Relatively rapid growth has occurred in the Austin area during the past two decades, making it one of the fastest growing cities in the U.S. This growth is attributable to its many natural, cultural and educational amenities. Areas in the western, southwestern, and northern portions of the metropolitan area have been undergoing particularly intense growth, with the accompanying pressures to develop infrastructure in response to that growth.
The Austin metropolitan area is characterized by a very diverse set of geographic and environmental conditions. These include the Edwards Plateau, the Rolling Prairie. the Blackland Prairie, and the terraces and flood plains of the Colorado River and its tributaries. Each of these regions differs significantly from the others in topography, surface geology, soil types and characteristic vegetation. Much of the southwest portion of Travis County is located within the Edwards Aquifer recharge zone or in contributing zones such as the Barton Creek watershed. Barton Creek and other watersheds provide a significant portion of the recharge to the part of the Edwards Aquifer discharging to Barton Springs. A large number of homes to the west and southwest of Austin are currently served by individual on-site wastewater treatment systems. Density of development tends to be much lower overall in those portions of the City as compared with other parts of the Austin area due to a variety of factors, including certain environmental controls, real estate market preferences, preserved natural areas, and conditions that are difficult for construction. As limitations are placed on, or occur naturally for the density of development, the user costs for providing centralized collection and treatment tend to increase. Thus, the need to consider either individual or cluster-type on-site treatment and disposal systems becomes evident.
The objective of the Study Phase of this project has been to identify and evaluate a variety of alternative wastewater collection, treatment and disposal technologies for their suitability and cost-effectiveness for environmental conditions in the study area, and to evaluate approaches for effectively managing decentralized wastewater systems. Phases II and III of the project will consist of the design, construction and monitoring of onsite systems and technologies based on recommendations from the Study Phase, to demonstrate their applicability to local conditions. A steering committee composed of representatives from several City of Austin departments and professional staff from the Austin-Travis County Health and Human Services Department (ATCHHSD) are providing direction and review for the project. City departments represented on the steering committee include the Water & Wastewater Utility, the Drainage Utility Department (formerly Environmental and Conservation Services Department), the Development Services Department (formerly Planning and Development Department), and the Public Works and Transportation Department.
The major task areas in the Study Phase of the project have included:
- Identification and mapping of representative geographic land types in the study area;
- Identification of candidate collection, treatment and disposal systems;
- Evaluation of alternative systems for their suitability and cost-effectiveness in local conditions;
- Identification of relevant federal, state and local regulations;
- Identification and description of options for local management structures; and
- Evaluation of management approaches for applicability to local conditions.
Fifteen different land types were identified and mapped for the study area. The map was developed by City of Austin staff in the Water/Wastewater Utility and Planning and Development Department, with technical direction provided by Community Environmental Services, Inc. (CES), the Consultant for the project. Computerized geographic information systems (GIS) resources from federal, State and local sources were used to create the map. Features were identified for each of the land types that will affect the selection and costs of appropriate wastewater collection systems, and of onsite treatment and disposal systems.
Lists of candidate technologies were compiled for alternative types of wastewater collection, and onsite treatment and disposal systems to be evaluated in the study. Fact sheets describing the onsite treatment and disposal systems options were developed, and include such information as performance data, common design modifications, applicability and limitations of the system, and the developmental status of the technology. Available published technical literature, performance and cost information were used for the development of the fact sheets. Collection systems fact sheets were obtained from the National Small Flows Clearinghouse, and attached as an appendix in the report along with those developed for onsite treatment and disposal systems. Candidate systems evaluated included 7 collection system options, 17 onsite treatment options, and 13 onsite disposal system options.
As a part of the effort to obtain information about the performance and costs of alternative systems that would be most relevant to local conditions, a questionnaire was distributed to approximately 175 property owners who have some type of alternative onsite wastewater system within either the Austin-Travis County or LCRA onsite regulatory jurisdictions. There was about a 26% response to the questionnaire, and responses were received from residents having one of about 10 different types of alternative systems. Information received from respondents was found to be very helpful for identifying those system types which appear to be having the most problems, and for obtaining local cost information from residents about their systems. Just under one third of the respondents reported some type of problem with their system. Only about half of the residents indicated that any type of regular or periodic maintenance had been recommended for their system, even though most of the systems included in the survey require some type of regular or periodic maintenance.
Evaluation matrices were developed to rate collection systems, onsite treatment systems, and onsite disposal systems for each of the fifteen representative land types, and are included in Section 4 of the report. Criteria used for rating systems in the matrices included such factors as environmental suitability, costs, legal/regulatory considerations, operational reliability, land area requirements, aesthetics, management requirements, availability of performance data, and the availability of local technical expertise for the design and construction of the system. Tables outlining the principal advantages and disadvantages of the different system types were also developed and included in the report (Section 4).
