Evaluation of the Ecological Impacts of Open-Loop Vaporization Technology at Offshore Liquified Natural Gas Terminals

R. Dreas Nielsen, Thomas Ginn, Ph.D., Paul D. Boehm, Ph.D., Linda Ziccardi

Introduction

To meet an anticipated increase in the demand for natural gas in the United States, several new offshore terminals for the receipt and distribution of liquefied natural gas (LNG) have been licensed or proposed for construction in the Gulf of Mexico. All of these facilities are designed to use open loop vaporization (OLV) technology, in which warm water is used to re-gasify the LNG. Seawater used in the OLV systems is cooled by 13 to 22 degrees F, and is chlorinated to prevent fouling. Environmental impact statements (EISs) prepared by the U.S. Coast Guard (USCG) have found that the OLV systems of these proposed facilities will have minimal impact on marine resources in the Gulf.

A substantial number of comments on the EISs focused on the potential impacts to fisheries in the Gulf. Many of the comments centered on the potential impacts to key species such as red drum (Sciaenops ocellatus) and red snapper (Lutjanus campechanus). To address these concerns, Exponent was retained by the Center for LNG to assess the scientific validity of the overall conclusions of the EISs. This evaluation focused on the data sources, the assumptions, the data summarization methods, the fish population models, and the assessment criteria used in the EISs.

Data Used for Impact Assessments

The EISs for the proposed LNG facilities estimated potential impacts to fish populations using ichthyoplankton data collected as part of the Southeast Area Monitoring and Assessment Program (SEAMAP), which is administered cooperatively by the Gulf States Marine Fisheries Commission and the National Marine Fisheries Service Southeast Regional Office. The SEAMAP data set contains measurements of ichthyoplankton abundances from throughout the Gulf, collected over a period of more than two decades. Overall, the SEAMAP data set is adequate for characterizing the affected environment and for predicting potential impacts from OLV facilities. However, these data also have some limitations that introduce substantial uncertainty into impact predictions.

The strengths of the SEAMAP data set are its geographic coverage, its temporal duration (from 1982 to 2003), the use of consistent sampling methods throughout, and identification of larval fish to the level of species wherever possible. The weaknesses of the SEAMAP data set are the absence of depth-stratified samples, the proportion of larvae that could not be identified to species, the absence of any species-specific information for eggs, and limitations in the temporal and spatial coverage in the vicinity of specific LNG facilities. Overall, there is no clearly better alternative for use in assessing the potential entrainment impacts of LNG facilities. The data set should be used, however, with recognition of the potential impact of its limitations.

The data used in the EISs for fish life history characteristics were extracted from publications in the scientific literature. Mortality rates and life stage durations for eggs, larvae, and juveniles were estimated based on field studies. However, these rates and durations are estimated from observed age distributions, and are not known with certainty, even for important species such as red drum and red snapper. Overall, the life history parameters used in the EISs are based on relevant field studies. However, a recent (2005) synthesis of life history studies conducted by another author provides alternatives to some of the life history parameters used in the EISs. Because the recent synthesis was reviewed by the authors of the original population studies, the conclusions of the synthesis are recommended for use in future modeling of population level impacts.

Assumptions

The impact predictions made in the EISs relied on several important assumptions:

  • Ichthyoplankton abundances in the vicinity of offshore LNG facilities are adequately represented by SEAMAP samples that were taken up to a maximum of 50 miles away
  • The net efficiency (i.e., the proportion of organisms retained on a plankton net) is the same for fish eggs and larvae
  • All ichthyoplankton in the water column are equivalently susceptible to seawater intakes
  • No population-level compensation effects occur.

These assumptions all introduce uncertainty into the predicted impacts, and some introduce bias.

Ichthyoplankton are not homogeneously distributed throughout the northern Gulf. There are distinct spatial gradients in the abundances of key species over the distances (up to 50 miles) that were used to select SEAMAP data for use in the EISs. Because all selected SEAMAP data were averaged for each EIS, this variability was lost and uncertainty introduced into the analysis. For any given species and facility, this could lead to either an overestimate or an underestimate of potential impact. For one species (red drum) and facility (Gulf Landing) examined in detail, the assumption leads to an overestimate of abundance and potential impact.

Plankton nets are not 100 percent efficient because some organisms (i.e., eggs and larvae) may avoid or pass through the net. To estimate actual abundances from the SEAMAP data, the EISs assumed a net efficiency of 33 percent for both eggs and larvae. This value is within the likely range for the type of net used by the SEAMAP program. However, because of their smaller size, the net efficiency for eggs is likely to be lower than for larvae. Consequently, the EISs are likely to have underestimated egg abundances relative to larval abundances. This would result in an underestimate of potential impact.

Ichthyoplankton larvae often display distinct depth preferences that will at least partially isolate them from submerged seawater intakes. Although depth preferences may vary diurnally and with the age of the larvae, the entrainment estimates used in the EISs assume that all larvae are at the depth of the seawater intake at all times. In addition, the seawater intakes typically have a flow velocity no greater than 0.15 m/s, at which fish larvae have been shown to be able to avoid entrainment. The EISs calculated entrainment losses as the simple product of the overall ichthyoplankton abundance and the water usage rate, and so may have substantially overestimated the number of fish larvae lost from entrainment.

