Septic systems: Site limitations for private sewage disposal systems

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There are site limitations for private sewage disposal systems. Not all land is suitable for such systems. Land developers and builders should be able to spot land that's likely to give them trouble when it comes to a septic system. Experience does much to help in this area. After several years of buying and developing land, a person begins to recognize a good site.

Little signs can give you hints about the quality of land. For ex ample, bulges and occasional glimpses of rock on the land’s surface could mean that bedrock is close to the surface. Bedrock can interfere with a private sewage disposal system.

When I was developing land and building homes in Virginia, septic systems were a common part of my job. In all the jobs I did in Virginia that had septic systems, I never encountered bedrock. Most of the soil conditions were very good for leach fields. This has not been the case since I moved to Vermont.

Land in Vermont, where I now work, is rocky. Most of the rock is underground, but not by much. Bedrock, or ledge as it’s called in Vermont, can be within inches of the topsoil. It took me awhile to get used to this fact. It affects the installation of septic systems and foundations. Quoting a price for a job without knowing that ledge is pre sent can he a financial disaster. If you have to blast bedrock to get in a full foundation, and you haven’t planned for it, your profits can be destroyed.

Rock is not the only risk when it comes to septic systems. Some ground just won’t perk. If this is the case, the land might be deemed unbuildable. Buying land for development and then discovering that it has no acceptable septic sites can really ruin your day. Experienced land buyers put clauses in their purchase agreements to protect them from this type of risk. A typical land agreement contains a contingency clause that gives the buyer a chance to have the soil tested be fore an absolute commitment is made to buy the land. If the tests prove favorable, the deal goes through. When soils studies turn up problems, the contract could be voided or some adjustment might be made to the sales price.

The size of a building lot sometimes affects whether or not it can be approved for a septic system. Many houses that require a septic system also require a water well for drinking water. For obvious reasons, septic systems must not be installed too close to a water well. The minimum distance between the two is normally 100 feet, but it sometimes is more. I have seen exceptions that allowed less distance, but not many.

Since moving to Vermont, I’ve seen some building practices that I never experienced in Virginia. For one thing, I can’t imagine anyone getting a building permit and putting in a foundation before their well and septic locations have been chosen and approved. Yet, I know of a recent case where this happened. Let me tell you about it, so the same problem won’t come up with your building business.

A man in Vermont bought a piece of land and hired a builder to build his house. The builder had his site contractor clear the lot and install the septic system. It was passed without any problem by the lo cal code officer. Then the builder put in the footings and full basement walls. It was about this time that a problem was discovered.

The house needed a well. But, because of the septic system location, there was no room on the lot to install a well that would com ply with code requirements. It is not that the lot was too small for both a well and septic system. It was the location of the septic system that caused the problem. Basically, the builder created an unbuildable lot from one that had been buildable. I would not have wanted to be in that builder’s shoes.

In an effort to salvage his situation, the builder went to adjoining landowners. He asked for an easement so that the well for his house could be drilled on their property. It took some doing, but I believe an agreement was worked out. I don’t know what would have happened if the neighbors refused to cooperate. I suspect the builder would have lost a costly lawsuit.

The builder we just discussed made some very serious errors in judgment. He was lucky that the circumstances didn’t turn too ugly. When building a house, you are at risk any time that you must rely on a private septic system. And, it’s not only houses that can be at risk. Some commercial buildings depend upon private waste disposal systems. You must know what to look out for in order to protect yourself.

Let me tell you about a builder in Virginia who made a big mistake when bidding on a job. This builder went out to a building lot with the lot owner. After walking the property, the builder accepted a set of plans and went back to his office to work up a price for a new house.

After completing a quote, the builder was awarded a contract to build the house. It was not until the permit process started that the builder found out that the municipal sewer, which served many houses in the area, didn’t extend to the building lot where he was going to build. There was a public water supply, but no sewer. This left the builder with two options. He could either pay to have the street cut and the sewer extended, or he could pay for a septic system.

When the builder priced this project, he planned to pay a tap fee to connect to a city sewer. As I remember, the tap fee was around $3000. At any rate, the only money he had budgeted was the amount figured for the tap fee. It would cost much more to have the sewer extended. Installing a septic system would be difficult, due to the size and shape of the lot. A deal was worked out with the lot owner and the sewer was extended. I don’t know what type of financial adjustments were made between the builder and his customer, but I expect the builder made considerably less money than he had originally planned.

