esshup,
During construction of your groundwater pond, was it easy for you to discern the layer of sediment that tied your pond site to the local groundwater?
Or was there so much sand and gravel that MOST of your subsoil profile was directly tied to the groundwater?
If the latter, then have you been there during the construction phases of some of your client's ponds and observed thinner discrete layers that tied to the groundwater?
(Such that a less experienced pond builder could obviously conclude what they needed to deal with to either seal the pond, or leave that layer open for a groundwater pond?)
Yes to all except the latter unless you consider the last 10"-12" of gravel directly above the clay one of the discrete layers. Depending on the amount of soil moisture, I've seen water coming through just the gravel layer above the clay, or even through the clay and 4'-5' of the sand layer above it, sloughing off into the pond as it is dug. In those instances, the two choices are 1) keep the sides sloped back 4:1 as you dig to help prevent sloughing off and ending up in the bottom of the pond or 2) don't worry about the sloughing off, just dig a deep sump pit off to the side and keep pumping the water out of it as the pond is constructed.
It's been so bad that we've had to float the intake screen for the pump on an innertube to keep the intake hose from filling up with sand and getting completely blocked off. That happened, and it was so heavy that we ripped it in half trying to pick it up with the excavator and a 4" wide nylon strap under the intake pipe. Lots of dirty words said and then it was a run to the store to get banjo fittings to connect the now two piece hose back together once we got it cleaned out.