Several land types identified in this study present certain physical limitations for wastewater system alternatives, while others will tend to allow for the installation of essentially any type of system, with the selection likely to be based principally upon costs. Those land types with physically limiting conditions include those with one or more of the following features: steep slopes; shallow soils overlying weathered limestone and/or bedrock; shallow depth to ground water; location within the Edwards Aquifer recharge zone; and karstic conditions relatively near the surface. There have been concerns locally about potential adverse impacts to the Edwards Aquifer from conventional sewer systems, from both construction activities and operational problems such as lift station failures and overflows. In areas with rocky terrain and thin soils, trench construction has a significant impact on both environmental suitability and costs.
Several collection system alternatives evaluated in the matrices are used to overcome some of the disadvantages associated with conventional sewers in unfavorable conditions such as those mentioned above. Systems which use much smaller diameter lines, and thus may be laid in smaller trenches, are being used increasingly in areas with some of these sensitive environmental conditions. One of the advantages of several of the small diameter sewering options is that existing homes served by onsite wastewater systems can be retrofitted with these systems, either for "cluster" systems or wastewater collection systems leading to larger centralized treatment and disposal systems. Cluster systems are two or more homes served by the same final land treatment and disposal system (it is not considered an "onsite" system, since the effluent disposal field is "offsite"). All of the alternative collection systems considered have the advantage of smaller trench construction, which tends to reduce impacts from construction.
Onsite wastewater disposal systems consist of some type of pretreatment, followed by final surface or subsurface land treatment and disposal. Some land types have less soil treatment capabilities than others, and require more pretreatment of the wastewater prior to land disposal in order to prevent adverse environmental or public health impacts. The pretreatment portion of the system usually provides only a part of the total treatment for the system, since the soil and subsurface media provide at least some level of treatment in most of the land types in the study area. Exceptions to this, where very limited soil treatment potential would be expected include fractured bedrock located immediately beneath the effluent disposal trenches, without significant soil or other weathered subsurface media. Various types of alternative onsite treatment systems were described and evaluated in the study that can reliably provide enhanced treatment for wastewater constituents that may be of concern for certain local environmental conditions. Each type of system has advantages or disadvantages depending upon the specific site conditions and circumstances.
For any onsite wastewater treatment system, a careful physical site investigation is needed to select and design an appropriate wastewater system for those conditions. The land types identified for this study are used to describe representative local conditions, and are not to be used for the selection of suitable onsite system designs for specific sites. To evaluate options for particular sites, after determining the level of pretreatment required prior to final onsite disposal, it is essential to consider such factors as available space on the site, power requirements and availability for the various options, the acceptability of O&M requirements for options considered, overall costs, etc. Such factors as topography or space on the site, or the need for reliable power may limit options for a particular site.
Pretreatment by a septic tank only, or primary treatment, was considered acceptable prior to final subsurface disposal for nine of the fifteen land types in the study area, based on currently available data. Septic tanks alone may not adequately remove certain wastewater constituents such as pathogens or nitrogen prior to the effluent's final treatment and disposal in certain geophysical conditions. There is currently only very limited data available on the performance of onsite wastewater disposal systems in several of the study area's land types that occur in western Travis County. For subsurface disposal systems serving individual, cluster or community systems in these special types of environmental conditions, it may be important to utilize processes that enhance removal efficiencies for nitrogen and/or pathogens, prior to subsurface disposal of the effluent. As a continuing part of the Study Phase work, existing onsite wastewater systems installed in these areas will be monitored to determine the level of pretreatment needed for onsite systems in these conditions. Based on those monitoring results, recommendations will be made for system designs that are environmentally suitable for those areas.
Two types of technical recommendations were developed from the Study Phase of the project, and presented in Part 1 of the report. Those are: (1) the evaluation of collection, onsite pretreatment, and onsite disposal systems for their suitability to the fifteen land types identified in the study, and (2) recommendations for the demonstration and monitoring phase activities of this project. The focus of each of those two areas of interest is very distinct, although many of the same factors were considered to develop both sets of recommendations.
This type of study does not lend itself to simple conclusions and recommendations. All of the wastewater collection, treatment and disposal options considered in this study would be suitable for use in some given set of local circumstances. If a system is considered suitable for particular environmental conditions, its feasibility and cost-effectiveness as compared with other centralized (if available) or decentralized options will depend on a variety of other factors. For onsite treatment systems, there are numerous combinations of individual treatment processes that might be appropriate for a particular set of conditions. The effective management of both conventional and alternative onsite wastewater treatment systems will be critical to their successful long-term use. Providing necessary maintenance and repairs to these systems is essential for ensuring their proper functioning, and for preventing adverse health or environmental impacts, or nuisances.
In all of the representative land types identified, there is at least one combination of onsite treatment processes that can provide appropriate levels of treatment. Economies of scale suggest that the more homes or buildings a wastewater treatment and disposal system serves, the lower the total cost for each user. For conditions requiring higher levels of pretreatment prior to final land disposal, it is desirable to serve multiple homes with a single treatment and disposal system for minimizing costs and better facilitating care and management of the system. Small scale clustered residential and commercial wastewater systems using some of the alternative technologies evaluated in this study appear to be particularly applicable to western portions of the study area.
