Water Quality Considerations for Non-Hazardous Disposal Wells Injecting Under Pressure Chad Milligan, P.G. Nicole Franken, E.I.T.

Diminishing capacity of non-hazardous disposal wells injecting under pressure may be related to the water quality and treatment of injectate fluid. For one coal mine in southern Illinois, native groundwater infiltrating the mine is treated using five main components: coagulation and sedimentation, green sand filtration, reverse osmosis, chemical injection of biocide and anti-scalant, and disposal. The injection well primarily functions to dispose the concentrate generated from the reverse osmosis treatment system. The treatment and disposal of native groundwater infiltrating the mine was analyzed using a holistic approach, including an evaluation of the water quality by assessing the chemical and physical characteristics of water, water quantities, water treatment system, geochemistry, and applicable disposal well characteristics. The analysis identified specific minerals that may be precipitating from the concentrate and causing scaling issues within the disposal well, the specific location within the disposal well the scale could be forming, and recommendations to address the scaling issue both through a well stimulation plan and adjustments to the groundwater treatment system design and operation. Understanding how scale forms can help formulate a plan for treating the well. Temperature and pressure fluctuations can have an impact on solubility coefficients, and can also cause local fluctuations in the equilibrium ion concentration in the solution. Once the seed crystals start growing, the heterogeneous nucleation process may start at surface defects such as joints, seams, or areas with surface roughness. A high degree of turbulence can also start the process of scale deposition, such as restrictions in the well. This presentation will focus on why and where scale forms in a groundwater treatment and disposal system and how to prevent it, which will assist to avoid costly workovers and inefficiencies in chemical dosing. Diminishing capacity of non-hazardous disposal wells injecting under pressure may be related to the water quality and treatment of injectate fluid. For one coal mine in southern Illinois, native groundwater infiltrating the mine is treated using five main components: coagulation and sedimentation, green sand filtration, reverse osmosis, chemical injection of biocide and anti-scalant, and disposal. The injection well primarily functions to dispose the concentrate generated from the reverse osmosis treatment system. The treatment and disposal of native groundwater infiltrating the mine was analyzed using a holistic approach, including an evaluation of the water quality by assessing the chemical and physical characteristics of water, water quantities, water treatment system, geochemistry, and applicable disposal well characteristics. The analysis identified specific minerals that may be precipitating from the concentrate and causing scaling issues within the disposal well, the specific location within the disposal well the scale could be forming, and recommendations to address the scaling issue both through a well stimulation plan and adjustments to the groundwater treatment system design and operation. Understanding how scale forms can help formulate a plan for treating the well. Temperature and pressure fluctuations can have an impact on solubility coefficients, and can also cause local fluctuations in the equilibrium ion concentration in the solution. Once the seed crystals start growing, the heterogeneous nucleation process may start at surface defects such as joints, seams, or areas with surface roughness. A high degree of turbulence can also start the process of scale deposition, such as restrictions in the well. This presentation will focus on why and where scale forms in a groundwater treatment and disposal system and how to prevent it, which will assist to avoid costly workovers and inefficiencies in chemical dosing. About This Presentation

Nicole Franken is an Engineer in Training in the State of Kansas. She has a Bachelor of Science degree in Civil Engineering with an Environmental Emphasis from the University of Kansas. She has a broad range of experience in environmental engineering including regulatory compliance and permitting, remediation projects from initial site assessment through site closure, environmental liability cost modeling, wastewater treatment design, and hydraulic modeling. She has been involved with various aspects of UIC wells including the closure of a Class I UIC well in Texas and performing capacity reduction investigations. Chad Milligan is a licensed professional geologist in the states of Kansas and Illinois. He has a Bachelor of Science degree in Environmental Chemistry from Emporia State University and a Master’s Degree in Environmental Science from Wichita State University. He has over 20 years of experience in the environmental field and has been responsible for the permitting and regulatory compliance of Class I non-hazardous disposal wells in the States of Kansas and Illinois; the permitting of Class II disposal wells in Colorado; the permitting and regulatory compliance of Class III salt solution mining wells, and LPG storage caverns in Kansas; and the permitting and regulatory compliance of Class V UIC wells in Kansas. He also has a broad range of experience in water resources and has authored and co-authored a number of published reports relating to surface water and ground water quality in central Kansas. About the SCS Presenters

Background Information Coal Mine in Southern Illinois Native Groundwater Infiltrating Mine Treatment and Disposal System to Handle Groundwater – Pretreatment: Coagulation and Sedimentation – Reverse Osmosis Treatment System – Post-RO Treatment and Disposal Class I Non-Hazardous Well Injected Under Pressure

The Problem Primary Problem: Diminishing Disposal Volumes at Increased Pressures Other Concerns: Frequency of Filters Clogging, Variation in Water Quality

The Investigation System Overview: Process Flow Diagram

The Investigation System Overview: Process Flow Diagram

The Investigation Water Quality – Physical Characteristics Temperature, Solids, Color/Odor – Chemical Characteristics pH/Alkalinity, Hardness, Major Ions Water Quantity – Pre-Treatment Quantity – Post-RO Treatment and Disposal Quantity

The Investigation

GeoChemistry – Solubility Products – Visual Inspection – XRD/XRF Analyses

The Investigation Gamma Ray/CCL Logs Scale Formation Reaction

Conclusions Significant Temperature/Pressure Changes Observed Downhole (Especially Near Packer Throat) Visual Inspections, Solubility Product Analysis, XRD/XRF Analyses Indicated Mineral Formation of Gypsum, Quartz, Magnesite, and Calcite

Conclusions Recirculation of Concentrate Reducing Treatment Effectiveness Water Quality Investigation Indicated Ineffective Pre-Treatment Scaling Likely Causing Reduction in Disposal Capacity