To encourage septic tank maintenance, a variety of methods are being used by small towns.
By Daniel P. Duffy
As the saying goes, an ounce of prevention is worth a pound of cure. While we don’t normally think of a septic system with its simple gravity flow pipelines and its complete lack of moving parts to require extensive care and maintenance, both are necessary to ensure its long-term operation, and to avoid the capital cost of an expensive replacement. Septic systems are typically utilized in small towns and rural areas where population densities are too low to justify the construction of an extensive sanitary sewer system and centralized wastewater treatment facility. This article will describe the efforts of various small towns and rural communities to encourage septic tank maintenance. Each has its own unique approach, with a variety of methods used (public education, enactment of laws and regulations, zoning requirements, regular inspections, and enforcement of operating standards). First, however, we’ll examine the operation of a standard septic system and how it should be properly maintained.
Septic System Operations
The standard on-site wastewater treatment system for homes and small businesses consists of a basic septic field. A septic system is an underground series of pipes connected to a central distribution tank. The pipes are laid out in parallel at regular spacing intervals to form a belowground drainage field. Their walls are perforated or slotted to allow effluent to leave the pipes at regular rates of flow. Effluent from homes and businesses flows into the central tank. Flows leave the tank either directly through the pipes, or through one solid-walled pipe that carries the flows to a distribution box. Flows leave the distribution box into the connected drain field pipes.
Of critical importance to the functioning of the septic system is the size of central receiving tank. The volume of the central tank is directly proportional to the expected flow rate of the effluent. As a rule of thumb, the volume of the tank will be at least 50% more than the expected daily effluent flow. The tank serves as a settling basin that separates out the various components of the effluent into three zones, each of which is managed differently:
Scum—The upper zone is the layer in which lighter materials such as grease, oils, and fats form a layer of scum.
Clarified—The middle zone is the contaminated water that is left after the lighter and heavier materials have been separated out. This water layer contains suspended solids, live bacteria, and diluted chemicals such as nitrogen and phosphorus.
Solids—The lower zone consists of heavier organic solids that settle out and form a layer of sludge on the tank floor.
It is the scum and clarified water that flow out of the central tank, with the solids left behind (the sludge accumulates over time until it has to be manually removed and discarded). Flows out of the tank are via gravity discharge to the perforated pipe drainage field. Flows leave the pipes through the slots or perforations, to be treated by the natural filtering soils and their associated soil bacteria that lie below the drainage field. Flow into septic tanks is typically not constant but consists of a series of peak flows.
New flows push out the flows already in the pipelines, providing positive displacement to existing water and scum by the incoming effluent. As the water is displaced, the scum and water already in the tank flow out of a discharge pipe that is located near the top of the tank, but at the opposite end from the inflow pipe (where wastewater enters the tank). From the discharge pipe, the scum and water evenly flows to the perforated pipes of the drainage field.
These perforated or slotted pipes vary in diameter from 4 to 8 inches, depending on anticipated flow rates, the flow gradient of the pipes, and the required size of the septic field. Old-fashioned septic fields were constructed with vitrified clay pipes. Today, most are constructed with polyvinyl chloride, high-density polyethylene, or corrugated ABS. Construction is a four-stage process. First, 2- to 3-foot-wide trenches with depths of 4 to 6 feet are excavated to the minimum-required lengths determined by the septic field dimensions, and with a slope on their floors to allow for the minimum-required pipe flow gradient. With pipes and trenches graded to a flow gradient of at least 2%, the septic field pipes allow for gravity flow of the scum and water, down the pipes and out into the soil. The depth and length of the trenches vary with soil permeability.
