Benthic fauna in the vicinity of the Sand Island ocean outfall were sampled from 1986-2010. To assess the environmental quality, sediment grain size and sediment chemistry were measured. To identify the fauna, mollusk species and non-mollusk species sitings were tabulated.
Stations were located both within and on the boundary of the zone of initial dilution (ZID) and at distances of 1.2 to 2 km from the ZID boundary. In summary, the response patterns of benthic fauna near the Sand Island ocean outfall showed little or no indication of a strong influence by the diffuser effluent.
The sampling methodology used in this study generally followed the recommendations of Swartz (1978) and US EPA guidelines(EPA 1987a, 1987b), hereafter refered to as EPA procedures.
A modified 0.16-m2 van Veen grab sampler deployed from a stern-mounted A-frame on the research vessel Noi I Kai was used to obtain bottom samples at all seven stations. Penetration of the sampler was adequate for all replicates. The minimum penetration depth for all grabs was 6 cm and the maximum was 13 cm.
Six van Veen grabs were taken at each station. A subsample 7.6 cm in diameter by 5 cm deep was taken from each grab sample for infaunal analysis and a subsample 4.8 cm in diameter by 5 cm deep for mollusk analysis. Subsampling was necessary because the epifauna and infauna in the area are known to be both small and abundant and processing of the entire sample would be impractical. Replicated grab samples at each station, rather than replicated subsamples from one grab sample, were used to provide information on intrastation variability. All six nonmollusk subcores were processed on a 0.5-mm screen.
Samples for geochemical analyses (total organic carbon (TOC), oxidation-reduction potential (ORP), sediment oil and grease (O&G), total Kjeldahl nitrogen (TKN), and grain size) were obtained from the grabs from which the biological subcores were taken. Each replicate van Veen grab contained more than enough sediment for both purposes (methods HI0020117). Three subsamples 7.6 cm in diameter by 5 cm deep (one from each of three differnt grab samples) were taken from all stations. The top 2 cm of sediment of each subsample were used for geochemical analysis. Samples for TOC and sediment O&G analysis were put in screw-cap jars, placed on ice, and taken to the laboratory for analysis. Sediment analyses of sediment grain size, ORP, TKN, and O&G followed EPA procedures. Analysis of TOC was carried out by Severn Trent Laboritories (Colchester, Vermont), using the modified Lloyd Khan method, which utiliezes an infrafred detector to measure carbon dioxide. Inorganic carbon was removed from the samples by treating them with a 1:1 solution of hydrochloric acid prior to TOC analysis.