The EISs extrapolate the estimated losses of ichthyoplankton directly to equivalent losses of adult fish, using life history parameters to estimate the equivalent number of adult fish. In reality, fish populations demonstrate an ability to compensate for mortality, for example, through excess fecundity. The use of a model in the EISs that ignores compensation effects leads to an overestimation of populationlevel effects of entrainment.

Data Analyses

Three systematic flaws were found in the quantitative analyses carried out in the EISs. Two of these were related to the way that SEAMAP data were summarized, and one of them was a mathematical error in the life history model used.

When fish larvae could not be identified to species, the EISs distributed organisms that were identified only to the level of genus or family among the individual species in that genus or family in proportion to the relative abundance of those species. Although this approach is reasonable, the EISs applied it to each data set as a whole rather than applying it on a samplespecific basis. Because abundances of different species vary seasonally, relative abundances must be evaluated on a sample-specific basis to achieve accurate results. For one key species examined in detail (red drum), the approach used in the EISs overestimated abundance, and thus entrainment and impact.

Figure 1

The EISs also ignored seasonality when calculating confidence limits around estimated ichthyoplankton abundances (Figure 1). As a consequence, systematic seasonal variability was inappropriately represented as uncertainty, leading to a substantial overestimate of uncertainty and an inflation of the upper confidence limit for ichthyoplankton entrainment and impact. For red drum in the vicinity of the Gulf Landing facility, these two inappropriate data analysis approaches resulted in an estimate of 36 million larvae entrained annually, with 95 percent confidence limits ranging from 3 million to 69 million larvae. Correcting these defects resulted in an estimate of 16 million larvae entrained annually, with 95 percent confidence limits ranging from 13 million to 19 million larvae.

The life history model used in the EISs is one that has been endorsed by EPA for evaluation of ichthyoplankton entrainment at power plants. Exponent’s review of the model revealed an inherent flaw in the mathematical formulation of the model. The nature of this flaw results in an underestimate of the potential survival of entrained eggs and larvae. That is, more of the entrained eggs and larvae would have survived, had they not been entrained, than the EISs account for. Thus, this error may translate to additional errors in the estimates of impact in the EISs.

Modeling Approach and Endpoints

The EISs assessed entrainment impacts by extrapolating the numbers of entrained eggs and larvae to numbers of adult fish, using life history parameters for the intervening life stages. Empirical relationships between fish age, length, and weight were then used to calculate the adult weight of these fish. The total fish weight was then compared to various fishery landing statistics to evaluate the magnitude of the impacts.

The projection of egg and larval abundance to abundance and weights of fish of harvestable age requires extensive use of poorly known parameters. In addition, comparison of the results to fishery harvest levels provides no meaningful information about the potential impacts of LNG facilities on fish populations. These weaknesses lead to a high degree of uncertainty and an overestimate of potential impacts.

Instead of the forward projection approach used in the EISs, Exponent recommended that impact assessments should use an egg-equivalent (fecundity or hindcasting) approach, in which total entrainment losses of ichthyoplankton are related to egg production at the population level. Such assessments can be conducted with available data, do not require as many uncertain estimates of mortality rates, and provide more meaningful and interpretable endpoints. This approach is also compatible with stock assessment methods that are used to evaluate fish populations as a whole. A comparative application of egg-equivalent and fecundity hindcasting models to red drum at Gulf Landing indicated that the forward projection approach overpredicted mortality by a factor of 1,750.

Summary

Taken as a whole, the data inputs, assumptions, and model approaches used in the EISs for LNG facilities tended to significantly overestimate the potential for adverse impacts. The EISs do not quantitatively account for all the factors affecting these estimates, and so do not accurately describe the degree of overestimation associated with these values or their overall uncertainty. However, because the EISs concluded that the effects of the LNG regasification facilities would be minimal, despite the defects in the analyses conducted in the EISs, Exponent’s review supports, and even reinforces, the overall conclusions of the EISs.

Mr. Dreas Nielsen is a Managing Scientist in Exponent's Environmental Sciences and EcoSciences who specializes in collecting, managing, and analyzing environmental data. He can be reached at (425) 519-8750 or via email, nielsend@exponent.com.

Dr. Thomas Ginn is a Principal Scientist and Practice Director of Exponent's EcoSciences practice. He is a biologist with 30 years of experience specializing in ecotoxicology and ecological risk assessment. He can be reached at (623) 587-4121 or via email, ginnt@exponent.com.

Dr. Paul Boehm is a Group Vice President and Principal Scientist at Exponent, specializing in environmental forensics; liability assessment; chemistry of crude and refined petroleum, petrochemicals, PAHs, PCB, and Dioxins; oil spill and hazardous waste NRDA. He can be reached at (978) 461-1220 or via email, pboehm@exponent.com.

Ms. Linda Ziccardi is a Senior Ecologist in Exponent’s EcoSciences practice with 16 years of experience evaluating environmental impacts at industrial and development sites nationwide. She can be reached at (303) 544-2004 or via email, lziccardi@exponent.com.