Second, the bottom 2 to 3 feet of the trench is backfilled with gravel. Third, the perforated pipes are set on top of this gravel backfill and further bedded with another 3 inches of gravel. To prevent the downward migration of finer natural soils into the void spaces of the larger gravel, the pipe and gravel are often covered with a geotextile filter. Lastly, the pipe is then buried with soil backfill taken from the trench excavation. The permeability of the adjacent soil determines the overall size of the drainage field, with septic systems set in clays needing larger septic fields to compensate for the clay’s low permeability. Conversely, coarse-grained soils with high permeability can support smaller septic fields having equivalent treatment capacity.
Scum and water leaving the pipes percolate downward into the gravel placed below the pipes. After passing through the gravel, they flow down into the soil adjacent to the trenches. The gravel acts as a filter to remove bacteria, chemicals, and other contaminants. The gravel also serves as a high permeability flow medium that allows the effluent to clear the pipe for some distance before its real treatment begins. The absorption properties of the natural soil finish the treatment process. This is why such systems are referred to as soil absorption systems. Over time, a layer of biological scum grows along the sides and bottoms of the trenches. Formation of this scum can be assisted by the installation of the geotextile filter around the pipe and the gravel. This scum provides the system’s primary treatment medium. The treatment action is similar to that of a slow sand filter that also forms a layer of intercepting scum on its top surface.
Septic System Maintenance
The key to maximizing the effectiveness and operational lifetime of a septic system is its effluent retention time. Infrequent septic tank maintenance can result in the build up of excessive solids. For every cubic foot of volume already taken up in the tank by settled solids, there is one less cubic foot of volume for additional settlement. It is not the volume of build up that affects the performance of the septic tank so much, as it is the remaining depth available for settling; each particle type and size has a different settling velocity. The depth of available liquid allows particles to settle, so that the particles fall out before the flow passes through the tank. Insufficient depth does not provide sufficient time for settlement, compared to the time it takes for flows to pass through the tank, and the solids content of the effluent remains agitated.
Furthermore, exceptionally high built up solids can be re-agitated and re-suspended with each new slug of effluent entering the tank. These refloated solids are carried out into the septic field pipe system, where they can clog the perforations and slots, or even clog the pipeline itself.
How often should septic tanks be pumped? That depends on the size of the tank and its designed effluent rate. A minimum of 24 hours of retention time is typically called for, assuming that 50% of the retained solids are digested after settlement. Table 1 gives annual frequencies for tank pumping that would ensure this operational requirement is met.
Generally speaking, any septic tank that requires more than one lean up per year (with annual frequencies less than 1.0) is probably underdesigned for its effluent flow rate. Pumping is usually performed with a vacuum truck attached to a tanker truck for hauling the solids to a final treatment and disposal facility.
First, the sludge is stirred manually with a tool called the muck rake. This breaks through the scum layer floating at the top and loosens the congealed solids at the bottom, making them easier to evacuate with the vacuum hose. Muckraking continues as the hose sucks up the solids and sludge into the tanker truck.
Before, during, and after pumping, the pump operator will perform inspections of the septic tank and septic field. Before even opening the tank, the operator should look for signs of soil subsidence and possible collapse, saturated soil indicating possible system back-up and failure, and entrance structure safety.
Once the entrance is opened and the operator can look into the tank, he should examine the liquid levels to see if they are too high (indicating system back-up and clogging), or too low (indicating a leak in the tank).
He should also examine the physical state of the tank’s baffles, and measure the thickness and depth of the sludge and scum.
Typically, a tank should be pumped when sludge has accumulated to a height 18 inches or less, below the tank’s outlet.
Local Efforts and Programs
So how does a rural government or small township health department encourage, educate, and otherwise enforce, its standard for septic system maintenance on its residents? The following are examples of programs instituted in several rural counties nationwide illustrating how they work, and the challenges they have had to meet.
