Sewer Evaluation and Capacity Assurance Planning Minimizes SSOs

City of Hot Springs, Arkansas

Manhole Inspections

Flow Monitoring

3,200

grinder pumps

2 million

linear feet hydraulic model

18 to <3

SSO rate drop per 100 miles

The City of Hot Springs, facing compliance with an EPA regulatory action, initiated a citywide program to mitigate recurring sanitary sewer overflow (SSO) violations at a rate of 18 reported SSOs per 100 miles of sewer. The Hot Springs wastewater collection system is unique because of its mountainous topography. The system uses more than 3,200 grinder pumps to transport flows through the system.

The mandate of the regulatory action was to eliminate all wet-weather SSOs under the order's design storm. It was critical to understand performance issues and identify where excess flows were causing overflows. A systemwide flow monitoring program provided the foundation for hydraulic modeling to formulate a plan to address capacity issues contributing to overflows.

A combination of I/I reduction measures and capacity improvements were recommended with an estimated cost of $68,000,000.

Project Metrics

A complex InfoWorks hydraulic model was constructed for the entire system—2,100,000 LF of pipe, 72 lift stations, and 3,200 grinder pumps to evaluate capacity needs.
Design and construction inspection services repaired, replaced, upsized, and rehabilitated 5,500 manholes, 22,000 LF feet of gravity sewer, and 10,000 LF of force main.
UV disinfection improvements at the WWTP installed under an engineer-led design-build contract.
The number of reported SSOs have declined from 18 to less than three (3) per 100 miles of sewer, and the actual cost-to-construct was $70,000,000.

Project Leaders

Daniel Jackson, PE
Project Director

Services

EPA regulatory assistance
Sewer Evaluation and Capacity Assurance Plan (SECAP) development
65 flow meters
2,100,000 LF hydraulic model
12,082 manhole inspections
1,904,254 LF smoke testing
5,500 manholes rehabilitated
22,000 LF of gravity sewer and 10,000 LF of force main upgraded

Client

City of Hot Springs

Location

Hot Springs, Arkansas

Service Period

2008 — 2014

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