Constructing a Permanent Underground Cache, by JIR

If you are concerned about hiding a large amount of goods from looters, neighbors or other busybodies, remember that no indoor hiding place is likely to survive a determined search. If your home is the only place you have food and provisions, you may be forced to fight against very long odds to try to keep it. If you are forced to abandon your home in the middle of the night or burned out by looters, you might appreciate having a store of food and other gear in a safe, undetectable location where you can recover it. You might want to consider constructing a series of permanent underground caches. Underground is the safest place to hide something, but the most difficult to construct. There is no such thing as permanent, of course, but you can come pretty close if you follow a few rules and take a little care.

I have 3 large caches that I buried over the course of the last year. Having three redundant cache sites is pretty excessive, I know, but forgive me my excesses. I had the materials and the surplus supplies, so I used them. They cost very little to stock the way I do it and I had almost everything on hand anyway. They are cheap to construct if you can borrow or rent earth moving machinery and hey, you know what we say, two is one and one is none. Having three of them gives me more tactical options if I ever need them. I went a little overboard on waterproofing too because I was learning as I went along and found very little practical information on the web to help. I will pass on the procedures I used because they worked, and try to point out some of the stupid errors I made along the way.

The biggest problem with burying things is water. Soil is mostly permeable to water and may hold moisture year round. This will cause containers to rust away or otherwise degrade. Moisture inside your cache container can be a disaster causing rust and rot. If you can get around this problem, underground hiding places are excellent. They are temperature stable and very secure.

For containers, you need something extremely durable, and physically strong (to resist ground pressure), and completely rat-proof. You probably can’t waterproof your container well enough to prevent moisture from accumulating inside it, so you will need to put it somewhere dry and allow it to stay that way by diverting water away from it. You are shooting for a sort of man-made cave where your goods can stay dry and at a relatively constant temperature for decades.

Plastic buckets can work for small, temporary caches, but are unsuitable for unattended storage of longer than a few weeks. I feel that eventually, rodents will find any container you bury and if it’s not rodent proof, you will have rat damage. For long term, storage you will want something much bigger, stronger and rodent-proof. I feel that (New) Steel drums are an excellent choice for this. They are strong, water tight, and resist corrosion well. If you can get these, they are probably the easiest and best container. An even larger container can be made of road culvert if you can seal off the ends with rat-proof doors or panels. You could probably also use galvanized trash bins, or old refrigerators and other appliances, but these are less durable than an industrial drum and could collapse if driven over by a vehicle.

These containers can be buried almost anywhere the terrain and soil is suitable, but should be located in a place where nobody is likely to suspect anything of value is located. A hay field away from any public road, public grazing lands, forestry service lands, power cuts, or almost any scrub lands are ideal. There are endless possibilities. You can even bury these in your back yard or under a building if you wish. Bury it deep enough to ensure the top is under ground by at least 6 inches (a foot seems better to me and more temperature stable). Moving this much dirt around is pretty much insanity without a backhoe or other earth moving machinery, so avoid using large culvert unless you can bury them without attracting attention. If you must hand-dig, you should probably use a smaller container, like a drum. I started excavating by hand but that didn’t last very long. I dug for two hours and didn’t seem to make much of a dent in the ground. A back-hoe is definitely the way to go, but only if you can keep your cache sites a strict secret.

The key things you need to look for in a cache site are:

1. Deep water table and good drainage. This is a huge problem in my area and finding a good site is difficult. Your container will not be completely water tight and will quickly fill with water if your site is wrong. I determined this by testing two sites using plastic pails. The side of a gentle slope works pretty well. Avoid low ground that could collect rain run-off. If your soil is wet all the time, you are going to have to use a very large piece of plastic sheeting to divert water and protect your cache. The soil should ideally be dry year round once you get a couple of feet down. If not, you may still be ok if you use enough plastic to divert surface water around your cache. You can test your site by loading a cache drum or (perforated) bucket with a little cotton cloth (I used a couple of white bath towels), bury it using the same techniques you will use for your cache and leave it a year or at least leave it through your local wet season. When you dig it up and inspect, there should be no water damage to the towels and no evidence of water on the inside of the drum. One of my pails (buried in a flat, sort of wet forest floor) flooded in spite of the plastic sheeting, but the one buried into a slope had no sign of moisture at all. The ground water had passed over the top of the sheet and left the soil underneath dry.

