WATER
MANAGED AQUIFER RECHARGE
AQUIFER STORAGE RECOVERY (ASR)
Water managers throughout the world remain challenged to ensure an uninterrupted supply of fit-for-need water. The challenge is nowhere more acute than in arid regions where countries are keen to strategically secure their water reserves. In the absence of surface water supplies, surface storage tanks present a solution, but only in part as they come at a hefty cost and remain good for only a few days of respite in case of supply interruptions. While from a surface storage aspect the thought of several weeks of strategic reserves is daunting, Aquifer Storage Recovery (ASR) has been known in several parts of the world to be a reliable technique for water banking and being capable of providing significant volumes of water reserves. In some projects, surplus desalinated water in the winter months is directed to aquifers to create emergency reserves. In others, surface or suitably treated wastewater is harnessed for recharge.
With limited surface water sources and heavily depleted groundwater, countries stand to benefit from the practice of aquifer recharge not only for potable supplies, but also in meeting agricultural and industrial demand. It can also meet the needs of annual seasonal variations. From a simple recharge to arrest salt water intrusion in coastal areas, to depleted aquifer replenishment, dam water recharge and strategic storage, managed aquifer recharge plays a key role in any water management program.
Advanced tertiary or quaternary treated wastewater can address the concerns on TOC, trace compounds, pathogens, ions and salinity to become a dependable year-round source of aquifer recharge water for agricultural or industrial withdrawals and benefits.
COASTAL ZONE AQUIFER MANAGEMENT
In coastal areas groundwater is threatened by the intrusion of seawater into the aquifer making it unsuitable for potable or agricultural uses. In order to sustainably manage coastal water resources a diverse and holistic management approach of governance, management, and technical prowess is required. With a large portion of the global population living near the sea, increasing demand for water resources in coastal regions and heavy groundwater abstraction can lead to large economic losses and water scarcity.
Decision-makers and planners need to map out and understand how much groundwater is available and how best to draw it. Saltwater intrusion can be curtailed through the use of elaborate monitoring and mitigation plans while understanding the location of the boundary between freshwater and seawater in the aquifers. A better understanding can be derived through measuring groundwater level, the concentration of ions, and resistivity values. Recharge wells can be strategically placed to avoid the intrusion of saltwater. Other strategies can include a reduction in pumping, rearranging the pumping wells, pumping of seawater, and even subsurface barriers.
RIVER BASIN WATERSHED DAMS
River basins are an area of land that is drained by a river. In comparison, watersheds are similar areas of drainage but in addition to rivers they can also relate to marshes, lakes or groundwater. Together they form an important ecological component of any water resources management setting.
There are abundant smaller dams in arid regions with the primary function of arresting flash flood water flows and protecting villages and communities downstream. They however are also a source of pristine water available in their catchment area. Unfortunately, this water is often lost due to evaporation while natural recharge to the ground is hampered by silt fallout and deposition on the resulting lake floor. Recharging accumulated water to the aquifers for future agricultural or domestic withdrawals can be rewarding.
WATER QUALITY
It is not only the quantity of water that matters, but the quality of the water is an important factor for it to be useful. In planning any water resources, attention to water quality whether it be for consumption or disposal is of paramount importance. The main causes of poor water quality can be high levels of salinity, nutrients, metals, pathogens, and organic contaminants. These pollutants can originate from a wide range of sources including agriculture, industry, and urban areas.
Generally speaking, the control of pollutants at their source is more effective and cost-beneficial than any follow-up remediation actions. Strict water quality controls and required treatments need to be followed in order to protect human health and aquatic ecosystems from chemical and biological pollutants. New contaminants are continually emerging. Timely and quality monitoring supported by testing and data management is needed to avoid costly remedial solutions and any toxic contamination. Suitable software offers a simple and easy analysis of water quality data and automatic geochemical calculations of water type, sum of anions, sum of cations, ion balance, TDS, hardness, and others.
GROUNDWATER
HYDROGEOLOGY
The use of groundwater has been increasing over the years, especially in arid regions where it is relied upon for both potable and farming use. There are two main types of aquifers with relation to their confinement. Unconfined aquifers just below the shallow water table are drawn down into wells. These aquifers are recharged locally in short periods of time running in years. Confined aquifers on the other hand are much deeper and are renewed over much longer time scales running into centuries or even longer.
The sustainable extraction limit of an aquifer is usually unable to keep up with the rate of annual recharge, or renewal. Pumping aquifers causes groundwater levels to fall, affecting fragile ecosystems and increasing salinity. As a result of this groundwater use can easily lead to unsustainable exploitation with the overuse sometimes not detected until several decades later.
MONITORING
Water level and quality monitoring systems are used in conjunction with other technologies to better manage surface and groundwater resources.
Single level monitoring dataloggers collect vast amounts of data for long-term water level monitoring in projects such as aquifer storage recovery, coastal zone aquifer management, aquifer remediation, and surface water applications. These instruments help determine aquifer characteristics and heterogeneities. Each well in the project area can be equipped with a groundwater datalogger to continuously monitor water levels, providing a reliable log of changes in response to hydraulic pumping tests or recharge. The data collected is then analyzed using pumping and slug test data analysis software to determine the hydraulic properties of the aquifer. Electrical conductivity measurements can be correlated with chloride concentrations to monitor seawater intrusion providing valuable information for hydrologic modeling of seawater intrusion.
Multilevel water monitoring technology facilitates subsurface characterization technology that allows testing of hydraulic conductivity, long-term monitoring of fluid pressure, and collection of fluid samples from multiple zones within a single borehole. Multilevel monitoring is also instrumental in carbon sequestration projects monitoring pore pressure to evaluate slope stability, subsidence, and drainage and in assessing dewatering and remediation solutions. It also meets continuous monitoring of groundwater pressure at large dams, tunnels or shafts.
