Section 366.052 of the Texas Health and Safety Code exempts from permitting on-site sewage facilities for single residences located on a land tract that is 10 acres or larger. The sewage fields or lines must be at least 100 ft. from the property line and there are other requirements that the effluent must be kept 100 ft. distant from property lines, must not create a nuisance and must not pollute groundwater. In the local draft, no exemption from permitting of on-site sewage facilities is granted for lots greater than 10 acres since, without permitting and the inspections that accompany permit issuance, no determination can be made as to whether or not the OSSF would pollute groundwater or create a nuisance. In the absence of that knowledge, it must be assumed that the OSSF could create those conditions, especially groundwater pollution. Furthermore, within the functional lifespan of the OSSF, the 10 acre tract is likely to be subdivided so that the lot would no longer be more than 10 acres in size and the separation of sewage disposal lines from property lines could then be less than the 100 feet specified in the Health and Safety Code. This is especially true for large acreage lots located inside the city of Austin, to which this ordinance applies. Without assurance of the proper construction of the OSSF, public health and the environmental quality are at risk. Furthermore, the standards are intended to safeguard the residents of the property served by the OSSF as well as the public; inspections and permitting occur on their behalf to ensure adequate and safe sewage disposal and proper separation distances from environmental features. Finally, resale of the property is hindered, harming both the seller and the purchaser, if the property is served by a system that was never inspected when installed.
 

The local standards require that on-site sewage facility maintenance companies employ a Class C or higher (rather than a Class D required by the State rules) wastewater operator to oversee maintenance of systems. This provides greater public health and environmental protection because more training and experience is required of Class C operators than Class D operators and they would be better able to provide a higher quality maintenance of OSSF's. A Class C or above certificate is required by the State for operation and maintenance of larger wastewater treatment systems with many of the same processes now utilized by OSSFs (e.g., aerobic treatment, wetlands). Class D operators are only required to have 20 hours of classroom training with no relevant experience required under State certification requirements. Experience, in addition to classroom training is required for Class C operators. The kinds of OSSFs which require maintenance contracts are those of greater technical complexity and are more likely to break down. Maintenance provided by a more skilled company representative can extend significantly the functional lifespan of on-site sewage facilities and prevent failure which might result in exposure of humans or the environment to sewage waste. The TNRCC requirements for wastewater operators and for OSSF installer certification are listed in the References portion of this document under "Designer and Maintenance Contractor Qualification Requirements."
 

Section 285.3 (b) of the State rules lists as unauthorized types of on-site sewage facilities the following: Boreholes, cesspools, and seepage pits. The City of Austin wishes to notify its residents that injection wells and pit privies also are not allowed to be used because they both present a direct hazard of groundwater contamination. Pit privies also create hazards to human health through odor and breeding of files and insects.
 

Section 285.4 (a) of the State rules establishes lot sizes for approval of subdivisions intended to be served by OSSFs as .5 acres for subdivisions served by public water supplies and 1 acre for subdivisions served by individual water systems. In addition, this subsection allows lots smaller than those sizes to be developed with OSSFs if a site-specific sewage disposal plan is submitted. The State rules, under General considerations, in this subsection state, "The single most important factor concerning public health problems resulting from these (OSSF) failures is the residential dwelling density which is primarily a function of lot size." In agreement with that statement, the City of Austin proposes to establish higher lot size standards generally for OSSF sites, higher lot size standards for certain specified types of development and higher lot size standards for development in certain geographical areas of greater environmental risk.

A quote from Septic Systems Handbook by O. Benjamin Kaplan reads as follows:

Increased lot sizes provide for greater distance between OSSFs on adjoining properties, greater distance between the dwelling on a lot and the OSSF serving it, greater distance between any well located on a lot and wells located on adjacent properties, and greater distance between the OSSF and a well that is located on the same property. These greater distances provide land space through or over which movement of pollution from an OSSF is restricted. In all cases, the lower density of subdivisions planned for OSSFs also reduces the percentage of impervious cover in the subdivision, which provides benefits in runoff water quality. Use of smaller lots for OSSFs often results in the necessity of installing alternative types of treatment and disposal which involve higher technology or greater engineering skills and are, therefore, more expensive and prone to breakdown. By having adequate lot size, a savings can be realized in the use of standard, low tech treatment and disposal methods. Some, but by no means all, references regarding lot size standards are provided in the References list at the end of this document under the category "Lot Size."

Similarly, lots planned for the use of water wells need to be larger to provide for the sanitary easement required around the well and to reduce the density of wells and OSSFs within the subdivision. This sanitary easement is 100 ft. in all directions from the well for private wells and 150 ft. for public water wells. Thus for property with private wells, soil absorption disposal areas cannot be placed in an area around a well of 31,416 sq. ft. or 72% of an acre in size. In recognition of the area needed around a well, the local standards require a minimum of 2 acres for lots with wells and increases this to 3 acres in the DWPZ.

If lots are planned at the time of subdivision for nonresidential uses, there is no minimum lot size in the local standards; space must be available on the property of two times the designed disposal area or no less than 20 sq. ft. per gallon of projected average daily wastewater flow. This is to ensure adequate space to install the OSSF on a site which is not accessible to the public using the nonresidential facility. If, however, the nonresidential property will be served by a private well, there is a lot size requirement of 2 acres per living unit equivalent (360 gpd) flow (3 acres in the DWPZ).

When subdivision or resubdivision of land occurs for cluster systems, which might be necessary to deal with multiple failing systems in a given area, the lot size requirements are expressed as "average lot size" because each lot need not have the minimum size as long as there is a lower overall density of lots. The minimum average lot size is 1/2 acre, 3/4 acre in the Drinking Water Protection Zone.

