Attempt to locate buried sewer line with melted snow?

Question

I live in a housing addition (built 1965-1980) in the barren (no trees) Oklahoma panhandle. The first thing the new home owners in this area did was plant as many trees as possible.

Over last several years in my neighborhood many of these house sewer lines out to the alley main line are being dug up to replace either rotted (cast iron tree rooted pipe) or collapsed schedule 20 PVC (yes 20 not 40 schedule).

I guess my line is PVC because bent cloths-hangers & rented metal pipe finders won’t even blink to indicate cast iron. So knowing that at any time now it will be my turn to destroy my heavily treed back yard to replace my sewer line.

This town is trying to die & most plumbers have retired or moved off & not one of the remaining plumbers has a camera or pipe line sensor to run down the closet toilet to locate the line out in the yard. Also, there are no clean outs in yard which could indicate where to start digging.

My Question:

The next time it snows, if I pull the toilet off of the closet flange, configure a 4” to 24” square metal HVAC pipe duct funnel, set a 24” x 24” box fan on top of funnel, turn the central heat up sky high & blow hot house air down funnel into sewer line, would I be able to melt the snow so I can see where the pipe runs?

Answer 1

I doubt that you could get enough heat into the sewer line to melt the snow on the surface. Even if it did, that would only give you a vague idea where the pipe run is, though it would be more accurate than nothing.

I've got two alternate suggestions:

1. Ask the city. They'll know where the main sewer line is and, most likely, they'll know where your house is connected to it. Once you know where that point is, it's highly likely that the drain line runs straight back to the house in the shortest distance possible. Construction companies don't like to waste time and material making random routes when a straight line will do.

2. Rent a snake long enough to reach from your toilet to about 1/2 down your back yard. Run the snake down the drain, then use a metal detector to find the snake. Once you've got a good idea of location and direction, it's probably safe to presume that the run will continue in a straight line unless there's an obvious obstacle (that was there when the subdivision was built, not something added afterwards).

Answer 2

Tl;dr: physics says it's going to be very expensive.

Lets run some extremely rough numbers. This is going to approximate a lower limit on the heat required - you're likely to need far more. I've rounded massively, and more often than I should.

I'm going to assume a pipe buried 1 metre down, in soil that's at 0°C covered with a thin layer of frost/snow - just enough to indicate the temperature rise by melting.

The volume of soil that needs to be thawed will be considerably greater than the volume between the pipe and the surface, as the ground will conduct heat in all directions equally. I'm going to say you need to thaw a 3 square metre cross section (πr² with r=1m from the depth, rounded).

Dry soil has a density of around 1200kg/m³; the moisture content is likely to be 10-50% of this. With rounding that means 100-500kg of water per cubic metre, or 300--1500kg per metre of pipe run.

The latent heat of melting of water is 334kJ/kg, call it 300kJ/kg. That means for each linear metre of pipe, just to thaw the water in the soil if it's already at freezing point, you'll need 90--450MJ. 1kWh is 3.6MJ, so you'd need to deliver something like 30-150 kWh per linear metre of pipe.

This will go up if the soil is colder than freezing point, but not by all that much. The specific heat capacity of ice is 2.1kJ/kgK, so for each degree Celsius below freezing you'll need an extra 0.6-3MJ.

A thick layer of snow will make things far worse. Snow is a good insulator so more of the heat will go into the soil and less will reach the surface.

Lets see how much hot water you'd have to deliver to achieve that. A full bath holds the best part of 200 litres. At 60°C, cooling to to 0°C (which you won't manage) that's 50MJ (or about 14kWh, or £1.40 at UK gas prices). That means you need at least two very hot, full bathtubs per metre of pipe run.

At the price I pay converted to USD that's $3.40 per metre in heat - if you can deliver it with as much efficiency as I calculate, which you can't (and if the soil is exactly at freezing point, though this is a small effect). You could easily be into the tens of dollars per metre. You imply a fairly large plot of land, so you could well be into spending thousands of dollars on heat with no guarantee of success.

I wonder how much it would cost to hire ground penetrating radar; even with an operator it's probably cheaper and has a far higher chance of success.

Answer 3

I seriously doubt that running air from your heating system down a pipe 36" below grade in freezing weather will melt snow at grade level. Most counties, townships, etc., have phone numbers to call for locations of underground facilities. Try them. Check with other neighbors and see how their pipes were run in relation to their toilets and out their walls and make an educated guess on where your pipe exits the wall and dig a small hole to verify a location. Fom there, dig along the exposed pipe to the alley. You could also try contacting separate underground location companies. Some can run a sensor thhrough the pipe and then trace the signal above ground.

Answer 4

I recently had a plugged PVC sewer line and had to run a 100' snake down it. I was having trouble locating the cleanout downstream. So, I sent the snake down the line and ran it with someone else in the area of where we thought it might be and could hear the snake very clearly underground. If you want to identify were the line is, I recommend renting a snake for roughly $50 and doing it this way.

Answer 5

I'd be tempted to try audio. Buy a rape alarm: they're cheap, small and loud and if you lose it, it'll probably flush away. Take the connector off the end of a garden hose and attach the rape alarm to the hose securely. Set the alarm off and push the hose down the toilet. Go outside and listen - maybe use a stethoscope, they are cheap too.