Septic and Onsite Wastewater Systems

Septic and Onsite Wastewater Systems

3-Creeks Natural Area Floodplain Enhancement Project Presentation

Please join us for a Zoom webinar to learn more about the 3-Creeks Natural Area Floodplain Enhancement Project.

The project team will present concepts, answer questions, and allow for comments. Register link in advance of the meeting online. After registering, you will receive a confirmation email with the information needed to join the webinar on Dec. 2 at 6 p.m.

Register online

Stakeout Procedure


Stakeout sample

To determine if sufficient space exists on a lot with limited area for the proposed development, and ensure all septic components meet required setbacks.


  1. Clear tall brush in area of stakeout, approximately 10,000 sq ft (100'x100' or equivalent). Do not remove topsoil or otherwise grade the area. If the area is covered with brambles, clear a path to any features requiring a setback (ex: escarpment, stream, or well).
  2. Use a transit or laser (not a builders level) to mark points about 25 ft apart on the leach line. Make sure the line is at the same elevation (or within the allowed trench depth variation) throughout its length. Mark the points with stakes tall enough to be visible above any remaining brush. Color-code each line using alternating colors for each leach line. Alternatively, you can spray paint or drape string between stakes of each line. Do this for both the original and replacement drainfields.
  3. Stake the other septic components, such as the septic tank, and sand filter if required, as well as the house, accessory buildings, drive, and any other proposed development. If you do not know the actual house you can draw a general envelope of the area where the house could fit. Check with the Planning Section to ensure that all building envelopes meet their requirements for setback to the property lines.
  4. Accurately record the elevation at the beginning and end of each leach line, as well as the line lengths and color in a chart. Draw all the septic components and other developments on an accurate, to scale plot plan and submit it to the Soils Section for review. Provide a north arrow, and roads on your lot frontage. Draw in all features that require a setback, and the distance from the feature to the closest septic component.
Sample Chart
  Line # Color Beginning elevation Ending elevation Length (ft)
Original area 1 Red 0.64 0.64 58
  2 White 2.87 3.00 75
  3 Red 5.89 5.90 125
  4 White 7.03 7.38 125
  5 Red 8.90 9.02 92
Repair area 1 White 2.57 3.00 92
  2 Red 5.00 5.02 112.5
  3 White 6.49 6.63 112.5
  4 Red 7.80 8.10 112.5
Septic tank   Orange      
House   Blue      
Drive   Yellow      

* Check site evaluation for maximum trench depth variation

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Authorization Notice

Do I need an Authorization Notice?

An Authorization Notice is required when you propose to reconnect to an existing septic system, when there is an increase in flow, when there is a change in use (from residential to daycare, for example), or when a temporary dwelling is needed for hardship reasons*.


To apply for an Authorization Notice, submit an Existing System Evaluation Report (ESER) from a DEQ certified provider. If no previous records are available you will also need to provide a Record Drawing and Installed Materials List from a licensed septic installer or consultant.

System components may need to be uncovered for soils staff review if:

  • If the maintenance inspection report is in dispute by the county or property owner.
  • If there are no records on the system and the materials in the system are not consistent with a system installed prior to 1974
  • The new proposal (foundations or partition, for example) appears to conflict with minimum required setbacks to septic components (5 ft to the tank and 10 ft to the drainfield).

Evaluation Results

Based on the Inspection Report, we may require that the septic components be moved, replaced or supplemented. Any septic system construction will depend on the analysis of the test pits and other site conditions. Other than maintenance (pumping the tank or removing roots from any components) all work on the septic system must be done under a permit.

Altering the septic components

Minor changes to a septic system can be done under an alteration permit. If more than 50% of the drainfield is affected or if there is an increase in flow greater than 300 gallons per day or 50% of the system capacity (whichever is less), a site evaluation, rather than an authorization notice, is required and new construction permit, rather than an alteration permit will be required.

Repairs to the existing system

If system components are found to be in need of repair or replacement, a septic repair permit will be required. Test pits may be required for repairs to drainfield components.