Larger lot sizes are needed in subdivisions which are planned for the use of surface irrigation. In the draft the requirement is 2 acres/dwelling increased to 3 acres/dwelling in the Drinking Water Protection Zone. This additional space is needed in order to install the surface irrigated areas a greater distance from adjacent properties and a greater distance from the houses they serve. The reasons why greater distance is required is that the surface irrigation is often accomplished with spraying of treated effluent, creating aerosols of wastewater. Should the treatment system fail or malfunction, the reduced effluent quality could pose serious public and environmental health risks If disinfection required in a surface irrigation system is not functional (as many as 1/2 of the units are found to be out of disinfectant at any given time) the sprayed effluent is not effectively treated for pathogen reduction. There is a need to locate such systems away from homes and adjacent properties to reduce exposure to pathogens in untreated effluent in the likely event of treatment system failure and lack of disinfection.

Under the State rules, subdivisions can be created with lots that are smaller than the minimum ½ acre in size if the applicant submits a specific sewage disposal system plan approved by the permitting authority. In the draft local standards, the minimum lot sizes cannot be reduced by submission of site specific plans. This provision prevents a developer from subdividing property with specific plans for a certain OSSF of certain capacity, etc., on the lots in order to obtain a lot size smaller than that required by the rules. Later, when the lots are developed, the lot size may be inadequate but cannot be changed without re subdivision. The lot may be inadequate because the property owner desires a larger house, for example, than the original OSSF plan included or because site evaluation at that time indicates a need for a different type or a larger OSSF than was used for subdivision purposes. This requirement protects the environment by preventing a bypass of the requirements for lot size.

The local standards also exclude land within the known floodway or within the 25-year floodplain, if known, from lot size calculations. These are not excluded in the State rules. This exclusion provides greater environmental protection by assuring that each lot has sufficient area that is not in a drainageway for the installation of the OSSF and structure it serves. Since construction of new OSSFs is not allowed within 150 ft. of a Critical Environmental Feature or in a Critical Water Quality Zone, subdivision must adhere to this requirement. "Critical Environmental Feature" is a term applied to such features and recharge sites and the "Critical Water Quality Zone" is defined in the City’s Land Development Code. It corresponds roughly to the 100 year floodplain.
 

Protection of the environment and public health at the time of subdivision requires more than setting lot size alone. In order to prevent creation of lots with no area available for installation of a disposal field, the State rules provide that an area be shown available for this purpose. While the State requirement is that this be no less than two times the square footage of the area designed for the OSSF disposal, the local standards add a minimum of 7,200 square feet per dwelling unit. The square footage of the design area is often not known at the time of subdivision because the OSSF for the property has usually not yet been planned. The area of 7,200 sq. ft. would provide twice the space for drip irrigation to serve a 5 bedroom house, assuming a loading rate of not less than 0.1 gpd/sq. ft. or for surface irrigation, assuming that a replacement surface irrigation area is not required.

In the case of nonresidential subdivisions, the area is based upon the projected flow from the nonresidential use which usually is known at the time of nonresidential subdivision. It is 20 sq. ft. per gallon of flow. In the case of cluster systems, the area is based upon either the projected flow or a minimum of 7,200 sq.ft. per dwelling unit.
 

The local standards also address the slope that the area available must meet in order to prevent the staking out of lots that consist entirely of steep slopes and to facilitate development of lots with standard rather than non standard disposal systems. The requirements are that the area available have a slope of 15% or less, generally, and if the slope is up to but not including 30%, the lots must be designated for the use of drip irrigation or lined evapotranspiration systems only. State standards make no mention of the slope of the area designated at the time of subdivision, but for installation of systems, a slope of 30% or less is considered suitable.
 

The local standards also contains marginally more stringent standards for manufactured housing communities or multi-unit residential developments. Like the State rules the local standards allow a lot size lower than the minimum .5 acres per dwelling (State) or ¾ acre per dwelling (local). However, the local standards require that such development be served by a public water supply, not individual wells, and that over-all the property must contain at least 12,000 sq. ft. of unpaved area per living unit equivalent above the 25-year floodplain or the known floodway. The area available for an on-site system must total 7,200 sq. ft. and at least half of this area must be less than 15% slope. This is to ensure that there is area available of an appropriate slope for the on-site system serving such a community.
 

Many lots are not built out for years, even decades, after subdivision occurs. So, the development with OSSFs on existing small lots is allowed, but must not bypass any previously established lot size standards. The draft local standards allows development on small existing lots if a system meeting current construction standards can be designed; however, the draft contains a requirement that a single-family residential lot must be developed in accordance with the subdivision requirements in place at the time of preliminary plat approval. If no approval was obtained, then the lot must comply with the standards in effect at the time of first sale of a lot in the subdivision.

There are two exceptions in the local standards to the provision allowing development on small existing lots. If the use of the property is to be anything other than single-family or duplex residential use, the current lot size requirements must be met. This standard prevents the property owner from changing the use of property without meeting the lot size standards for the new intended use. The other exception is that, if the system being planned for the lot is a surface irrigation system, the current lot size standards must be met. Without this requirement, surface irrigation systems could be installed on smaller lots which were subdivided at a time when surface irrigation was not allowed in Austin and lots therefore did not have the larger size needed to accommodate these facilities.

The City draft also requires that easements or right-of way be excluded from the calculation of size when the easement or right of way might affect the placement of an on-site system planned for an existing lot.
 

In order to ensure that design work is of the highest quality, the State rules contain requirements that certain types of OSSF be designed by either an engineer or a sanitarian or, in some cases, by an engineer only. The higher quality of design likely to be provided by those with greater education in the field would result in systems less likely to cause pollution and public health problems. The requirement for a professional design, rather than design by an installer or homeowner, is based on the required training and experience, under state rules/laws, for sanitarians and engineers. To the list of those systems which require a professional design (either sanitarian or engineer) the draft local standards add low pressure dosing disposal. The local standards also add lined evapotranspiration disposal to the list of those requiring professional design and, when the installation of these involves the construction of structural stabilization or leak monitors, the designer must be an engineer. The local draft requires that when the sewage generating units are mobile home, manufactured housing or recreational vehicle parks either a sanitarian or engineer must design the on-site sewage facility. If they serve more than 8 living units the designer must be an engineer. The local standards also require a professional design for non standard disposal methods.

