Natural Background and the Anthropogenic Enrichment of Mercury in the Southern Florida Environment: A Review with a Discussion on Public Health.

Mercury (Hg) is a toxic metal that is easily released into the atmosphere as a gas or a particulate. Since Hg has serious health impacts based on human exposure, it is a major concern where it accumulates. Southern Florida is a region of high Hg deposition in the United States. It has entered the southern Florida environment for over 56 MY. For the past 3000 to 8000 years, Hg has accumulated in the Everglades peatlands, where approximately 42.3 metric tons of Hg was deposited. The pre-industrial source of mercury that was deposited into the Everglades was from the atmosphere, consisting of combined Saharan dust and marine evasion. Drainage and the development of the Everglades for agriculture, and other mixed land uses have caused a 65.7% reduction in the quantity of peat, therefore releasing approximately 28 metric tons of Hg into the southern Florida environment over a period of approximately 133 years. Both natural and man-made fires have facilitated the Hg release. The current range in mercury release into the southern Florida environment lies between 994.9 and 1249 kg/yr. The largest source of Hg currently entering the Florida environment is from combined atmospheric sources, including Saharan dust, aerosols, sea spray, and ocean flux/evasion at 257.1-514.2 kg/yr. The remobilization of Hg from the Everglades peatlands and fires is approximately 215 kg/yr. Other large contributors include waste to energy incinerators (204.1 kg/yr), medical waste and crematory incinerators (159.7+ kg/yr), and cement plant stack discharge (150.6 kg/yr). Minor emissions include fuel emissions from motorized vehicles, gas emissions from landfills, asphalt plants, and possible others. No data are available on controlled fires in the Everglades in sugar farming, which is lumped with the overall peatland loss of Hg to the environment. Hg has impacted wildlife in southern Florida with recorded excess concentrations in fish, birds, and apex predators. This bioaccumulation of Hg in animals led to the adoption of regulations (total maximum loads) to reduce the impacts on wildlife and warnings were given to consumers to avoid the consumption of fish that are considered to be contaminated. The deposition of atmospheric Hg in southern Florida has not been studied sufficiently to ascertain where it has had the greatest impacts. Hg has been found to accumulate on willow tree leaves in a natural environment in one recent study. No significant studies of the potential impacts on human health have been conducted in southern Florida, which should be started based on the high rates of Hg fallout in rainfall and known recycling for organic sediments containing high concentrations of Hg.

Groundwater sustainability assessment based on socio-economic and environmental variables: a simple dynamic indicator-based approach.

The Dehgolan aquifer, which lies in semiarid western Iran, was evaluated using a multi-influencing factor (MIF) analysis to determine groundwater sustainability. Eight indicators, including climatic variability, groundwater exploitation (pumping), groundwater quality, groundwater vulnerability, public participation, legal framework, water productivity, and occupation related to groundwater, were quantified and placed into a series of thematic maps within a GIS framework. Each factor was weighted based on the analyses obtained from the MIF model and the stacked maps were summed to yield a final map showing the degree of sustainability within the groundwater basin. The final groundwater sustainability map showed that 4% of the basin was in a critically unsustainable zone, 30% in an unsustainable zone, 40% in a semisustainable zone, 25% in a sustainable zone, and 1% in an ideally sustainable zone. The final map was validated using a receiver operating characteristic (ROC) method, cross-tabulation, and chi-square tests using groundwater-level decline as a test proxy. The analysis assessed the correlation between water levels that exhibited declines versus the degree of unsustainability of water levels and sustainable water use. The area under the curve was calculated to be 88%, cross-tabulation 64.4%, and the chi-square value was 260.5 with 4 degrees of freedom and values <0.05 (3.627E-55), which suggest that the final map has statistical significance. The sustainability analysis developed is useful as a baseline for development of governance laws to implement management methods in groundwater basins and it can be applied to a wide range of aquifer types in variable climates worldwide.