Clackamas County Septic and
Onsite Wastewater
150 Beavercreek Road
Oregon City, OR 97045

*Medical hardship Authorization Notices are required every 5 years as per OAR 340-071-0205

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Same Owner Easement Release Instructions

The Same Owner Easement form used by all field offices to site a system or a portion thereof onto adjacent property under the same ownership may establish an agreement and covenant between the Grantor and the State of Oregon through the Department of Environmental Quality.

Such an easement can not be released except through an action by the Department. The Regional Division Administrator must sign the easement release form. Before the Regional Division Administrator will sign the form, all documents related to releasing the easement must be in order, and must be passed through a short chain of review within the Department.

What documents must be assembled?

  1. One copy of the original (and current) easement;
  2. Written statement from the Legal Entity (e.g., City, County or Sanitary District) assuring the sewer connection has been made. If other than a sewer connection the property owner must provide a written statement describing why the easement is no longer needed;
  3. The completed original easement release form.

Where are these documents to be sent?

The property owner is to send the documents to the Agent in the appropriate County within the region. The documents will be reviewed, and verification that the easement should be vacated will be made. The Agent will forward the documents with a written statement that the easement should be vacated to the appropriate DEQ regional lead staff listed below. Once the DEQ regional lead staff person is satisfied that all is in order, they will forward all documents and a summary report to their manager or Regional Division Administrator for approval. Once the Regional Division Administrator signs the easement release form, all documents will be returned to the DEQ regional lead staff person. The DEQ regional lead staff person will return the original easement release form to the Agent and make copies of these documents for the Department file record. The Agent will return the original easement release form to the property owner and make a copy for their file record. The property owner now needs to complete the process by recording it at the county recorder's office and sending a copy of the recorded document back to the onsite office that holds the property file.

DEQ onsite program regional lead staff contacts

Western Oregon (North) Gary Artman
Western Oregon (Mid) Randy Trox
Western Oregon (South) Chuck Costanzo
503-471-2850 x224
Eastern Oregon Bob Baggett
503-388-6146 x230
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A Homeowner's Guide to Evaluating Service Contracts

Bruce J. Lesikar, Courtney O'Neill, Nancy Deal, George Loomis, David Gustafson, and David Lindbo


Proper operation and maintenance of onsite wastewater treatment systems is critical to ensure good performance. It is also an important way that you, the homeowner, can protect a significant investment. Having a service contract with a professional trained in the operation and maintenance (O&M) of onsite wastewater treatment technologies is a sound approach to achieving proper maintenance of your system.

O&M service visits often result in early detection of problems that could lead to a malfunction. Early detection makes it possible to take remedial action before a system becomes a public health hazard, detriment to the environment, or a liability for the homeowner. Some counties and states have regulations that require a certain amount of system management. Whether or not they are required in your area, routine service will ensure that onsite wastewater treatment systems will continue to be a permanent and effective part of our wastewater treatment infrastructure.

People seeking services from a maintenance service provider desire proper service for a fair price, but they often don't know what services are necessary for their system. As an onsite wastewater treatment system owner, you should be aware of the different contracts that may be available and know exactly what service you can expect. In many cases, fees for service agreements are comparable to or less than those charged for centralized sewer service.

Communicating with the service provider

The following terms and definitions are provided to establish an understanding of terms that might appear in an O&M service contract.

Service is the action of performing activities such as, but not limited to, inspection, operation, and maintenance of system components.

Inspection is the process of identifying the current status of system performance for reporting purposes. Inspections may be performed for various purposes including monitoring, troubleshooting, or point of sale evaluation. An inspection would be performed at the first service of a contract or during contract negotiation.

Operation is the action of assessing the functionality of each component of the system. Each component must be operational in order for the entire system to achieve the desired performance. For example, a properly operating septic tank exhibits three distinct layers, indicating that solids are settling to the bottom and scum is rising to the surface, allowing a clear zone to develop in the middle. Likewise, chlorine must be present in a chlorinator for it to be operating properly.