To the list of systems which must be designed by an engineer, the local standards add the following types of systems: Those using intermittent sand filtration, those serving institutions that will discharge more than 2,000 gpd, those using non-standard treatment processes, those using concrete tanks that are not precast, those using secondary treatment and disinfection. The intent of any on site facility design is to provide the most efficient and economical means to treat and dispose of wastewater such that public health and environmental protection are ensured along with similar considerations for the consumer. Engineers are required by state law to be trained in design and as such are held liable for their services rendered. There is a mechanism through the Professional Engineers Board of Registration to hold engineers accountable for their work. Training in basic physical engineering principles is critical for designing more complex systems which are showing up more regularly due to advancement in technologies. Also very important is being able to understand physical and technical differences between what will work reliably for an anticipated reasonable life of a system as opposed to accepting what a vendor of a product might wish to sell. This is a result of training and a working knowledge of hydraulics and physical and biological treatment processes. Legislative intent during the previous session was very clear in that it recognized that sanitarians are not trained in design. Therefore the only enhancements made for sanitarians were those not associated with design but with educational and training requirements instead.

Reference material related to the requirements for designer qualifications is listed in the References at the end of this document under "Designer and Maintenance Contractor Qualification Requirements."
 

State regulations require that cluster systems be operated under a maintenance and ownership agreement. The local standards seek to strengthen this requirement by clearly requiring creation via the agreement of a management authority in which the responsibility and authority for operation and maintenance rests. This entity must be have the necessary easements and the planning materials submitted must include a description of the management authority and its structure and any legal instruments necessary for the creation of a management authority. Proper operation and maintenance of such a system is essential to preventing pollution and public health hazards, and the more clearly defined the entity is that provides operation and maintenance the better that service is likely to be.

The local standards add to the State regulations some specific requirements for cluster systems which will enhance their operational characteristics and provide additional protection from pollution and health hazards. These include the installation of effluent filters or screens in the tanks located on the individual properties, shut-off valves which are accessible to the management authority located where the effluent would enter the common portion of the system, and legally recorded easements. The requirement for effluent filters provides greater protection to the cluster system from movement of solids into the common portion of the system, and thereby will enhance the long term performance of the system and prevent damage from occurring. These are more important for cluster systems because the occupants of the dwellings may feel less responsible for the centralized portion of the system and may be less conscientious in their wastewater disposal practices. An additional requirement for a shut-off valve between the individual tank and the central portion of the system enables the maintenance organization to shut off the flow from an individual system should that become necessary to prevent sewage from entering and damaging or severely overloading the common portion of the cluster system.

The draft local standards also require electronic monitoring and automatic notification for failure of system pumps and compressors to be provided either to the maintenance authority or to the provider of the monitoring equipment so that failing components will be quickly repaired. To reduce the potential for pollution, the local standards add a requirement that the shared treatment and disposal components of a cluster system may not be located in the 100-year floodplain. Components on the individual properties may not be located in the 25-year floodplain.

Finally, the State regulations states that each person using a cluster system must be a party to the operation agreement. The local standard clarifies that this is the property owner of the individual lot, rather than only a tenant.
 

Due to the technology used or the special operating circumstances of certain kinds of OSSFs, greater protection of the environment and public health can be achieved through continuous operation of these systems under a maintenance agreement. The maintenance company can perform preventive services and rapidly respond in the case of failure of any components of the system. The State rules require maintenance agreements for certain types of systems, and the local draft adds to the types of systems requiring maintenance contracts the following: Those serving uses other than single-family residences or duplexes with flows exceeding 500 gpd, those using sand filtration and those using any non-standard or proprietary treatment processes. The maintenance agreement is helpful in situations of high flow because any failure of the OSSF could result in the discharge of greater amounts of sewage in a short time period. Systems utilizing sand filtration require periodic maintenance to clean the sand surface and check for effluent bypassing filtration. Non standard treatment systems, such as sludge processes, recirculating sand filters, trickling filters and rotating biological contactors, include components subject to breakdown or processes that require closer monitoring or processes that require effluent sampling to assure adequate performance.

While the State rules present the maintenance agreement requirements in the context of surface irrigation systems, the local draft establishes that these requirements are applicable to all circumstances in which a maintenance agreement is required. The draft also increases the standards for maintenance work by requiring that those performing the work be trained in the type of facility they maintain and that their work be supervised by the Installer II or Class C wastewater operator required for the maintenance company. When sampling is performed it is to be done in accordance with accepted sampling and testing criteria (Standard Methods for the Examination of Water and Wastewater published by the American Public Health Association).

The local draft raises the standards for chlorinators by requiring that they be compatible with the treatment unit used and be either commercially manufactured or built to commercial manufacturing specifications. Chlorinators are a key component of the OSSF that protects the public from exposure to partially treated effluent. This provision ensures chlorination with equipment designed and evaluated specifically for the purpose of wastewater treatment. These would be of appropriate capacity and use the correct type of chemicals for wastewater rather than those for other disinfection uses (such as swimming pool water disinfection). Faulty chlorinators have been identified as significant problems in jurisdictions in which surface irrigation is common.

The City draft also increases the submittal requirements for OSSFs which require maintenance agreements by specifying that the planning material for these OSSFs set forth where and when sampling is to be performed. The monitoring plan is reviewed and approved before a permit is issued to construct the system.

Additional material relating to maintenance requirements is provided at the end of this document in the References section titled "Maintenance and Periodic Re-inspection Requirements, Secondary Treatment, Pretreatment Tank Sizing (for Secondary Treatment Processes), and Septic Tank Pumping Intervals."
 