L'aquifère de Dehgolan, qui se trouve dans la partie semiaride occidental de l'Iran, a fait l'objet d'une évaluation à l'aide d'une analyse des facteurs d'influence multiples (FIM) afin de déterminer la durabilité des eaux souterraines. Huit indicateurs, dont la variabilité climatique, l'exploitation des eaux souterraines (pompage), la qualité des eaux souterraines, la vulnérabilité des eaux souterraines, la participation publique, le cadre juridique, la productivité de l'eau et l'occupation des sols liée aux eaux souterraines, ont été quantifiés et placés dans une série de cartes thématiques d'un SIG. Chaque facteur a été pondéré en fonction des analyses obtenues par le modèle FIM et les cartes superposées ont été additionnées pour produire une carte finale montrant le degré de durabilité du bassin d'eau souterraine. La carte finale de la durabilité des eaux souterraines a montré que 4% du bassin était dans une zone gravement non durable, 30% dans une zone non durable, 40% dans une zone semidurable, 25% dans une zone durable, et 1% dans une zone idéalement durable. La carte finale a été validée à l'aide d'une méthode de caractéristique d'exploitation du récepteur (ROC), de tableaux croisés et de tests du chi carré utilisant la baisse du niveau des eaux souterraines comme test de proxy. L'analyse a évalué la corrélation entre les niveaux d'eau qui ont présenté des baisses et le degré de non-durabilité des niveaux d'eau et d'utilisation durable de l'eau. L'aire sous la courbe a été calculée à 88%, le tableau croisé à 64.4%, et la valeur du chi-carré était de 260.5 avec 4 degrés de liberté et des valeurs <0.05 (3.627E−55), suggérant que la carte finale a une signification statistique. L'analyse de durabilité développée est. utile comme base de référence pour le développement de lois de gouvernance pour mettre en œuvre des méthodes de gestion dans les bassins d'eaux souterraines et elle peut être appliquée à un large éventail de types d'aquifères dans des climats variables dans le monde entier.

Se evaluó el acuífero de Dehgolan, situado en la zona semiárida del oeste de Irán, mediante un análisis de factores de influencia múltiple (MIF) para determinar la sostenibilidad de las aguas subterráneas. Se cuantificaron ocho indicadores, entre ellos la variabilidad climática, la explotación de las aguas subterráneas (bombeo), la calidad y la vulnerabilidad de las aguas subterráneas, la participación pública, el marco jurídico, la productividad del agua y la ocupación relacionada con las aguas subterráneas, y se incluyeron en una serie de mapas temáticos dentro de un marco GIS. Cada factor se ponderó en función de los análisis obtenidos del modelo MIF y los mapas agrupados se sumaron para obtener un mapa final que mostraba el grado de sostenibilidad dentro de la cuenca de aguas subterráneas. El mapa final de sostenibilidad de las aguas subterráneas mostró que el 4% de la cuenca se encontraba en una zona críticamente insostenible, el 30% en una zona insostenible, el 40% en una zona semisostenible, el 25% en una zona sostenible y el 1% en una zona idealmente sostenible. El mapa final se validó mediante un método de características operativas del receptor (ROC), tabulaciones cruzadas y pruebas de chi-cuadrado utilizando el descenso del nivel de las aguas subterráneas como prueba de aproximación. El análisis evaluó la correlación entre los niveles de agua que presentaban descensos frente al grado de insostenibilidad de los niveles de agua y el uso sostenible del agua. El área bajo la curva se calculó en un 88%, la tabulación cruzada en un 64.4%, y el valor de chi-cuadrado fue de 260.5 con 4 grados de libertad y valores <0.05 (3.627E−55), lo que sugiere que el mapa final tiene significación estadística. El análisis de sostenibilidad desarrollado es útil como base para el desarrollo de normas de gobernanza para implementar métodos de gestión en las cuencas subterráneas y puede aplicarse a una amplia gama de tipos de acuíferos en climas variables en todo el mundo.

