According to [1], "the normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg." According to [2], the density of topsoil ranges from 1,100 to 2,500 kg/m^3. One acre is about 4,000 m^2, so a conservative estimate is that there is about 1.3 kg of uranium in 1 meter of top soil on a 1 acre lot. (4000 m^3 * 1100 kg/m^3 * 3x10^-7). That's just the low end - taking the midway point for both yields over 40kg (4000 m^3 * 1800 kg/m^3 * 6 mg/kg).

[1] https://en.wikipedia.org/wiki/Uranium_in_the_environment

[2] https://structx.com/Soil_Properties_002.html

Do the math. Average crustal abundance of U is around 3 ppm.

for a house in my neighbourhood I'd guess ~100 mg

According to Wikipedia(https://en.wikipedia.org/wiki/Uranium_in_the_environment):

"According to the United Nations Scientific Committee on the Effects of Atomic Radiation the normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg."

So let's say 5mg/kg. 200kg of soil per gram. How much area do you need to make 200kg of soil if you're going down 1m? I'd guess not much...

So I think OP is wrong and it's more like 'several grams'.

As others have pointed out here, no, I was not off. It's a bit of a shocker to realize how much U is out there. There's a reason one should test your basement for radon before you buy a house.