Acceptable is a condition in which a component is performing its intended purpose and is considered to be in an operable state or operational.

Unacceptable means a condition in which a component is not operational. This condition indicates the need for maintenance, repair, replacement, upgrade or further investigation.

Maintenance is the action of performing routine activities to keep the system operational. This may include making minor repairs or replacements to ensure continued proper performance of the system. Examples of maintenance activities include cleaning and/or replacement of air filters, cleaning effluent screens, cleaning pump intakes, cleaning the air delivery system, and removal of residuals from tanks (pumping).

Repair is the action of fixing or replacing substandard or damaged components. Repairs may be required repairs, recommended repairs, or upgrades. A required repair refers to the repair of a component that must be operating for the system to properly treat wastewater. Examples of instances where required repairs are indicated include a baffle missing in a septic tank, an air pump not performing, or an effluent pump not performing. Recommended repairs refer to items that are still operating but may be reaching the end of their useful life. An example of this is when the discharge rate for an effluent pump decreases over time and approaches the minimum acceptable rate.

Replacement is the process of exchanging a component with an equivalent component. For example, a broken valve is replaced with the same model valve, the effluent pump is replaced with a pump that has the same operating characteristics, and a riser cover is replaced with the same type riser cover. While the new component might look different, it would perform equally as well as the one it replaced.

Upgrade is the action of creating a better system by adding a component or increasing the effectiveness of a component. Upgrades do not necessarily change system performance; instead, they make the system easier to maintain or increase the robustness of the treatment process. Examples of upgrades may include addition of effluent screens, adding risers to frequently accessed components, installing additional sensors to the system, adding remote monitoring, or changing the type of disinfection component used.

Monitoring is the action of verifying performance requirements for a regulatory authority. This may include collecting samples for analysis of nutrients and pathogens to assess the treatment performance of system components. Monitoring may also include measuring the amount of flow to various system components to make sure that recommended rates are not exceeded.

Reporting is the action of submitting a detailed account of operation and maintenance activities performed on a system. Reports are sent to the system owner and to the permitting authority. Reports serve to document the activities performed at the site as well as the current status of the onsite wastewater treatment system.

Troubleshooting is the act of locating and eliminating sources of trouble. It is not included in maintenance, monitoring, or operation. Troubleshooting is a separate category, because the service provider evaluates the system to determine why it is not meeting performance criteria. Troubleshooting requires the service provider to have in-depth knowledge of treatment processes and how the treatment components react to various wastewater constituents. A service provider capable of conducting troubleshooting is a specialist in the field.

Mitigation is the act of fixing a system that is in failure. Fixing the system should be preceded by an evaluation of all the components (source, pretreatment, final treatment and dispersal) to determine the reason for the malfunction.

Compensation is the action of receiving a fair price for proper service and is critical to the management process. Compensation is generally received in the form of a base contract fee. Fees for repairs, replacement parts, maintenance, and associated labor costs for additional service may apply. Consumers must clearly understand what is included in the base price and what is considered an extra charge. Also, it should be understood how authorization is given to allow the extra charges to be accrued.

Contract (Service Contract) is a legal document that describes the relationship between a facility owner and service provider. The service contract should list services included in the base price, services requiring an extra charge, maintenance parts included in the base price, maintenance activities outside the scope of the contract, and facility owner's responsibilities regarding use of the onsite wastewater treatment system.

Management (System Management) is a collective term that describes the necessary steps to conduct operational services, maintenance, monitoring, and compensation. All of these activities are essential to proper performance of onsite wastewater treatment systems. Program management is a broader term that includes system maintenance activities and additional functions (permitting, residuals management, enforcement, etc.) needed to have onsite or clustered wastewater treatment a permanent part of our wastewater infrastructure.

