The blackwater planter at our home is approximately 11 feet wide by 32 feet long and about 6 feet deep with a slight downward grade from West to East. It is an EPDM lined pit that half filled with gravel and topped off with naitve soil. The effluent from the conventional septic tank drains directly into the BW planter and should the water level exceed a few feet from the bottom of the pit, it overflows into a conventional gravel drainfield.
Since the water is so far below the soil surface, you have to water the plants in the BW planter for a while until their roots hit paydirt! Once they find the blackwater, the plants go nuts and the standing water level in the planter drops as they transpire the water!
In the picture, "NitrogenGradient", I believe you can see the effect of nitrate uptake since the effluent is fresh out of the septic tank at the Western side of the BW planter and the plants are taller on that side. But, then again, there could be a million other reasons why the plants are taller on the septic tank side of the BW planter. It will take some serious water testing to find out for sure what's going on.
Enjoy the BW planter pictures!
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