Some regions have the opposite problem. Trying to cache anything deeply in Arizona, for instance hits rock-hard clay a foot deep. Even with a pick it’s almost impossible to dig through. If your soil bottoms out in caliche clay or bedrock, underground storage may not be for you. Even if you manage to blast your way down deep enough, water is likely to gather there when it rains and flood your site. There, drainage is almost non-existent.

2. Remote or at least hidden location. Nobody can know you have hidden something there. Security is key. If anyone knows you have buried something, you will probably lose your cache. Your site should have a hidden approach and egress route to facilitate recovery. Ideally, it should be in an area where people simply won’t go. There should be nothing nearby that could draw people to the area like water or game or even fire-wood. If you use earth moving machinery, you need to do it where nobody will wonder why and investigate.

3. Room to bury your containers between trees or other obstacles without leaving signs that you were there. You may need several drums to cache all your gear and supplies. In the case of a big cache, you will want room to move earth-moving machinery around the site. Digging through thick roots by hand is soul-destroying work. Make it easy on yourself and find a nicer place to dig, or rent a back-hoe.

Choose your sites with great care and the rest is easy. The general procedure is simple. Bury the drum or culvert laying on it’s side and before you replace the sod or leaf litter, pack dirt around the drum and then lay down a generous portion of heavy plastic sheeting. Cover the sheet with a foot of soil and replace the sod or leaf litter. With the sod layer in place, the cache will be undetectable without a metal detector in a few weeks.

What should you include in your cache for permanent storage and how do you pack it?

Waterproof each item separately as if it were going underwater, if possible. All foods stored underground should be canned in enameled cans or glass jars. Glass is fragile, but won’t ever rust away, even if your cache leaks. If you go this route as I did, add an oxygen absorber and dip the lids in paraffin to waterproof them and your jars should last virtually forever. To minimize breakage, you can wrap each jar in newspaper, or tie them into the legs of pants or wrap them in other clothing, like sweaters and jackets. This seems wasteful of space, but you may be glad you included extra the clothing later. Whatever you use, I recommend you pad your jars excessively. If your disaster turns out to be an earthquake, you will be glade you did and newspaper is cheap. Loading your cache should probably be done at the site if you use glass. Too much rattling around will cause breakage. If you can pack the container very tight and fill all the free space with cloth or paper, it may ride in the back of a truck, but I can’t recommend this. Each drum will be very heavy when loaded.

Contents: The purpose of these caches (for me) are to be stand-alone survival kits for long term sustainment. Each one should assume that this is the only supply you will have. That way, if you need to bug-out and leave all your gear behind, you can re-supply, even if all of your sites but one are compromised. I know that’s a tall order, but try to store only items that will be hard to get after TEOTWAWKI or very likely to be needed. It can be done rather cheaply if you take a minimalist approach and leave out the frills.

Food: (The most important thing to store)
All of the foods stored in this type of long term cache should be dry goods with very long shelf lives. I store mostly wheat and beans, with some white rice, salt and white sugar. I also include some garlic powder, vitamin C crystals, peppercorns and cinnamon. That’s it. I don’t even try to store baking powder since it won’t last more than a few years. You really can’t store anything in here that you will want to rotate. Digging these things up often is a bad idea. Not only could you give away your cache location, but loosening the dirt around them every year may cause them to take on water. I recommend inspecting each cache infrequently. I checked all of my caches after a year and took one completely apart to check the weapons and clothing integrity. They were all bone dry (and the weapons were still greasy and unchanged). I hike by each of them every few weeks to see if the area has been disturbed, but I doubt if I will dig them up again for several years. I don’t feel the need.

Before you start trying to store a whole armory, ask yourself two questions: “If this is the only weaponry I have available, can I get by?” and “Do I really need to store this?” Your answers will be different from mine, but try to minimize your weapons. Every cubic inch you use for weapons is space you won’t have for food or clothing or other vital supplies. All weapons are costly and if you spend a lot on them, you are really going to get your feelings hurt if one of them rusts solid or gets stolen by a construction crew that accidentally digs up your cache. Keep it simple, cheap and expendable. Almost any old surplus military rifle is ideal for this kind of storage, but your choice is your own.