Mahoning County, OH
This northeastern Ohio county on the border with Pennsylvania, mails reminders to over 2,000 households of several rural communities (Milton, Berlin, Ellsworth, and Smith townships) that own and operate septic systems. The reminders advise residents to pump septic systems, or face possible system failure—and thousands of dollars of repair costs—in the future. Though there is no law that requires homeowners to get their septic systems maintained, these reminders have been positively received by septic system owners, who often don’t know enough about maintaining their systems. The county informs residents that each septic system is different, and requires pumping at different intervals. Included with the reminder, is a list of licensed pumpers recommended by the county for septic tank clean out. Pumpers are part of the reminder system. Each time a septic tank is serviced, the county board is informed, and the data is used to track the next round of reminders.
Since the program inception in 1997, thousands of county residents have been prompted to perform preventative maintenance, saving them money, and protecting the local environment. The result also includes the creation of an extensive database used by the county to conduct statistical analysis of the effectiveness of septic pumping for reducing onsite system failures.
In addition to the reminder system, the county performs point of sale inspections of septic systems. These inspections have been preformed as part of a six-year overall effectiveness evaluation, running from January 1, 2000, to December 31, 2006. The resultant statistical analysis showed that 49% of the systems with no record of pumping maintenance were at the point of failure three years later, while only 37% of those that had been pumped were near failure. This represents a significant statistical difference in failure rates.
Prince Georges County, MD
Strict rule enforcement, a reliance on hard engineering, and continuous inspections of septic systems are emphasized by Prince Georges County, MD. Prior to installing a septic system, a homeowner must conduct percolation tests, to determine if the soil is suitable for an individual septic system, or if the system has to be increased in size. The results of these tests, along with the septic system’s engineering plans, must be reviewed and approved by the county board of health before a permit for construction and operation can be issued. The county also sends inspectors to observe and evaluate the installation of new septic systems.
Where domiciles are constructed as part of housing developments, the county reviews existing building permits and “use and occupancy” permit applications for properties already served by septic systems, to determine whether new systems can either be connected or expanded to accommodate the new households. An overall, regional assessment of community septic systems is provided by a review and approval of subdivision plants to be serviced by these systems.
Flexibility and innovation in septic system design is allowed under the provision for the potential installation of Innovative and Alternative (I&A) septic systems, which can be used in areas where restrictive property tract sizes or poor soil conditions (including very high groundwater) make standard septic system design impossible. As part of the permitting process for I&A systems, the county performs routine monitoring of their performance.
A system of inspections and evaluations is extended to standard septic systems utilized by sensitive or critical facilities (foster care homes, adult care facilities, child day care facilities, camps, schools, and institutional facilities).
In addition to direct inspections and evaluations of individual septic systems, the county conducts sanitary water and sewer surveys.
These surveys are performed in conjunction with the board and other member communities of the Washington Suburban Sanitary Commission.
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Bethlehem Township, NJ
Home to 3,820 people in 1,593 households, Bethlehem Township provides information on septic system management to its residents, while enforcing these standards through its Municipal Code. Even in this age of the Internet and instantaneous telecommunications, there is still a place for booklets and informational brochures. This is the approach taken by Bethlehem Township in rural New Jersey. The township regularly publishes and mails out a 40-page long information booklet entitled, “Country Wisdom: Guidelines for Better Living in Bethlehem Township.” In addition to helpful information on coexisting with local wildlife, managing pests, protecting water sources, keeping the air clean, and identifying local vegetation, newcomers to the township can learn about other features of rural life such as composting, water wells, recycling, trash collection, and septic systems. The phrase “country wisdom” is to rural residents what the term “street smarts” is to city dwellers. Published by the township’s nine-member environmental commission, the booklet is the first of its kind in New Jersey, and is intended to meet the needs of the residents of a single community. Response to the booklet has been uniformly positive. Moving from an urban home serviced by a sewer system to a property with a septic tank can be difficult. Information booklets such as this can ease the transition.
