Do I need to grout my wells?

Discussion in 'Geothermal Loops' started by Douglas Nathe, Oct 27, 2017.

  1. Douglas Nathe

    Douglas Nathe New Member

    We will be installing wells for vertical closed loops. Our location is about 400' from a lake and the water table is about 4' below grade. I am expecting the well to be full of water at all times. The soil is very sandy as well, so I would be surprised to see the wells maintain a low water level.

    Is there a thermal advantage to still use grout even if the well will be full of water?

    Can we pass on the grout and if there is an issue perform grouting at a later date?
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Fully grout. It's generally code in most areas. And if it is not code, it is best practices.

    It is to protect cross contamination of aquifers among other things.
    waterpirate likes this.
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Water conductivity is around .65-.70, grout conductivity is from 0.4 - 1.6.....unless you have convection in the water.
  4. arkie6

    arkie6 Active Member Forum Leader

    Saturated sand has a much higher thermal conductivity (>3.0) than water alone. The high thermal conductivity grouts use sand to increase thermal conductivity. If allowed in your area, you could backfill with sand to within ~20' of the surface and then seal the top of the well bore with Bentonite grout or swelling sodium bentonite chips or pellets to seal out surface water.

    But if you are drilling wells in sandy soil, you may have problems with the well sides collapsing during drilling unless casing is used. If the sandy soil is only near the surface, a temporary casing may be required that can then be removed after the drilling is complete. Are there other wells in your area? Your state water well commission, assuming you have one, will keep records of wells drilled, location, and what is encountered during drilling. These records should be searchable online.

    Google your state + water well commission to see what is available and what the rules are regarding backfilling geothermal wells in your area.
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You have to careful, the conductivity of saturated sand depends to a good degree on the grain size of the sand, which is one of the reasons expensive silica sand was used grout material. Grout conductivity and its impact on borehole performance is a science for itself, throw the cost and the effort (transportation, freezing of the sand bags in the winter , pumping it down a borehole....etc) in the mix, and this becomes a discussion way beyond a DIY install.
    Last edited: Nov 5, 2017
  6. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Best practices always include grout. Not for performance but to protect the aquifer or aquifers from contamination and mixing with each other. In your case also the lakes water. Typically a grout with 20% solids content is the standard without the addition of sand or graphite.

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