O aquífero Dehgolan, que fica no semiárido oeste do Irã, foi avaliado através da análise do fator de múltipla influência (FMI) para determinar a sustentabilidade das águas subterrâneas. Oito indicadores, incluindo variabilidade climática, explotação de águas subterrâneas (bombeamento), qualidade das águas subterrâneas, vulnerabilidade das águas subterrâneas, participação pública, marco legal, produtividade da água e ocupação relacionada às águas subterrâneas, foram quantificados e colocados em uma série de mapas temáticos dentro de uma estrutura SIG. Cada fator foi ponderado com base nas análises obtidas do modelo FMI e os mapas empilhados foram somados para produzir um mapa final mostrando o grau de sustentabilidade dentro da bacia subterrânea. O mapa final de sustentabilidade das águas subterrâneas mostrou que 4% da bacia estava em uma zona criticamente insustentável, 30% em uma zona insustentável, 40% em uma zona semisustentável, 25% em uma zona sustentável e 1% em uma zona idealmente sustentável. O mapa final foi validado usando um método de característica operacional do receptor (COR), tabulação cruzada e testes de qui-quadrado utilizando o declínio do nível das águas subterrâneas como proxy de teste. A análise avaliou a correlação entre os níveis de água que apresentaram declínio versus o grau de insustentabilidade dos níveis de água e uso sustentável da água. A área sob a curva foi calculada em 88%, tabulação cruzada 64.4%, e o valor do qui-quadrado foi de 260.5 com 4 graus de liberdade e valores <0.05 (3.627E−55), o que sugere que o mapa final tem significado. A análise de sustentabilidade desenvolvida é útil como base para o desenvolvimento de leis de governança para implementar métodos de gestão em bacias subterrâneas e pode ser aplicada a uma ampla gama de tipos de aquíferos em climas variáveis em todo o mundo.

Economics and Energy Consumption of Brackish Water Reverse Osmosis Desalination: Innovations and Impacts of Feedwater Quality.

Brackish water desalination, using the reverse osmosis (BWRO) process, has become common in global regions, where vast reserves of brackish groundwater are found (e.g., the United States, North Africa). A literature survey and detailed analyses of several BWRO facilities in Florida have revealed some interesting and valuable information on the costs and energy use. Depending on the capacity, water quality, and additional scope items, the capital cost (CAPEX) ranges from USD 500 to USD 2947/m3 of the capacity (USD 690-USD 4067/m3 corrected for inflation to 2020). The highest number was associated with the City of Cape Coral North Plant, Florida, which had an expanded project scope. The general range of the operating cost (OPEX) is USD 0.39 to USD 0.66/m3 (cannot be corrected for inflation), for a range of capacities from 10,000 to 70,000 m3/d. The feed-water quality, in the range of 2000 to 6000 mg/L of the total dissolved solids, does not significantly impact the OPEX. There is a significant scaling trend, with OPEX cost reducing as plant capacity increases, but there is considerable scatter based on the pre- and post-treatment complexity. Many BWRO facilities operate with long-term increases in the salinity of the feedwater (groundwater), caused by pumping-induced vertical and horizontal migration of the higher salinity water. Any cost and energy increase that is caused by the higher feed water salinity, can be significantly mitigated by using energy recovery, which is not commonly used in BWRO operations. OPEX in BWRO systems is likely to remain relatively constant, based on the limitation on the plant capacity, caused by the brackish water availability at a given site. Seawater reverse osmosis facilities, with a very large capacity, have a lower OPEX compared to the upper range of BWRO, because of capacity scaling, special electrical energy deals, and process design certainty.

Index-based Groundwater Sustainability Assessment in the Socio-Economic Context: a Case Study in the Western Iran.

The groundwater sustainability of an alluvial aquifer in the western Iran was examined by using eight different social, economic, and environmental indicators. Differing types of indicators were used including groundwater extraction, groundwater quality, and groundwater vulnerability from the environmental indicators proposed by UNESCO 2007 and the legal framework, institutional capacity, public participation, knowledge generation, and promotion and water productivity from five researcher-developed indicators. A questionnaire and an AHP analysis were used to assess groundwater sustainability in the Mahidasht aquifer. Using AHP method, the indicators were formulated as spatial thematic maps resulting in calculation of the groundwater sustainability index (GSI). Then, the final GSI was divided into four categories, including sustainable, near sustainable, unsustainable, and highly or critically unsustainable. The AHP results showed that most parts of the study area are contained within the unsustainable category. The questionnaire method also showed that the study area with the score of 1.47 belongs within the unsustainable category. The validation of AHP results indicated 97% of the area had more than 1-m of drawdown in the groundwater level and 62% of it had more than 10-m of decline in the water level. The results showed that different socio-economic and environmental indicators can provide a helpful overview of groundwater sustainability conditions for future planning and decision-making in water management. Few studies of water management using socio-economic indicators have been conducted in Iran, Therefore this study provides a novel method of groundwater sustainability assessment by using the concepts of sustainable development, and integrated spatial indicators.

