PLANNING FOR THE FUTURE: A REGIONAL MASTER PLAN APPROACH WITH THE OPPORTUNITY TO MINIMIZE FUTURE OPERATION AND MAINTENANCE CONCERNS

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1 PLANNING FOR THE FUTURE: A REGIONAL MASTER PLAN APPROACH WITH THE OPPORTUNITY TO MINIMIZE FUTURE OPERATION AND MAINTENANCE CONCERNS ABSTRACT Robert Skip Notte*, PE, LEED AP, Dewberry, snotte@dewberry.com Erik Messina, EI, Dewberry The Stockbridge Area Wastewater Master Plan investigated an 840 acre service area in York County South Carolina centered around the intersection of Gold Hill Road and South Carolina Highway 160. This service area is part of the overall collection and conveyance system for York County and is supported by the Jackson Branch Interceptor. The service area is located at the top of the overall interceptor service area. York County partnered with Dewberry to provide a phased build-out plan over a 25-year period to obtain a road map for future capital improvement projects and allow for direction to private developers. In the development of this master plan, the project team was required to create an existing conditions baseline for the service area that involved as-built plan investigation, in-field survey, flow monitoring and rainfall data collection, and the development of a new sewer system model. To develop and calibrate the new sewer model, the project team was required to combine the newly collected data with theoretical flow data to generate multi-year extended simulations. One of the initial challenges of this project included the balance of the cost associated with an investigative technique vs. the ultimate benefit of the data that would be collected. The project team worked diligently in the development of the project scope and work activities to ensure that the final master plan could be an accurate account of existing and future events, while not over-studying or investigating any one aspect of the project area. Upon completion of the existing conditions model and assumptions, the project team investigated different development alternatives, providing three overall Options for the County. The first option continued with the current approach that the County has been facing in this service area since its inception, developer constructed systems that are donated to the County upon completion. However, the existing topography across the service area has forced, and will continue to force multiple pump stations that are likely to serve a single private development. The second and third Options considered the elimination of two existing pump stations, and the potential of three more future stations, to develop a regional approach to a portion of the service area. This approach required a detailed implementation plan and capital improvement program to ensure coordination with current and future developers. KEYWORDS Master Plan, Waste Water Model, Capital Improvement Projects, Flow Monitoring, Inflow, Infiltration, York County, Pump Station, Regional INTRODUCTION The Stockbridge Area Wastewater Master Plan investigated an 840 acre service area in York County South Carolina centered around the intersection of Gold Hill Road and South Carolina Highway 160. This service area is at the top of the Jackson Branch Interceptor, and is a geographic region which has previously experienced and is anticipated to experience significant growth over the next planning horizon (25 year period). Based on the goal of understanding the limitations of the current collection and conveyance system, and the opportunities for expansion and upgrade to support the future needs of the service area, York County contracted with Dewberry to complete an in-depth analysis of the project area and prepare a master plan. The in-depth analysis was to include the following: (1) identification of existing pump station and forcemain condition(s), pump rate(s), and available capacity; (2) identification of existing gravity collection and conveyance system average daily flow rate, peak flow rate, and available capacity; (3) identification of projected growth within the service area, type of

2 land use, and timing for growth over the 25 year planning horizon; (4) preparation of a waste water model to replicate the existing conditions and provide guidance on potential improvements required to support future growth projections; and (5) identification of capital improvement projects associated with projected growth, including anticipated costs. The development of the master plan was completed with close coordination with County Personnel from both the Engineering Department and the Public Works Department, and drew upon existing information provided by the County, as well as new information obtained through field verification. METHODOLOGY The project methodology was broken down in to three distinct tasks: (1) evaluation of the existing waste water system, (2) development of service area growth projections, and (3) preparation of a future demand analysis. Evaluation of the existing waste water system The Dewberry Team initiated the project by evaluating the existing data and information provided by the County. This existing data included previous master plans for the larger service area, of which the Stockbridge Service Area was a sub-drainage area, as well as previous design notes and plans for most of the collection and conveyance system. In addition, field investigation of the three (3) pump station in the service area, along with draw down tests, were completed to verify existing conditions versus theoretical design conditions. These draw down tests immediately drew attention to the fact that each of the three (3) County owned pump stations are currently not operating near their original design points. Two of the stations are operating below their design rates by up to 60%, and one station is operating above its design point by approximately 35%. Table 1 provides the results of the draw down tests.

