A number of column samplers are commercially available. All are basically a long hollow tube that is lowered into the lagoon. Once the sampler reaches the bottom, the top is stoppered and you lift out a complete column. Be sure sampler is long enough to reach the bottom of the lagoon, and the diameter of the tube is wide enough to collect an undisturbed sludge sample. To collect samples from each lagoon layer, use a discrete sampler that takes a small volume of waste from each layer.
Discrete samplers use pressure to force liquid and sludge into a small collection vessel.
Plans for building an accurate, but easy to use, discrete sampler called the sidewinder are available from the OSU Biosystems and Agricultural Engineering Department. Slurry from Waste Storage Pond and Settling Basin Layers form in a waste storage pond just as they do in a lagoon. Since you spread the entire contents, you must take samples while the pond is mixed or agitated. Use the bucket-throw or dipping methods to collect samples from agitated ponds. Solids content of the slurry change as the pond is pumped.