Decentralized vs Centralized Systems in South Texas Community

Decentralized wastewater treatment systems are often a good economical approach to public health protection and water quality protection for small communities. However, when development in these communities does not consider the shortcomings of decentralized systems, the impact can be more than a simple nuisance. In areas where soils are not conducive to subsurface disposal and development is unregulated and dense, decentralized systems pose a health hazard and environmental hazard as they will be prone to failure resulting in exposures to concentrated waste. Addressing these issues can be a complicated, technical, financial and political problem. This case study looks at a community in south Texas that leveraged local funds with state and federal grants to solve this problem.
Kerr County is in South Texas (TX) and is located about 45 miles northwest of San Antonio, in the Texas hill country. The county has been facing severe problems with failing septic systems in eastern areas of the county. These were reported to the Commissioners' Court by the Kerr County Environmental Health Department. The staff of Environmental Health were frustrated with systems in various densely developed areas within East Kerr County and specifically, around Center Point. The problems were exacerbated by the fact that many of the property owners did not have the financial means to repair or replace their failing systems.
Failing systems pose a threat to public health as these systems become pathways for spreading various waterborne diseases among the community. In addition, failing septic systems contribute to the degradation of water quality in natural waterways. Since this community is literally on the banks of the Guadalupe River, the environmental concerns are also not trivial. The Clean Water State Revolving Fund (CWSRF) is a fund established to provide financing to solve just this type of problem. The County applied to the TWDB for funds to find solutions to the problem and then to implement those solutions. The problems of the community are made worse by the size of the area with issues. The various neighborhoods that are so densely populated that individual systems cannot be supported are spread out over an area that covers about 3.6 square miles. The distance from the most remote part of the area to the closest wastewater treatment plant is 10.7 miles as the crow flies. Centralizing wastewater collection for this large an area is a huge task and involves miles of pipelines and pumping systems. Can the cost of these improvements outweigh the cost of decentralized systems? Consider that to effectively decentralize the system approximately ten small decentralized systems would be needed, each with its own NPDES permit as the individual properties simply are not large enough to accommodate onsite disposal systems.
The purpose of this project is basically to solve the public health and environmental problems identified by the Environmental Health Department in this area. The low to moderate income areas qualify as Colonias since these areas are within 150 miles of the US-Mexico border and thus grant funds are available to address these types of problems. Another benefit of the project will be economic development. With an organized sewage collection system, growth can occur that can stimulate economic activity in the area. The East Kerr County Wastewater Collection Project provides sewer service to communities without sewers. The communities used onsite sewage disposal systems in areas that are not amenable to effect disposal onsite. These systems were developed on lots that are too small to accommodate conventional septic disposal systems. In addition, the soil conditions do not provide sufficient capacity for effective and safe leaching of septic tank effluents. To compound problems, these communities exist near the Guadalupe River. To address the health hazards, nuisance conditions and environmental harm caused by large numbers of malfunctioning septic systems, the Kerr County Commissioner's Court initiated this project to provide sewer service to these areas to eliminate the onsite disposal systems. The project includes over 27 miles of new gravity sewer in sizes ranging from 6-inch to 15-inch diameter. It includes 11 lift stations and about 6 miles of force main. In addition, it includes expansion of the Comfort Wastewater Treatment Plant to accommodate the new flows.
The expansion of the Comfort Wastewater Treatment Plant is accomplished by altering the operating mode of the system from an extended aeration process to a conventional activated sludge process and by providing wet weather flow control to reduce the peak flow of the system. The project included a new aerobic digester to facilitate solids reduction and stabilization previously achieved by the long mean cell retention time of the aeration basin. In addition, an excess flow basin was constructed to reduce the peak flows into the plant which, with the improved settleability of the activated sludge achieved by the reduction in mean cell retention time improved the effectiveness of the existing clarifiers. Thus, the capacity of the WWTP was increased from 0.35 MGD to 0.525 MGD without new clarifiers or aeration facilities. The overall construction cost of the Comfort WWTP was about $5,110,000. The project is broken into three phases with a total project cost of about $64 million dollars and will serve over 900 properties. This is largest single project ever undertaken by Kerr County. To accomplish this enormous feat requires the creative leveraging of local funds with state and federal funds. Funding for the project includes Clean Water State Revolving Fund (CWSRF) Loans with partial principal forgiveness, Economically Distressed Areas Program (EDAP) grants, Colonia Fund -Construction grants, Colonia Economically Distressed Areas Program grants, and Community Development Fund grants. More than 80% of the funding for this project is being provided in the form of grants and loan forgiveness. Less than 20% of the total financing is being provided by loans that must be paid back by the County. This is an incredible leveraging of funds to accomplish this ambitious project without overstressing the finances of County residents and the residents in East Kerr County and Center Point. Since less than 20% of the funding is from loans and 80% from grants, the project will be paid for by the users of the system through affordable wastewater rates. The pie chart shown in Figure 3 summarizes the funding from each agency.
The county has seen success in project implementation. The Phase 1 construction of the project is completed and currently Phase 2, and Phase 3 construction activities are ongoing. The entire construction is estimated to be completed in Fall 2022.