Frequency of service activities

Without exception, all onsite wastewater treatment systems require some level of service. However, the frequency of service activities is typically determined by four factors:

  • Regulations
  • Site conditions
  • Technology
  • Wastewater source or use

Regulatory authorities are mainly established to protect public and environmental health. Thus, in developing regulations that define the frequency of system monitoring activities, these authorities consider the relative risk to public health and the environment. Additionally, population density is also taken into account. Where risk is perceived as high, required monitoring frequency is increased. System monitoring at an appropriate frequency measures the performance of onsite wastewater treatment systems and minimizes risk of exposure to pathogens.

Site conditions will influence the required frequency of service. This is again because of environmental/public health risks and population density. Environmental risk is based upon the sensitivity of your site to the addition of wastewater.

A site with deep, medium textured, well drained soil has an excellent ability to accept and treat wastewater; the environmental risk is low. A site with extreme soil texture (excessively sandy, clayey, or rocky), or a site with shallow soil overlying rock has limited treatment and/or dispersal capability. Likewise, a site with seasonally saturated soil or poor surface drainage has a limited ability to accept or treat wastewater. Wastewater treatment systems located on these tougher sites pose a greater risk to public and environmental health.

Systems located near surface water such as lakes, rivers, or wetlands are also a greater risk to public health and the environment, because there is a greater chance of human contact with the wastewater. Additionally, as population density increases and wastewater treatment systems are placed on smaller lots, the risk is greater that pathogens leaving underperforming systems may reach the neighbors. In many areas, increased population also means an increase in the number of water wells that may become contaminated by inadequately treated wastewater from nonperforming systems.

Wastewater treatment technologies require specific service activities based on their treatment processes. Ultimately, service activities are unavoidable, because all treatment technologies require some level of service to keep them functioning properly. The manufacturer of each technology generally establishes service guidelines to ensure proper operation of their product.

In general, advanced treatment technologies require more frequent service visits, because they are more complex. If a specific configuration of treatment components and wastewater loading requires additional service visits to keep the system operating properly, the system designer may specify more frequent service.

Wastewater source or use may well be the most important factor to determine the required frequency of service. All wastewater treatment systems have a design loading rate based upon a specific quantity and strength of wastewater.

Wastewater quantity is the amount of wastewater that a source or use generates. This is usually estimated based upon the number of people that might occupy a residence or business on a daily basis. Wastewater strength depends on people's tendency to put additional waste material into the system.

For example, the use of a garbage disposal typically results in higher strength wastewater, because a greater amount of fats, oils, and grease (known as FOGs), and other solids are introduced. The wastewater source or use determines the actual loading rate to the onsite wastewater treatment system.

Generally, when systems are designed, it is assumed that the onsite wastewater treatment system will not be loaded at a rate greater than 70 percent of the design rate. A treatment system loaded at a rate near or equal to the design rate will usually require flow equalization or flow moderation to limit peak loads to the system.

Understanding your onsite wastewater treatment system

The first step for selecting a maintenance provider requires a simple understanding of the system. The onsite wastewater treatment system can be divided into four components: wastewater source or use, wastewater collection, pretreatment, and final treatment and dispersal (Figure 1).

The wastewater source or use is the facility that the wastewater treatment system serves. This may be a residence or a commercial operation. The wastewater collection system is generally the plumbing that conveys the wastewater to the pretreatment component.

Pretreatment components remove contaminants (nutrients and pathogens) from wastewater to produce effluent of sufficient quality to be accepted and treated by the final treatment and dispersal component. A septic tank is the most commonly used pretreatment component. Additional pretreatment components that may be used are aerobic treatment units, media filters, constructed wetlands, and/or disinfection units. Site conditions and the nature of the final treatment and dispersal component determine which pretreatment components are used.

Figure 1 - Typical components of an onsite wastewater treatment system

Onsite wastewater treatment system

The final treatment and dispersal component accepts the effluent from the pretreatment component, completes the treatment process, and disperses the effluent into the receiving environment. It may be constructed of a media filled trench, gravel-less trench technology, low pressure pipe drainfield, drip distribution field, or spray distribution field. Your designer selected the required components to construct a system that could accept the wastewater from your facility and disperse clean water back into the environment.