I chose two inexpensive weapons for each of my caches and a small amount of ammunition: I chose an SKS carbine because I had several of these and like them. I bought several at $130 each a few years ago. I fired them to confirm the iron sight’s zero and was planning to sell them or store them for hard times. When I decided to store them underground, I cleaned three of them well, took them apart and packed them in automotive grease in a cotton sheet and enclosed the whole thing in plastic. The bores, chambers and mechanisms including the trigger mechanisms are literally packed solid in grease. The whole assembly is then dropped into a section of 8 inch PVC pipe with a moisture absorbing silica gel pack and the cap glued on with pipe glue. It’s just that simple.

In each cache I also store a .38 revolver with 6 inch bbl. I got a deal on these for $190 each, but they were almost as expensive as the food I stored. If I had it to do over, I would probably not bother storing pistols, or use ones I already had. They are all good quality weapons, police surplus, packed in grease and wrapped in cotton before sealing them in plastic bags. Are they ideal? Not even close, but they are all serviceable handguns and adequate for my purposes. This pistol will fit neatly into the PVC container with the carbine, or you can hedge your bets and prepare a separate container for it out of a short section of 6 inch pipe. The pipe container that I have checked didn’t seem to change even after a year of storage. I used a quality (Quaker state) automotive grease and it looked pretty much the same a year later.

I also stored ammunition and other metal objects the same way, but my ammo is sealed by itself. I don’t think exposure to grease or solvents is harmful to ammo, but why take chances? My ammo is sealed in glass jars and well padded before sealing in a pipe section. I chose to store 20 loaded stripper clips of 7.62×39 FMJ and 50 loose rounds of .38+P 158gr lead SWC hollow points. In two of my caches, I also included a couple of speed loaders and a holster, almost as an afterthought. I forgot to include a cleaning kit and need to add that sometime.

I have a sheath knife and a Machete stored at each site for chores. Both are greased and sealed with the firearms. The only metal tools I store outside of a PVC container are a short handled shovel and a small pick which I threw in after oiling them. Neither of these tools had changed much after a year, but the oil had evaporated or dried up.

Clothing and bedding:
Each cache site has 2 sleeping bags and 4 blankets, all polyester. Why? Besides being cheap, polyester can sit for years under water and still come out functional. Polyester is sensitive to sunlight, but not water. Besides that, I got a deal on them. I wrapped each sleeping bag in a 10×12 poly tarp and 550 cord to make a shelter out of if needed and seal the whole thing in a plastic trash bag. I bought the poly tarp new and I probably should have left it in the plastic bag it came with.

Each cache has some “Goodwill” clothes, new underwear, socks and a pair of my old army boots stored in plastic bags inside a couple of plastic boxes. For my wife, I bought new sneakers. she is not the boot type. These clothes are the most vulnerable part of the cache and cannot survive water submersion. So far, none of them have been harmed by underground storage.

A .50 ammo can holds a first aid kit (I know, these have a limited shelf life), Grain mill (dismantled), lighter, matches two (polyester) hammocks and a small supply of bug repellent, Leatherman tool, Polar Pur water treatment crystals, a small water filter and other sundries. I have toyed with including some cash or gold in this ammo can, since I have space, but opted instead to stuff some more socks and underwear in it. You might want to place a few silver or gold coins in the can, just in case. This can and the contents were bought new and represents a lot of the money I spent to build these caches. Just the water filters and grain mills were around $60 each. You can probably skimp a little on the sundries and still have a viable kit, but I got a little giddy while I was shopping. Be careful what you choose for water purification. Bleach bleeds through most containers in time and will rust all the metal around it and so will iodine. My Polar Pur crystals are still sealed and haven’t leaked yet. Next time I open the caches I intend to remove the Polar Pur bottles from my ammo can, just in case.

Each of my caches also contain two cheap stock pots, a camping mess kit, some utensils, hobo stove and a collapsible 5 gallon jug for potable water. In my last two caches, I added a couple of 5 gallon buckets because they are so useful and I had the space. These buckets contain wheat, but I don’t yet know if it will go bad. (It survived the first year).

