This paper addresses the historical environmental impact of Bydgoszcz’s ‘Old Gasworks,’ located on Jagiellońska Street on the Brda River—one of Poland’s oldest and longest-operating gas production facilities. Municipal gas derived from dry coal distillation served both municipal and industrial purposes until 1973. However, the production process, marked by significant nuisances, particularly affected the ground and water environment. Pollutants, primarily organic compounds such as aromatic hydrocarbons, including PAHs (polycyclic aromatic hydrocarbons), and BTEX hydrocarbons (benzene, toluene, ethylbenzene, xylenes), phenol and mineral oil, entered the environment through equipment failures, leaks, and the improper storage of wastewater and technological waste. One of the major sources of contamination was inadequately executed construction activities related to the dismantling of installations and the liquidation of sewage and waste storage tanks. This paper presents the findings of a comprehensive study focusing on hydrocarbon concentrations in groundwater at the ‘Old Gasworks’ in Bydgoszcz and proposes effective methods for treating the water environment.