The State rules require that soil profile holes be dug to a depth of only 2 ft. or to a restrictive horizon. This matches the State requirements that standard disposal excavations not be within 2 ft of either groundwater or restrictive horizons. The local standards increase the depth soil profile holes must be dug to 4 ft. in the Drinking Water Protection Zone and 3 ft. elsewhere. These requirements are consistent with the increased separation distance between the bottom of a drainfield excavation and either groundwater or restrictive horizons. Also consistent with these increases is the requirement that the type and size of the OSSF be determined by the most restrictive soil class located within 4 ft. and 3 ft., respectively, of the bottom of the proposed excavation. In order to apply greater standards for separation from groundwater and restrictive horizons, it is necessary to require that excavations be dug to the greater depths.

The State rules refer to soil profile holes as "soil borings" or "backhoe pits" which is unclear as to the method of excavation. The use of the term "borings" implies that the examination can be achieved in a hole bored to the depth required. The local standards clarify that the excavation must be done by backhoe unless the permitting authority has approved another method for the site. Because they are small diameter holes, cores or borings do not allow examination of the soil profile at depths of up to 4 ft. Groundwater or drainage mottles might go undetected in examination of such a hole. Under the local standards, for a particular site, the permitting authority could approve another method of digging, including hand digging, if there are physical limitations to using backhoe equipment.
 

The draft contains additional protective requirements in the city’s Drinking Water Protection Zone that there be at least 3 ft. of suitable soil below the bottom of the drainfield, and that there be no restrictive horizon within this depth. Where the State rules specify that a restrictive horizon is determined by the presence of material which an auger will not penetrate, the local standards specify that this refers to a hand, not a mechanical, auger. Mechanical augers will penetrate material which is restrictive to effluent passage. In the Drinking Water Protection Zone, separation of the proposed drainfield excavation from groundwater or drainage mottles indicative of groundwater must be 4 ft. to provide more soil through which effluent must pass before reaching the groundwater. Elsewhere the depth to groundwater must be no less than 3 ft. below the excavation. These limitations apply to standard disposal methods. The use of additional treatment and non standard or proprietary disposal methods enables installation with shallower depth to groundwater or restrictive horizons.

The following is a quote from "Vertical Separation, A Review of Available Scientific Literature and a Listing of Fifteen Other States" (Office of Community Environmental Health, Washington State Department of Health, October 1990):

"For effective treatment, it is essential that on-site sewage systems include, among other things provisions for adequate vertical separation. Vertical separation primarily affects degradation of organic nutrients (i.e., BOD₅) and removal of bacteria and viruses. It also plays a role in converting nitrogen to soluble nitrate (NO₃) ions which can then readily migrate into the groundwater unless denitrifying conditions are present."

The amount of vertical separation necessary is still being debated, as there is disagreement over the degree of treatment needed. Research so far shows that 2 to 4 feet of vertical separation will adequately remove bacteria (<200 fecal coliforms per 100 milliliters), depending on soil type and conditions. In order to assure an unsaturated zone of 2 feet, it usually is necessary to construct a system with even greater separation in order to account for groundwater mounding.

The 2 to 4 feet mentioned in this scientific literature only addresses bacteria removal, and does not consider depths needed to ensure sufficient nitrogen removal (which may require greater separation depths due to the high mobility of the nitrate ion). Another quote from this literature is as follows:

When the soil was allowed to become oxidized large amounts of nitrogen were converted to nitrate which rapidly leached to the groundwater. Therefore, nitrate leachate was the greatest environmental hazard identified in the study. Reneau et al (1985) summarized the research on processes and transport through the soil of nitrogen and phosphorus. They concur with the findings of Brown et al (1977).

The City’s required separation distances are consistent with the conclusions and recommendations drawn from the above scientific literature review.

Monitoring data collected from existing onsite wastewater systems using conventional septic tank pretreatment followed by either low-pressure dosed disposal or conventional gravity flow distribution supports the need to maintain vertical separation distances in the City’s Drinking Water Protection Zone (DWPZ) which are greater than the state minimal standards. Lysimeters have been installed downgrade of drainfields in areas within the DWPZ, and monitored for an extended period of time to determine levels of performance that could be expected from systems served by septic tanks and either LPD or gravity flow subsurface distribution systems in hill country limestone conditions. The systems monitored were constructed under standards requiring a minimum of 4 feet of vertical separation to rock or groundwater. Particular consideration was given to monitoring levels of fecal bacteria and total nitrogen. Preliminary results show that, while average nitrogen levels tend to be less than 10 mg/L, monitored levels exceeded 10 mg/L on a number of occasions, indicating that short-circuiting of effluent is occurring at times without sufficient soil treatment. Fecal bacteria levels were at times very high and may be of even greater concern than nitrogen levels, in terms of maintaining sufficient vertical separation distances to rock or groundwater. Fecal coliform averaged a minimum of close to 500 CFU/100ml at one site to several thousand at other sites, with ranges up to as much as 240,000. Reducing minimal separation distances to rock or groundwater will tend to increase levels of nitrate-nitrogen and bacteria or viruses reaching rock or groundwater. Therefore, the City proposes to require a minimum of 4 feet to groundwater in the DWPZ, and 3 feet to rock in the DWPZ for subsurface disposal methods that utilize only septic tank pretreatment.

Some additional reference material related to soil depth and separation from groundwater or restrictive horizons is listed at the end of the document in the References section titled "Vertical Separation Distances to Rock or Groundwater."
 

On-site sewage facility components (treatment and disposal units) must be installed at a protective horizontal distance from environmental features such as water wells, streams, ponds, lakes, building foundations, property lines, swimming pools and other structures. The reason for this separation is to provide land across or through which the effluent would have to pass to contaminate surface or groundwater. While the State rules provide a table listing a number of separation distances, the local standards have greater distances for some situations. The local standards make a distinction between lakes which provide drinking water (such as Lake Austin) and other lakes which are not water supply lakes. While the State rules require a separation for soil absorption and unlined evapotranspiration disposal areas from any lake of 75 ft. and will allow 50 ft. where secondary treatment and disinfection are used, the local standards require that these disposal areas be 100 ft. from a water supply lake (75 ft. if low pressure dosing is used and 50 ft. if low pressure dosing is used with secondary treatment or nitrogen reduction and disinfection are used).