Knowing the type of system will help you determine your service needs. Start with the local permitting authority to obtain the following basic information.

  • Where is your onsite wastewater treatment system located on your property?
  • What pretreatment and final treatment and dispersal technologies are used to treat the wastewater generated in your home or commercial facility?
  • Are there any special laws or regulations regarding the service of your onsite wastewater treatment system?

Now that you have the basic information on your system, you can begin to evaluate your service needs in detail.

Who is required to have a service contract?

Legal requirements for service contracts vary from state to state. Consult your local or state agencies to learn whether or not you are required to have such a contract for your system, but remember that all systems benefit from regular service.

How do you know what service is necessary for your system?

Most manufacturers provide a list of maintenance activities for components or systems they produce. The manufacturer may specify the frequency for service activities or estimate the hours required to maintain the system. The manufacturer should also provide an estimate of parts that may need to be replaced and the frequency for their replacement. If no information on your system is available, check similar technologies, seek advice from a professional, or check with your local regulator for any guidelines or regulations that may be in place in your area for certain technologies.

What types of service contracts are available?

A variety of service contracts are available. It is important that homeowners know exactly what service they will receive under any service contract they consider. It is no surprise that as the amount of service provided increases, the cost also increases to cover the additional activities. A description of different types of contracts follows.

Monitoring Contract is a contract for monitoring the onsite wastewater treatment system performance. The service provider records system data and collects samples for laboratory analysis. The results are delivered to you and to any permitting authority that may require such monitoring.

Operating Contract is a contract to assess the current operational status of each system component. The service provider identifies components that need maintenance or repair but does not perform these services under this contract.

Maintenance Contract is a contract to conduct routine activities needed to keep the components operating properly. The service provider performs maintenance recommended by the manufacturer to keep the onsite wastewater treatment system functioning. This contract may not include the less frequent activities such as removal of residuals from the treatment components (pumping).

Repair Contracts is a contract for replacement of components as they break or if they are not operating properly. The contract should be evaluated to determine what is covered regarding parts and the labor to replace them.

Management Contract is a relatively new type of contract that is an all-inclusive plan. This contract might be considered equivalent to being served by a centralized sewer system. The service provider performs all required activities for monitoring, operation, maintenance, and repair. A few providers even include mitigation as a part of the contract.

Currently, only a few service providers offer management contracts. Most service contracts are typically a combination of the other contracts listed above.

For example, a service contract may cover monitoring and operation or may include monitoring, operation, and maintenance (MOM). MOM contracts are recommended as the minimum level of service. This is because the service provider conducts required performance monitoring specified by the permitting authority, evaluates the operational status of the components, and provides routine maintenance activities. The service provider may offer other services such as non-routine maintenance and repairs on a fee basis. MOM contracts may or may not include less frequent activities such as residuals removal (pumping).

It is important to note that having a service contract never relieves the homeowner of their responsibility regarding wastewater constituents that they add to the system.

How do I compare service contracts?

The homeowner or facility owner must compare not only price but also what is included in the base price of the contract. The previous discussion was provided to increase your understanding of the types of service that may be required to keep your system performing satisfactorily.

You should evaluate any contract thoroughly to determine:

  • What services are included in the base price?
  • What services are available for an additional fee?
  • What is the hourly rate for performing additional services?
  • When does an additional charge begin to accrue?
  • How is the additional service and associated fee approved?
  • When is payment due for the services performed?
  • What information will you, the homeowner, receive to let you know what base service was performed and when that service occurred?
  • How will you know when someone will arrive to conduct the service?
  • How should you contact the service provider when an alarm has sounded indicating the need for service? What is the charge for that extra service call?
  • How will troubleshooting and subsequent repairs be handled when a system needs extra service?
  • What is the homeowner or facility owner's responsibility regarding wastewater loading to the onsite wastewater treatment system?
  • What are the homeowner's required activities associated with the operation ofthe system?

