hydrogen sulfide levels through the GAG contactors and iron and manganese in the greensand filters. Additional depth is required for upper and lower distribution systems, and adequate freeboard to achieve desired media expansion during backwashing. It is anticipated that these design parameters will be similar to the Maplewood facility. Conceptual Level Construction Cost Comparison Based on allowing adequate Spacing between filters for maintenance access and piping connections, a general footprint necessary to accommodate the filters is recommended to be a rectangular area of 65 feet long by 18 feet wide, or approximately 1,170 ft^. This area is also illustrated in the preliminary building layout, included with this memo as Attachment A. If the vessels were placed within the treatment facility building, they would then logically add 1,170 ft^ of additional square footage to the building size, with associated additional material costs. If the vessels were placed outside, the building could not only be reduced in footprint, but also in height, as the vessels would likely govern the necessary eave height. For aesthetic reasons, a perimeter curtain wall, assumed to be of GMU construction, could be provided on two sides of the slab that supports the vessels. A security fence could be installed across the backside if desired. W:\2006\0697005.01_HDR Renton Well\06-Corrspnd\6.03-Othef\2007\02cwk1tm.Pressufe Vessel Placement TM.doc J. D. Wilson, P.E. Ray Sled, P.E. City of Renton Water Utility 27 February 2007 Page 3 Kennedy/Jenks Consultants Table 1 offers a conceptual level opinion of probable construction cost for the two alternatives, and includes only the differing items discussed above in order to establish a comparative cost associated with this issue. Other building costs are not considered. The table indicates that, on a conceptual level, approximately $400,000 in capital costs could be saved by placement of the vessels outside. Table 1: Table 1; Costs Alternative/Item Conceptual Level Opinion of Probable Construction Installed Material Quantity Assumptions Instaiied Unit Price Assumptions Capitai Cost Exterior Piacement 1170 ft^ concrete slab 12-inch slab $500/CY material $40/CY excavation/fill $23,400 Structure OMU curtain wall 10-foot height 36 LF for 2 sides $25/SF material $9,000 Subtotal $32,400 Sales tax 8.8% Mobilization, bond, and insurance 10%$29,100 Contractor OH&P 22% Estimate contingency 30% TOTAL $61,500 Interior Placement 1170 ft^ Additional Building $200/SF material $234,000 10-to 16-foot eaves Additional Building Height 165 LF for 4 sides just building vessel area $25/SF material $24,800 Subtotal $258,800 Sales tax 8.8% Mobilization, bond, and insurance 10% Contractor OH&P 22% Estimate contingency 30% $232,400 TOTAL $491,200 Other Considerations Table 2 lists other additional considerations not included within the cost comparison, including advantages and disadvantages for each of the two alternatives. W;\2006\0697005.01_HDR Renton Well\06-Corrspnd\6.03-Other\2007\02cwk1tm.Pressure Vessel Plaqement TM.doc J. D.Wilson, P.E. Ray Sled, P.E. City of Renton Water Utility 27 February 2007 Page 4 Kennedy/Jenks Consultants Table 2: Table 2: Alternative Other Considerations Advantages Disadvantages Exterior Placement Lower HVAC requirements Operational noise, mostly associated with actuation of combination air valves Potential reduction in sprinkler system size ("H" occupancy) • Exposure of vessels and appurtenances to weather Lower interior condensation issues • Higher security/vandalism risk Easier vessel access for media loading/unloading • Exposure of operators to weather during maintenance • Easier control of combination air valve discharge Interior Placement Containment of noise • Higher HVAC requirements Vessels less vulnerable, more protected • Larger sprinkler system required with building "H" occupancy Operators protected from weather during maintenance • Increased need for dehumidification for condensation control • More difficult access for media loading/unloading • More difficult control of combination air valve discharge Recommendation Due to the capital cost savings, as well as the overall simplification of O&M requirements, the City should move forward with design of the new treatment facility for Well 5A with the pressure vessels located outside of the new building. Photos of a similar installation for a groundwater treatment facility are included as Attachment B. Attachments W:\2006\0697005.01_HDR Renton Well\06-Corrspnd\6.03-Other\2007\02cwk1tm.Pressure Vessel Placement TM.doc Attachment A Preliminary Building Layout W:\2006\0697005.01_HDR Renton Well\06-Corrspnd\6.03-Other\2007\02cwk1tm.Pressure Vessel Placement TM.doc PLOT DATE: 01/22/07 TIME: 13: 41 Renton Well 5A.dwg<Building) "fT CHLORINE CONTACT BASIN BW BASIN AREA RESERVED FOR FUTURE 02 STORAGE AND AIR EDUCTOR t P F ft PIPE GALLERY BW RE :ycle BW TO PUMPS 10' OR 12" ROLLUP DOOR BLOWERS MECHANICA 10'x 14 POLY PUMPS/BLOWERS 20' X 28 STANDBY GENERATOR 12'x20 ELECTRICAL 12'x20 CHEMICALS 20' X 24 HYPO CONTROL HW TANK SINK BACKFLOW PREVFLOUR LAV 10'x6 J DOUBLE DOORS 10'OR 12 ROLLUP DOOR 10' OR 12' ROLLUP DOOR HR City of Renton Renton Well 5A Possible Building Layout January 2007 FIGURE Attachment B Photos of Exterior Pressure Vessel installation W:\2006\0697005.01_HDR Renton Well\b6-Corrspnd\6.03-OtherV2007\02cwk1tm.Pressure Vessel Placement TM.doc *;?^^\\\\ fi m