Similarly, the local standards require that lined evapotranspiration beds be at least 100 ft. from a water supply lake and if a leak monitor is used, this distance can be 50 ft. The State rules allow lined evapotranspiration beds to be no closer than 50 ft, regardless of whether or not there is a leak monitor included.

There are a number of greater separation distances required for surface irrigation in the local standards. The irrigated areas must be 150 ft. from a drinking water supply lake and 75 ft. from a non water supply lake while the State rules specify a separation of 50 ft. for any lake. The local standards require that the irrigated area be 25 ft. from a dwelling and the State rules have no separation distance requirement. Under the local standards the irrigated area must be 10 ft. from an up-slope property line (the same standard as in the State rules), but they must be 25 ft., not 10 ft., from a down-slope property line. Finally, the local rules require that the irrigated area be 50 ft. from a sharp slope or break while the State rules require a separation of only 25 ft.

The purpose of these separation requirements is to reduce the potential for treated effluent to come in contact with humans or pets, or to drift or run off onto adjacent properties, or into critical water supplies. To quote from Natural Systems for Waste Management and Treatment, by Reed, Crites and Middlebrooks, "For surface-application systems, the surface runoff of applied wastewater is known as tailwater. Collection of tailwater and its return to either the storage pond or the distribution system are an integral part of the design. In addition, sprinkler-application systems may employ tailwater runoff control to avoid off-site discharge of applied wastewater." For individual residences utilizing surface irrigation of effluent, the design and construction of true tailwater collection and return structures for controlling surface runoff of effluent is generally not feasible, particularly given the occasional intense hill country rainfall events. Quantities of water that would need to be collected, stored and re-applied would be too great for individual residential properties. Therefore, in the City’s proposed rules, an alternate approach is used which relies on requiring sufficient lot sizes and horizontal setbacks to create buffers between adjacent properties and water supplies. In this way, there is an opportunity for additional treatment to occur through overland flow processes, such that potential impacts are lessened.
 

In the criteria for septic tanks, the local standards contain requirements additional to those in the State rules. The purpose for these additions is to provide for superior installation of these treatment components. The local standards require that cleanout ports on septic tanks be located to allow direct access to tank components that require periodic inspection and maintenance. The higher quality of maintenance which can be accomplished with properly located cleanout ports will extend the life of the system and prevent treatment process breakdown with possible backup of sewage into the home or business.

The State rules specify that tanks must not leak and must be structurally sound. The local standards enhance this by requiring that the tanks be leak tested before being covered. The testing would either be in accordance with the manufacturer’s specifications and by filling with clean water for a 24-hour period. Since damage to tanks can occur in transit to the OSSF site, the likelihood of tank leakage and subsequent pollution of groundwater is reduced by leak testing in place after installation. This testing has historically been required by the City’s permitting authority. Additional material relating to leak testing of septic tanks is listed at the end of this document in the References section titled "Septic Tank Leak Testing."

The local standards also require that each model of prefabricated tanks must be approved by the permitting authority as meeting standards before that model is placed in use. Under the State rules the standards which tanks must meet include the ASTM standard C1227-93, Standard, "Specifications for Precast Concrete Septic Tanks." By utilizing pre approval of models the permitting authority can verify compliance with this standard.

Finally, while the State rules do not require pretreatment tanks for secondary treatment units, the local standards require that a pretreatment tank be used and that the tank have a minimum capacity determined by the manufacturer or designer of the secondary treatment unit. This will provide greater protection against surges in flow to the secondary treatment unit and improve the quality of effluent reaching the secondary treatment unit, without causing reduction in the biological treatment provided by the unit. Its performance and functional lifespan are thus increased.
 

In order to improve the construction of intermittent sand filters, the local draft requires that the media to be used must be certified as the correct media by the supplier, a registered engineer or another professional authority approved by the permitting authority. Use of sand media which contains too many fines can result in very premature clogging of a sand filter. In areas of the country where intermittent sand filter are commonly used, failure due to too many fines in filter media has been documented. Use of too coarse media can result in insufficient treatment. A requirement that watertight boot-type inserts be used where piping penetrates the liner of the filter bed is also included, as is a requirement to leak test the liner both before and after the underdrain gravel medium is installed. The boot-type watertight insert is necessary to prevent water from leaking into or out of the liner where pipes penetrate the plastic liner. Finally, the City draft requires that sand filters must include maintenance features necessary for routine maintenance, including pipe turn-ups and valves for flushing pipes that distribute wastewater across the sand filter. These additional requirement, not mentioned in the State rules, will result in more reliable treatment of the effluent by the intermittent sand filter.

Additional material relating to intermittent sand filter designs is listed at the end of this document in the References section titled "Intermittent Sand Filters."
 

In its requirements for standard disposal processes, the local standards include a prohibition of the use of chipped tires in absorptive drainfields. The State rules allow the use of chipped tires. Experimental use of chipped tires was recently attempted in order to see if this could be a use for recycling of tires. However, they present a hazard with the imbedded metal that may perforate liners. In addition, the chemical and biological reactions which need to occur on the surface of the porous media are not facilitated by the use of chipped tires. The effectiveness of tire chips as a media are unproven and they may contribute pollutants to the leachate in OSSFs.

The draft also includes requirements intended to provide enhanced protection through higher standards (greater thickness and durability) for the liners for evapotranspiration beds and a requirement that watertight boot-type inserts be used where piping penetrates the liner. The requirements include liners of at least 30 mil thickness made of polyvinyl chloride or high density polyethylene intended by the manufacturer to be used as liner material. The State rules specify impervious rubber or plastic material having a thickness of at least 20 mils.

