An arch shape cross section chamber for receiving and dispersing stormwater when buried beneath the surface of the earth is corrugated and has a cross section geometry which is a continuous curve. Preferably, the curve is a truncated semi-ellipse. A chamber also has a combination of a standard corrugations along most of the length, in combination with smaller end corrugation with standard corrugations, to enable joining of chambers in overlap fashion, as a string; corrugations which have elliptically curved corrugation widths when viewed from the side of the chamber; and, sidewall base flanges which have turned up outer edges in combination with fins which connect said edges with the curved chamber sidewall. A domed end cap is adapted to both close the end of the chamber and to be positioned within the chamber length to provide a baffle.