shelf life under ground water tank

6 years is probably a god estimation, but since you are in such a dry area "Arizona", it might last 15-50 years or more.

Did you hit any water when you dug your hole?

The plastic sheeting is a good idea, as long as you can keep a pitch away from your tank "obviously".

Good luck!

Hi,

I do not believe that the plastic will help unless it completely seals the tank. As I recall the earth in Arizona is very alkaline so much so that despite the minilmal rain there, the soil will cause even copper ground rods to disappear. As a result, the solid copper bars are required to be encased in concrete for protection. I do believe, however, that with proper cathodic protection, you may be able to extend the life of the tank considerably, and with minimum cost. I suggest that a Cathodic Protection firm in your area be contacted and either use their service or perform the recommended burial and connection of sacrificing electrodes.

Bob Freudenberg

Hi,

Cathodic protection for steel pipe lines (in particular natural gas lines) is a practically fool-proof process as a long term solution for buried steel corrosion potentials. El Paso Natural Gas Company has one of the best libraries in the world for applying cathodic protection to buried steel pipe lines. As a former oil field technician, our company, Baroid Well Services, offered cathodic protection technology for buried oil field pipelines and/or refinery equipment.

El Paso Natural Gas has had two 24 inch pipe lines from West Texas to California in operation since 1952, almost 60 years, so corrosion technology has kept these lines protected (700+ miles of buried steel pipeline). This is a good example of technological exellence in protecting industrial materials.

The corrosive potentials are lower for Arizona soil conditons because of alkaline properties, and even better is not influenced by residual moisture in the ground.

There are many kinds of sacrificial anodes, like attached zinc ingots, that could give you good corrosion protection. Plastic liners do not seem the best way to protect bury steel. It would be better to have porous soils around the tank to allow for drainage of surrounding soils. Differential solid conductivity potentials can be a problem but your soil conditions will govern the corrosion potential, and ground resistivity differentials need to be addressed like those used at a sewage treatment plant site. In some places, an electric charge on the vessel will protect against oxidation (formation of iron oxide).

There should be many inexpensive options to consider in the WWW information resources. Think about how well a "galvanized" (zinc coated) wash tub is in protecting corrosion of a steel wash tub.

DRS

Another option, if you're hesitant to install proper cathodic protection and monitor it every year, is to replace the steel tank with a polyethylene (PE) tank when the steel tank rusts thru.

In case you are taking the tank out, why not sandblast it and spray zinc on it about 0.006" thick and the tank will last a lifetime without any corrosion. Attaching Zinc ingots is another foolproof idea as suggested by another member. Zinc Spray would still be the best. I am sure you can find somebody in your state who would do the job in the field with portable equipment with a wire spray gun. The process is simple and affordable

vshwn7@aol.com

I suspect that your problem will not be the external corrosion, but from the "grey water" inside. Especially is you're collecting water from "new improved" washing detergents and bleaches.

I had a grey water system using standard 200L drums and they coroded through from the inside in less than 2 years. First sign of failure was blistering of the external paint, followed by copious leaking. (These were above ground off ground on timber frames.) The corosion seemed similar above and below the general water level, so even the air space above the collected water was subject to intense corrosion.

If you want this to be a "permanent" item, then I suggest that while the tank is empty and relatively dry that you line the inside with fiberglass/resin (effectively using the tank as the mould) and then you're set for life. Or if you're into a little hard work you could cement render the inside surface. (My preference since I'm familiar with that method from salvaging numerous farm tanks in the past.)

There is also a product made from soybeans. It out gasses some formaldehyde while forming, but manufacturer claims inert after that. They advertise "quality air" inside home after spraying in between studs. A closed cell foam is supposed to keep out moisture. Might be expensive, but possibly permanent. Sand and plastic, out of the sun may have worked for a long time

Guess what, Mr. Engineer,

I was starting to think like you in that the inside coatings are just as important to the life of the steel tank. Good thinking. Experience is a good teacher, but the job is not finished until all the alternatives are considered, and an economic analysis done on all of the alternatives.

It is possible that the scrap value of the steel tank would be more than the cost differential to buy a polypropelene storage tank, and you would end up with a good storage tank and some extra pocket money.

You may even have to examine the earth forces on a buried plastic tank that is almost empty, so it may be even better to save the cost of digging a hole, and put the storage tank above ground. If ground water is present, the boyanncy forces could cause an empty tank to come out of the hole.

A simple engineering task can be full of unexpected consequences. Have we forgotten something?

DRS

_____________________________________________________________________

Einstien said, "Keep it simple, but not any simpler."

There are HEAPS of other things to consider. I've palyed with grey water alternatives for nearly 40 years from when I started using mum's laundry water for the gardens on the farm. (Water was scarce and our total household storage was less than 10,000L if all rainwater tanks were full.)

From experience, grey water tanks should only be "surge accumulators" to harvest what cannot be immediately used, but should be emptied on each cycle. Grey water if stored rapidly becomes putrid and offensive.

With a burried tank, he will need to review load bearing, not only of the sides as you mentioned, but also the lid because kids, animals or even cars might just happen to need to rtavel over that space.

With ANY tank, he will need to consider the safety aspects if ever they need to get inside it. Tanks become death traps surprisingly fast, small openings, no air circulation, extreme humidity no directional landmarks,.....

With tank below ground he will have the challenge of mounting a pump reliably into the bottom.

