Thursday, September 13, 2012

The Doctor and His Septic System

I was waiting in a doctor’s exam room when he arrived with friendly banter about a sport I had no knowledge of due to lack of interest. I laughed and said he should try a topic I was interested in or knew something about. Kidding, I suggested we talk about groundwater or septic systems. He immediately launched into the horrifying story of how he operates his septic system and his concerns about its operation. He apparently had lived in his house for 15 years and never once pumped his septic tank. Instead he had two drain fields which he switched between every six months and dutifully poured septic system additives down the drain every month. He had been using some “granules” but now was pouring a “blue liquid” and was worried about the new liquid. He had no idea of the basics about septic system operation and maintenance, and no idea about what he had probably done to his system. The good news is that neither he, nor his neighbors are using the groundwater and he has adequate money to fix his system. So, this is for a certain wonderful doctor who shall remain nameless. (By the way, dear doctor, you can build a fabulous new alternative septic system for less than the cost of a new mid-range luxury sedan. That is the upper end of what fixing your problems will cost.)
Failing septic system from NCDH presentation

A typical septic system has four main components: a pipe from the home, a septic tank, a leach or drain field (alternative systems might have drip fields, sand mounds or peat tanks where a leach field is not possible or has failed), and the soil. The septic tank is a buried, watertight container typically made of concrete, fiberglass, or polyethylene. It holds the wastewater long enough to allow solids to settle out (forming sludge) and oil and grease to float to the surface (as scum). The septic tank also allows partial decomposition (by natural bacterial action) of the solid fecal matter. Compartments and a T-shaped outlet in the septic tank are intended to prevent the sludge and scum from leaving the tank and traveling into the leach field area. Some newer systems have screens and filters to keep solids from entering the leach field, but older systems typically do not. These filters and screens can become clogged and need to be cleaned out regularly to prevent septic sludge from backing up into the house.

Septic tank wastewater flows (by gravity or pump) to the leach field, where it percolates into the soil, which provides final treatment by natural soil filtration which removes harmful bacteria, viruses, and nutrients. Suitable soil is necessary for successful wastewater treatment. Microbes in the soil can digest or remove most human produced biological contaminants from wastewater before it eventually reaches groundwater. There are also Alternative systems (or AOSS) that have additional treatment tanks or components like peat moss tanks or sand filters to assist in the filtration process. For a septic system to work properly, the waste stream cannot contain too much solid material or scum. High quantities of solids in the waste stream will overwhelm the leach field. Initially, nitrogen and fecal bacteria will be released to the groundwater as the soil becomes saturated with solids and scum. Eventually the perforations in the pipes to the leach field through which waste water flows can become clogged and the waste may ultimately backup through the system into your home or surface in the yard.

To keep a septic system operating optimally, a septic tank must be pumped every few years to remove the scum and solid layers. Steady use of water throughout the day and water conservation should be practiced because too large a flow of waste water and the solids in the tank will be stirred up and not settle and be carried out to the drain field. Also, the drain field does not have an unlimited capacity. The more water your family uses, the greater the likelihood of problems with the septic system. Finally, you need to limit what goes down the drain to prevent bacterial die-off in the tank so that it will continue to function as designed. Die-off of the bacterial necessary for a septic system to perform properly has been seen in experiments where excessive amount of harsh household chemicals were added to the septic tank. As little as of 1.85 gallons of liquid bleach, 5.0 gallons of liquid Lysol cleaner, or 11.3 grams of Drano drain cleaner added to a 1,000-gallon septic tank have caused die-off of the bacteria in experiments. Other factors that can cause die-off include the excessive use of anti-bacterial agents, and, in certain cases, antibiotic medications taken by members of a household.

However, in normal use, you do not need to add a chemical or biological stimulator or an enhancer to a septic tank that is designed, operated, and maintained properly. The naturally occurring bacteria are already present within human fecal matter are adequate for the system to function properly. Contrary to popular belief, chemical additives, such as caustic hydroxides and sulfuric acid, should never be added to a septic system. Adding these chemicals will destroy the bacterial population in the septic tank, change the permeability characteristics of the soil absorption system, and may cause groundwater contamination.