The depth range for pumped effluent drainfield lines is changed from the State requirement of 1.5 ft. to 3 ft. deep to a range of 1.5 ft. to 2.5 ft. This specifies more shallow placement of these lines which keeps them closer to the root zone and in soil where evapotranspiration is enhanced. The function and longevity of the pumped effluent drainfield are thus extended.

The vertical separation required by the local standards between the bottom of the trenches in a pumped effluent drainfield and groundwater or restrictive horizons are depicted in two tables attached, one for the Drinking Water Protection Zone and one for other areas. The separations take into account the level of treatment provided prior to disposal, the soil type in which the effluent is placed and whether or not the site is in the DWPZ or not.

The elusive nature of tracking subsurface pollutant movement mentioned at the beginning of this document is exemplified in scientific data and discussions related to establishing sound vertical separation distances by local jurisdictions in their rules. The vast majority of scientific data on this subject points to a need for minimum separation of two to four feet, or even greater of suitable soil (good organic soil such as a sandy loam) to remove key pollutants to an acceptable level. On the west side of Austin, there are very few areas that would have these favorable conditions. In most areas, where two to four feet of diggable material is present, the soil tends to have large amounts of coarse limestone fragments, and will not remove most pollutants as efficiently as say a sandy loam. Therefore, a benchmark distance of 2-4 feet of suitable soil must be increased to a greater distance to facilitate more treatment in local marginal soils that overly sensitive environmental conditions or watersheds. [Despite requests from local engineers and scientists to categorize it differently, TNRCC staff have continued to consider these "caliche" soils a "Class III" soil, which is "suitable" under the state rules.]

Effluent passes through different soil types at differing rates and receives different amounts of treatment by the soil. Therefore, the effluent can be placed closer to groundwater or restrictive horizons if more treatment is given to the effluent before final disposal. The differential standard thus assure greater protection in general and enhanced protection in the DWPZ.

Additional references regarding vertical separation distances are located at the end of this document in the References section titled "Vertical Separation Distances to Rock or Groundwater" and in the section titled "Nitrogen Removal."
 

In many areas of the City, the presence of limestone outcrop and/or thin soils with coarse limestone fragments does not offer sufficient soil treatment capabilities. These conditions are common to the City’s Drinking Water Protection Zone. One wastewater pollutant which is readily formed when wastewater effluent is applied to the types of soils characteristic of the hill country is nitrate-nitrogen. Federal drinking water standards limit nitrate-nitrogen to 10 mg/L (as nitrogen) due to health risks associated with higher levels of the nitrate form of nitrogen in drinking water, including methamoglobinemia ("blue baby syndrome") in infants. In areas where the City has concerns about impacts to drinking water supplies in these types of conditions, the City may require that total nitrogen removal be provided to an appropriate level as an annual average, prior to subsurface disposal of the effluent. [While NSF or other accepted testing programs of proprietary treatment units may provide performance test results on a daily, weekly or monthly basis, these results are not meaningful for actual operating OSSF’s, since sampling may only occur several times a year. Therefore, annual averages are used as limits for system performance.]

With regard to proprietary disposal systems, the local standards provide for only a 20 percent reduction in drainfield length for leaching chambers. The 40% reduction allowed in the State rules was based upon a theory that because no gravel is used with these chambers, the absorptive area could be reduced. This theory, the so called "shadow effect", has not been substantiated. In fact, leaching chambers may increase the effects of hydraulic and pollutant loading in the soil treatment zone, since they do not have gravel. The "shadow effect" theorizes that a drop of water behaves similarly to a ray of light as it travels downward through the gravel media in a disposal trench; and that, like a shadow cast by a rock, one would find dry dirt beneath the stone at the base of the trench. In terms of direct reproducible field experience, City staff have not found dry soil beneath gravel in the portions of disposal trenches that have regularly received wastewater effluent. Surface tension principles and phenomena, which can be demonstrated in either the field or laboratory, support this observation. Further, as water droplets travel downward through the gravel, treatment occurs on the surface of the gravel where bacterial cultures form over time, which are responsible for the biological treatment processes. This is called an attached growth biological treatment process, much like a trickling filter. Due to their structure, leaching chambers do not enhance evapotranspiration and do increase soil saturation and subsequent anaerobic conditions. In addition, the research upon which the 40% reduction was based was performed in arid regions of the state. Central Texas is not an arid region. The City therefore believes that, at best, only a 20 percent reduction is warranted for these systems in order to reduce the likelihood of failure of the drainfield.

In order to improve the functional performance and longevity of drip irrigation systems, the local draft calls for automatic flushing of filtration units and the emitters back to the treatment units. If this flushing must be performed manually it is less likely to be done by the homeowner and clogging problems will be more common. Site visits to some properties using drip emitters with manual field switching and back flushing features confirms this.

Vertical separation between drip emitters and groundwater or restrictive horizons is also reflected in the same attached figures initially referenced in the section on pumped effluent drainfields. Due to more shallow placement of drip emitter lines, more evapotranspiration can be expected to occur in dry weather conditions. Less infiltration of effluent will occur with more attenuation of pollutants in the root zone. Therefore, these lines can be placed closer vertically to groundwater or restrictive horizons than can other disposal excavations. Again, however, the level of pretreatment, the soil in which the wastewater is applied and whether or not the site is in the Drinking Water Protection Zone determine the differing separation depths.

Additional references regarding vertical separation distances are located at the end of this document in the References section titled "Vertical Separation Distances to Rock or Groundwater" and in the section titled "Nitrogen Removal."
 

The local standards include more protective provisions regarding non standard disposal processes than those contained in the State rules. Vertical separation between the bottom of low pressure dosed trenches and groundwater or restrictive horizons is described in the above referenced attached figures. Mound disposal systems are required to meet the same separation depth standards as low pressure dosed drainfields. The depth is measured from the bottom of the excavation built into the mound.

