ANGOLA ALGERIA CAMEROON CHAD. CONGO EGYPT.. EQUATORIAL GUINEA GABON LIBYA. NIGERIA SOUTH AFRICA SUDAN TUNISIA OTHERS
NPDES's Produced Water Permitting Requirements by USEPA
NPDES permits are required
to contain limits and monitoring requirements that ensure that appropriate
treatment technology is applied to discharges and the water quality of the
receiving water is protected. The regulations require that technology-based
limits are consistent with the best available treatment technology economically
achievable (BAT). After BAT-based limits are established, additional limits and
conditions are often included in permits to afford additional protection for the
receiving water.
Technology-Based Limitations
For the oil and gas extraction industry EPA has issued Effluent Limitations
Guidelines that establish technology-based limits for produced water (see 40 CFR
Part 435). These Guidelines are divided into sub-categories to account for
wellhead location and economic factors associated with the operation. The
Effluent Limitations Guidelines for the oil and gas extraction industry are
divided into five sub-categories based on location. These sub-categories are:
Offshore, Coastal, Onshore, Agricultural and Wildlife Use and Striper. Wells
located in the open ocean are covered under the Offshore subcategory. Coastal
sub-category wells are those located in bays and estuaries. Three
sub-categories, onshore, striper and agriculture and wildlife, cover wells
located on land.
Re-injection has been established as BAT Effluent Guidelines for the Onshore and
Coastal sub-category produced water discharges in most cases. As a result, the
discharge of produced water from Coastal and Onshore sub-category wells is
prohibited except in
Cook Inlet,
Alaska.
Due to a lack of disposal capability and the adverse conditions in Cook Inlet,
Offshore sub-category produced water limits were determined to be appropriate
for facilities in that location.
The Striper sub-category covers wells that are located onshore and produce less
than 10 barrels per day when operating at a maximum feasible production rate.
The national Effluent Limitations Guidelines did not establish technology-based
limits for produced water from Striper sub-category wells. Instead, EPA Region 6
established technology based limits for Stripper sub-category wells located in
Texas east of the 98th meridian. Produced water from those wells is authorised
to be discharged; however, the oil and grease concentration is limited to a
monthly average of 25mg/l and a maximum of 35mg/l. Additional limits, required
to protect water quality, are applied to those discharges and are discussed
later in this paper.
In some cases produced water from wells located onshore, west of the 98th
meridian, can be authorised to be discharged under the Agricultural and Wildlife
Use sub-category. In order to be covered under that sub-category, the produced
water must be of good enough quality to be used for wildlife or livestock
watering or irrigation and must be used for at least one of those uses. The
technology-based oil and grease limit established by the Effluent Limitations
Guidelines for Agricultural and Wildlife Use sub-category produced water is a
maximum oil and grease concentration of 35mg/l. EPA does not currently have any
permits authorising discharges from Agricultural and Wildlife Use sub-category
wells. However, a permit authorising a discharge would need to include limits to
ensure that the produced water is of good enough quality to be used by wildlife
or livestock watering or for irrigation. To meet that requirement permits will
contain limits for total dissolved solids in discharges as well as applicable
water quality criteria.
The Offshore sub-category Effluent Guidelines limit oil and grease in produced
water discharges to an average of 29mg/l and a maximum of 42mg/l. Those limits
are based on dissolved gas floatation technology. The oil and grease limits have
been difficult to achieve in some cases where dissolved oil is present in the
produced water. Operators have resolved that issue by adjusting the pH of
produced water prior to treatment. The same oil and grease limits apply to
Coastal sub-category produced water discharges in Cook Inlet.
The transfer of produced water between different sub-categories is also
addressed by the Effluent Limitations Guidelines (see 40 CFR Part 435, Subpart
G). The more stringent of the technology-based limits for either the location of
the well head or the location where produced water is disposed of apply. An
example is produced water originating from an offshore well which is transported
to shore for disposal. In that case, the more stringent discharge prohibition of
the Onshore sub-category Effluent Guidelines would apply. Likewise, if Onshore
or Coastal sub-category produced water were transferred offshore, the discharge
prohibition applying to the location of the wellhead would apply.
Water Quality-based Limitations
When discharges are made to state waters, permits must contain limits necessary
to ensure that state water quality standards are met. State waters include all
inland waters and extend to the outer boundary of the territorial seas, three
miles offshore. The EPA has issued two general permits for facilities located in
the territorial seas of
Louisiana
and Texas. The Texas permit includes whole effluent toxicity limits to comply
with the Texas standards for acute and chronic toxicity. The
Louisiana
permit also includes several limits based on state water quality standards for
lead, phenols, thallium and benzene. Those standards were developed to protect
aquatic life and human health.
If permits are issued that authorise discharges from the Stripper or Agriculture
and Wildlife Use sub-categories, state water quality standards will need to be
addressed. For Stripper sub-category wells, those standards will typically be
applied based on in-stream dilution at the edge of a mixing zone or a zone of
initial dilution. Since Agriculture and Wildlife Use sub-category produced water
must be good enough to be used for irrigation or watering, the water quality
standards will be applied at the end of the pipe, without taking into account
in-stream dilution.
Discharges to the oceans are required to contain conditions that ensure
compliance with Federal Ocean Discharge Criteria (Clean Water Act section 403(c)
and 40 CFR Part 125). EPA has traditionally relied on whole effluent toxicity
limits to ensure compliance with Ocean Discharge Criteria.