Pond Boss Forums GENERAL QUESTIONS Pond Boss building new home foundation slab close to water

Hello. We are building a home and need to know how many feet we should stay away from the existing pond's water edge? My concerns are making sure the pond structure is not compromised, and of course the home foundation is not compromised.

Currently my Gen. Contractor has the home build foundation very close to the water's edge (within 12 feet) and my concern is either damaging the pond structurally, and/or damage to the home foundation later due to any water seepage from the pond. The elevation of the foundation would be one or two feet higher than pond water level (peak season) but water saturation into the soil toward the home still a concern.

I know that some home structures are built right up to the edge of waterlines, and they have no issues when built correctly. We are not doing that, but the contractor does currently have it scheduled to be very close, like 10-12 feet from the water's edge. I guess the real question would be, what is the bare minimum footage from the water's edge should I insist on with the builder when constructing my home foundation.

Here are a few facts:
Pond is 40+ years old maybe older.
There is no dam per se - IOW, no soil was removed and put in place for a dam. I believe they just dug a hole and removed the dirt/caleche to use for nearby road.
Mostly caleche and clay soil surrounds the pond.
Full most of the year, but gets very low if insufficient rainfall during summer months.
There is a spillway and has always seemed to work well during peak rain season, allowing water to flow out, without damaging any retaining walls around of the pond.
At full peak, there is one low spot that gets very saturated, and unfortunately that is very close to one corner of where the foundation is to be placed. The blue highlighted area in the picture links below pinpoint that low spot.

Here are a couple pics of where the contractor has suggested to build, and lay of the land/pond.

This is an overhead view. The red rectangle is the proposed home build site:
https://i.postimg.cc/1XMdzKyn/homestead-foundation-placement.png

Looking at the build site from one of the side view - pond is to the left with blue indicating low area of concern:
https://i.postimg.cc/k4NK3Jmw/IMG-5129-modified-jpg.png

I can post more pics if it would help. I close on the loan on Friday, 9/29/2023 (TODAY!!). Soon after we'll have to make a decision on the foundation placement.

Thanks a ton for any advice anyone can give me, no matter how big or small you think it may be.

Welcome to Pond Boss!!

I don't have any expertise in what you're asking about, but if it was me, I would steer clear of any area that gets damp or swampy near the pond as far as the foundation of your new structure.

And skip having a basement, unless you want an in-house swimming pool.

First question: Is your pond fed with surface water, or is it a groundwater pond? (In the first type, the water level will go down during extended periods of no rain, the second type MAY go down.) Does a big rain fill your pond almost immediately and start water flow through the spillway?

I am going to assume a surface water pond for the sake of discussion.

Well-formed caliche is usually porous and permeable. If your subsoils are clay and caliche, then they probably broke up the caliche horizons and spread that material throughout the clay and then compacted to form your seals.

If you are 10-12 feet back from the edge of the pond, then you are PROBABLY out of the zone where they excavated ground or came back and built the clay blankets to seal the pond. The most likely exception would be if they needed a lot of good clay material (like for building the core trench in a dam) and they borrowed material from your house site - and you say that does not appear to be the case. However, in that case, your site might be located on some poorly compacted, crappy "fill" material.

All ponds leak - but when the leak rate is very low, then we call that a sealed pond. I expect the subsoils at your home site will probably be saturated! However, in clay soils with a footings type foundation, that may not necessarily be a bad thing.

Basements and foundations in clay soils frequently crack and shift due to wet/dry cycles in the clay. Clay actually expands in the presence of water and then subsequently contracts as it dries.

I don't see any particular problems with a properly constructed slab home with the foundation footings built in always wet clay. (I would raise the site and build an elevated slab.) They need specialty rebar for wet conditions and probably a vapor barrier under the slab so moisture is not constantly being drawn up under your home. (Any free water will make the construction job a little tougher when they are working below the water level in the pond.)

*** (I am a geologist, and NOT a home construction guy. Geological advice from someone several hundred miles away is a little sketchy to begin with. My home construction advice is definitely worthless - just throwing out some ideas for you to ask your contractor.)

However, the best way to determine your actual conditions at the home site is to dig a couple of sample holes! This can easily be done with a mini-excavator or a backhoe. You might ask your house contractor to do this. Cost should be just a few hundred bucks, but well worth it to get your home design optimized BEFORE construction starts. (I would have him dig the test holes some evening when their equipment has just been released from a previous job. Dig the holes and then measure the water fill-up the next morning. Then have them backfill.)

P.S. I do not like the well-built waterway marked in your photos. That was constructed for a reason. Have you observed the water flows through that waterway during a big rain? I suspect you will need to divert that waterway a little farther from the home site, AND build your slab grade above the flood water levels in that waterway.

Good luck on your "home beside the pond" project. It should be a beauty when everything is completed!

I wouldn't worry about water getting into the basement if these 2 things are done.

1) Seal the outside of the basement walls after they are poured and the forms removed.

2) Have an under slab drain installed before the concrete floor is poured. Basically the slab is poured on top of compacted 6"-8" thick pea gravel base that has drain tubes in it that drains to a sump pump. Visqueen is laid on top of the gravel and the slab is then poured. Then after the outside of the walls are sealed, have a french drain installed around the whole basement and have that terminate into a sump pit with a grid based sump pump and a battery backup sump pump. The basement should stay dry then because no water will make it to the basement wall or floor to wick through the concrete.

+1. Proper slope around the house to drain water away is also necessary.

Like Fishingrod said above, you will need to dig a few sample holes in the area where you are contemplating building your house, you will know in a few minutes, or your contractor will, whether your ground is saturated or not, and therefore build able or not.

I do a lot of grade and house pad work here local and you could build a home halfway into the pond if you wanted around here, but we have a lot of heavy tight clay, you dig a foot into the pond bottom and you will find dry tight clay that is ok for building on, it would actually be better for the pond being close to keep the clay moist to a certain degree, that way it will stay at the same moisture content and not move as much, where you run into a lot of problems with it to build on is when it dries out and shrinks in a hot dry summer then gets wet and swells when the rainy season moves in. That being said, I am not familiar at all with caleshe type soils, and what properties they bring into the equation.

An experienced contractor will be able to steer you in the right direction tho, and it wont hurt to pick the brain of a few old timers that are familiar with building in the area, and have dirt working experience, in the local coffee shop some morning if you know of any. usually you buy em a cup of coffee and start the conversation you will get more knowledge, or some might call it bullshit in an hr then you thought possible. them old timers are always looking for a new subject to talk about, and somebody that can use some of their knowledge and wisdom.

Building a home close to a water source can be tricky, but it's great that you're thinking about the potential issues. It's essential to strike the right balance between proximity and safety. Given the age and characteristics of your pond, it's wise to be cautious.
For expert advice on construction and property-related matters, you might want to consult with professionals like https://www.decosta.group/. They can provide valuable insights and guidance tailored to your specific situation. Ultimately, ensuring a safe and stable foundation for your new home is paramount. Good luck with your construction project!