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EPA's Region 6 Office

Serving: Arkansas, Louisiana, New Mexico, Oklahoma, Texas, and 66 Tribal Nations

Synthetic Based Muds Q&A

NPDES Discharges from Offshore Oil & Gas Operators in the Western Portion of the Gulf of Mexico

EPA Region 6 and the Offshore Operators Committee (OOC) worked together to develop a list of common Questions and Answers to the Feb. 16, 2002, permit modifications (NPDES No. GMG290000). EPA and OOC met on March 11, 2002, and the following table lists the questions and answers to help clarify permit requirements.

No. Category Question Answer
1 BMP If operating under a BMP having achieved the ROC monitoring requirement and the cuttings dryer fails, does the operator have to revert to ROC monitoring under a revised discharge configuration or can the operator continue to operate under the BMP until the cuttings dryer is repaired? If the operator has addressed maintenance and repair of cuttings dryers and other solids control equipment in the BMP, then discharge may continue under the BMP option with no ROC monitoring while the equipment is being repaired.
2 Formation Oil If a formation oil sample fails the RPE test and the operator wishes to confirm the results of the RPE test with the GC/MS compliance assurance method, must the operator convert to zero discharge while awaiting the results of the GC/MS test?  Is the operator required to confirm an RPE failure? 1) No.  The results of the GC/MS complaince assurance method shall supercede the results of the RPE test.  The sample will be considered in violation of the permit limit upon confirmation by GC/MS; however, the permit exceedance will begin on the date of the RPE failure.  It is acceptable to run the GC/MS prior to running the RPE. 2) No. An RPE test failure does not need to be confirmed; confirmation with GC/MS is at the operator's discretion. 
3 Formation Oil If a GC/MS test is run on the mud sent to my rig, does the mud have to be re-tested if I use it on another well? No.  If the mud is tested before it is shipped offshore by GC/MS, no additional GC/MS tests are required unless the mud is shipped back to shore for processing.
4 General Is a bulk discharge of SBM associated with an emergency riser disconnect allowed under the permit? No.  A discharge of SBM from an emergency riser disconnect would be considered a spill and is reportable to the Coast Guard and MMS. 
5 Marine Riser After displacement of SBM in the marine riser with seawater (prior to disconnect) can the seawater with residual SBM that was adhered to the interior wall of the riser be discharged as a "miscellaneous discharge". Yes.
6 ROC Do I have to monitor ROC when (1) under-reaming/hole opening; (2) back-reaming and circulating the hole clean (e.g., removing cuttings beds); (3) wall cavings from the well? (1) Under-reaming/hole opening: you are generating new cuttings and will have to perform ROC monitoring on these cuttings.  (2) Back-reaming/circulating: you are not generating new cuttings and no additional ROC monitoring is required. (3) Cavings: these are not new cuttings and no additional ROC monitoring is required.
7 ROC You have sampled three 500 ft sections in a day of drilling while using the cuttings dryer; now it goes offline and you are discharging from the shakers. Must I perform additional ROC monitoring? Provided you have met the requirements of the permit Part II. Section B.3. Proper Operation and Maintenance, you have fulfilled the monitoring required by the permit (I.e., maximum of three samples per day).
8 ROC I am doing ROC monitoring with no BMP.  The dryer goes down for a short period and is being repaired. Must I change my discharge configuation for ROC monitoring? Provided you have met the requirements of the permit Part II. Section B.3. Proper Operation and Maintenance, you may continue to employ the same discharge configuration as before the dryer goes down for the remainder of the day or 500' interval if a sample has already been taken.  If the dryer is still down during the following day or interval, the discharge configuration should be modified.
9 ROC Can I base my mass fraction calculations on the rate of discharge from different devices by using sample collection times that are different? Yes.
10 ROC If I satisfy the "representative sample" requirement, can I collect one sample from a combined discharge point where multiple types of solids control devices (e.g., cuttings dryer and fines unit) have been combined as opposed to applying the mass fraction method to the individual streams? Yes, as long as the "representative sample" requirement is satisfied, collecting a single sample for combined waste streams is allowed.
11 ROC/BMP Under the BMP option, the ROC was in compliance for the first 1/3rd of the SBM interval, and I want to deepen the well beyond the planned depth.  Must revert back to ROC monitoring? No.  The SBM total footage relates to the PLANNED depth (MMS APD depth) where SBM is used, not the ACTUAL interval.  The permit refers to the "anticipated total feet to be drilled".
12 ROC/BMP I am using the BMP option, and I am forced to drill a by-pass (i.e., mechanical sidetrack) around a fish (i.e., obstruction in the well) after ROC monitoring has been dicontinued.  Must I resume ROC monitoring? No.  A by-pass is simply an extension of the pilot hole, similar to a well-deepening.
13 ROC/BMP I am using the BMP option, and I want to drill a geological sidetrack to a new sub-surface target after I have discontinued ROC monitoring.  Must I resume ROC monitoring? No, provided the sidetrack is not deeper than the original well's PLANNED depth.  If the sidetrack has a greater measured depth, you will have to resume ROC monitoring until at least 1/3 of the SBM interval has been monitored.  In this case, the additional ROC monitoring can be additive to the monitoring for the original well.
14 ROC/BMP I am drilling up a long cement plug.  Must I perform ROC monitoring? Yes.  If you are in a hole section where you should be monitoring ROC (e.g., first 1/3rd of the interval drilled with SBM under the BMP option) you should perform ROC monitoring for the cement cuttings (the permit definition for drill cuttings includes cured cement).  If you are in a hole section where you have discontinued ROC monitoring under the BMP option, there is no need to resume ROC monitoring.
15 Stock Limits My well was spudded prior to February 16, 2002 using SBM.  Do I need to certify compliance with the stock limits for the base fluids in my mud on my rig prior to February 16th?  If I need additional shipments of SBM after February 16, 2002 will I need to certify compliance on base fluids and newly formulated mud brought to the rig? 1)  For the mud that was being used prior to February 16, 2002, no supplier certification for the base fluids is needed.  2)  For mud shipments received after February 16, 2002, certification is required if stock base fluids are added to the SBM after that date.  Existing inventories of SBM prior to the effective date of the permit do not require certification of the base fluids.   
16 SVD The BOP is pumped out and filled with sea water every two weeks. The sea water is used for pressure testing the BOP.  The water is then dumped overboard.  There will be some SBM residue on the sides of the BOP and small quantities will be dumped overboard with the sea water after the test.  Is this small amount of SBM considered a small volume discharge or is it considered "de minimis"?  The SBM discharged during BOP testing is considered "de minimis" since it is a very minor volume and can't be measured.  De minimis discharges must be contained to the extent practicable to prevent discharge.
17 SVD Can I apply the small volume discharge default values to sand traps? Yes.  A small volume discharge from a sand trap can be included in the pit cleanout default values for the well.  Alternately, the density, volume and ROC can be measured and included in the well average.
18 Toxicity If the well is spudded with WBM and the monthly SPP toxicity test is run and passed and later in the month the mud system is changed to SBM, do I need to collect another  SPP toxicity sample during the same month. No.  The SPP toxicity requirements apply to all drill cuttings. 
19 Toxicity I have reached the end of drilling with SBM and grabbed a sample for toxicity testing (i.e., 4-day sediment toxicity at end of drilling and SPP aquatic toxicity at end-of-well). The end of drilling occurs at the end of the month, and some SVDs (e.g., pit clean out and interface fluids) occur early in the next month. Do I need to grab another sample for toxicity testing in the succeeding month for the SVDs? No. The permit states under the Sediment Toxicity Discharge Limitation: "The final monthly sample shall be collected at the end of drilling with non-aqueous based drilling fluids."


