Question 6 of 7: Landfill Leachate EIA, Peak-Flow Effluent Control, Industrial VOC Reduction

Problem 6: Landfill Leachate EIA, Peak-Flow Effluent Control, Industrial VOC Reduction (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Three key EIA issues to minimize a leachate plume's groundwater impact, sized for a doubling population. 1. Composite liner and leachate-collection system design sized for the full 10-year+ expanded waste volume, not just current tonnage. Because the service population will double, the EIA must confirm the liner/leachate-collection-system capacity and cell sequencing are designed for the site's full projected life and peak leachate generation rate, not just the tonnage at opening — an undersized system is the leading cause of leachate breakthrough at landfills that outgrow their original design basis. 2. Site hydrogeological characterization and a groundwater monitoring-well network capable of detecting an early plume. The EIA must characterize the local aquifer's flow direction and velocity and establish a monitoring-well network (upgradient background wells plus downgradient sentinel wells) dense enough to detect a leachate plume before it reaches any drinking-water well or discharge point, with a defined trigger-and-response protocol if contaminant indicators exceed background. 3. Attenuation buffer and setback from any water-supply well or surface-water body. Given the larger footprint a doubled-population landfill implies, the EIA must confirm an adequate horizontal separation and natural/engineered attenuation buffer exists between the waste footprint and the nearest water-supply well or fish-bearing stream, since setback distance is often the simplest and most defensible protection against an undetected liner failure.

(ii) Three engineering methods to improve peak-flow effluent quantity/quality control. 1. Upstream flow equalization and in-system storage. An equalization basin or increased in-line interceptor storage captures the peak wet-weather flow and releases it to the treatment train once hydraulic capacity is available, smoothing the flow the plant must treat at any one time rather than forcing a bypass. 2. Real-time control (RTC) of pumping stations and gates. Instrumented, coordinated control of upstream pump stations and diversion gates (informed by rainfall/flow forecasting) actively redistributes wet-weather flow across available system and plant capacity, reducing the peak the plant sees compared to uncontrolled gravity/fixed-speed operation. 3. High-rate peak-flow treatment (e.g. chemically enhanced primary treatment or ballasted flocculation) for the excess flow beyond secondary capacity. Rather than bypassing flow in excess of the biological secondary train's capacity, a dedicated high-rate physical-chemical treatment train polishes the excess flow to a level suitable for disinfection and discharge, directly improving both the quantity actually captured and the quality of what is ultimately discharged during the storm event.

(iii) VOC reduction — one technical and two non-technical solutions. Technical: fit the plant's process exhaust with a regenerative thermal oxidizer (RTO) or activated-carbon adsorption system sized to the specific VOC load and concentration, converting or capturing the VOCs before they reach the stack rather than relying on dilution. Non-technical (1): process scheduling and operational timing — shift the plant's highest-VOC-emitting batch operations to periods and wind conditions least likely to carry emissions toward the residential community, reducing exposure without new capital equipment. Non-technical (2): leak detection and repair (LDAR) administrative program — a documented, scheduled inspection and prompt-repair program for valves, flanges and seals (the plant's actual largest source of fugitive VOC loss in many industrial processes) reduces emissions through management practice and accountability rather than a hardware change.