A strategy was identified for subsequent phases of this project that will facilitate the collection of meaningful information in a cost-efficient manner, for demonstrating the applicability of alternative wastewater systems in the study area. Several of the rating factors in the evaluation matrices were used as criteria for identifying those systems which are of particular interest for local demonstration and factors include the availability of performance data for that type of system, the expected suitability of the system for specific local conditions where conventional systems might not be appropriate, and the anticipated reliability and long-term costs of the system. Recommendations for the Phase II and III design, construction and monitoring of demonstration systems were developed using these evaluation criteria. It was also recommended that monitoring be performed as possible for existing alternative systems operating locally that appear to be appropriate and cost-effective for conditions in the study area. In addition, Phase II and III activities will include working with vendors to monitor certain types of onsite treatment units locally under either controlled testing or actual field operating conditions, as those opportunities are identified for systems appearing to have particular merit for local conditions. The majority of the laboratory analyses will be performed by the City's Water & Wastewater Utility laboratories to help minimize costs associated with the monitoring activities, and to better maintain the quality of test results. Some QA/QC testing will be performed by a private laboratory. Results from the Study Phase monitoring activities, and the Phase II and III demonstration and monitoring of alternative systems will be used to make final recommendations for wastewater alternatives that appear most suitable for land types in the study area.
Part 2 of this report presents a variety of options and considerations concerning the management of onsite wastewater systems, as they relate to conditions in the study area. "Management" in this context means carrying out a set of policies and practices related to the permitting and care of either centralized or decentralized wastewater systems to ensure public health and environmental protection in a manner, and to an extent that is acceptable locally and in accordance with regulatory requirements. As stated previously, the proper maintenance of onsite systems is essential to their successful long-term operation. Most of the management considerations discussed in the report pertain primarily to onsite or decentralized options, since the City of Austin currently has in place a well established management program for its centralized wastewater collection and treatment facilities.
Management programs and practices currently in use in and around the study area are described in the report, as well as a number of other programs being used by jurisdictions elsewhere in the U.S. and Canada. Relevant federal, State and local rules affecting onsite systems are identified in the report (Section 6). The Chapter 317 rules for the State of Texas covering collection and larger scale wastewater treatment systems, and the Chapter 285 rules for onsite wastewater systems are currently in the revision process. Four overall management structures are presented, each with different numbers and types of management activities and levels of involvement in the care of onsite wastewater systems. These four basic structures are presented to identify general options for the City of Austin and Travis County when considering approaches for managing decentralized systems in the Austin area. ATCHHSD is the entity currently responsible for the permitting and regulatory oversight of onsite systems in the study area. The current management activities performed by ATCHHSD are some of the more basic services performed by onsite systems management jurisdictions, of those programs presented in the report.
Options were presented for how various management activities might be carried out locally, along with some of the advantages and disadvantages of those approaches. Recommendations were made for certain changes in local management practices, and for changes in State and local rules that may impede the use of certain appropriate decentralized alternatives. Recommendations from Part 2 of the Study Phase report include:
- Develop and utilize a wastewater service planning approach based on an impartial evaluation of both centralized and decentralized options for their cost-effectiveness and appropriateness for local conditions. This process should be distinguished from, and follow, planning based on such considerations as environmental impacts from development densities and land uses.
- Revise certain City ordinances to eliminate requirements that show undue bias in favor of conventional centralized wastewater service.
- Change City watershed ordinance requirements for onsite systems so as to recognize the role of pretreatment prior to final effluent disposal for onsite wastewater treatment systems, particularly in areas with sensitive environmental conditions. Consideration should also be given to this by ATCHHSD staff for further development and revision of their design criteria for onsite systems.
- Initiate a very active public education program to provide helpful information to the public about onsite and other decentralized options described in the studs'.
- Require periodic inspections and renewals of the license to operate for all onsite systems in the study area.
- Adopt requirements for pumping septic tanks within the ATCHHSD's jurisdiction at acceptable time intervals. Systems with other types of treatment units should also have maintenance requirements at intervals that will help to ensure proper functioning, and prevent failures and adverse impacts.
- Increase or improve upon record keeping activities by the ATCHHSD or other designated local management authority, so as to maintain current records for onsite systems in their jurisdiction. Records/files for onsite systems should include a record of when the septic tank was last pumped.
Potential sources of funding to implement the above measures for which additional funds would be needed, include minimal user fees charged to residents with onsite systems, grant funding, or general funds of the City or County. It is suggested that any major changes to local management practices be phased in over a relatively long time period, beginning with the adoption of fairly basic reinspection and maintenance requirements such as those above. Input from the public will be a necessary and very important part of the process, particularly if significant changes are made to current practices. The Water & Wastewater Utility and the ATCHHSD should work cooperatively to select an appropriate local management approach, and begin jointly developing a detailed strategy for evaluating and implementing onsite and other decentralized alternatives along with centralized options in an unbiased manner. An approach should be developed that will result in the most appropriate and cost-effective wastewater service for particular local conditions.
Information provided by Community Environmental Services Inc.