avoid back ups and spill overs in parallel the individual filtration beds may vary and may be graduated as well as shown in fig2 multi level drainfield modular structure 10 comprises five vertically aligned and spaced filtration beds or layers 12 liquid effluent 14 is drawn from the system 39 s septic tank not shown through distribution box 16 forced by pump 18 through feed line 20 into top distribution perforated pipe 22a and sprayed over the surface of top filtration bed 12a through which liquid 14 percolates and drains into second distribution pipe 22b by gravity the cycle of spraying percolating and draining of liquid 14 is repeated flowing through perforated pipes 22b e onto each of the remaining filtration beds 12b 12e until the treated effluent reaches holding area 24 from which it may be directed through control valve 26 either to be discharged as clean ground water if sufficiently purified or recirculated through feed line 20 39 shown in dash lines valve 26 39 operating in tandem with valve 26 and pump 18 into filtration layers 12 a second time circulating air introduced at 28 into the spaces 30 between layers 12 meets sprayed droplets of effluent 14 at each.