  • BMP = Best Management Practices
  • ROC = Retention on Cuttings
  • RPE = Reverse Phase Extraction
  • GC/MS = Gas Chromatograph / Mass Spectrophotometer
  • SBM = Synthetic Based Muds
  • Fish=Obstruction in the well.
  • BOP=Blow Out Preventer
  • WBM=Water Based Mud
  • SPP=Suspended Particulate Phase
  • SVD=Small Volume Dischage

Compliance status of existing drilling fluids with the new offshore general permit requirements for synthetic based drilling fluids has been raised as an issue by industry. The permit has new stock base fluids limitations for sediment toxicity, biodegradation, PAH content, and oil contamination, which are required to be met before drilling. Drilling fluids which were formulated prior to the permit's effective date (February 16, 2002) most likely contain base fluids for which compliance with the stock base fluid limitations is not known. Those fluids may be able to comply with the new limits, but testing was not done prior to the permit's effective date of February 16, 2002. To resolve this issue EPA has determined that drilling fluids in existence prior to February 16, 2002 will be considered compliant with the stock base fluid limitations as long as any new synthetic base fluids added after that date have been tested in accordance with the monitoring requirements of the permit and are in compliance with all applicable limits. Discharged drill cuttings must still be tested for and in compliance with the limits for: base fluids retained on cuttings, sediment toxicity, crude oil contamination, free oil, and suspended particulate phase toxicity. In addition, any barite added to drilling fluids must meet the limits for cadmium and mercury of 3 mg/kg and 1 mg/kg, respectively.

Offshore Operators Committee


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