West Hackberry Strategic Petroleum Reserve Site Brine Disposal Monitoring, Year I Report, Final Report
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Abstract
The physical, chemical and biological attributes are described for: 1) a coastal marine environment centered about a Department of Energy Strategic Petroleum Reserve (SPR) brine disposal site located 11.4 km off the southwest coast of Louisiana; and 2) the lower Calcasieu and Sabine estuarine systems that provide leach waters for the SPR project. During the study period, the daily discharge averaged 529,000 barrels and 216 parts per thousand brine, representing a loading of 18,000 metric tons of salt per day. Currents in the study area were westward in all months except July and were spatially coherent over long distances. Hydrographic surveys and in situ instrumentation detected a salinity difference between the diffuser site and the control sites which was attributed to the brine plume; typical differences were about 2 parts per thousand, but ranged up to 4.6 parts per thousand. No effect on the natural ambient water temperature was measured. Vertical profiles at the diffuser site showed plume effects as high as 3 m above the bottom. No thermal anomalies were introduced by the plume. Within 6 km of the diffuser, the birne is diluted by the diffuser to 4 or 5 parts per thousand above the ambient salinity and further diluted by the diffuser to 1 parts per thousand above the ambient salinity. An empirical procedure based upon measured plume data was developed to estimate the above ambient contours if the average bottom current, brine salinity, and brine discharge rate were known. The results of this procedure show reasonable agreement with the measured plume tracks. Water and sediment quality results indicate that brine discharge had no definite impact on the area surrounding the diffuser. Nutrient levels of offshore and inshore waters were similar when considered for each sampling period. Water temperature, dissolved oxygen, pH, turbidity, and oil and grease at or near the diffuser compared to controls showed no adverse change resulting from the discharge of brine. Analyses for special pollutants indicated possible transport of low levels of some priority pollutants from the Intracoastal Waterway to the offshore diffuser area. A grid of stations centered at the brine diffuser was monitored monthly for biological attributes during the first twelve months of brine discharge. Temporal and spatial distributions of species abundance and diversity were measured for the following: 1) macrobenthic invertebrates, 2) fishes and epibenthic megafauna, and 3) phytoplankton. These assemblages were studied relative to physical and chemical variations occurring the study area. Emphasis is placed on dominant taxa and those species which support commercial and recreational fisheries. The marine fauna and flora of the diffuser area were characteristic of coastal assemblages of the northwestern Gulf coast. Dramatic seasonal population fluctuations were documented, but communities were relatively homogeneous within sampling cruises. The macrobenthic community was numerically dominated by polychaetes; the nekters were typical of the white shrimp community; and the phytoplankton community was dominated by estuarine and neritic diatom species. One of the primary objectives of this monitoring program was the assessment of brine-related impacts on biotic communities. During the course of the year-long investigation changes in biological communities were observed. Seasonal variability in species abundances was a predominate feature as dramatic population fluctuations occurred in all groups studied. Differences among stations of relatively small magnitude were observed for many species and biomass estimates studied. Some of these differences were consistent when specific comparisons were made between control and diffuser area stations. They include: statistically significant differences in population densities of certain numerically dominant macrobenthic species, and significantly lower values for coefficient of condition (weight at length) of certain nekton target species collected in the vicinity of the brine diffuser, (.05 < alpha < .10 for brown shrimp, sand seatrout, spot and southern kingfish; .20 < alpha < .25 for banded drum). None of the observed changes in biotic communities were catastrophic in nature and all other measured parameters were either within expected ranges of or could not be attributed to diffuser activities. Estuarine hydrography studies found that Calcasieu Lake was more saline than Sabine Lake and Intracoastal Waterway by an average of 8 parts per thousand. The measurements at the raw water intake for leaching operations showed the water was more saline than that in Sabine Lake by an average of 2.3 parts per thousand. Except during the fall of the year, both Calcasieu and Sabine Lakes were more saline in the southern portion of each lake which is nearest the Gulf of Mexico. No data collected during this study suggest that the brine discharge from the diffuser entered either of the lakes although an early concern was that the brine plume would enter Calcasieu Lake through Calcasieu Pass which is 15.9 km northeast of the diffuser. The longest measured and predicted distances of the +1 contour were 5.7 km and 7.25 km respectively. Water and sediment quality results indicate that brine discharge had no definite impact on the area surrounding the diffuser. Nutrient levels of offshore and inshore waters were similar when considered for each sampling period. Water temperature, dissolved oxygen, pH, turbidity, and oil and grease at or near the diffuser compared to controls showed no adverse change resulting from the discharge of brine. The fauna and flora of the estuarine stations were typical of coastal plains estuaries. The data varied greatly among stations primarily based on sediment type, salinity, or depth regimes.