The answers to all of these questions are necessary to help you make an informed decision regarding the selection of a service contract and provider. The least expensive base service contract may not be the best deal when evaluating the contracts. It is important to know what is included in the base price and which services will require an additional fee.

How do I locate a local service provider?

Contact the local permitting authority to obtain a listing of the professionals in your area approved for service on your particular system. Or, contact the manufacturer of your onsite wastewater treatment system and ask them for a listing of approved service providers in your area. System installers may also be able to provide you with potential names.


Wastewater will continue to be generated as a part of our daily activities. Effective management of this wastewater is critical to protecting public health, environmental health, and property value. All wastewater treatment technologies require service. However, the type and frequency of service depends on the specific technologies that make up your system, and how you use it.

There may also be regulatory requirements that must be met. Several different types of service contracts are available to the homeowner. The basic monitoring contract only meets minimum regulatory requirements. Additional contracts can offer greater service and limit the homeowner's involvement in the operation, maintenance, and monitoring of their system.

Therefore, one question to ask yourself when evaluating service contracts is to determine what level of involvement you wish to have in the service of your system. When evaluating contract options, you should have a clear understanding of who is responsible for the different actions (you or your service provider) and what is included in the base price of the contract.

In the absence of a maintenance contract, homeowners should at least keep a maintenance record that reminds them of what service is needed and when that service should be performed. It is also helpful to maintain a list of local service providers that can assist in performance of different types of activities.

Some tasks should be left to professionals to ensure the job is performed correctly and so that you do not subject yourself and your family to undue health risks. A service contract guarantees that your system is getting the proper attention it needs, and can save you time, money and the hassle of maintaining the system yourself.

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Soil Site Evaluation

A soil site evaluation determines if a septic system can be approved on a lot. The test considers all options including standard and sand filter systems. The "cheapest-best" system is always prescripted. If the minimum DEQ rules cannot be met a denial notice will be issued. If approval is granted a separate septic installation permit may be applied for by the property owner.

Site criteria

The suitability of a site for a septic system is largely determined by the type and depth of soil and the depth to the water table. Other factors include the size of the property, the slope, location of the system relative to streams, wells, cuts and fills, and whether sewer service is available.

Application process

The following must be submitted to the Septic and Onsite Wastewater program at the time of application:

  1. The application form must be filled out completely and signed by the property owner. Multiple lots will require an application for each lot.
  2. An acceptable plot plan (per example).
  3. Fee of $835 for each lot.

Note: An Entrance Permit may be required to construct an access point to the property. Contact Transportation Engineering for more information.

To ensure the quickest and most accurate possible analysis of your site please pay special attention to the following guidelines. Sites that do not adhere to the following risk denial or an extended review time.

Test pits

View Test Pit Preparation for Onsite Sewage Evaluations

  1. Provide a minimum of two test pits (maximum of six).
  2. Test pits must be dug per Test Pit Preparation guide.
  3. Keep the "spoils" pile at least two feet away from the edge of the test pit.
  4. Test pits should be spaced 100' apart in the area where you intend to locate the original and replacement drainfields.
  5. Locate the test pits in an area no smaller than 100' x 100' and no larger than five acres.
  6. Test pits should be located on the driest part of the property and should not be located within any of the setbacks. (see setback list)
  7. Test pits must be dug when you apply. Failure to have test pits dug when our inspector visits the site will result in your project being delayed

Site preparation

  1. If the test pits are not easy to find, mark a trail to them in the field
  2. Identify the property corners on site using clearly marked stakes or similar means.
  3. Post yellow permit card at the public end of your driveway or access road.


The owner will be notified by mail. Due to staffing concerns and a high volume of applications the Soil Site Evaluation may take several weeks to complete. Unfortunately it is not possible to schedule on-site visits at this time. Please contact us at 503-742-4740 or email for additional questions.

