The trench is dug down through the top soil, rock, sand or any material that would let water pass until a good clay soil layer is reached.
(The trench; is dug down; ) (a good clay soil layer; is reached; ) (any material; would let; water pass; T:until a good clay soil layer is reached) Context(any material would let,List([59, 86))):(water; pass; T:until a good clay soil layer is reached)
any material would let,List([59, 86))
The trench a good clay soil layer any material water
is dug down is reached would let pass
water pass T:until a good clay soil layer is reached
T:until a good clay soil layer is reached