With overflow provisions, he will have to direct excess flow into the sewer and so will there face the necessity to ensure that sewage NEVER backfluses into the system.

I had not imagined him to have a substantial tank that would be of significant scrap value, since tanks of that nature would have thicker wall section and prolonged endurance. That's why I suggested an internal skin of suitable reliable material.

Wow a bunch of great suggestions, but I should be more specific. in Arizona the water is very hard and the soil is very alkaline. the tank is a light weight galvanized weighing about 1,000 lbs or less 6'2" dia. 13' long. the rust out about the ground being very hard would probably slow any leaks like you mentioned as long as i do not use gravel around it I almost started to think about doing just that. I will have an oxgenator in the tank to keep the putrid smell at a minimum. I didn't think a cathode but how about a anode in the tank itself?

Hi Mcjoe,

Sounds like your tank will hold about 3000 gallons. Your tank will be laid horizontal (13 feet long), we assume. We assume that you will have manhole access to the surface for oxygen venting, and to access the oxygenator, and will have a sump pump to remove grey water to the farm. You say that you will have the top side of the tank having 2" exposed above surface. If the outside of the tank has galvanized coating (sprayed on), then beware of "holidays" (holes) in the coating (the metal corrodes around exposed steel), and that ground elevation around the tank is not subject to surface water invasion. The plastic liner at the surface will divert ocassional ground wettness (provide for surface drainage using slopes around the tank). You could use some of your excavated material to raise the ground level a foot or two around the tank.

Good work for you to think about using "grey" water. Around here the sewer people use "grey water" on the golf courses. You could consider using "solar distillation" to recycle your water and purify it to reduce sluge contamination on the crops. Your might consider a sludge filter and a separate "sludge" pond or basin to remove solids.

Clean water is becoming a premium, anywhere, and growing organic plants(INSECTICIDE FREE) is beneficial to our health, and if we grow our own food, we save lots of motor transportation COSTS and pollution from exhausts.

Your idea for "holding" grey water is super. We need to make the best use of our precious water supplies, save money, and clean up the air. It will be even greater when people start conserving any "costly" commodity, and using solar energy appliances. Think "solar' and think "conservation", and we will get out of debt.

Have we forgottern anything?

DRS

-------------------------------------------------------------------------------

Doing anything is better than doing nothing.......When you don't have money for bells and whistles, you don't spend or waste money you do not have. Think good, but think cheap.

You should likely provide for some kind of run-off and drainage for when your tank is full.

I don't think an anode will do it, maybe someone out there may have better experience. The oxygenator may do fine.

In the old days in our area for septic and grey water they used to just dig a hole, sometimes add a rock retaining wall to stabilize the sides, and cover the hole with small cedar logs 8" to 10" in size, add a old piece or two of tin roofing. then plant grass on top. There are still a few of these around and they are 50 plus years old and still functioning. Of course they wont let us use these any more.

When you change out the old systems, you dig not more than 6" to 10" into the surrounding soil, and you find dry soil.

I guess it all depends on what kind of ground you have to work with. Soap scum and grease make a great penetrating coating on soil.

i think you should let the water department take care of your laundry water. in that way you don't have to worry about a tank blowing up in your backyard. water department will give you clean water everytime.

Hey there Water Boy,

It sounds like you have plenty of water (lakes,ponds,oceans, rivers) where you live.

Out here in New Mexico (Tularosa), people fight over scarce water supplies. Before there were well drilling machines (<1900), everyone had metal roofs and cisterns. If you were lucky to live near a steadyflow creek, like we have the Tularosa Creek, you would use an acsecia irrigation sytem to farm, if you had water rights.

We are thinking of using rain water from a modern cistern for "psuedo hydroponics" for commercial greenhouse organic farming, since ground water here is alkaline, and RO treatment is cost-prohibitive.

A one inch rain will provide 7.5 gallons of clean water over a 12 square foot area. So, if we have a 1200 sq. ft. roof, we can collect 750 gallons from a one inch rain storm.

I would'nt live where "control freaks" tell me how I can use my rain water. I feel sorry for you.

God Bless America, please.

DRS

have you checked with your local code enforcement?? in many places it is not legal to use or store greywater. and in many arid locales you don't even have the right to the rainwater that runs off of your roof.

Wow. This sounds bizarre - who would own the water in your rain barrels?

Very hard to believe!

Using the plastic was probably a counterproductive notion...as it will only serve to retain moisture that would have otherwise dissipated (fallen or evaporated away) relatively quickly, leaving the tank in dry (you might say, shelf-like) conditions.

The key factor to be considered (over and above galvanization of the tank surface) is the gauge of the metal used. In other words, the service life of the tank will be most closely related to the tank's rust-through period given the local atmospheric and soil-type (field/moisture and acidity...) conditions. By rust-through period would be meant the time duration of ongoing corrosion (if and as corrosion can continue in any one location) before which the tank will remain serviceable and not in jeopardy of collapse or rupture under force from within or without.

In your area it would probably not be unreasonable to envision a service life of most tanks as being approximately that of the life expectancy of an adult human being...or certainly long enough such that the prospect of tank repair or replacement should become a concern in the near term (say, of less than 10 to 30 years or so).

Just FYI, from the instant your tank became imbedded in its underground location, it no longer had any "shelf life''...which is the life expectancy of a product on the shelf before it is used in any way. Your question would better have referred to the tank's expected "service" life.