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Guide for Septic Tank Replacement

The septic tank is a vital component of your home's wastewater treatment system. Its primary purpose is to receive all of the wastewater generated in your home and retain the wastewater for at least 24 hours:

During the retention period, solids present in the wastewater will settle to the tank bottom if they are heavier than water (the sludge layer), or rise to the top of the tank if they are lighter than water (the scum layer). The liquid in the clear zone (between the sludge and scum layers) is discharged from the septic tank to other components of system, and ultimately to the drainfield. The tank must have sufficient capacity to store the accumulated sludge and scum for several years. Periodically, the tank must be pumped to remove the solids before they are discharged from the tank and cause damage to the drainfield or other vital system components. After many years, some septic tanks (especially those made of metal) deteriorate to the extent that they are no longer water-tight and/or they are no longer structurally sound.

When the useful life of the septic tank has been reached, it must be replaced.

Septic tank selection

  • The septic tank that serves a single family dwelling must have a minimum volume of 1,000 gallons.
  • A home with more than 4 bedrooms must use a tank having a minimum volume of 1,500 gallons. The tank must be on the DEQ list of Approved Tanks and Distribution Units.
  • Be aware that some DEQ approved tanks may not be suitable for your site based on groundwater condition.

Septic tank placement for systems that were built after June of 1977

Installation Guide

Each tank manufacturer has prepared an installation guide that provides instructions to follow when placing that manufacturer's tank. It is very important that the manufacturer's guide be closely followed to insure the tank remains structurally sound and water-tight after it is placed in the ground. The tank location must be excavated large enough to accommodate the tank.

Setting the Tank

Bedding material (for example, pea gravel) is placed in the bottom of the excavation to provide a stable leveling base. The tank must be placed level from side-to-side and end-to-end. The depth of excavation must be determined before setting the tank to insure that the building sewer pipe can maintain the minimum/maximum grade set by the plumbing code once it is connected to the tank inlet fitting.

Gravity or Pump

Similarly, the effluent sewer pipe that connects to the tank outlet fitting must have a minimum fall of 2 inches, and maintain a minimum grade of 4 inches per 100 feet. Be aware that the tank outlet must also be at least 2 inches higher than the top of the gravel in the first or highest dispersal trench. A pump will be required to lift sewage to the drainfield if the minimum fall and grade requirements for the effluent sewer pipe can not be met.

Septic tank placemement for systems that were built before July of 1977

If it is reasonably possible to do so, the tank placement must meet with same standards for placement as described above for systems built after June of 1977. Clackamas County has found that some septic systems built prior to July of 1977 do not have sufficient fall between the septic tank and the drainfield to meet the current DEQ requirement. When this minimum elevation difference can't be met, it is possible to comply with the DEQ standard by using a pump to lift septic tank effluent to the drainfield, however at significant additional cost.

However, in consideration of several factors, including the system's age, its expected useful life, and the cost for installation of a pump and its associated components, the County may issue a minor repair permit for a septic tank replacement without requiring a pump if all the following requirements are met:

  1. The system must have been installed prior to July of 1977, substantially in compliance with the standards that were in effect at the time of installation;
  2. The system serves an owner-occupied single family residence;
  3. The septic tank installer must check and verify that the effluent sewer pipe between the septic tank and the drainfield has at least two inches of fall;
  4. The property owner(s) must submit a signed affidavit on a County form stating that the installation of a pump (and other necessary components) to lift septic tank effluent to the drainfield is an unreasonable requirement, and that he/she understands that the useful life of the system may be significantly reduced without the pump. Additionally, the property owner(s) shall hold harmless the county, its employees and agents if the system should fail or otherwise not perform in a satisfactory manner.

Maintain Setbacks

When a septic tank is replaced, it must meet established minimum setbacks from buildings, property lines, wells and other features that may be present on the landform if it is reasonably possible to do so. Please refer to the attached table of minimum separation distances. If you determine that the tank must be located closer to an item than listed in the table, written approval from the County must be obtained before placing the tank.

