WorldWide Drilling Resource

Environmental Monitoring by Thomas Kwader, Ph.D., P.G. Injection Wells - A Safe Alternative to Dispose of Wastewaters? Injection wells are regulated in the United States by the Environmental Protection Agency. There are six classes of injection wells, including: Class Use Class I Inject hazardous wastes, industrial nonhazardous l iquids, or municipal wastewater beneath the lowermost USDW (un- derground source of drinking water). Class II Inject brines and other fluids associated with oil and gas production, and hydrocarbons for storage. Class III Inject fluids associated with solution mining of minerals beneath the lowermost USDW. Class IV Inject hazardous or radioactive wastes into or above USDWs. These wells are banned unless authorized under a federal or state groundwater remediation project. Class V All injection wells not included in Classes I-IV. In general, Class V wells inject nonhazardous fluids into or above USDWs and are typically shallow, on-site disposal systems. However, there are some deep Class V wells that inject below USDWs. Class VI Inject carbon dioxide (CO 2 ) for long-term storage, also known as Geologic Sequestration of CO 2 . Classes I, II, and IV are in the most common classes permitted. Injection wells have been in use for more than 50 years. The quality of injected water ranges from drinking water quality to hazardous to human health. Only drinking water quality effluent is allowed to be returned into our aquifers (with proper permits). Most other contaminated waters must be injected beneath competent confining geologic units, well below drinking water aquifers into highly mineralized zones (>10,000 mg/L, total dissolved solids). Properly permitted and constructed wells have a very good record of success for wastewater disposal. Deep well injection is very cost effective for the disposal of oilfield brines, some fracturing wastewaters, and domestic sewage wastewaters (common in South Florida). The permitting of deep injection wells involves many safeguards to protect our aquifers, including injection rate/pressures, injection only into known permeable zones capable of receiving those volumes and fluids compatible with the existing forma- tions, and formation pore waters. Mechanical Integrity Testing (MIT) of wells periodi- cally assures the wells are not leaking into unintended zones, along with separate monitoring wells located nearby acting as early detection points to assure mechanical integrity of the injection well. Properly constructed injection wells provide a means of disposing of wastes which would otherwise be cost prohibitive and/or not possible to dispose by other conventional means. Tom Tom Kwader may be contacted via e-mail to michele@ worldwidedrillingresource.com 34 DECEMBER 2015 WorldWide Drilling Resource ®