Innovative Approach to Expanding the Olentangy WTP September 28, 2017 Spencer Sheldon, WTP Superintendent Bret M. Casey, P.E., BCEE
Who is Del-Co Water? Member owned 501-(c) Non-Profit Corporation Governed by a Board of 10 Directors Must be a member Serve 3 year terms 8 Delaware County members (max 2 per township) 1 Morrow County member 1 At-Large member (from any county) Incorporated in 1969, Served 1 st customer in 1974 Currently serving customers in Seven Counties (Delaware, Morrow, Marion, Knox, Franklin, Union and Crawford Counties)
Del-Co Service Area Del-Co Columbus 800 square miles 400 square miles Serves 140,000 people Serves 1,200,000 1800 mi of piping 3600 miles of piping 4 plants with 11 mgd average demand High seasonal peak demand 3 plants with 150 mgd average demand Moderate seasonal peak
1. Olentangy Plant Complex 19.2 MGD (28.8) 2. Ralph E. Scott Plant 6.55 MGD 3. Timothy F. McNamara Plant / Reservoirs 4.0 MGD 4. Morrow County Office 5. Thomas E. Steward Plant 6.0 MGD 6. City Columbus/Del-Co New Upland Reservoir 6 4 5 1 2 3
Del-Co Historic Peaking Factors Drive Expansion Needs
Olentangy WTP Expansion Additional treatment capacity necessary to meet future demands Master plan evaluated new plant vs. Olentangy expansion Expansion more cost-effective Expansion details 16.2 MGD pump station and pipeline to pump Del-Co s allocation from Columbus reservoir from O Shaughnessy to Olentangy WTP reservoirs Expand Olentangy WTP from 19.2 MGD to 28.8 MGD Columbus John R. Doutt Upground Reservoir
Olentangy WTP Original Design Started up in 2007 replaced an existing 7 MGD WTP (single-stage lime softening) Originally approved for 12.3 MGD (filters at 4 gpm/ft 2 ) with hydraulic capacity for 19.2 MGD. Filters were high-rated with successful demonstration study after startup to 6.25 gpm/ft 2. Current approved capacity is 19.2 MGD. Not intended to expand beyond 19.2 MGD source water limitations
Olentangy WTP Overview
Olentangy WTP Original Design Plant was designed as two-stage lime softening plant for several reasons 4 hours detention time required for treating surface water split between 1 st stage sedimentation and 2 nd stage softening basins. Separate sedimentation from softening. Avoids recycling taste and odor causing compounds in softening residuals. Potential for low ph coagulation for additional TOC removal.
Consistent, high quality, low turbidity raw water supply.
Plant Operational Experience with Two-Stage Softening Following startup, freezing in first stage basins during winter caused chains on chain and flight collectors to break. After startup, plant stopped feeding ferric to 1 st stage during cold months to avoid running collectors operated as single stage softening. Taste and odor issues experienced with previous plant have not occurred following startup of new plant. Plant has not fed PAC. Jar testing and full scale operational data have shown no additional TOC removal with low ph coagulation. Plant feeds less ferric with single stage operation than two-stage
Results of Original Demonstration Study UFRV Max Raw Turbidity Max Filter Influent Turbidity Summer two-stage Filter Run 1-6 Fall single-stage Filter Run 7-13 30000 25000 20000 Filter water turbidity < 0.1 NTU UFRV > 7000 gal/ft 2 14.00 12.00 10.00 Winter single-stage Filter Run 14-24 UFRV (Gal/SF) 15000 8.00 6.00 Turbidity (NTU) Spring two-stage Filter Run 25-31 10000 4.00 5000 2.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 0.00 Filter Run
Proposed Expansion Approach Master plan recommended the following to increase capacity: Raise 1 st stage basin walls Add plates or tubes to 1 st stage basins to increase loading rate of basins Add 3 rd solids contact clarifier Add two new filters Hazen recommended the following: Keep flow through 1 st stage at 19.2 MGD avoids modifications to basins During peak flows > 19.2 MGD, bypass a portion of the flow around 1 st stage directly to solids contact clarifier. Operate two solids contact clarifiers two-stage, one as single stage. OEPA Approved Capacity Document allows upflow clarifiers (with softening) at 1.75 gpm/ft 2. 4 hours detention time no longer required. Clarifiers designed for 1.5 gpm/ft 2.
However There was a catch The original filter demonstration study was done with a mix of single stage and two stage softening. EPA required an additional 30 day demonstration study with single stage softening. Demonstration done during May 2017. Not enough demand to run clarifier at rated capacity of 9.6 MGD. Bypassed finished water to reservoir.
Demonstration Study Description Plant flow maintained at 9.6 MGD rated capacity of one solids contact clarifier No ferric added in 1 st stage 9.6 MGD routed to single solids contact clarifier ferric and lime added Recarbonated water split between two filters. High rate filter operated at 6.25 gpm/ft 2, control filter at 3.1 gpm/ft 2. 0-2.5 MGD finished water discharged to furthest upstream reservoir to maintain 9.6 MGD through plant.
Results of Updated Demonstration Study All filtered water turbidity samples generally < 0.1 and all samples < 0.3 NTU TOC removal average 45% (25% required) UFRV (gal/sf) 25000 20000 15000 10000 60 50 40 30 20 Filter Run Time (hrs) UFRV range 7800 19,900 gal/ft 2 5000 10 Water fleas in Reservoir 4 reduced filter run times for runs 12-16. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Filter Run High-Rate Filter UFRV Run Time 0
Update Approach operate singlestage except during WQ events in reservoirs HAB event (has not occurred) Water fleas
Additional Water Quality Evaluation Scope Evaluated WQ changes associated with blending water from Scioto. Minimal impact to plant raw water. Evaluated GAC not needed for meeting Stage 2 D/DBP
Additional Water Quality Evaluation Scope Evaluated UV not needed for meeting LT2. Del-Co decided to install UV for added barrier (no disinfection credit). Evaluated chlorate issues related to sodium hypochlorite. Installing dilution system with hypo as part of expansion to reduce degradation/chlorate issues.
Project Status Demonstration study approved operation in single-stage at 6.25 gpm/ft 2 filtration rate. Final plan approval items being resolved Project to bid October 2017, substantial completion scheduled June 2019 Project funding through USDA loan Project includes: 3 rd solids contact clarifier Two new filters, two UV reactors downstream of filters Additional 1 mgal clearwell Chemical feed improvements
Thank You