Additional references regarding vertical separation distances are located at the end of this document in the References section titled "Vertical Separation Distances to Rock or Groundwater" and in the section titled "Nitrogen Removal."

Due to concern about the surface irrigation of effluent in on-site sewage facilities, the City of Austin intends to have more stringent requirements for the effluent used for irrigation and to base the effluent quality on whether or not the area irrigated is accessible to the public or to the occupants of a home. In areas where access is restricted, lower effluent quality is allowed; however, greater public health protection is provided by higher effluent quality in areas accessible to the public. For areas with restrictive access, the effluent must meet the following standards which are similar to those in the Chapter 285 State rules:

Biological Oxygen Demand and Total Suspended Solids	30 day average of 20 milligrams per liter or less and A single grab measure of 45 milligrams per liter or less
pH	6.0 to 9.0
Fecal Coliform	A geometric mean of 100 colony forming units per 100 milliliters or less and A single grab measure of 200 colony forming units per 100 milliliters
Chlorine	1 milligram per liter free and residual

For areas with access unrestricted, the effluent must meet the following standards which are similar to those in the State’s Chapter 210 rules for Type I Reclaimed Water (where human exposure is assumed to occur):

Biological Oxygen Demand and Total Suspended Solids	30 day average of 5 milligrams per liter or less and A single grab measure of 15 milligrams per liter or less
pH	6.0 to 9.0
Fecal Coliform	A geometric mean of 20 colony forming units per 100 milliliters or less and A single grab measure of 75 colony forming units per 100 milliliters
Chlorine	1 milligram per liter free and residual

Where access to the areas where surface application of wastewater is not restricted (such as on residential properties), it is essential that sufficient treatment be provided to the wastewater before it is land applied so that public and environmental health are protected. For larger scale wastewater systems relying solely on surface irrigation of effluent for disposal, such features as storage ponds are required for wet weather conditions so that wastewater is only applied under suitable climatic conditions and at times when the effluent will not have adverse public or environmental health impacts. Storage ponds (or other types of storage facilities) are not required for residential scale OSSFs using surface irrigation for disposal. Thus, the quality of effluent produced from the system must be continuously such that it may be applied under any conditions. In its Chapter 210 rules, the State of Texas has set forth the quality of effluent considered suitable for surface application where public access is unrestricted and where public exposure to the effluent is likely. While that effluent quality is superior to what is proposed in these rules where public access is unrestricted, it was used as a basis in determining reasonable guidelines. Adjustments were made based on existing proven technologies in the OSSF industry, and the quality of effluent that can reasonably be produced on a regular basis utilizing currently available treatment methods. These effluent quality standards are combined with other requirements for surface irrigation in the proposed City rules to minimize risks to public and environmental health from the surface application treated wastewater.

In the local standards there are a number of additional requirements for surface irrigation systems which are intended to provide greater protection of public health and better performance and greater longevity for these systems. Due to the common occurrence of rock outcroppings in the Central Texas region, areas of rock outcroppings are specified as unacceptable for surface application of effluent. The application area would therefore need to be either relocated or increased in size if it contained rock outcroppings. For purposes of designing surface irrigation systems in Austin, the City draft specifies that an irrigation application rate (Ri) of 0.055 gallons per square foot per day be used. This increases the required application area over that which would be determined based upon the 0.064 rate indicated in the State rules. Distribution of the effluent over a wider area will improve treatment in the topsoil given the rainfall amounts common to Central Texas. Surface application distribution piping is required in the draft to be placed below ground to prevent disconnection of the piping, to protect the piping from damage and to prevent human contact with the piping. The State rules do not specify subsurface placement of the distribution piping. In the local standards sprinklers are required to be controlled by commercial irrigation timers in all cases since these will more reliably control application timing and thereby prevent human exposure to the effluent. The State rules require these timers only when the setback of the irrigated area from property lines is less than 20 ft. In addition, the local standard is that irrigation be limited to night-time hours, again to reduce human exposure. Additionally, the local standards require that a hose bib be installed in the effluent line in the pump tank readily accessible to the ground surface for access to perform sampling.

The local draft also calls for electronic monitoring of system pump or compressor functions and automatic notification to either the maintenance company or to the monitoring equipment provider. This will ensure that failure of these components in the surface irrigation system is corrected faster. Additional requirements to reduce human exposure are that a property owner prevent spray irrigated effluent from crossing property lines, that surface irrigation areas be clearly marked for multifamily, cluster or nonresidential properties so that the public does not enter the area, and that surface runoff be prevented from entering or leaving an irrigated area.

Due to the improved distribution capability of low pressure dosing, the local standards requires that it be used in soil substitution drainfields. Similarly, in newly constructed drainfields following aerobic units, secondary treatment and disinfection, some form of pressure distribution is required. In retrofitting with secondary treatment and disinfection, pressure distribution is not required.

Reference material regarding surface irrigation is listed at the end of this document in the References section titled "Effluent Irrigation Standards."
 

The local standard contain some other requirements not found in the State rules. The draft requires that pump tanks be sized for one day of flow above the alarm-on level. This would allow adequate time to obtain service of a failed pump and reduce the likelihood of overflow and exposure of effluent. The State rules only require that these tanks be sized for 1/3 day (8 hours) and that this may be reduced to 4 hours average flow when multiple pumps are used.

The local standards specify that the owner of a composting toilet handle material removed from the unit in compliance with federal regulations and State law (Part 503 of Title 40 of the Code of Federal Regulations and Chapter 312 of the Texas Health and Safety Code. This might prevent the unintended application of this material to gardens or other sites where human contact is possible. This requirement is consistent with federal and state requirements for the final disposition of composted fecal material.
 

The proper dismantling of sewage tanks of any type is important to preventing accidental drowning or injury by humans entering the site in the future. For this reason, the local standards require that the lid be crushed or removed to prevent the creation of any void space in the tank after the addition of soil or fill material. In addition, the City requires inspection of the dismantled tank so that it can ensure that the work was done properly and so that records for an old OSSF can be cleared from the permitting authority files. These items are not required under the State standards.

