Wastewater: Rapid Growth Demands Responsible Planning

When water runs down their drain or their toilet is flushed, many people give little thought about what happens to the wastewater, but collecting and treating that wastewater is one of the most vital core services provided by the City of College Station. With as many as 40,000 new residents expected in the next two decades, meeting our wastewater collection and treatment needs presents considerable challenges. That’s why a responsible Wastewater Master Plan has been developed by city staff and HDR engineers

The City of College Station owns, operates and maintains a reliable wastewater collection, treatment and disposal system for close to 84,000 residents and businesses (the A&M campus is not part of the system). The collection system consists of about 300 miles of gravity sewers and nearly seven miles of force mains.  Treatment and disposal systems are provided by the Carters Creek Wastewater Treatment Plant and the Lick Creek Wastewater Treatment Plant, which combine to treat an average annual influent dry weather flow of approximately seven million gallons per day. 

This plan quantifies the cost of providing needed services and facilities, and recognizes the significant investment residents previously have made on similar services and facilities.  Failure to implement the plan will result in lower service levels, reduced economic activity and could slow the city’s growth potential.

A Challenge and an Opportunity
Our Wastewater Master Plan study has concluded that our collection system and treatment plants will require significant capital investment in the next two decades to keep up with our rapid growth.  Rehabilitation of the collection system in older parts of town has become essential, and sewer trunk lines also must be upgraded to handle the increasing load.  In addition, our two major treatment plants will require expansion in the 2020s if the growth projections are accurate. 

The bad news is that this will necessitate large capital expenditures – and possibly rate increases — in the next 15 to 20 years. The good news is that as we upgrade the capacity of our treatment plants, we have the opportunity to implement an innovative treatment regimen that will generate revenue by taking advantage of a renewable energy source. New technologies are being developed that use sewage sludge, restaurant grease, yard waste and perhaps even animal waste to produce methane, which is then used to generate electricity.  This electricity is partially used to drive the treatment process, and the rest can be sold and used for Renewable Energy Credits.  We will be investigating the feasibility and dependability of this technology and are hopeful this process can be used to offset some of the capital costs.

Wastewater Master Plan Summary
Because the overall collection/treatment system is large and complex, the Wastewater Master Plan is divided into five subsections – temporary flow monitoring, demand analysis, facilities planning evaluation, collection system evaluation and future collection system map.

Temporary Flow Monitoring
The wastewater collection system flow was evaluated from Dec. 5, 2009 to Feb. 8, 2010.  This evaluation included the identification of major sub-basins for the Carters Creek and Lick Creek sewer sheds, the installation of 19 temporary flow meters in the respective sub-basins, and the installation of nine rain gauges throughout the city.  The dry and wet weather system characteristics were collected and used to calibrate the hydraulic computer model of the collection system.  

Demand Analysis
The demand analysis addresses the existing and future sanitary sewer demands on the overall wastewater collection and treatment systems.  The 2009 Comprehensive Plan projected population growth, and where and how land may be used in the future. The Comprehensive Plan also projected development densities, which are expressed as Living Unit Equivalent/Acre (LUE). A LUE measures the typical flow of wastewater produced by a single family residence.  Action dates for the treatment plant expansion are based upon Texas Commission on Environmental Quality (TCEQ) rules that require planning for new treatment capacity to begin when monthly average inflows for a wastewater plant exceed 75 percent of the plant’s permitted capacity for three consecutive months.  Future LUE projections were used to calculate the annual growth rates, which determine the action dates:

Facilities Planning Evaluation
Existing wastewater treatment facilities are evaluated along with several sludge processing alternatives and nutrient removal using a biological process.  Existing treatment and disposal is provided by the Carters Creek and Lick Creek treatment plants.  The overall evaluation found that expansions are needed at both plants by 2018 due to exceeding permitted capacities, compliance issues with recent TCEQ rules, excessive organic loading at the aeration basins, and potential improvements needed to implement future nutrient removal. 

The overall evaluation also examined several sludge alternatives and considered advantages and disadvantages to each of the alternatives including estimated capital costs, operations and maintenance, increased permitting requirements, co-generation capabilities, etc.  We anticipate that within the next one or two permit cycles, infrastructure for nutrient removal will be have to be added to the facilities. 

Collection System Evaluation
The existing wastewater collection system and the future collection system needs were evaluated using the temporary flow monitoring data collected from Dec. 5, 2009 to Feb. 8, 2010.   The evaluation discussed proposed interceptors expected as part of future development, how the proposed interceptors affect the carrying capacity of the existing interceptors, deficiencies in the existing system, projected time frames of when the system will need to be expanded, potential lift station needs, and proposed collection system improvements with planning level cost estimates.   About 14 percent of the total length of pipe in the existing sewer system will require rehabilitation by 2030.  Existing lift stations have sufficient capacity to serve the current population but as growth continues, capacity will need to be increased at six of the 10 lift stations.  A total of 42 miles of new gravity and force main extensions will be required to service future annexation areas, and a total of eight new lift stations will need to be constructed — mostly in the Lick Creek sewer shed — to convey flow to the Lick Creek plant. This chart summarizes the estimated capital expenses in the next decade:

Future Collection System Map
The future collection system map shows collection lines that are anticipated to be extended or needed to increase existing collection system capacities.  This map will be used by city staff to identify potential oversize participation opportunities as development occurs.

If you have any questions or comments about the Wastewater Master Plan, we encourage you to submit them at the bottom of this blog.

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