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Dont know if my abandoned septic tank is safe...
19 August 2006


Q. I have a concern about a septic tank installed in 1969 when the house was built that was drained at the time public sewer was put in but not dug up or crushed. It has been about 20 years since the sewer line was installed and I was wondering if this tank would eventually present problems. I am considering some new construction and would not appreciate losing it in a sink hole one day. I'm inclined to contact a septic company to have it crushed but don't know what all that would be involved, the c ost to expect, or if I should do something else. Your advice would be appreciated.

A. When septic tanks were abandoned as public sewer became available, the normal course of action was to pump them, then fill them with sand or gravel. If your house was built in 1969 it was a fair bet the tank may have been made of steel rather than co ncrete. Both were available but steel tanks were cheaper and easier to install. Steel septic tank use was discontinued in the mid 1970s and you could just about set your watch to them because as they reached age 20 they all seemed to collapse. What a me ss. I have a plumber friend who use to jokingly repeat how much he loved his job as he would sit on the back-hoe mucking out the stinking hole of a collapsed steel septic tank. Nowadays when a septic system is abandoned both the drywells (if the system h as them) and the septic tank, even if its concrete, have to be filled. If you donít know whether or not yours was filled, you should find out. As long ago as it was abandoned Iíd want to be sure.

You can hire a septic hauler or one who only performs septic testing, the type of testing known as ďPick and ShovelĒ-- which involves exactly as it sounds-- to locate and expose the old tank to both identify exactly where it is, let you know what it was made of and whether of not it has been filled properly. But equally important in my estimation is to locate and identify whether or not the dispersal system of this old septic consisted drain field trenches or drywells. A drain field trench if you enco unter it digging footers for an addition, or even a hole for a swimming pool, will be of little consequence.

Old drywells, on the other hand, scare me for a couple of reasons and they are life and death.

A drywell is a round, deep hole in the ground that can be 30 or more feet deep. The way they were constructed was the hole was dug either with a backhoe or a large truck mounted auger rig to a depth that was determined by the soilís absorption quality. Then a seven foot round circle of concrete blocks were stacked to about a foot and half below what would be finished grade and a round concrete top was placed upon that. The septic tank outflow line was piped over to it and the area between the block and the earth wall of the hole was then filled in with stone. Sometimes the drywell walls were round concrete dug well rings stacked and the stone placed against them. The cast concrete top normally had a four inch hole into which a pipe would be installed to the surface and you could spot the drywell location by that. But not always.

Drywells, should they deteriorate, can be very dangerous should you fall into one. If you fall in while alone you could scream your head off and no one is likely to hear you. A horrible demise to be sure. Iíve had homeowners call me reporting a sudden 8 foot diameter sinkhole having appeared in their yard,usually after a spell of very wet weather. I tell them not to go near it and get hold of a dirt contractor to fill it as soon as possible. A dirt contractor is a excavator. There are two pages of them in the phone book. They have the right machines and trucks to get the job done.

The cost of doing all this will vary according to what is found but if I had an abandoned and mysterious septic system in my yard Iíd want to know all about it for both safety and planning purposes. The Anne Arundel County Health Dept. on Truman Parkway has the plans of septic systems installed, with a permit-- some were installed without, on file going back to around 1988. Yours went in 19 years before that so get it checked.

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