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Earth Best Management Practices Septic Systems: Proper Installation Protects Groundwater

Best Management Practices Series:
Proper Installation of Septic System Protects Groundwater

A New House Goes Up:
Matching it with a septic system that will not pollute any wells

Privette houseBack when Steve Privette of Willow Springs was a kid, his neighbor's sewer system plugged up. He remembers that somebody dug up the line and unclogged it with a snake tool. Money was tight in those days and the system was not repaired properly, so after that, water from that septic tank would surface and run into his yard. “It would stink, and I didn't like mowing in that area, because it was always mushy,” Mr. Privette recalls. “But the prettiest tomatoes grew there, even though no one ever planted any seeds. But Dad would never let us eat them.”

The seeds came from tomatoes that had been eaten and passed through the septic system. The fruits were well-watered and well-fertilized, also by the septic system. His Dad was right to not eat them; plants fertilized by human waste might contain bacteria that could make people sick.

Mr. Privette grew up in rural Howell County, Missouri, outside of city limits. In that area, everyone who lives in the country is responsible for the water that goes down their drains, with no help from the city or any other government.  Most rural residents in the watersheds of south central Missouri and northern Arkansas use septic systems to treat their wastewater. But there are no laws requiring a sewer system. If a homeowner doesn't have the money to install or repair a septic tank, lagoon, or other system, some of them just let the waste flow out onto the ground.

Mowing around those tomatoes was Mr. Privette's first experience with a failed septic system. But he became a lawyer after he grew up, and he has seen a number of court cases in which someone sued someone else because sewage backed up and flooded a basement. “You do not want that. There's nothing you can do to wash out the smell or get rid of the mold. The house is never the same,” he said.

Septic System Failure Is Common in Southern Missouri Watersheds

click for full size imageThere is another possible problem with septic systems, and it's a big one. The geology in south central Missouri is known as “karst,” which means there are thick layers of porous limestone rock under the ground, with not much soil on top. In this karst landscape, the most likely thing to happen when a septic system fails is that the polluted water will flow straight down through the rocks and quickly end up in the groundwater. Since most rural residents get their household water from wells, and since those wells are often located very close to septic tanks, that means those people could be drinking recycled toilet water.

This really does happen. A 2005 study by the Howell County Health Department discovered that water in 42 percent of the wells in that county were contaminated with fecal bacteria.  That kind of bacteria can only come from the insides of a living creature, so its source might be livestock manure, wildlife droppings, or human waste. The chairman of the health department said, “We think the majority of bad wells are being polluted from their own septic systems.”

See related story: Health Dept. Gets Positive Feedback on Proposed Sewer Ordinance. Read more about the 2005 well water study in the Health Department's May 2006 news release (PDF).

Mr. Privette Builds A New House

Returning to Steve Privette's story, in 2006 he decided to build a new house. It is located north of Willow Springs, in a rural area at the headwaters of the Eleven Point River watershed [map].

Mr. Privette had learned from his experiences. He definitely did not want to mow around mush, have sewage back up into his basement, or drink well water that had started out in his toilet. Even though no law required him to put in any particular system (or any system at all), he wanted to do the right thing. To make sure the job was done correctly, he hired Tony Summers with All Pumps and Septic, Willow Springs, because Mr. Summers is a trained and licensed septic system installer.

How A Septic System Works

Mr. Summers explained the parts of a septic system. A pipe carrying wastewater runs from the house into a big buried tank, called a septic tank. These tanks are made of fiberglass, concrete, or steel. Most installers do not put in steel tanks any more because they rot out and leak, but many older homes have steel tanks.

“Septic” means “to make putrid” (become rotten and stinky). As wastewater sits in a septic tank, the solids settle down to the bottom of the tank, and grease and other scummy substances float to the top. Bacteria inside the tank get to work, decomposing the scum and solids to make them “septic.”  About 95 percent of the solids are turned to liquid by the bacteria, said Mr. Summers. A second pipe, on the other end of the tank, allows water to exit. A “baffle,” or small barrier, keeps the scum and solids from passing out of the tank with the water.

After leaving the septic tank, the wastewater flows into one of several “lateral lines,” which are located in a big area called a drainfield. The lateral lines which Mr. Summers installs are made of open-bottomed plastic tubes with lots of holes. These are laid down inside long, level trenches, then covered with soil. Because the lateral lines are level, the water spreads throughout them and seeps out evenly. This distributes the wastewater throughout the entire drainfield, where it is absorbed into the ground. If the trenches are not level, the water will all run downhill to the lowest spot, which can cause the system to fail.

Once the water has passed out of the pipes and into the surrounding soil, anything that might still be suspended in the wastewater should be further decomposed by bacteria in the soil. The soil also is expected to act as a filter, purifying the wastewater as it slowly seeps deeper into the groundwater.