For well and septic system installation, the municipality’s sanitarian serves as the enforcement officer. The sanitarian has the power to issue stop work orders, revoke building permits, or deny certificates of occupancy if approved installation and construction techniques are not followed. Special homes for retirees (elder cottage housing opportunity, or Echo units) allow either a 1,000-gallon holding tank or a hook-up to an existing septic system (provided the existing septic system is already sized so as to accommodate its new users), as an allowed sanitary waste water system. Plans for new septic systems must meet the standards established by the New Jersey Department of Environmental Protection and be approved by the township’s Board of Health.
Charlotte County, FL
Sometimes the best measure of a system or an organization is how it responds to adversity and failure. Charlotte County, FL has had more than its share of troubles concerning its septic systems, from a court challenge from the state of Florida that wanted the county to install a $600 million sanitary sewer system, to the impact of Hurricane Charley that stretched limited county resources and personnel almost to the breaking point.
The out-of-court settlement with the state required the county to mandate the use of special aerobic treatment systems that typically cost twice as much as a standard septic system.
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| Septic tank basics |
A variation of a standard septic system that relies entirely on soil treatment of the wastewater, an aerobic unit utilizes air pumped into the waste to accelerate its decomposition. Though more expensive to operate, aerobic units require smaller drain fields, and produce fewer pollutants. However, if the air pump breaks down, the lack of decomposition results in greater pollution in the drain field. As such, owners of these systems (there are 2,100 in the county) are required by state law to sign a maintenance contract with a certified company for biannual inspections. Local health officials also perform annual inspections to each homeowner’s system, as well as inspections of the maintenance companies.
Meanwhile, the county inspection program has gotten back on track. Normally scheduled to occur every three years, they were skipped in 2004 because of the hurricane. Now performed on a regular basis, septic system inspections can continue now that there is sufficient personnel and budget. The county also plans to begin testing water taken from canals and other bodies of water as a means of evaluating how well the aerobic systems are working. Environmental specialists at the Health Department review septic tank permit applications. These have to be prepared by registered engineers and septic tank contractors, and must meet the requirements of the state of Florida and Charlotte County. Environmental Health department personnel also inspect all septic system installations and issue annual permits to aerobic systems. In many ways, the county is responding to the “law of unintended consequences.” Taxpayers did not want to ante up for a full sanitary sewer system, and residential developers wanted the aerobic systems to minimize the amount of land required by individual households so they could maximize the profitability of each developed acre.
Along with these effects of the market’s “hidden hand” came the side effects of environmental issues with which the county is now coping.
Kent County, MI
Often, the requirements for proper septic system installation, maintenance, and operation are imposed from above, but are demanded from below. Kent County, MI, and its seat, Grand Rapids, are home to over half a million people in over 200,000 households. In the only state that lacks a statewide sanitary code governing septic systems, the Clean Water Fund (a private citizens group working in conjunction with the Frey Foundation, the Grand Rapids Community Foundation, and the Sebastian Foundation) estimates that over one million gallons of untreated waste from toilets, and drains is seeping into the county’s groundwater, lakes, and streams.
Their report, “Kent County's Underground Threat/Protecting Families from Failing Septic Systems,” is a follow-up to a study performed in 2002, by the Annis Water Resources Institute. The bacteria and viruses from untreated septic waste negatively impacts local water, presenting a potentially serious health risk, and cause algae blooms that degrade surface water quality. This last impact has the potential to reduce the attractiveness of local lakes and ponds to sports enthusiasts by impacting wildlife.
To avoid this fate, their report calls on the county to enforce basic standards of septic system inspection, treatment, and oversight. These include advising new property owners that they own septic systems; providing property owners with information on the proper care and maintenance of a septic system; requiring septic system inspections at point of sale; imposing fees on septic waste haulers to support the inspection program; instituting a county loan program to assist low-income owners of septic systems; and limiting the number and extent of septic systems per acre. Such a program represents the basic minimum requirements of a rural septic inspection program.
Daniel P. Duffy, P.E., is employed by URS Corp. in Akron, OH.
OW - March/April 2008 |
