A manhole base assembly and a method for making the same, in which a non-cylindrical, low-volume concrete base is fully lined to protect the concrete against chemical and physical attack while in service. This lined concrete manhole base assembly may be readily produced using a modular manhole form assembly which can be configured for a wide variety of geometrical configurations compatible with, e.g., varying pipe angles, elevations and sizes. The form assembly is configurable to provide any desired angle and elevation for the pipe apertures using existing, standard sets of form assembly materials, and may also be used in conjunction with industry-standard cylindrical casting jackets for compatibility with existing casting operations. The resulting system provides for flexible construction of a wide variety of lined manhole base assemblies at minimal cost, reduced concrete consumption and reduced operational complexity. The modular nature of the production form assembly also facilitates reduced inventory requirements when various manhole base assembly geometries are needed.