Building the sites:
Since I was unable to easily get new industrial drums, I went with galvanized road culvert. Three foot diameter culvert is expensive if new, but you might be able to salvage something like this from a construction site. That’s what I did. I got three sections of 8 foot culvert for the price of cutting it up and was able to use them all, even though one is dented slightly and a little shorter. Culvert is probably a lot more trouble than drums, but drums are expensive and you will need several per cache site. The companies I contacted didn’t even want to give me a quote on six drums. I think most people who sell new drums deal in volume. So I gave up and looked for something else, in this case 3 ft diameter road culvert. Smaller diameter culvert would probably work just as well and would be a lot easier to bury and haul around. If I were doing this over I would choose one foot diameter culvert no more than 4 or 5 feet long and use a lot of them.

To prepare a culvert as a long term cache, you need to rat-proof it. I used two sheet metal panels cut from an old refrigerator and held by stainless steel 1/8th inch bolts. The panel was cut to fit the corrugation very closely and held in place by two lengths of angle iron bolted to the culvert. There are a lot of ways to do this, I just had some angle iron and sheet metal lying around and threw it together. I highly recommend you arrange some kind of door instead. A door would be much more convenient for inspecting the cache. The method I chose means I have to uncover each bolt head by digging a lot more dirt from underneath the culvert than would be needed with a door. Further, a welded on door would probably be much stronger and tighter. My panels have about 1/8th inch open space between the sheet metal and the culvert wall, not very tight. I also lined my first two culvert bottoms with mixed sand and cat litter, but I don’t really know what I was thinking. This step is unnecessary and I almost broke my back doing it. To load the culvert with supplies, it’s easiest to work from both ends and then close it up. On my first site, I buried one end and then tried to load it, (bad planning). Since most of my storage containers are tubes or round, I stack my supplies on their sides. Most of the space is taken up with 1/2 gallon glass jars full of wheat or other foods. Each jar is padded with clothing or newspaper.

Beware, culvert pipe weighs a lot. I was able to bury and man-handle mine into position all alone, but I used a borrowed Bobcat earth mover and a winch to do it. (Be very careful not to make chain marks on nearby trees if you use a winch. Pad the trees to avoid damaging the bark.) If you try to bury one of these by hand, you will probably die of exhaustion before you get the hole dug. Digging a 5 foot x 14 foot trench is a lot of work, even with machinery. Once you have your hole, you can load and seal your cache and then cover it over with at least a foot of dirt. Pack the dirt in tightly around your culvert or drums. This prevents the dirt from settling later and allowing water to drain in.

Lay a sheet of heavy plastic over the site, after packing in the drums with fill dirt. You can buy rolls of heavy plastic at any hardware store.
Get at least 6 mil plastic and it should hold up for many years. The plastic should be under at least a few inches of soil and positioned to re-route water under the soil surface so it won’t seep into your cache. The sod should placed back over the whole thing. Replace as much ground cover as possible to camouflage the site and get rid of any machine marks or tracks. If you did a good job of choosing and sealing your site, the inside is surprisingly dry and temperature stable.

I highly recommend adding an inventory sheet near one of the ends. Without mine I would have had no idea what I was looking at or what I stored by the time I cracked open the cache.

One last challenge: Excess dirt. You are going to have to figure out how to dispose of a lot of dirt. I didn’t anticipate this. I used a Bobcat [earth mover] to move a lot of it over the site and scatter it, but I still had to load a lot of it in my truck bed and haul it away. I took it to a low area and dumped it. But this is a lot of work. I did the same thing at all three sites since I had no better solution. I don’t recommend leaving a huge pile of dirt next to your cache for obvious reasons. Think it through before you start and you will have more fun than I did.

Conclusion: I have used temporary underground and underwater caches for years in the military, so I suspected a long term cache could be constructed, but until I tried it, I was still a little apprehensive. After inspecting all three sites and checking one of them thoroughly, I have lost much of my trepidation. If you take care to protect everything from moisture and vermin, you can store supplies underground for extended periods. If you live in a place where you are likely to be looted, beat them to the punch and hide it first. When the looters come to call, they will find the cupboard bare. – JIR