Capacity Assessment Models: Engineering and Operational Uses April 16, 2013 Chip Smith, PE Woolpert, Charlotte NC David Powell, PhD, PE Woolpert, Chesapeake VA Special Thanks to City of Hampton Public Works
Presentation Outline q Development of the Capacity Assessment Model Ø Why Required by a Regional Consent Order for SSOs Ø How Overview of the development of the Model q Other Uses for the Model were created Ø System capacity for new development Ø Investigating potential rehabilitation issues Ø Operations and Maintenance Identifying 2 nd Tier Cleaning Locations
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Chesapea ke Bay City of Hampton Overview Atlantic Ocean
Regional System Includes > 500 Miles of Interceptors and 82 Regional Pump Stations
City Hampton Sewer Collection System q Wastewater Operations Division Ø 104 sewage pump stations Ø 11,055 manholes Ø 477 miles of sanitary sewer piping Ø 136 square miles of coverage Ø 46,054 customer accounts Founded in 1613 Ø Collects/transports ~ 8.5 MGD to HRSD on dry days Ø 70 MGD wet weather peak
Hampton s Capacity Assessment Model q Regional Consent Order Requirements Ø Baseline Dry Weather Flows Ø 2, 5, 10 -Year Peak Flow Recurrence Ø Current System Configuration Ø Current Conditions with 2030 Population Ø Identify Locations of Simulated SSOs Ø Identify Surcharged MHs < 1.5 feet Below Rim q Hampton wanted an all pipes model Ø 73% of system is > 50 years old Ø In-fill development is an issue
Capacity Assessment Challenges q 35 PS s connected to HRSD Force Mains Ø Subject to varying HRSD pressures q 300+ City Gravity connections to HRSD Gravity Mains Ø Subject to HRSD surcharging q Capacity Assessment Divided into Phases Ø Simulated overflows checked by free discharge runs Ø PS s analyzed at Policy Head Design Condition Ø PS s analyzed at Actual Head HRSD Model
Capacity Assessment Results 11,000 Structures in System q Results for Dry Weather Flow Conditions Ø 48 structures exceeded 1.5 foot free board criteria q Results for 2-yr Rain Peak Flow Event Ø 72 structures q Results for 5-yr Rain Peak Flow Event Ø 162 structures q Results for 10-yr Rain Peak Flow Event Ø 419 structures
Engineering and Operational Uses q Models are typically the realm of the Engineering department Capital Improvement & Master Planning q Additional uses/scenarios increase value Ø System capacity for new development Ø Investigating potential rehabilitation issues Ø Operations and Maintenance Identifying 2 nd Tier Cleaning Locations
Area of Studies L NT L E I F M IN- ELOP DEV N 1,000 ft
New Development q Infill development q Low area, upstream of low point
New Development q Determine if city infrastructure has capacity restriction Ø Regional conveyance system has current limitation, but ongoing plans already include fully developed flows q Developed flow parameters for the areas Ø Base sewage flow per residential unit Ø RDII flow used adjacent area s wet weather parameters q Run the 10-year Peak Flow Event worst case scenario Ø Free Discharge conditions Ø Downstream tailwater conditions from RHM
New Development q Examined HGL, dimensionless parameter Ratio of 10-yr Peak Q to Mannings Q Undeveloped 0.86 Developed 0.89 q No city capacity restrictions limitation is downstream in regional system q Time savings and verification of institutional knowledge
Investigating Potential Issues q 2,600 LF of CIPP lining in low-lying area Ø Sand buildup in pipe Ø Suspected leaky joints q Starred location is known low point q Highlighted section was to be lined
Investigating Potential Issues q Determine impact of reduced pipe diameter on water levels at low manhole during peak event q Subject to surcharging from the downstream interceptor q Multiple influences make this a sensitive location
Investigating Potential Issues q Lining does not increase HGL significantly q Larger problem is downstream capacity
Operations and Maintenance Identifying 2 nd Tier Cleaning Locations q Hampton O&M staff has a high frequency Hot Spot cleaning program 1 st Tier Cleaning Locations q Just now started using model results to identify areas with minimal velocity that result in sedimentation build up q Quickly identify the location and impact of reverse grade pipes (seen on previous slide) not on Hot Spot list q Model results will be compared with FOG program and Food Services Establishments to better prioritize cleaning program
In Summary q Models are not limited to Capital Improvement and Master Planning q Models can have a significant role in evaluating rehabilitation alternatives q Models are capable of supporting operations staff to improve system performance efficiently Ø Still working on getting it to make coffee
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