Service Access Riser and Cover Requirement

The septic tank must have at least one service access riser assembly and cover that extends to finished grade or higher. The riser must be securely attached to the septic tank and be water-tight. It must be at least 20 inches in diameter when the soil cover over the tank does not exceed 36 inches of depth. The minimum diameter of the riser must be at least 30 inches if the backfill depth exceeds 36 inches. Multi-compartment tanks must have the above-described riser above each compartment. The riser cover must have a gasket for odor control, and it must be securely fastened to the riser to prevent unauthorized access.

Septic Tank Anti-Flotation Requirement

A septic tank that is placed at a location where a groundwater table is present at any time during the year may be required to have anti-flotation measures. The need to use anti-flotation may not be apparent until after the tank has been placed and inspected by the County. The tank manufacturer has prepared instructions to follow if anti-flotation measures are required. Please be aware that some septic tanks can not be used at locations where the groundwater level rises higher than the bottom of the septic tank.

Connection to Existing System

The connection point between the tank and the absorption system must be exposed for inspection. This requires locating and uncovering the first box of a serial system, the distribution box of an equal distribution system, the connection point to an existing drywell, or the transition from effluent sewer line to absorption trench in older systems without a box.

Testing the tank for leakage

The 24-Hour Water Test

After the septic tank has been installed, following the manufacturer's guidelines, it must be tested to demonstrate that it is water-tight by the test procedure established by DEQ.

  1. The tank must be filled with water to a level that is 2 inches higher than the point of connection of the riser to the top of the tank. CAUTION, THE TANK CAN BE DAMAGED IF IT IS FILLED WITH WATER ANY HIGHER THAN 2 INCHES ABOVE THE RISER/TANK TOP JOINT.
  2. Mark the water lever, time, date and your initials using a permanent marker.
  3. After 24 hours, check the water level.
  4. If it has dropped more than one inch over the test period, the cause of the loss must be determined and fixed.
  5. The tank must successfully pass the water test before calling the County for an inspection.
  6. Do not remove or add any water to the tank during or after the 24 hour test so that the inspector can check the tank.

Tank Decommissioning

The tank that has been replaced must be decommissioned in accordance with standards established by DEQ. The tank must be pumped by a licensed sewage disposal service pumping service to remove all of the septage. The tank must then be removed from the property and disposed of properly, or it must be filled with reject sand or bar-run gravel. The tank installer must provide the county with a completed Tank Decommissioning Certificate and the pumping receipt.

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Deck Setback Guidance

The Dept. of Environmental Quality in conjunction with the Dept. of Commerce, provides the following guidance document on setbacks from decks to septic tanks and drain fields.

Information from the State Building Codes indicated that decks over 30 inches in height require a building permit and thus are a "structure". The following is a proposed guidance on setbacks from decks to septic tanks and drain fields.

Decks over 30 inches in height

Decks over 30 inches in height are required to have a 5 foot separation from the septic tank and a 10 foot separation from the drain fields. The measurements are to be taken from the location of the pier block or other supporting device. In the case of cantilevered decks, the tank and field may be partially under the deck as long as they are 5 feet from deck's supporting device(s).

For existing or new septic tanks that are not or not planned to be the required 5 feet from the deck structure but are accessible for pumping, the local Building Dept. official or a Professional Engineer may certify there are no structural problems associated with the reduced setback for consideration by the Agent.

Decks under 30 inches in height

Decks under 30 inches in height are not required to maintain a set back from the tank or drain fields to the deck structure, or it's supporting devices (ie pier blocks).

All decks

All decks, regardless of height, must:

  1. not have any obstruction over, or within 5 feet of the tank that would impair pumping, and
  2. be over or within 10 feet of a drain field if they cause the drain field to be inaccessible to a back hoe for repairs.

In the opinion of the Agent if the tank location appears to compromise the decks support structure, the agent should notify the local Building Department.

CDC 02/22/2005, rev. 05/04/2005, rev 06/29.05

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