permit the system to breathe application_number US 16653302 A description fig1 and 2 generally illustrate the drainage system 20 with which the invention is concerned and include a pair of horizontal perforated drain pipe units 22 and 24 placed within and extending longitudinally along trench 26 and laterally spaced from each other to provide the central open chamber 28 while drain pipe units 22 and 24 may be of various types they are preferably pre assembled drainage units such as those illustrated in fig2 of u s pat no 5 015 123 and include a central perforated pipe 30 surrounded by a plurality of lightweight plastic aggregate 32 held in place by a surrounding net 34 a cover 40 constructed according to the first embodiment of fig3 6 extends across the top of drainage units 22 and 24 and includes a retaining section 41 having side portions 42 and 44 which conform in shape and size to the outer surface and configuration of pipe units 22 and 24 and a center portion 46 connected to the side portions and functioning to maintain the pipe units 22 and 24 in laterally spaced relation to form the center chamber 28 in a typical installation the width of trench 26 may be 24 inches and the depth may be approximately 22 inches units 22 and 24 may be approximately 10 inches in diameter and the perforated pipe 30 within the units may be approximately 4 inches in diameter when the storage system 20 is placed within the trench the distance between the top of the cover and the top of the trench will be approximately 10 to 11.