where n is the number of baseline loading ob

servations.

(5) To compare baseline loading data to observations from the annual monitoring period, repeat steps 1-3 for the set of monitoring observations. Label the results of the calculations M' and R'. Let m be the number of monitoring observations.

(6) The subtle trigger (Tm) of the monitoring data is calculated as:

NOTE: When subsetting the data for each of steps 3a-3d, the subset should include all observations greater than or equal to the median calculated in the previous step. If the median calculated in the previous step is not an actual observation, it is not included in the new subset of observations. The new median value will then be calculated using the median procedure, based on whether the number of points in the subset is odd or even.

(5) Method for applying the single observation trigger (L) to determine when the baseline level has been exceeded

If two successive monthly monitoring observations both exceed L, immediately begin weekly monitoring for four weeks (four weekly samples).

(a) If three or fewer of the weekly observations exceed L, resume monthly monitoring

(b) If all four weekly observations exceed L, the baseline pollution loading has been exceeded.

(1.815 *R') Tm = M'

vm (7) If Tm > Tb, the median loading of the monitoring observations has exceeded the baseline loading.

B. Method 2 sor Calculating and Applying an

Annual Trigger (T) Method 2 applies the Wilcoxon-Mann-Whitney test to determine whether the median loading of the monitoring observations has exceeded the baseline median. No baseline value T is calculated.

(1) Steps for Conducting the Wilcoxon-Mann

Whitney Test (a) Let n be the number of baseline loading observations taken, and let m be the number of monitoring loading observations taken. In order to sufficiently characterize pollutant loadings during baseline determination and during each annual monitoring period, it is required that at least one sample result be obtained per month for a period of 12 months.

(b) Order the combined baseline and monitoring observations from smallest to largest.

(c) Assign a rank to each observation based on the assigned order: the smallest observation will have rank 1, the next smallest will have rank 2, and so forth, up to the highest observation, which will have rank n + m.

(1) If two or more observations are tied (have the same value), then the average rank for those observations should be used. For example, suppose the following four values are being ranked: 3, 4, 6, 4 Since 3 is the lowest of the four numbers, it would be assigned a rank of 1. The highest of the four numbers is 6, and would be assigned a rank of 4. The other two numbers are both 4. Rather than assign one a rank of 2 and the other a rank of 3, the average of 2 and 3 (1.e., 2.5) is given to both numbers.

(d) Sum all the assigned ranks of the n baseline observations, and let this sum be Sn.

(e) Obtain the critical value (C) from Table 1. When 12 monthly data are available for both baseline and monitoring (i.e., n = 12 and m = 12), the critical value C is 99.

(f) Compare C to So. If S, is less than c, then the monitoring loadings have exceeded the baseline loadings.

III. PROCEDURE FOR CALCULATING AND

APPLYING AN ANNUAL TRIGGER A. Method 1 for Calculating and Applying an

Annual Trigger (T) (1) Calculate M and M, of the baseline loading data as described above under Method 1 for the single observation trigger.

(2) Calculate M-, as the median of the baseline data which are less than or equal to the sample median M.

(3) Calculate the interquartile range, R = (M, - M-1).

(4) The annual trigger for baseline (Tb) is calculated as:

Subpart C-Onshore Subcategory 435.30 Applicability; description of the on

shore subcategory. 435.31 Specialized definitions. 435.32 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best praticable control technology currently available.

Subpart A-Offshore Subcategory Sec. 435.10 Applicability: description of the off

shore subcategory. 435.11 Specialized definitions. 435.12 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best practicable control technology currently

available (BPT). 435.13 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best available technology economically

achievable (BAT). 435.14 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best conventional pollutant control tech

nology (BCT). 435.15 Standards of performance for new

sources (NSPS). APPENDIX 1 TO SUBPART OF PART 435

STATIC SHEEN TEST
APPENDIX 2 TO SUBPART A OF PART 435

DRILLING FLUIDS TOXICITY TEST
APPENDIX 3 TO SUBPART A OF PART 435—-PRO-

CEDURE FOR MIXING BASE FLUIDS WITH

SEDIMENTS
APPENDIX 4 TO SUBPART A OF PART 435-DE-

TERMINATION OF BIODEGRADATION OF SYN-
THETIC BASE FLUIDS IN A MARINE CLOSED
BOTTLE TEST SYSTEM: SUMMARY OF MODI-

FICATIONS TO ISO 11734:1995
APPENDIX 5 TO SUBPART A OF PART 435-DE-

TERMINATION OF CRUDE OIL CONTAMINA-
TION IN NON-AQUEOUS DRILLING FLUIDS BY
GAS CHROMATOGRAPHY/MASS SPECTROM-

ETRY (GC/MS)
APPENDIX 6 TO SUBPART A OF PART 435_RE-

VERSE PHASE EXTRACTION (RPE) METHOD

Subpart D-Coastal Subcategory 435.40 Applicability; description of the

coastal subcategory. 435.41 Specialized definitions. 435.42 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best practicable control technology currently

