of fig1 and to fig3 which is an enlarged fragmentary view of ground water channel 6 of fig2 ground water channel 6 is formed along the invert of existing storm sewer pipe 2 between impermeable lining 8 and existing pipe 2 ground water channel 6 is formed by first drilling or otherwise forming a plurality of spaced apart holes 18 along the length of existing pipe 2 generally at any locations where contaminated ground water is in contact with the outside of existing pipe 2 in order to promote the inward flow collection of ground water in the preferred embodiment based on specific flow calculations a series of one inch diameter holes were drilled at approximately 3 foot centers along the invert of pipe 2 more or less core holes may be used depending upon the specific ground water conditions high density polyethylene hdpe drainage net 20 is disposed along the length of the invert of existing pipe 2 drainage net 20 is also disposed between lining 8 and pipe 2 adjacent any holes 18 cracks and joints extending downwardly about the circumference of lining 8 to provide a plurality of flow paths down to ground water channel 6 drainage net 20 as illustrated in fig4 is a criss cross mesh of ribs 22a and 22b which.