Green method of stemming the tide of invasive marine and freshwater organisms by natural filtration of shipping ballast water.

Marine and freshwater pollution caused by transport of invasive species in shipping ballast water is a major global problem and will increase in magnitude as shipping of commodities increases in the future. An economical method to preclude biological organisms in the seawater used for ballast is to exclude them at the source port. Integrated natural filtration using onshore wells or seabed gallery systems has been thoroughly investigated for use as pretreatment for seawater desalination systems and has proven to be environmentally acceptable and economic. Thus, the use of this proven filtration technology to another issue, ballast water treatment, is an innovative method of providing marine organism free seawater by non-destructive means in port-based facilities. This method is ecosystem-friendly in that no chemicals or destructive processes are used. Design and construction of well or seabed gallery intake systems for production of ballast seawater are feasible in virtually all global port facilities.

Cumene Contamination in Groundwater: Observed Concentrations, Evaluation of Remediation by Sulfate Enhanced Bioremediation (SEB), and Public Health Issues.

Isopropylbenzene (cumene) is commonly encountered in groundwater at petroleum release sites due to its natural occurrence in crude oil and historical use as a fuel additive. The cumene concentrations detected at these sites often exceed regulatory guidelines or standards for states with stringent groundwater regulations. Recent laboratory analytical data collected at historical petroleum underground storage tank (UST) release sites have revealed that cumene persists at concentrations exceeding the default cleanup criterion, while other common petroleum constituents are below detection limits or low enough to allow natural attenuation as a remediation strategy. This effectively makes cumene the driver for active remediation at some sites. An insignificant amount of research has been conducted for the in-situ remediation of cumene. Sulfate Enhanced Biodegradation (SEB) is evaluated in a field case study. The results from the field case study show an approximate 92% decrease in plume area following three rounds of SEB injections. An additional objective of this research was to determine the cumene concentration in fuels currently being used to determine future impacts. A review of safety data sheets from several fuel suppliers revealed that cumene concentrations in gasoline are reported typically as wide ranges due to the proprietary formulations. Several fuels from different suppliers were analyzed to determine a baseline of cumene concentration in modern fuels. The results of the analysis indicated that cumene accounts for approximately 0.01% (diesel) to 0.13% (premium gasoline) of the overall fuel composition. Cumene generally is considered to be of low human health toxicity, with the principal concern being eye, skin, and respiratory irritation following inhalation of vapors in an occupational setting, but it has been regulated in Florida at very low concentrations based on organoleptic considerations.

A GIS-expert-based approach for groundwater quality monitoring network design in an alluvial aquifer: a case study and a practical guide.

Groundwater quality monitoring is a critical part of water management in all groundwater basins. In order to be effective and to meet the required needs, groundwater quality monitoring networks (GQMNs) must be designed to be able to operate long-term and economically without minimal disruption. The analytical hierarchical process (AHP), a multi-criteria decision-making program, was used to design a GQMN for an alluvial aquifer located in the Islam Abad plain west of Kermanshah province, Iran. This semi-arid area is subject to groundwater depletion and water quality changes. The model used 8 primary criteria sub-divided with 5 sub-criteria based on a combination of empirical data and expert opinion. The primary criteria included density of wells, well discharge, well depth, water quality (conductivity), flow direction, annual groundwater extraction, water level declines, and accessibility. The model showed that 59 of 254 production wells in the basin could provide optimal monitoring locations. When a second screening of the wells was used to determine constraints (physical conditions of the wells and pumps, owner permission of use, type of the pump, etc.), the number of wells was reduced to 13 wells. An initial round of water sampling and chemical analysis demonstrated that the design of the GQMN met the goals of the water management agency of the region.

Aquifer Storage and Recovery Using Saline Aquifers: Hydrogeological Controls and Opportunities.