available (BPT). 435.43 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best available technology economically

achievable (BAT). 435.44 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best conventional pollutant control tech

nology (BCT). 435.45 Standards of performance for new

sources (NSPS). 435.46 Pretreatment standards of perform

ance for existing sources (PSES). 435.47 Pretreatment standards of perform

ance for new sources (PSNS). APPENDIX 1 TO SUBPART D OF PART 435-PRO

CEDURE FOR DETERMINING WHEN COASTAL
COOK INLET OPERATORS QUALIFY FOR AN
EXEMPTION FROM THE ZERO DISCHARGE
REQUIREMENT FOR EMO-CUTTINGS AND
SBF-CUTTINGS IN COASTAL COOK INLET,
ALASKA

Subpart E-Agricultural and Wildlife Water

Use Subcategory 435.50 Applicability; description of the bene

ficial use subcategory. 435.51 Specialized definitions. 435.52 Effluent limitations guidelines rep

resenting the degree of effluent reduction attainable by the application of the best practicable control technology currently available.

Subpart F-Stripper Subcategory 435.60 Applicability; description of the

stripper subcategory. 435.61 Specialized definitions.

Subpart G-General Provisions 435.70 Applicability.

AUTHORITY: 33 U.S.C. 1311, 1314, 1316, 1317, 1318, 1342 and 1361.

SOURCE: 44 FR 22075, Apr. 13, 1979, unless otherwise noted.

Subpart A-Offshore Subcategory

SOURCE: 58 FR 12504, Mar. 4, 1993, unless otherwise noted.

$ 435.10 Applicability; description of

the offshore subcategory. The provisions of this subpart are applicable to those facilities engaged in field exploration, drilling, well production, and well treatment in the oil and gas industry which are located in waters that are seaward of the inner boundary of the territorial seas (“offshore”') as defined in section 502(g) of the Clean Water Act.

tice 13B-2 supplemented with the specifications, sampling methods, and averaging method for retention values provided in Appendix 7 of Subpart A of this part.

(e) Biodegradation rate as applied to BAT effluent limitations and NSPS for drilling fluids and drill cuttings refers to the ISO 11734:1995 method: "Water quality-Evaluation of the 'ultimate anaerobic biodegradability of organic compounds in digested sludge—Method by measurement of the biogas production (1995 edition)" supplemented with modifications in Appendix 4 of 40 CFR part 435, subpart A. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from the American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036. Copies may be inspected at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202–741-6030, or go to: http://www.archives.gov federal_register/ code_of_federal_regulations/ ibr locations.html. A copy may also be inspected at EPA's Water Docket, 401 M Street SW., Washington, DC 20460.

(f) Daily values as applied to produced water effluent limitations and NSPS means the daily measurements used to assess compliance with the maximum for any one day.

(g) Deck drainage means any waste resulting from deck washings, spillage, rainwater, and runoff from gutters and drains including drip pans and work areas within facilities subject to this Subpart.

(h) Development facility means any fixed or mobile structure subject to this subpart that is engaged in the drilling of productive wells.

(i) Diesel oil refers to the grade of distillate fuel oil, as specified in the American Society for Testing and Materials Standard Specification for Diesel Fuel Oils D975–91, that is typically used as the continuous phase in conventional oil-based drilling fluids. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be

(61 FR 66123, Dec. 16, 1996)

$ 435.11 Specialized definitions.

For the purpose of this subpart:

(a) Except as provided below, the general definitions, abbreviations and methods of analysis set forth in 40 CFR part 401 shall apply to this subpart.

(b) Average of daily values for 30 consecutive days means the average of the daily values obtained during any 30 consecutive day period.

(c) Base fluid means the continuous phase or suspending medium of a drilling fluid formulation.

(d) Base fluid retained on cuttings as applied to BAT effluent limitations and NSPS refers to the American Petroleum Institute Recommended Prac