As they appear

Things are not always as they appear. In the case of our last example, the builder assumed that public water and a sewer were available for the building lot. Unfortunately, the sewer connection was not readily available. This situation is not as rare as you might think.

I’ve run into a number of building lots that have municipal hook ups for water, but nothing available for private waste disposal systems. With my contingency clauses and inspections, I’ve never been put in a bind from this type of problem. But, a buyer or builder who doesn’t research the options that are available could get in big trouble very quickly.

Some people assume that a lot is going to be suitable for a septic system just because lots on either side of it use septic systems. This is not always the case. I’ve seen property where, out of five acres of land, there might be only one or two sites suitable for a standard septic system. This situation is not uncommon, so watch out. Make sure that you have an approved septic location established before you make any firm commitments to buy or build.


The grade of a building lot can affect the type of septic system that can be installed. If the grade does not allow for a gravity system, the price goes up considerably. Pump stations can be used, but they are expensive. If you’re building houses on spec, you might have trouble selling one that relies on a pump station. People don’t like the thought of replacing pumps at some time in the future. And, many people are afraid the pumps are going to fail, leaving them without sanitary conditions until the pump can be replaced.

The naked eye is a natural wonder, but it can’t always accurately detect the slope of a piece of land. Looks can be deceiving. Unless the land leaves no room for doubt, it’s best to check the elevation with a transit. You can’t afford to bid on a regular septic system and then wind up having to install pump systems.

A safe way

There is a safe way to work with land when a septic system is required. You can go by reports provided by experts. Even this isn’t foolproof, but it’s as good as it gets. If you have a soils engineer de sign a septic system, you can be pretty sure that it's going to work pretty much as drawn. Since every jurisdiction I know requires a septic design before issuing a building permit, it makes sense to go ahead and get the design completed early in the game.

I’ve dealt with two types of situations when getting septic de signs. In Virginia, the designs were drawn by a county official. The cost, if there was one, was very minimal. Let me tell you how this process worked.

A representative of the county would come out and bore test pits with an auger. This was done by hand, so there was no need to clear the land for heavy equipment. After digging the pits, a perk test was done. A few days later, a finished design was provided by the county. It didn’t take long or cost much to have a detailed plan created. The plan was official, so it could be counted on for permit acquisition.

Things are done differently where I work in Vermont. Here, soils studies are done by independent engineers. The cost for these studies is normally around $250. As a builder, I hire an engineer to test the soils and draw a septic design. I can then use that design to obtain a septic permit from the code enforcement office. This process is more expensive than the one in Virginia, but in the scheme of things, it's still a bargain. I’d rather pay $250 to avoid walking into a problem. It beats spending thousands of dollars trying to fix a mistake.

If you are buying land, make sure that your purchase agreement provides a contingency allowing you to have the land approved for a septic system before you are committed to going through with the sale, It is wise to specify in your contingency what type or types of septic designs are acceptable. Some types of systems cost much more than others. If your contract merely states that the land must be suit able for a septic system, you would have to complete the sale regardless of the system cost, as long as one can be installed.

When bidding jobs, your quote should make clear what your limits are in regards to site conditions. Specify the type of septic system your quote is based on, and provide language that protects you if some other type of system becomes required. Don’t take any chances when dealing with septic systems, because the money you lose can be significant.

A standard system

A standard septic system is built with a gravity flow. Its drain field, or leach field as it's often called, is made up of perforated pipe and crushed stone. This is the least expensive septic system to install. Unless the soil does not perk well, you normally can use a standard system.

Chamber systems

Chamber systems are much more expensive than pipe-and-gravel systems. Section 11 describes these systems in detail, but let me give you a brief description of them here, so you can see how they can affect your site selections.

Chamber systems are used when soil doesn’t perk well. If the soil can perk, but not perk well, a chamber system might be your only choice. How do these systems work? Basically, the chambers hold effluent from the septic tank until it can be absorbed by the ground. Unlike a perforated pipe, which releases effluent quickly, the chamber controls the flow of effluent at a rate acceptable to the soil conditions. Where a pipe-and-gravel system might flood an area with effluent, a chamber system can distribute the liquid more slowly and under controlled circumstances.

The cost of a chamber system can easily be twice that of a pipe- and -gravel system. In my area, it’s not unusual for a chamber system to cost up to $10,000—that’s a lot of money for a septic system. And, if you happen to bid a job based on a gravel system, at say $4000, the extra $6000 spent on chambers is going to deflate your profit very quickly.

