Aquifer Exemptions (AE) and AE Map
On April 23, 1982, the U.S. Environmental Protection Agency (EPA) granted primacy to the Railroad Commission of Texas (Commission) to administer the Class II Underground Injection Control (UIC) program under Section 1425 of the Safe Drinking Water Act (SDWA). Class II wells are injection wells that are associated with oil and gas production. Section 1425 of the SDWA allows EPA to approve an existing state Class II UIC program if the state shows that the program is effective in preventing endangerment of underground sources of drinking water.
Underground source of drinking water (USDW) means an aquifer or its portion: (a) (1) Which supplies any public water system; or (2) Which contains a sufficient quantity of ground water to supply a public water system; and (i) Currently supplies drinking water for human consumption; or (ii) Contains fewer than 10,000 mg/l total dissolved solids; andfrom 40 CFR §144.3
(b) Which is not an exempted aquifer.
The federal UIC regulations allow EPA to exempt aquifers that do not currently, and will not in the future, serve as a source of drinking water, based on certain criteria. Aquifer exemptions allow the interval to be used for oil or mineral extraction or disposal purposes in compliance with EPA’s UIC regulations. By definition, an exempted aquifer is not a USDW.
On the date of primacy, EPA granted aquifer exemptions for all existing Class II injection wells and all existing hydrocarbon producing zones.
For subsequent applications, the Commission’s review and approval process for Class II wells assures aquifer protection on a case-by-case basis. In Texas, numerous hydrocarbon-producing reservoirs contain or may contain water with less than 10,000 ppm [parts per million, which are equivalent to milligrams per liter (mg/l)] total dissolved solids. Numerous undelineated aquifers containing water with less than 10,000 ppm total dissolved solids also exist in Texas. The EPA maintains the Aquifer Exemptions Map which shows exempted aquifers in Texas.
Groundwater Advisory Unit Review
The Commission’s Groundwater Advisory Unit (GAU) provides geologic interpretation of the base of strata that contains groundwater with a TDS content of less than 10,000 mg/l. The GAU does not determine whether the proposed injection interval contains a sufficient quantity of ground water to supply a public water system or whether the aquifer supplies drinking water for human consumption. Therefore, the GAU’s determination is more conservative than the EPA definition for USDW.
Injection into reservoirs productive of oil, gas, or geothermal resources is regulated under the Commission’s Statewide Rule 46 (16 Texas Administrative Code § 3.46). The purpose of the injection is typically for enhanced recovery (Type 3 wells) but it may also be disposal (Type 2 wells). If the GAU determines that the proposed injection interval contains water with a TDS concentration of less than 10,000 mg/l, UIC will determine whether the proposed injection interval is an exempt aquifer. When the proposed injection interval is a productive zone that contains water with less than 10,000 mg/l TDS, the Commission limits injection to waters produced with hydrocarbons and then returned to the zone from which they were produced or waters with a lesser TDS concentration. This Fluid Source Limit (FSL) allows the oil and gas operator to safely manage the produced fluids, maintain the water drive in a producing field, and produce the hydrocarbons in that field.
Injection into reservoirs not productive of oil, gas, or geothermal resources is regulated under the Commission’s Statewide Rule 9 (16 Texas Administrative Code §3.9). The Commission’s GAU provides geologic interpretation of the base of strata that contains groundwater with a TDS content of less than 10,000 mg/l. The GAU does not determine whether the proposed injection interval contains a sufficient quantity of ground water to supply a public water system or whether the aquifer supplies drinking water for human consumption. Therefore, the GAU’s determination is more conservative than the EPA definition for USDW.
UIC’s review process under Statewide Rule 9 may authorize completion of a disposal well in an aquifer that contain less than 10,000 ppm TDS when the aquifer cannot now or will not in the future serve as a source of drinking water. Conditions that may indicate the aquifer will not serve as a source of drinking water in the future are as follows:
- It is situated at a depth or location which makes recovery of water for drinking water purposes economically or technologically impractical;
- It is so contaminated that it would be economically or technologically impractical to render that water fit for human consumption; or
- The total dissolved solids content of the ground water is more than 3,000 and less than 10,000 mg/l and it is not reasonably expected to supply a public water system.
UIC would not consider an aquifer exemption— even when costs of producing drinking water are prohibitive— if alternative disposal zones are economically and technically practical.
Aquifer Exemptions Since RRC UIC Primacy
November 2021 - Trueblood Resources, Inc., Fitzgerald (15772) Lease, Slocum (84144-001) Field, Anderson County, Texas
Staff of the Railroad Commission (“Staff”) received a permit application (Tracking No. 53741) from Trueblood Resources, Inc. for an injection well for an enhanced oil recovery project in the Slocum field on April 21, 2021. Staff finds that the project involves injection into water with a total dissolved solids concentration of less than 10,000 milligrams per liter and, therefore, requires expansion of an existing aquifer exemption for the Slocum field. The expansion of the aquifer exemption will not include any portion of an aquifer that is being used as a drinking water source. The aquifer exemption for the Carrizo sand between approximately 560 and 670 feet below ground surface in the J. Crawford survey, A-189.