Often, manufacturers of biological additives market their use to restore the bacterial balance in a septic tank on a monthly basis as part of a routine maintenance program. As mentioned above this is not necessary because these bacteria are already present in human feces. These kinds of additives are thought to be harmless to the functioning of a system. A lack of need has not stopped manufacturers from advertising their products. However, some studies indicate that enzymatic products might have the ability to reduce the amount of oil and grease in the septic tank, but the oil and grease flows out of the tank to the soil. The scum layer in a septic tank “holds” fats, grease, and floatables, preventing their escape to the drain field. Enzymatic products can “break up” this scum layer and increase its mobility, allowing it to enter the soil absorption system. So you save on pumping your septic tank and instead slowly destroy the functioning of your drain field.

Manufacturers’ claims that septic additives either eliminate the need for pumping of a septic tank or can restore permeability of the soil absorption system are entirely unsubstantiated according to Cornell University. No product has been demonstrated to allow a homeowner to escape regular septic tank pumping and maintenance, but can contribute to the premature failing of a soil absorption system. The drain field has a limited lifetime and capacity. After a few years, the solids that accumulate in the septic tank should be pumped out and disposed of at an approved location. If not removed, these solids will eventually overflow, accumulate in the drain field, and clog the pores in the soil and the openings in the pipes. While some clogging of soil pores occurs slowly even in a properly functioning system, excess solids from a poorly maintained tank or a tank where enzyme additives were used instead of pumping the tank can completely close all soil pores so that no wastewater can flow into the soil. The sewage effluent will then either back up into the house, flow across the ground surface over the drain field, or find another area of release in the septic system. If this happens, you may need to construct a new drain field on a different part of your lot or install an alternative treatment system like peat tanks or sand filters. Pumping the septic tank after the soil drain field has become completely clogged will not rejuvenate the system only alleviate the surfacing of waste water until the tank fills up again. I am intrigued by the idea that the Doctor’s alternating drain fields every six months might have slowed the clogging of the drain field by allowing it to rest for half of each year. Usually, a second leach field is installed when the primary field is failing and used this way when the second leach field developed problems also. 
From NC Department of Health presentation

In some cases where the drain field has become clogged and no longer can adequately absorb the wastewater, the toilets and sinks might not drain freely. A black residue may remain at the bottom of the toilet.  If the drain field can absorb the effluent, but no longer treat it, the sewage may contaminate the groundwater or surface water with fecal coliform bacteria and it could take a long time to identify that problem unless you and your neighbors are using the groundwater as a drinking water supply and test your water. Contaminated groundwater often looks and tastes just fine. If your drain field has become clogged, but is not backing up into your home there are several other signs: The ground near the drain field or other section of the septic system maybe wet or mushy, even during dry weather. The visible liquid in these wet areas is often dark (sometimes nearly black).The area around the failure may have a distinctive odor and flies are often attracted to the failure (especially in the hotter season). The lawn may grow greener in these areas. The grass is a brighter green over a failing drain field, distribution valve or other failed component.

While I know my doctor would never try to disguise a failing septic system in selling his home, not all people are as honorable. Before buying a home with a septic system, have it inspected by a licensed individual or Professional Engineer specializing in septic systems and knowledgeable about local geology and soils. If the property is also on well water thoroughly test the water quality, also. Though commercially available dyes and tracers can be used to confirm a suspected problem, they will not identify all septic system failures, due to the type of failure (releasing untreated waste water into the subsurface) or due to intentional masking of the problem. If you pump a septic tank it will take several days or more than a week (depending on the size of the tank and household) for water to be released to the drain field again. That is generally more than enough time for the wet areas of the yard to dry out and will keep the tracer dyes from being seen in the yard.

Commercially available dyes and tracers are best used to establish the flow path of wastewater and confirm a suspected problem. Dyes and tracers are most efficiently used to confirm cross-contamination of wells by nearby septic systems. They can be used to identify which of nearby septic systems is the source of a well contamination problem much less expensively than a DNA test on the waste bacteria (oh yeah, with enough money you can do that, too).  Tracking of sewage effluent in groundwater and surface water systems is complex and difficult to predict using dyes and tracers. Just because the dye or tracer does not appear does not mean that untreated sewage is not contaminating surface and groundwater systems or that a septic system is working properly.

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