Aquifer storage and recovery (ASR) is a valuable tool for managing variations in the supply and demand of freshwater, but system performance is highly dependent upon system-specific hydrogeological conditions including the salinity of the storage-zone native groundwater. ASR systems using storage zones containing saline (>10,000 mg/L of total dissolved solids) groundwater tend to have relatively low recovery efficiencies (REs). However, the drawbacks of low REs may be offset by lesser treatment requirements and may be of secondary importance where the stored water (e.g., excess reclaimed, surface, and storm waters) would otherwise go to waste and pose disposal costs. Density-dependent, solute-transport modeling results demonstrate that the RE of ASR systems using a saline storage zone is most strongly controlled by parameters controlling free convection (e.g., horizontal hydraulic conductivity) and mixing of recharged and native groundwater (e.g., dispersivity and aquifer heterogeneity). Preferred storage zone conditions are moderate hydraulic conductivities (5 to 20 m/d), low degrees of aquifer heterogeneity, and primary porosity-dominated siliclastic and limestones lithologies with effective porosities greater than 5%. Where hydrogeological conditions are less favorable, operational options are available to improve RE, such as preferential recovery from the top of the storage zone. Injection of large volumes of excess water currently not needed into saline aquifers could create valuable water resources that could be tapped in the future during times of greater need.

Natural Radiation in the Rocks, Soils, and Groundwater of Southern Florida with a Discussion on Potential Health Impacts.

Southern Florida is underlain by rocks and sediments that naturally contain radioactive isotopes. The primary origin of the radioactive isotopes is Miocene-aged phosphate deposits that can be enriched in uranium-238 and its daughter isotopes. Nodular phosphate containing radionuclides from the Miocene has been reworked into younger formations and is ubiquitous in southern Florida. When the nodular phosphate is exposed to groundwater with geochemical conditions favorable for its dissolution, uranium, radium, and radon may be released into the groundwater system. Uranium concentrations have been measured above the 30 µg/L drinking water standard at only one location in Lee County. Radium226/228 exceedances of the drinking water standard have been documented in numerous wells in Sarasota County. Indoor radon activities have exceeded the 4 piC/L guideline in five southern Florida counties. The exceedance of radioactivity standards in drinking water does not occur in municipal drinking water supplies, but rather only in some domestic self-supply wells. Health risks for exposure to radiation from domestic self-supply wells could be mitigated by testing of well water and, if necessary, switching to the use of a different aquifer or treatment process. While the risk of exposure to radon in indoor air in southern Florida is generally low, some areas are enriched in soil radon that migrates into structures, which could be addressed by improved ventilation.

Natural Background and Anthropogenic Arsenic Enrichment in Florida Soils, Surface Water, and Groundwater: A Review with a Discussion on Public Health Risk.

Florida geologic units and soils contain a wide range in concentrations of naturally-occurring arsenic. The average range of bulk rock concentrations is 1 to 13.1 mg/kg with concentrations in accessary minerals being over 1000 mg/kg. Florida soils contain natural arsenic concentrations which can exceed 10 mg/kg in some circumstances, with organic-rich soils often having the highest concentrations. Anthropogenic sources of arsenic have added about 610,000 metric tons of arsenic into the Florida environment since 1970, thereby increasing background concentrations in soils. The anthropogenic sources of arsenic in soils include: pesticides (used in Florida beginning in the 1890's), fertilizers, chromated copper arsenate (CCA)-treated wood, soil amendments, cattle-dipping vats, chicken litter, sludges from water treatment plants, and others. The default Soil Cleanup Target Level (SCTL) in Florida for arsenic in residential soils is 2.1 mg/kg which is below some naturally-occurring background concentrations in soils and anthropogenic concentrations in agricultural soils. A review of risk considerations shows that adverse health impacts associated with exposure to arsenic is dependent on many factors and that the Florida cleanup levels are very conservative. Exposure to arsenic in soils at concentrations that exceed the Florida default cleanup level set specifically for residential environments does not necessarily pose a meaningful a priori public health risk, given important considerations such as the form of arsenic present, the route(s) of exposure, and the actual circumstances of exposure (e.g., frequency, duration, and magnitude).

Seabed gallery intakes: Investigation of the water pretreatment effectiveness of the active layer using a long-term column experiment.