On occasion OSSF tanks are installed and for one reason or another are not put into immediate use. In these cases, the local draft provides for assurance by the permitting authority that the tank is properly closed and protected from vandalism and damage and does not present a hazard to humans who might enter the area. This also is not mentioned in the State standards.
 

The operation of an on-site sewage facility is primarily performed by the homeowner. For this reason, the homeowner needs information to enable proper operation of the system. This information, which is required in the draft to be supplied by the designer, is specific to the type of on-site sewage facility. The State standards call for the system installer to provide a set list of maintenance, management and water conservation practices which are common to almost all systems. The requirements in the local standards are that information also be provided by the designer and be specific to the operation of the system installed for them.

As discussed in an article in the Spring 2000 issue of Small Flows quarterly (published by National Small flows Clearinghouse), "One of the most common reasons that onsite systems fail is a lack of ongoing maintenance. This is why many communities focus their onsite system management efforts on providing regularly scheduled inspections and maintenance….Many wastewater treatment technologies require regular maintenance to be effective. Systems also need regular inspections so that the need for maintenance or repairs can be identified and addressed quickly."

While the State rules do not specify an interval of time between pumping of septic tanks, the local standard requires pumping every 4 years. OSSF regulatory authorities were contacted in jurisdictions across the U.S., with similar experiences found in most areas. There was general agreement that the soundest approach is to require either (1) annual inspections including opening septic tanks and measuring sludge levels, or (2) mandatory periodic pumping intervals to prevent excess build-up of solids in tanks. This is a preventive measure that can save property owners very costly field replacements, if solids are carried into the field lines from the septic tank.

While the State rules mention that it is not advisable to allow water softener back flush to enter an on-site sewage facility, the local standards explicitly prohibit it. The treatment of wastewater in a septic tank depends upon a balance of microorganisms which digest the sewage wastes through anaerobic processes. In an aerobic treatment plant, there is another mixture of desirable organisms which accomplish treatment through aerobic processes. Water softener back flush contains significant amounts of salts which would alter the chemical balance in the treatment system and kill the much needed micro organisms. Treatment of the wastewater would, therefore, be inadequate.
 

The City of Austin Land Development Code currently states "For a lot in the Edwards Aquifer Recharge Zone that is not served by a sanitary sewer, an alternative sewage disposal system that does not use a conventional soil absorption drainfield is required." The intent of this requirement, while it is not worded consistent with the State rules for on-site sewage facilities, is to utilize higher treatment and/or better disposal methods in the aquifer recharge zone. For development of the local standards for on-site sewage facilities, reconciliation with the Land Development Code was necessary to consolidate requirements for on-site sewage facilities. To capture the intent of the Land Development Code in language consistent with the State rules, this section has been reworded to prohibit use of standard septic tank treatment in combination with gravity soil absorption disposal.

Some form of pressure distribution of effluent must, therefore, be used for facilities using only septic tank treatment or else higher levels of treatment must be included in facilities using only gravity soil absorption for disposal. Pressure (pumped) distribution of effluent can provide much more uniform subsurface application of wastewater than conventional gravity subsurface disposal which enhances treatment processes. Pressure distribution systems also facilitate alternate dosing and resting cycles in the disposal field, which helps maintain better soil treatment conditions and can significantly increase the life of the disposal system. Better effluent distribution is particularly important in the Edwards Aquifer recharge zone, where disposal fields are underlain by karst limestone conditions. Site evaluation methods used for small-scale onsite systems cannot ensure either the presence or absence of conditions in the disposal area that may allow only partially treated effluent to recharge directly into the aquifer, particularly during wet weather.
 

While the State standards make no mention of installation of on-site sewage facilities where organized sewage disposal system are in place, the local standards prohibit construction, alteration repair, extension or operation of such systems when the organized sewage system is within 100 ft of the property. There are exceptions to this requirement and it can be allowed if the property owner has been denied service by the organized system, if the permitting authority documents that connection to the sewer is not feasible, if the on-site sewage facility is a greywater system, or if the OSSF is a composting toilet or incinerating toilet. If the lot meets the size requirements and site conditions and a site-specific design is provided and if there will be no adverse effect on public health or the environment, the permitting authority can also allow installation of an on-site system with a sewer system nearby.

Under the local standards, when sewer is extended to within 100 ft. of the property line, with the same exceptions listed above, the property owner must connect to that system. This requirement is within the authority of a municipality to require connection to sewer. If the permitting authority finds that the on-site sewage facility may continue to be used, based on such factors as the type of facility served, the age, condition, and capacity of the on-site sewage facility, the availability of records on the system and changes to the system or the generating unit, the property owner need not connect to the sewer system when it is extended.

While not absolutely requiring connection to an available sewer, this section forces evaluation of the best public health and environmental protection in circumstances where sewer is available. It’s primary use is in the conversion to sewer where an on-site sewage facility has failed and reconstruction of the facility cannot be performed in compliance with State and local construction standards. As sewer is extended into neighborhoods, use of the on-site sewage facilities continues under the exceptions to the connection requirements. However, when continued use of the on-site sewage facility is not longer appropriate, connection can be required.

The State rules are silent on the subject, but the local standards include a prohibition against using blasting in the installation or repair or remodeling of an on-site sewage facility. If used inappropriately, for example blasting the bedrock below a drainfield, the use of explosives could result in a direct channeling of effluent wastes into groundwater below a rock layer. Once the disposal field is installed and put into operation there may never be any evidence of failure of the system at the surface while untreated or poorly treated effluent flows into underground caverns or the aquifers. There are rarely some appropriate needs for explosives and with a prohibition in the local standards the only way it could be used would be if a variance were granted. The permitting authority could therefore allow blasting on a case-by-case basis if the applicants demonstrate that it is necessary and that equivalent environmental and public health protection is provided.