Removal and Cost of Hitting Rock or Water During Inground Pool Construction
River Pools has installed over 1,000 inground fiberglass pools throughout Virginia and surrounding areas since 2001. We have worked in a wide variety of soil conditions, ranging from coastal areas that are literally below sea level, to mountainous regions engorged with bedrock.
As such, we have had to learn to deal with both high water tables (ground water) and the removal of rock for the installation of our pools.
If you are considering an inground pool, you likely have a myriad of questions regarding how water and rock can influence the construction of your project, and whether the soil condition should impact which type of pool you purchase.
Today, we're going to tackle these questions and hopefully give you the information you need to feel comfortable moving one step closer to owning your own backyard pool. So let's jump right in!
Question 1: Is It Possible to Tell If I Will Hit Rock or Water before the Installation of My Inground Pool?
There is an amazing online resource that allows you to check any location in the United States for the approximate depth of bedrock.
- Visit SoilWeb: An Online Soil Survey Browser, a website provided by the California Soil Resource Lab.
- Once there click "Menu" in the upper left corner.
- Then click "Zoom to Location" and enter your address.
- Find your home on the image and click to drop a pin there.
- Click "Map Unit Data" in the upper left and it will give either the depth of bedrock in cms, or "n/a" if it's not near the surface.
Keep in mind that this is only an approximation, but it will give you an idea. This resource also provides a depth for "water table" but this is the depth of the first layer of moist soil, not necessarily the depth at which you will hit ground water. Thanks to the UC Davis California Soil Research Lab for providing this great resource.
To check for groundwater, the best bet is often to dig test holes with a post hole digger or piece of equipment, if available, to reveal the water table depth. Keep in mind that the depth of groundwater can vary greatly depending on tide, rainfall, season, etc.
Question 2: Should Fiberglass, Concrete, or Vinyl Liner Pools Be Avoided In Areas With Rock or Groundwater?
The short answer is No. Any of these pool types will work well in any condition so long as they are constructed correctly.
One myth that we encounter on a regular basis is that fiberglass pools should not be installed in areas with high water tables because they are likely to float. If this were true, we would have experienced this at River Pools after installing so many pools in high water table areas, but we have not had a single pool float after the construction of the pool was completed. However, if this is a concern for you, you should learn more about our advanced installation methodology (as part of The River Pools Way, which literally ties the pool into the ground and provides a way to alleviate hydrostatic pressure.
Regarding vinyl liner pools and high water tables, the only concern is the liner "floating up", which happens whenever there is enough groundwater to cause the liner to lift from the floor of the pool. When the water recedes, the liner returns to the pool floor, but because it does not re-seat in exactly the same place, it leave nasty wrinkles behind. This does not have any structural consequence, but it is unsightly and unpleasant.
Regarding the performance of fiberglass pools in areas with large amounts of rock, we have found that they do extremely well.
We attribute the success of our fiberglass pool installations in both high water table and rocky conditions to our unique installation methodology in The River Pools Way, which "locks" the pool, plumbing, and patio in place. Look for a dealer in your area that uses The River Pools Way.
Question 3: How Is Rock Removed for My Pool Installation?
Keep in mind that many types of rock can be removed with normal excavating equipment.
However, when bedrock is encountered, we will rent a "hoe ram," which is an excavator with a huge jackhammer attachment.
This busts up the rock which we can then remove with our excavator. In most cases, the rock needs to be hauled away because it cannot be used on site.
Question 4: How Much Does Rock Removal Cost?
Every situation is different, but in our case we can usually remove the rock within a day or two.
When you factor in the cost to rent the equipment and haul away and dispose of the rock, we typically charge between $3,500 and $5,500.
However, we do not hit rock that often, so when we do, we tend to give the customer the benefit of only paying our direct cost.
If we had to do this on a regular basis, we could not stay in business charging so little.
We would probably charge between $8,000 and $10,000 to cover not only the rental and disposal cost, but also our labor, and the fact we were tied up for a day or two removing rock instead of installing another pool.
Question 5: How Is Ground Water Removed for the Installation of My Pool?
The type of pool directly impacts how groundwater is mitigated during construction.
One distinct advantage of installing a fiberglass pool shell is that it happens so quickly. Usually within a day or two of breaking ground, the pool is installed and full of water. This being the case, we only need to keep the water "at bay" for several hours.
Once the pool is full, the groundwater is no longer a concern (although we do continue to remove it with a submersible pump until the patio is poured).
We remove ground water during installation by first starting the excavation at the deep end of the pool when possible.
This allows the water to continuously flow to the deepest point where it can be pumped out.
At the deepest point we will dig a hole approximately 12" deeper than the bottom of the pool, place clean stone in the hole, and place a submersible pump there to remove the water. Sometimes more than one pump is needed.
During excavation, the pumps will likely clog with sediment so it's wise to cover them with filter fabric. We've found this method to work extremely well and require minimal effort.
In contrast, concrete (also called gunite) pools take much longer to install, typically three to six months or even more. This makes the process of ground water removal a long term burden on such projects.
The same method described above can be employed, or because of the greater chance of cave-ins resulting from having the hole open for such a long period of time, well-points can be installed as a semi-permanent way of controlling ground water around the entire perimeter of the pool.
Well points are basically pipes driven or washed into the ground that have a series of screens that water can be sucked through.
They are connected to a pump that draws the water out of the ground and discharges it away from the pool area.
Question 6: How Much Does Ground Water Removal Cost?
In our case, the only time we've had to charge a customer for ground water related issues were several cases where an extremely high water table caused the sides of the excavation to cave in and thus required the use of significantly more stone backfill material than originally estimated.
We include one additional load of stone in our contract for cases like this, but we have had one or two instances that went to extremes and we had to ask the customer to at least cover this cost.
In areas with purely sandy soil and high water tables, well points could be used to prevent this. However, in these cased the soils would not permeate well enough to use them.
Well, we hope this has answered your questions. If you have additional rock or water related pool construction questions, or comments, please leave them below.
Also, did you know that River Pools also manufactures fiberglass pools and distributes them through our authorized dealers throughout the country?
That's right, we offer a full line of fiberglass pool designs.
Thanks, have a great day, and happy swimming!
Editor's note: This blog article was updated on January 7, 2019.
vinyl liner pool photo credit: www.poolspanews.com