Mgp Industrial Wastewater Treatment Review and Case Study

Providing gas for cooking, heating and lighting to residential and commercial customers, manufactured gas plants (MGPs) have influenced life in the United States since the early 1800's. Although these plants have ceased operations decades ago, they continue to impact many communities across the United States. Through residual by-products that had been routinely stockpiled or accidentally spilled on sites of former MGPs or discharged to local waterbodies, MGP operations have impacted local soil and groundwater as well as surface waters and river sediments. This paper presents background information on the manufactured gas process including a brief history of its development and production, the rise and fall of the industry, and the distribution of sites around the country. The paper then addresses the types of contaminants that are typically found at former MGP sites, the range in concentration of these contaminants in site groundwaters, and the treatment methods most often employed to treat these contaminants to levels acceptable for discharge to local waterways or treatment plants. The paper also discusses a case study of a unique treatment scenario for a major northeast electric utility involving the dewatering and treatment of hydroelectric plant tunnel water impacted by MGP type waste. The water pumped from the tunnel during tunnel repairs required treatment prior to discharge to the county POTW for final disposal. To meet the tunnel repair schedule, a pumping and treatment system was designed, constructed and on-line on a fast track schedule within a 5 month period. The design parameters for the project site included wastewater characterization and onsite treatability studies, development of the process design basis, conceptual and detailed design within a tight footprint and access limitations to the local sewer, system construction, startup and shakedown, performance testing, and temporary (2 months) operations. In addition to the design elements that were considered, the project was fasttracked to minimize the economic impacts of the tunnel shutdown. The treatment system consisted of the following unit operations: flow equalization with DNAPL and LNAPL separation, oil adsorption, air stripping with vapor phase carbon treatment, filtration, granular activated carbon adsorption, and high-head effluent pumping. These treatment operations were selected to address removal of various contaminants including BTEX and PAHs, oil and grease, and metals. The system was designed for two flow conditions; at a maximum flow rate of 400 gpm to provide rapid initial tunnel dewatering of river water and an average flow rate of 150 gpm to address groundwater infiltration that would be encountered during tunnel maintenance. The project achieved the utility's objectives of effectively treating the impacted tunnel waters, with a reliable treatment system. The treatment plant consistently met the effluent permit limits imposed by the county POTW. The treatment system provided uninterrupted service and ensured efficient tunnel dewatering which was an essential element of safe working conditions for the tunnel maintenance crew.