In the oil and gas sector with unconventional plays such as shale gas, oil sands, coal bed methane and others, activities have an increasing potential to interface with groundwater resources. Multilevel monitoring instruments provide detailed monitoring to help protect groundwater resources and document regulatory compliance throughout the life of the project.
MODELING
Aquifer characterization is a process in which the three-dimensional structure, hydraulic and transport properties and chemistry of aquifers is evaluated. It provides the foundation for groundwater modeling. Groundwater modeling software is widely used for simulating groundwater flow and contaminant transport.
Such software helps delineate well capture zones for water supply projects, design and optimize pumping well locations for mine dewatering, determine contaminant fate and exposure pathways for risk assessment and simulate surface water-groundwater interactions. The software is also used for watershed scale and regional groundwater modeling, evaluating groundwater remediation systems, aquifer storage and recovery (ASR) and evaluating saltwater intrusion.
MINING OPERATIONS
Another area of monitoring is in mining operations where monitoring technologies provide real-time intelligence to support decision-making. It can be used in different mining phases such as exploration and feasibility, planning and construction, operations, and closure. Multilevel monitoring addresses a wide variety of these impacts, including site characterization for environmental impact assessment, waste piles, monitoring of leach operations, closure analyses and tailings and process water ponds.
Water plays a critical role in mining operations and makes a significant impact on water resources. The high usage of water leads to depleting water supplies while discharges or seepage from tailings or waste rock impoundments result in polluting water resources. The use of water-related technologies allows accurate site assessments to be carried out, simplifying complex water management challenges in mining projects.
WATER MANAGEMENT
As urbanization gains momentum, more and more people are shifting to cities in search of better livelihood and lifestyle. Inevitably this means a requirement for more water supplies, more wastewater disposal, and greater energy use to provide these services. The increasing demands for water, energy, and other resources in urban centers and megacities is putting pressure on water authorities to adopt new approaches to water resources planning as part of broader urban sustainability and livability. Careful cost-benefit analysis matching against stakeholder needs can bring affordable, sustainable solutions to the most challenging of settings.
Astute water managers balance potable demands along with irrigation, agricultural and industrial withdrawals, juggling water balance equations to ensure water security and availability throughout the year. They remain challenged to ensure an uninterrupted supply of fit-for-need water. Arid countries with limited surface capacities are looking to initiatives to strategically secure their water reserves. Several countries are in the process of bolstering their fall back supplies, building surface storage tanks to increase emergency supplies by several days. This solution does address the need to provide respite in case of supply interruptions but only in part and alone it does come at a hefty cost. While from a built surface storage aspect the thought of several weeks of strategic reserves is daunting, Managed Aquifer Recharge (MAR) has been known in several parts of the world to be a reliable technique for water banking and being capable of providing up to several months of water reserves.
Whereas securing water supplies help meet demand, network losses work in the opposite direction and can be costly in terms of both financial and resource loss. This non-revenue water can continue to pile up unless timely actions are taken to arrest and remediate the issue. Aging networks have been estimated to typically lose anywhere from 20-40% of the water supply. Leak detection can play an important role in identifying the weak points responsible for the majority of loss. With the majority of the network structure buried in the ground, the visual determination of leaks is not possible unless water has reached the surface.
The primary method used for detecting leaks is acoustic where instruments are used to capture the noise of escaping water. Another method that is used is that of measuring unexplainable pressure differences using flow meters and pressure gauges. Smart water can play an intelligent role in not only being a tool for better managing water resources but also in relation to non-revenue water and leaks detection. A comprehensive approach utilizes smart meters, databases, artificial intelligence, machine learning to create state-of-the-art water resources management practices.
WATER TREATMENT
DESALINATION
Seawater or brackish water? Centralized or decentralized? Thermal or membrane? And more recently, fossil or renewable? These are some of the questions that come up in the very early stages of visualizing a water desalination project. The choice between seawater and brackish water is dictated by the setting, just as is the decision on centralized and decentralized. These are also dependent on available budgets, allowable time to action and experience. Seawater is abundant in a coastal setting. Brackish water aquifers need to be tested and modeled to ensure uninterrupted supplies for the life of the project. They present the complication of brine discharge though overall project capital and operating costs can be considerably less in a brackish water plant than in seawater.
Although centralized systems can offer economies of scale at the plant level, additional networking costs can make decisions tilt in favour of decentralized plants especially when demand points are scattered. In both cases, with their costs coming down, membrane based treatment systems are becoming the technology of choice. With suitable pre-treatment, reverse osmosis (RO) desalination is scaling new heights. Recent advances in electro dialysis reversal (EDR) from a commercial and technical aspect is breathing new life in this technology. With its high recovery, it warrants a feasibility comparison in areas where brine discharge can be a burden. Albeit, EDR economical range of operation is limited to lower brackish water salinities.
WATER REUSE
Many of the considerations in play in water reuse are similar to those in desalination. Wastewater treated to a high quality, tertiary or quaternary, offers beneficial use and helps derive value. There is considerable potential to improve urban sustainability by recovering water, energy and carbon. Selected technologies can also help remove nutrients from wastewater which can be a further source of revenue by reusing them in the city and as fertilizer for food production.
When it comes to industries, more and more are starting to meet their water needs through water reuse methodologies, thereby saving pristine freshwater for potable uses. In such a scenario, it is understandable that even for the most intrepid operators the use of wastewater treated to an advanced level using proven technologies can offer all the benefits of pristine freshwater without the issues of seasonal supply shortages and cost overburden.