Designing A Septic System For Mr. Privette

After arriving at the construction site for Mr. Privette's new house, Mr. Summers first looked for the best spot in the yard to install the septic system. He made sure the location was downhill from the house, was not near the well, and was not close to anything else that might cause a problem later. Then he examined the soil in the chosen area. A system that works well in deep, loamy soil might not drain properly in heavy clay, or might drain too quickly in very rocky soil. A septic system must be designed to fit the soil type. In some situations, a soil scientist is hired to do a precise soil analysis.

Next, Mr. Summers looked at the house size and the number of bedrooms. He needed to know this so he could design the system to safely dispose of wastewater for the most number of people who might live there in the future, not just the number in Mr. Privette's family right now.

Based on all this information, Mr. Summers recommended a 1500 gallon concrete septic tank, with 500 running feet of lateral line. This is a large system, because the house is very large. “I could make the system a lot smaller and not be breaking the law, and nobody would say a word,“ Mr. Summers said. “But if he (Mr. Privette) sold the house to a family with six kids, then the smaller system wouldn't be big enough.“ The smallest system that Mr. Summers will put in is a 1000 gallon septic tank and 200 running feet of lateral line, “even if it's a one-bedroom trailer house,” he said.

Installing The Septic System

On a hot August day, Mr. Summers sent backhoe operator Carl Roberts to start digging a trench from the new house out into the yard. The house was still under construction. When the trench was done, Mr. Roberts cut white plastic pipe and hooked it up to the drain coming out of the new house. He ran pipe all the way down the trench, glued it together, then refilled the trench, covering the pipe with soil.

Digging the trench from the house  Hooking the pipe up to the house Covering the trench to the house
Next, the backhoe operator dug a deep, rectangular hole in which to bury the septic tank. After lunch, a boom truck arrived, bringing the precast concrete septic tank. It weighs about 12,000 pounds. The truck driver used a remote control to operate the boom. He guided the boom perfectly as it lifted the giant tank off the truck and lowered it into the hole. This is a dangerous job, because a worker could get crushed if the operator made the wrong move. Also, the tank is so heavy the boom truck could turn over. Once the tank was safely in the hole, the workers made sure it was sitting level.  Then they hooked up the pipe from the house, so water could flow into the tank. Using a hose, they filled the tank half full of clean water. This is done to keep the tank from floating out of the hole if there is a rainstorm before the job is finished.
The hole is ready for the septic tank. The driver operates the boom by remote control as it lifts the concrete tank off the truck. The tank dangles in the air.
The tank is positioned into the hole. Checking the tank for level. Pipe is connected to the tank.
After that, Mr. Summers and Mr. Roberts installed “cleanouts.” These are pipes which stick out of the tank and will be above the ground after the tank is covered. After several years of use, most septic tanks get full of partly-solid mushy material. In order for the system to work properly, these solids must be periodically pumped out by a septic cleaning service truck.  The cleanout pipes allow the pump truck to access the tank.  When the cleanouts were glued in, the backhoe partially covered the tank.
Cleanouts are installed. Tank is partially covered up. Digging the lateral lines.
The next moring, Mr. Roberts dug a series of trenches for the lateral lines. He used a tool called a transit to make sure each trench was level. When finished, he had five trenches 100 feet long and about 20 inches deep.  They were two feet wide and 10 feet apart.  Then he laid the pipes for the lateral lines in each trench. The ribbed black plastic pipe comes in short pieces that snap together, lying on the bottom of the trench like a wiggly black snake. The pipes are open on the bottom, which allows wastewater to easily soak into the soil. 
Lateral lines close up. Big view of drain field, with lateral lines. On the tripod is the transit used to level each trench. Long view shows partly
buried tank and concrete
distribution box, with cover on.
The last step was to connect the one pipe coming out of the septic tank to the five lateral lines.  This is done with a small concrete distribution box, which has one incoming pipe (white in photos) and five outgoing pipes (blue in photos). The distribution box sits level, so that each outgoing pipe receives the same amount of wastewater.  When everything was hooked up and checked over, the whole system was covered up with soil.  After the grass grows back, no one will be able see where the septic system lays underneath the ground.
Close up of distribution box, with cover off. Box is carefully leveled, so all five pipes receive equal amounts of wastewater. Blue pipes connect the distribution
box to the five lateral lines.
Second view of pipes from the distribution box connecting to the lateral lines.
privette house finished The finished house.

Photos and text by Denise Henderson Vaughn.

The development of content for the *Best Management Practices Series* is funded in part by the U.S. Environmental Protection Agency Region 7, through the Missouri Department of Natural Resources, under Section 319 of the Clean Water Act. DNR Subgrant #G04-NPS-17.