Seabed gallery intake systems used for seawater reverse osmosis facilities employ the same principle of water treatment as slow sand filtration in freshwater systems. An investigation concerning the effectiveness of the active layer (top layer) in improving raw water quality was conducted by using a long-term bench-scale columns experiment. Two different media types, silica and carbonate sand, were tested in 1 m columns to evaluate the effectiveness of media type in terms of algae, bacteria, Natural Organic Matter (NOM) and Transparent Exopolymer Particles (TEP) removal over a period of 620 days. Nearly all algae in the silica sand column, 87% (σ = 0.04) of the bacteria, 59% (σ = 0.11) of the biopolymer fraction of NOM, 59% (σ = 0.16) of particulate and 32% (σ = 0.25) of colloidal TEP were removed during the last 330 days of the experiment. Total removal was observed in the carbonate sand column for algal concentration, while the bacterial removal was lower at 74% (σ = 0.08). Removal of biopolymers, particulate and colloidal TEP were higher in the carbonate column during the last 330 days with 72% (σ = 0.15), 66% (σ = 0.08) and 36% (σ = 0.12) removed for these organics respectively. Removal of these key organics through the 1 m thick column, representing the active layer, will likely reduce the rate of biofouling, reduce chemical usage and minimize operating cost in SWRO systems. The data show that the media will require several months at the beginning of operation to reach equilibrium so that high organic removal rates can be achieved. No development of a "schmutzdecke" layer occurred. The experimental results suggest that unlike freshwater slow sand filtration wherein most water treatment occurs in the upper 10 cm, in seawater systems treatment occurs throughout the full active layer depth of 1 m. The results of this study will help in designing and operating seabed gallery intake systems in varied geological conditions.

Evolution of Heterogeneous Mixed Siliciclastic/Carbonate Aquifers Containing Metastable Sediments.

Mixed carbonate and siliciclastic marine sediments commonly become freshwater aquifers in eastern coastal regions of the United States and many other global locations. As these deposits age, the carbonate fraction of the sediment is commonly removed by dissolution and the aquifer can become a solely siliciclastic system or contain zones or beds of pure quartz sand. During aquifer evolution, the sediment grain size characteristics, hydraulic conductivity, and porosity change. An investigation of these changes using mixed carbonate/siliciclastic sediment samples collected from a modern barrier island beach in southern Florida showed that the average mean grain diameter decreased with removal of the carbonate fraction, but the average hydraulic conductivity and porosity increased slightly, but not to statistical significance. This counterintuitive result occurs because of the change in the pore types from a combined shelter and intergranular pore system producing a dual porosity system in the mixed sediments to a single intergranular pore system in the siliciclastic sediment fraction. Within the mixed carbonate/siliciclastic sediment, in the pure carbonate fraction, large shell fractions form grain-supported large pores, which become filled with sand-sized quartz as the shell fragments decrease in size or as the sediment becomes compacted. The hydraulic conductivity increases because the shell fragments that were oriented perpendicular to flow caused an increase in the length of the flow path, or a larger scale tortuosity, compared with the flow through pure quartz sand.

Aquifer Treatment of Sea Water to Remove Natural Organic Matter Before Desalination.

An investigation of a sea water reverse osmosis desalination facility located in western Saudi Arabia has shown that aquifer treatment of the raw sea water provides a high degree of removal of natural organic matter (NOM) that causes membrane biofouling. The aquifer is a carbonate system that has a good hydraulic connection to the sea and 14 wells are used to induce sea water movement 400 to 450 m from the sea to the wells. During aquifer transport virtually all of the algae, over 90% of the bacteria, over 90% of the biopolymer fraction of NOM, and high percentages of the humic substance, building blocks, and some of the low molecular weight fractions of NOM are removed. Between 44 and over 90% of the transparent exopolymer particles (TEP) are removed with a corresponding significant reduction in concentration of the colloidal fraction of TEP. The removal rate for TEP appears to be greater in carbonate aquifers compared to siliciclastic systems. Although the production wells range in age from 4 months to 14 years, no significant difference in the degree of water treatment provided by the aquifer was found.

Solute-Transport Predictive Uncertainty in Alternative Water Supply, Storage, and Treatment Systems.

