however the term arch shape will encompass cross sectional shapes such as trapezoid triangle rectangle octagonal hexagonal and so forth furthermore although the endplates are preferably formed as one piece they may be assembled of separate pieces the endplate can be made from any material which is stable in the leaching environment and provides the desired structural integrity including but not limited to thermoplastic and thermoset materials or combinations thereof with polyethylene particularly high density polyethylene with general characteristics similar to those seen heretofore in chambers preferred typical densities exceed about 0 8 grams per cubic centimeter g cc with about 0 9 to about 1 g cc preferred and about 0 94 to about 0 97 g cc especially preferred some possible high density polyethylenes are alathon and petrothene commercially available from equistar chemicals houston tex sclair and novapol commercially available from nova chemicals pittsburgh pa martex and pcr commercially available from phillips chemical bartlesville okal and fortiflex commercially available from solvay polyers houston tex and the like 0022 fig2 illustrates a plan view of an embodiment of the endplate 1 this endplate 1 includes in the central portion 15 drill guide s 2 pipe guides or scores 3 pipe stops 5 and support stations 11 and along the periphery snap connectors 7 and barrier 9 the pipe scores 3 are scores in the central portion 15 of the endplate 1 which set forth various pipe diameters and locations which.