JAMES E. VAN BLARICUM

EPA selected the C16-C18 IO, which is the most popular drilling fluid in the GOM, as the basis for the sediment toxicity rate ratio limitation instead of the vegetable ester or low viscosity ester for several reasons:

(1) EPA does not believe that

vegetable esters can be used in all drilling situations; and (2) EPA does not have sufficient field testing information that low viscosity esters can be used in all drilling situations (see Section V.F.1.a).

SIGNAL OIL AND GAS

In addition, because of the uncertainty about ester performance, operators

may not be encouraged to switch from OBFs or WBFs to SBF when properly installed and maintained. Specifically, vendor supplied data associated with these cuttings dryer deployments suggest that the overall cuttings dryer downtime (i.e., time when cuttings dryer equipment is not operable) is approximately 1 to 2% (Docket No. W-98-26, Record No. IV.A.a.6).

EPA finds this small downtime percentage as acceptable.

EPA discussed how it revised the BAT/NSPS-level solids control equipment configuration used in its analyses in the April 2000 NODA (65 FR 21559). EPA also discussed a range of management options regarding the BAT limitation for SBF retention on SBF-cuttings:

(1) Two discharges from the BAT/NSPS-level solids control equipment configuration (i.e., one discharge from the cuttings dryer and another discharge from the fines removal unit);

(2) one discharge from the BAT/ NSPS-level solids control equipment configuration (i.e., one discharge from the cuttings dryer with the fines from the fines removal unit

captured for zero discharge); and

(3) zero discharge of SBF-cuttings.

JAMES E. VAN BLARICUM

These three options are labeled as BAT/NSPS Option 1, BAT/NSPS Option 2, and BAT/NSPS Option 3, respectively. EPA estimates that 97% and 3% of the total cuttings are generated by cuttings dryer and fines removal unit, respectively.

EPA developed two numerical well averaged ROC limitations (i.e., one for SBFs with the stock base fluid performance similar to esters and another for SBFs with the stock base fluid performance similar to C16-C18 internal olefins) and based both of these

ROC limitations on the technology of only one discharge from the cuttings dryer with the fines from the fines removal unit captured for zero discharge (i.e., BAT/NSPS Option 2).

SIGNAL OIL AND GAS

The numerical well averaged ROC maximum limitation for SBFs (i.e., 9.4%) with the environmental characteristics of esters is based on a combination of data from horizontal centrifuge, vertical centrifuge, squeeze press, and High-G linear shaker cuttings dryer technologies. The numerical well averaged ROC maximum limitation for SBFs (i.e., 6.9%) with the environmental characteristics of C16-C18 internal olefins is

based on a combination of data from horizontal and vertical centrifuge cuttings dryer technologies. EPA estimates that operators, generally installing new equipment where none has been used in the past, will be able to choose from among the better technologies, designs, operating procedures, and maintenance procedures that EPA has considered to be among the best available technologies.

JAMES E. VAN BLARICUM

EPA data demonstrates that operators properly using these cuttings dryer technologies will be able to comply with these final ROC numerical limitations. Data submitted to EPA show that operators using the vertical centrifuge and horizontal

centrifuge are capable of achieving the lower ROC limitation (i.e., 6.9%). Data submitted to EPA also show that operators using the vertical centrifuge, horizontal centrifuge, squeeze press, and High-G linear shaker are capable of achieving the higher ROC limitation (i.e., 9.4%).

More details on the observed performance of the individual technologies and details of calculation for the numerical limits are presented in the SBF Statistical Support Document and SBF Development Document. EPA developed the two ROC limitations because EPA used a two part approach to control SBF-cuttings discharges. The first part is the control of which SBF are allowed for discharge through use of stock limitations (e.g., sediment toxicity, biodegradation, PAH content, metals content) and discharge limitations (e.g., diesel oil prohibition, formation oil prohibition, sediment toxicity, aqueous toxicity).

SIGNAL OIL AND GAS

The second part is the control of the quantity of SBF discharged with SBF-cuttings. As previously stated, EPA and industry sediment toxicity and biodegradation laboratory studies show that both vegetable esters and low viscosity esters have better environmental performance than all other SBF base fluids. However, because the technical availability of product substitution with esters was not demonstrated across the offshore subcategory, EPA rejected the option of basing sediment toxicity and biodegradation stock limitations and standards on vegetable esters and low viscosity esters (see V.F.1.a).

JAMES E. VAN BLARICUM

EPA is sufficiently satisfied, however, that both esters provide better environmental performance (e.g., sediment toxicity, biodegradation). Consequently, EPA is promulgating a higher retention on cuttings discharge limitation to encourage operators to use esters when possible. EPA estimates that a higher retention on cuttings discharge

limitation for esters is equivalent to the same level of control as a lower retention on cuttings discharge limitation for all other SBFs that have poorer sediment toxicity and biodegradation performances.

SIGNAL OIL AND GAS

In response to the April 2000 NODA, EPA received comments from an ester-based SBF manufacturer that EPA should create an incentive for operators to use ester-based SBFs by basing the ROC limitation for ester-based SBFs on baseline solids control equipment (e.g., primary and secondary shale shakers, fines removal unit) (Docket No. W-98-26, Record No. IV.A.a.7). In late comments, this same commentor claimed that a ROC limitation based on any cuttings dryer technology would not provide any incentive for the use of ester-based SBFs (Docket No. W-98- 26, Record No. IV.A.a.38). Further, they argued that the superior laboratory performance of these ester base fluids in terms of sediment toxicity and biodegradation justifies allowing them to be discharged with a ROC limitation based on baseline solids control equipment.

JAMES E. VAN BLARICUM

EPA estimates that a ROC BAT limitation based on the baseline solids control equipment is above 15.3%. While EPA is willing to expand the technology basis to allow the use of less effective cuttings dryers for ester-based SBFs (e.g., squeeze press, High-G linear shakes), EPA is unwilling to entirely abandon the use of cuttings dryers for ester-based SBF drilling operations. EPA is unwilling to set a higher ROC limitation for SBFs with the environmental performance of ester-based SBFs based on baseline solids control technology because the environmental improvement resulting from the use of improved solids control technology (i.e., cuttings dryers) outweighs the incremental ester

laboratory sediment toxi city and biodegradation performance over internal olefins. Cuttings dryers promote pollution prevention through increased re-use of drilling fluids and prevent significant amounts