Alternative water supply, storage, and treatment (AWSST) systems, which utilize aquifers to supply, store, and naturally treat water, are increasingly being implemented globally to address water scarcity and safety. The failure of some AWSST systems to meet water quality expectations was caused by conceptual model error, in which local hydrogeological conditions were less favorable than recognized or considered during project feasibility assessments, economic analyses, and design. More successful implementation of AWSST projects requires that conceptual model error be explicitly and rigorously addressed. Recommended approaches to addressing conceptual model uncertainty include more detailed aquifer characterization, recognition of a wide suite of possible alternative conceptual models, and then screening the models as to whether or not they are plausible and relevant in terms of materially impacting predictive results. Subjective professional judgement remains the basis for assigning probabilities to relevant conceptual models (contingencies).

Subsurface intake systems: Green choice for improving feed water quality at SWRO desalination plants, Jeddah, Saudi Arabia.

An investigation of three seawater reverse osmosis facilities located along the shoreline of the Red Sea of Saudi Arabia that use well intake systems showed that the pumping-induced flow of raw seawater through a coastal aquifer significantly improves feed water quality. A comparison between the surface seawater and the discharge from the wells shows that turbidity, algae, bacteria, total organic carbon, most fractions of natural organic matter (NOM), and particulate and colloidal transparent exopolymer particles (TEP) have significant reductions in concentration. Nearly all of the algae, up to 99% of the bacteria, between 84 and 100% of the biopolymer fraction of NOM, and a high percentage of the TEP were removed during transport. The data suggest that the flowpath length and hydraulic retention time in the aquifer play the most important roles in removal of the organic matter. Since the collective concentrations of bacteria, biopolymers, and TEP in the intake seawater play important roles in the biofouling of SWRO membranes, the observed reductions suggest that the desalination facilities that use well intakes systems will have a potentially lower fouling rate compared to open-ocean intake systems. Furthermore, well intake system intakes also reduce the need for chemical usage during complex pretreatment systems required for operation of SWRO facilities using open-ocean intakes and reduce environmental impacts.

Determination of hydraulic conductivity from grain-size distribution for different depositional environments.

Over 400 unlithified sediment samples were collected from four different depositional environments in global locations and the grain-size distribution, porosity, and hydraulic conductivity were measured using standard methods. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations (e.g., Hazen, Carman-Kozeny) commonly used to estimate hydraulic conductivity from grain-size distribution. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values with errors ranging to over 500%. To improve the empirical estimation methodology, the samples were grouped by depositional environment and subdivided into subgroups based on lithology and mud percentage. The empirical methods were then analyzed to assess which methods best estimated the measured values. Modifications of the empirical equations, including changes to special coefficients and addition of offsets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, offshore marine, and river sediments. Estimated hydraulic conductivity errors were reduced to 6 to 7.1 m/day for the beach subgroups, 3.4 to 7.1 m/day for dune subgroups, and 2.2 to 11 m/day for offshore sediments subgroups. Improvements were made for river environments, but still produced high errors between 13 and 23 m/day.

Restoration of wadi aquifers by artificial recharge with treated waste water.

Fresh water resources within the Kingdom of Saudi Arabia are a rare and precious commodity that must be managed within a context of integrated water management. Wadi aquifers contain a high percentage of the naturally occurring fresh groundwater in the Kingdom. This resource is currently overused and has become depleted or contaminated at many locations. One resource that could be used to restore or enhance the fresh water resources within wadi aquifers is treated municipal waste water (reclaimed water). Each year about 80 percent of the country's treated municipal waste water is discharged to waste without any beneficial use. These discharges not only represent a lost water resource, but also create a number of adverse environmental impacts, such as damage to sensitive nearshore marine environments and creation of high-salinity interior surface water areas. An investigation of the hydrogeology of wadi aquifers in Saudi Arabia revealed that these aquifers can be used to develop aquifer recharge and recovery (ARR) systems that will be able to treat the impaired-quality water, store it until needed, and allow recovery of the water for transmittal to areas in demand. Full-engineered ARR systems can be designed at high capacities within wadi aquifer systems that can operate in concert with the natural role of wadis, while providing the required functions of additional treatment, storage and recovery of reclaimed water, while reducing the need to develop additional, energy-intensive desalination to meet new water supply demands.