Pump stations

Pump stations can be another big expense in some septic systems. The cost of the pump station, the pump and its control, and the added labor for installation can add thousands of dollars to the cost of a standard septic system. If you were unlucky enough to get stuck with a pumped chamber system when you had planned on a gravity gravel system, you could lose much of your building profit all at once.


Trees are another factor to consider when doing a site inspection for a septic system. Tree roots and drain fields don’t mix very well. Any trees in the area of the septic system must be removed. Even trees near the edges of the area should be removed. How much open space should exist between a septic system and trees? It depends on the types of trees that are growing in the area. Some trees have roots that reach out much farther than others. You can get a good idea of how far the roots extend by looking at the branches on the tree. The spread of the branches is often similar to the spread of the roots. If there is any doubt, the professional who draws your septic design can tell you which trees to leave standing.

Burying a septic tank

Burying a septic tank requires a fairly deep hole. Even if you are using a low-profile tank, the depth requirement can be several feet. If you work in an area where bedrock is present, as I do, you must be cautious. You could run into a situation where rock prevents you from burying a septic tank. This was almost the case on my personal home.

When I built my most recent home, the land I chose consisted of a lot of bedrock. When digging footings for the house, my site con tractor hit solid rock in less than two feet of excavation. I knew we would hit rock at a shallow depth, so this didn’t alarm me. It did, however, make it difficult to install the water line from my well at a depth that would prevent it from freezing. In fact, I had to use an in line heat tape to protect the water service. The rock also created some concern on how we would bury my septic tank.

When I bought the land, I probed it with a metal rod to determine how far below the surface I would encounter ledge. Numerous probe sites showed that 18 inches was the most I would be able to dig in many areas. However, in some areas, the bedrock was deeper. With the use of my probe, I was able to plot a location for the foundation, well, and septic system.

My site work turned out pretty much as expected. Since I had probed the soil, there were no big surprises. By using the natural slope of the land and some fill, I was able to bury a low-profile septic tank without any real trouble. However, if the land had not consisted of a natural slope, I might not have been able to get my septic tank buried without blasting the bedrock. It might have been necessary for me to build some type of mound system to overcome the problems associated with rock. This would have been very expensive. My preliminary site evaluation proved very helpful in setting and staying within a budget.

A stiff, small-diameter steel rod with a sharp point is very helpful when probing septic locations. The rod can be used before a system is installed to establish any underground obstacles. But, make sure that the area you are probing does not contain any underground utilities. Jamming your probe rod through buried electrical wires can be a shocking experience.

After a septic system is installed, a probe rod can be used to locate the septic tank if you ever have to find it again. Someone should pinpoint the tank location and record the information for future reference. The property owner needs access to the tank openings in order to have the system pumped out periodically. In any event, a good probe rod comes in handy.

Underground water

Underground water can present problems when installing a septic system. This problem is usually detected when test pits are dug for perk tests. However, it's possible for the path of the water to evade detection until full-scale excavation starts. For this reason, you should have some type of language in your contracts to indemnify you against underground obstacles, such as water.

I’ve never had a problem with water when installing a septic system, but I have had it get in the way while remodeling a basement. My helper and I broke up a concrete floor in a basement once and found a fast-flowing stream just below it. The water was so abundant that it had washed out the crushed stone used under the concrete. If this much water can run under someone’s basement floor, it could certainly pose a problem for a septic system.

Driveways and parking areas

When you assess a lot for a septic system, consider the placement of driveways and parking areas. Even though a septic system is below ground, it's not wise to drive vehicles over the system. The weight and movement could damage the drain field to a point where it would require replacement. You don’t need this type of warranty work, so make sure that all vehicular traffic avoids the septic system.


Erosion can be a problem with some building lots and land. If you in stall a septic field on the side of a hill, you must make sure that the soil covering the field remains in place. This can be done by planting grass or some other ground cover. When checking out a piece of land, you need to take the erosion factor into consideration. The cost of preventing a wash-out over the septic system can add a significant amount of expense to your job.


Set-backs are something else that you should check on before committing to a septic design. Many localities require that all improvements made on a piece of land must be kept a minimum distance from the property lines. A typical set-back for a side property line is 15 feet, but this is not always the case. Where I live, there are no set backs. But, I’ve seen set-back requirements that were more than 15 feet. This can become a big factor in the installation of a septic system. Let me give you an example.