3 Table 1 STOCKBRIDGE SERVICE AREA COUNTY OWNED/OPERATED PUMP STATION DRAW DOWN TEST RESULTS Date Pump Station Pump Design Flow (GPM) Design Dynamic Head (Feet) Actual Flow (GPM) Actual Dynamic Head (Feet) 9/25/13 Stockbridge NA 9/25/13 Stockbridge ** NA 10/3/13 Stockbridge /3/13 Stockbridge ** /3/13* Stockbridge /3/13* Stockbridge ** /25/13 Palmetto Plantation 1(Stg 1 & 2) /74, /81, /3/13* Palmetto Plantation 1(Stg 1 & 2) /74, *** 80.75/80.75, /3/13* Palmetto Plantation 2(Stg 1 & 2) /74, /85.5, 171 9/25/13 Palmetto /25/13 Palmetto /3/13 Palmetto /3/13 Palmetto /3/13 Palmetto /3/13 Palmetto * Only the Stockbridge PS or Palmetto Plantation PS was operating during test to ensure that coupled forcemain was providing results specific to the respective pump station. **Pump 2 includes a mixing valve to break-up grease in the wetwell. It is believed that this mixing valve may not be functioning correctly, resulting in a decrease of flow rate through the pump. Therefore, the pump 2 flow rate will not be considered in the current overall flow rate for the station. *** Flow rate assumed to be an anomaly based on September 25, 2013 rate for same pump setup. Therefore, this test will not be considered in the current overall flow rate for the station.

4 Upon completion of the evaluation of existing data, it was quickly identified that there were several sections of the collection and conveyance system that the County did not have the original design documentation. Each of these sections were evaluated for significance when developing the new waste water model for the service area, and field topographic and location data was obtained for sections required to ensure adequate calibration of the model. At the same time, the Dewberry Team began a 30-day flow monitoring period of the existing collection and conveyance system, which ultimately expanded to 49-days based on the need to obtain data from significant rain events. The service area was broken into six (6) sub-drainage areas, and two rain gauges were included in the data collection. The information gathered during the flow monitoring period was utilized to calibrate the existing conditions waste water model, verify the significance of inflow and/or infiltration on system capacity, adjust triggers for upgrading system features, and validate waste water demands for growth projections. Table 2 provides a quick overview of the flow monitoring results. Table 2 Flow Monitor Location STOCKBRIDGE SERVICE AREA FLOW MONITORING RESULTS Average Percent of Peak Daily Percent of Daily Flow Est. Flow (GPD) Est. (GPD) Capacity* Capacity* Sewer Pipe Size (Inches) Peak 15- Min Flow (GPM) Percent of Est. Capacity* ,000 16% 567, % % ,000 14% 280, % % , % 270, % % , % 287, % % , % 196, % % , % 109, % % The completion of this phase of the master plan development resulted in a calibrated existing conditions waste water model that accurately reflected the flows being experienced by the system and the County. The model platform used for this master plan was the Innovyze InfoSewer program. Development of service area growth projections After development of the existing conditions waste water model, the Dewberry team worked with the County to identify the service area growth projections. These projections included the anticipated development and redevelopment of land within the service area, along with anticipated waste water flows from different types of land uses. The thorough existing system evaluation and model calibration allowed for the standardization of multiple parameters that would be used in the growth projections. These parameters included: percentage of land use, development density, flow rates, peaking factors, and pump station run periods. In addition, five (5) time-steps were identified as analysis points for the master plan. They were based on 5 year increments with the build-out occurring 25 years in the future. Preparation of future demand analysis Once the growth projections were developed, the future waste water system analysis was completed. This included a 24-hour extended period simulation that brought different parcels of land (with a future projected land use) into the model in one of the five, 5 year time-steps. In addition, a conceptual layout of the future collection and conveyance system was developed to support the new parcels, as well as evaluation of the diminishing capacities within the current collection and conveyance system. The conceptual layout of the future collection and conveyance system offered three Options for the overall service area, with two of the Options varying based on forcemain alignment and discharge point. RESULTS

