75 



2.2.10 



UPDATE OF DRILLING WASTES FATE 

 AND EFFECTS STUDIES IN THE MARINE ENVIRONMENT 



Mr. Maurice (Mo) Jones, Director 



ENSR Environmental Laboratory 



Houston, TX 



To assist the Minerals Management Service (MMS) in designing offshore studies to detect impacts associated 

 with long-term oil and gas activities, it would be useful to review selected papers from the recently released 

 proceedings of the 1988 International Conference on Drilling Wastes (Engclhardt et al. 1989). Several 

 conclusions should be considered by members of the workshop charged with identifying needs of the MMS Gulf 

 of Mexico Environmental Studies Program. 



Of the forty papers presented at the symposium, half dealt with the marine environment. Of these 20 papers, 

 nine were concerned with the fate and effects of oil-based muds (OBM), which were discharged under 

 international regulations (typically prohibited by U.S. Environmental Protection Agency regulations). The 11 

 water-based muds (WBM) papers were roughly half field and half lab studies, with a few additional papers 

 discussing modeling (two papers) and testing protocols (four papers). Only three fate and effects papers 

 concerned Gulf of Mexico sites specifically. While the WBM studies are the most relevant to this workshop due 

 to the prohibitions on discharging OBM in the Gulf, OBM studies are possibly pertinent when considering long- 

 term, low-level hydrocarbon contamination. In the short time allotted today, clearly all 20 papers cannot be 

 thoroughly reviewed, but selected issues relevant to designing long-term monitoring are noted as follows. 



Boothe and Presley's study (1989) was exemplary because they developed good retrospective data on the 

 discharges including amounts and types, then tied this operational data to assessment survey data through a mass 

 balance approach in sediments within 500 m of six offshore drilling sites (exploration, development, and 

 production) in water depths ranging from 13-102 m in the Gulf of Mexico. An improved "bulls-eye" sampling 

 strategy was employed. Using barium as a mass balance tracer, they found that deep-water development and 

 production sites had by far the largest barium and other trace element (Zn, Cd, Cu, Pb) retention. Presumably, 

 other mud constituents behaved similarly. Shallow water sites retained <1.5% total barium. Few large scale 

 MMS fate studies, such as are being discussed here today, have placed adequate emphasis on first describing the 

 inputs to the system and the comparing inputs to remaining levels. I heartily recommend that the workshop 

 adopt a similar approach and consider mass balance approaches when feasible. 



The relatively efficient dispersal mechanisms observed by Boothe and Presley (1989) in shallow waters was also 

 observed by Jones (1989) in Galveston Bay. Precisely measured doses of drilling wastes to enclosed in situ 

 mesocosms resulted in barium enrichment in the sediments up to 40,200 ppm at the highest dose. Within six 

 months, these elevated levels, comparable to values found around production sites offshore, were reduced to 

 background levels in this shallow estuary (<2m). The authors speculated that a combination of resuspension, 

 bioturbation, and density transport into deeper sediments were the dispersal mechanisms that accounted for the 

 rapid decrease. A precise understanding of these dispersal mechanisms, their relative importance, the associated 

 biotic (e.g., tube dwelling polychaetes), and abiotic (e.g., weather events) elements, are critical to understanding 

 the processes that govern fate and effect. I recommend that the workshop incorporate into its planning 

 consideration of investigating these mechanisms. 



Jenkins et al. (1989) found elevated barium levels down current of an exploratory well offshore California. Using 

 an improved "bulls-eye" sampling pattern, he also identified statistically significant bioaccumulation of barium in 

 two benthic species (clam and polychaete). Jenkins went further than most similar studies in that he tried to 

 determine the potential significance of the bioaccumulation observed to the population. His group fractionated 

 the organisms and studied the form of the accumulated barium. They determined that the barium remained as 

 insoluble BaSC^, that very little became bioavailable, and thus no toxicity was observed or expected to occur. 

 This study is good in that it seeks to understand the meaning of an observation and, again, its implication for the 

 health of the population and community. Similarly, we should look for ways to understand the significance of 

 our findings. 



