Bog Filter - Day 3

At the bottom of the filter goes the pipe distribution network. I opted for 1" PVC and I cut slots every 3/4" or so down the length of the horizontal runs. The vertical runs at the ends are capped and available for cleanouts.

The distribution system goes into the bottom of the pond. Pat had fun experimenting with new photo editing software. Thanks Pat!

The pond gets filled with 3/8" pea gravel. This provides the surface area for a bacterial film to develop, allowing biological growth to reduce the nitrogen. Further nutrient reduction takes place when plants are placed into the gravel. The water level in the bog is just even with the top of the gravel.

This is what a half-ton of pea gravel looks like. It is pretty dusty when delivered so it must be rinsed before placing into the filter, otherwise you just introduce all that rock dust into the pond system.

So I figure that I shoveled a ton of gravel that morning - first into a bucket to swish around with water, then into the filter.

Now the bog filter is full to a 12" depth with gravel. We put a piece of plexiglas onto the low point to create a small sheet-flow waterflow into the pond. Now we'll see if it works...

Bog Filter - Day 2

No wait – here's the biggest heat wave of the season. I had been planning a long bicycle trip (three days) to ride to Williamsport, PA to see Chili. It was going to be great – all the way up the Susquehanna River Valley. I decided that would not be a good idea with heat expected in the upper 90's to low 100's. So what did I do instead? I started digging another big hole.

A bog filter needs to be 10 – 30% of the volume of the pond to be filtered. It also needs to be set at a higher elevation than the pond so that water can flow from the filter to the pond. That's great if your pond is set into a hillside, but since ours is in a very level spot I had to build up the perimeter to get a raised elevation. Hence the cinder blocks. A bog filter needs to be 12” deep, so I set the 8” high cinder blocks at least 2” into the ground, leveled everything up then dug down another 8” through very hard, rocky soil.

You really need to make sure no sharp rocks will cut the liner, so all the soil that I removed from the hole was passed through a 1/4” sieve. That added a lot of work, but the sifted soil was pretty smooth and allowed me to pack it into a curved shape for the basin. I added some old sheetrock under the soil just to keep big rocks from poking through. Then the liner went in. I set it to flow over the edge into the pond, with a ledge 2” lower than the rest of the sides.

Next came water – always a nervous moment to see whether I can actually read a level or not – but it filled just fine and I worked most of the wrinkles out (a flat sheet of plastic can't make a hemisphere shape without folds). After that, it was time for a swim with a cold beer.