5 Option 1 included proceeding with the current development approach for the County within the services area, which allows individual developers to create collection and conveyance systems for specific projects, with little or no regard to the adjacent parcels, and then convey the ownership of the system to the County once the project is complete. This approach resulted in the potential of four new pump stations within a ½ mile radius, which also includes two existing County owned stations, for a total of six pump stations within a ½ mile radius. In addition to the significant amount of pump stations in a small geographic area, the majority of the waste water was passing through a minimum of two stations, and some was being pumped three times before discharge to the Jackson Branch Interceptor. Option 1 also required significant improvements to the existing collection and conveyance system due to the path of the waste water from the northwest to the southeast. The overall project costs of all capital improvements outlined in Option 1 at build-out were estimated at $4,424,000. Options 2 and 3 eliminated the potential for three of the four future pump stations, and two of the existing County owned pump stations in the northwest corner of the service area, by creating a new regional interceptor and pump station. These two options varied only by the alignment and discharge location of the new regional pump station forcemain. There were pro s and con s to the new regional forcemain alignment and discharge location, which included the potential need for upsizing 7,000 linear feet of gravity sewer, versus the installation of variable frequency drives at the new regional pump station and one of the other County owned pump stations due to manifolding of forcemains. The overall project costs of all capital improvements outlined in Option 2 and 3 at build-out were estimated at $6,607,000 and $5,535,000, respectively. DISCUSSION AND CONCLUSION The Stockbridge Area Waste Water Master Plan provides York County with a road map for the future development in this 840 acre service area. The development of a new waste water model, using the Innovyze InfoSewer platform, allowed for an analysis of the existing and future collection and conveyance system which yielded a strong recommendation to support a new regional interceptor and pump station. In addition, the thorough collection of field data through the completion of pump station draw down tests and flow monitoring, allowed for the identification of potential operational and maintenance concerns, as well as recalibration of some County Standards. The large variation in the existing pump station draw down test results versus the original design calculations and verification originally provided some concern about the current capacity within the system. However, through confirming interviews of maintenance personnel regarding zero to minor instances of sanitary sewer overflows, it is believed that each of the pump stations were originally constructed to support larger flows, therefore, had not reached a critical level where the flow rate variations had become a concern. Additional investigation appeared to indicate that the manifolding of forcemains for two pump stations, and the short run time of the third pump station, are likely the culprits for the decrease in pumping capacity at two of the pump stations. There is a high probability that on a continual basis, the pump stations with decreased pumping capacity are no longer reaching 2 feet per second (FPS) in their respective forcemains, and solids are no longer being scoured during a pump run cycle. This build-up of solids would then increase the overall dynamic head for each pump station by decreasing forcemain diameter, resulting in a lower flow rate. As stated above, the data obtained through the flow monitoring activity was used to calibrate the existing conditions waste water model, verify the significance of inflow and/or infiltration on system capacity, adjust triggers for upgrading system features, and validate waste water demands for growth projections. This empirical data became the foundation for the development of the waste water model, and helped to adjust some of the parameters used by the County. First, the data confirmed that the land use demand projections used by previous County projects were conservative, while the waste water treatment plants hydraulic loadings for residential units was more applicable to what is being experienced by the current collection and conveyance system. Second, the lack of recorded inflow or infiltration during the flow monitoring period provided the County with an understanding that their current collection system was well constructed and there is minimal potential of lost capacity due to rain water runoff. This information also allowed the County to relax some of their typical triggers for requiring upsizing of gravity sewer pipes based on percent full capacity. Previously, the County would require upsizing of 10 diameter and less gravity sewer when the capacity reached 50%, and 12 diameter and greater when the capacity reached 75%. However, based on the flow monitoring data, the 10 diameter and less pipe triggers

6 were raised 10% to 60%, and the 12 diameter and greater pipe triggers were raised 5% to 80%. This contributed to a reduction in the overall length of gravity sewer requiring upsizing in the 25 year planning period by up to 50% depending on the Option selected. The ability for the County to reduce the overall future operation and maintenance of the service area through the implementation of a regional interceptor and pump station was well received by both the Engineering Department and Public Works Department. The concerns with Option 1 centered on the multiple pump stations, which would required the County to potentially ensure continual operation of as many as seven pump stations for the 840 acre service area, not to mention the inefficiency of having to pump the waste water, re-pump the waste water, and in some instances, pump the waste water again to get it to the Jackson Branch Interceptor. Even though six of the seven pump stations would likely be small (10 horsepower or less), the inefficiency of this option in regards to sewage age, odor control, power, and wear and tear on materials and equipment quickly outweighed the anticipated reduction in capital cost (between $1.1 Million and $2.2 Million dollars). As stated earlier, the difference between Option 2 and 3 is alignment and discharge location of the forcemain from the new regional pump station. While the forcemain for Option 2 was shorter, it also required the upsizing of approximately 7,000 LF of gravity sewer through existing residential developments. Option 3 requires a longer forcemain, the manifolding of the forcemains from two pump stations, and the installation of variable frequency drives to minimize the potential of significant head/flow rate variation, but has been proven to be the most desirable Option for the County at an overall project cost that is approximately $1 Million less than Option 2. In conclusion, this master plan provided the County with three Options to address the growth in the Stockbridge service area. After evaluation of the existing conditions, proposed growth over a 25 year build-out horizon, and total project costs, Option 3 became the recommended path forward. This Option provides for a regional approach to handling waste water in this service area, and significantly reduces the number of pump stations that the County would likely own and operate in the future.