Let’s say that you are buying a piece of land to develop into building lots. You’ve had your perk tests done and your septic de signs drawn. On paper, there doesn’t seem to be any problem. All of the wells and septic systems fit on their individual lots according to the plot plan. But, when you go to get your permits, you find that the zoning requirements establish side set-backs of 20 feet. Based on this, some of your septic systems encroach on the set-back zone. This, of course, makes them unacceptable. You might be able to obtain a variance that would allow the drain fields to run into the set-back zone, but not necessarily. If you can’t bend the rules, you can’t install the septic systems. Do your homework, and make sure that what you have sketched on paper can actually be installed.

Read the fine print

When you are looking at a septic design, it’s important to read the fine print. A design gives you all the specifications needed to bid a job. You should read the design carefully to determine exactly what types of materials are specified. It is a good idea to take the design with you when you do an on-site inspection. A long tape measure should also be considered standard equipment in your field inspections.

When you arrive at the building site, use the septic design to lay out the system. Once you have the septic site staked out, you can see more clearly any obstacles, such as trees, that might be in your way. When you stake out the field, you don’t normally have to be precise. The idea here is to see approximately what you are dealing with in terms of a work area. How difficult is it going to be to get equipment to the site? This is something you might not think about, but you should.

A few years ago, I oversaw the construction of a house that had a leach field high on top of a hill. A pump station was installed behind the house to pump effluent up to the field. The topography made it difficult to get crushed stone to the site. Trucks couldn’t back up to the work area and dump their loads. Instead, the gravel had to be ferried up the hill in the bucket of a backhoe. This procedure didn’t make the job impossible, but it did make it much more expensive. As a bidding contractor, you have to keep your eyes open for such problems.

By studying the septic design, you can determine the length of the drain lines. Also, there are details that show the depth of the trenches. With this information, you can use your probe rod to take random tests for underground obstructions.

Is the work area large enough to accommodate the piles of dirt and gravel that accumulate as the work progresses? If limited space forces you to work the field in sections, it’s going to take longer to construct the system. Whenever there is an increase in time, there is usually an increase in cost.

If trees must he removed, what are you going to do with the stumps? Getting rid of tree stumps has become a problem in the area I work. At one time, it was common practice to bury the stumps, but this is no longer the case. More often than not, stumps are hauled away to be ground up. The hauling and disposal fees for stumps can add a lot to the cost of a septic system. Keep this in mind if you are responsible for clearing the work area and disposing of unwanted debris.

Pay attention to all the details on the septic design. Everything needed to price a septic system should be on the design. Once you combine the design with a physical inspection, you should be in a good position to work up an accurate price.

Site visits

Site visits should be considered a mandatory step when bidding jobs that require private waste disposal systems. You can tell a lot from a septic design, but you can’t formulate a safe bid until you walk the land where the system is to be installed.

Many contractors try to use averages when figuring jobs. For ex ample, they include so much per square foot for framing costs and so much per square foot for siding work. They might use a per-fixture price to estimate plumbing costs. This method can work. I’ve estimated jobs based on a square-foot factor or fixture factor, but you can never be very sure about this method of pricing. It’s even more risky to use averages when a septic system is involved.

Unless you do a full-blown take-off and work-up on a job, you can’t be sure of your prices. Even when you go to the trouble of figuring every little cost, there is always some risk of error. Considering how much money could be at stake with a septic system, it would be very dangerous to simply plug a generic figure into a bid proposal.

It’s important to get quotes from contractors who are in the business of installing septic systems. You should get the quotes before you offer prices to customers. Builders and general contractors don't always have enough experience in each trade to produce accurate estimates on their own. This is why wise builders get firm prices from subcontractors before presenting any price to their customers.

Assuming that you are going to be acting as a general contractor, you should take your septic contractor out to the job site for a first hand look at the lay of the land. Unless you insist that your subcontractor visit the work area, you can’t be sure that you are going to get an accurate price. Most septic contractors won’t offer you a price until completing a field inspection. Contractors who are willing to give you phone quotes are playing the odds. As long as you know they are going to stand behind their prices, you can go along with them. But, only you can decide if you are willing to take the risk of doing without a physical inspection of the work site. Personally, I wouldn’t trust a quote from anyone who had not first looked at the site.
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Updated: Sunday, February 21, 2010 10:41