Unconfined Coastal Aquifer Research Articles

Numerical assessment of compressed air injection for mitigating seawater intrusion in a coastal unconfined aquifer

Subsurface fluids injection is a viable alternative for controlling seawater intrusion in coastal regions, and freshwater is usually served for valid fluids to generate pressure ridge towards the ocean. But other fluids injection, such as compressed air, which presents clean and readily available, is a more attractive solution for repulsing the intruded seawater where freshwater is insufficient. In this study, the performance of compressed air injection (i.e., air barriers) for mitigating seawater intrusion in a coastal unconfined aquifer was quantificationally assessed using a coupled water-air two-phase flow and saltwater transport model. As compressed air is introduced into the aquifer at the toe of saltwater wedge, the seaward hydraulic gradient adjacent to the coast is produced driven by the generated airflow, thereby causing salt-freshwater interface to retreat to the ocean. The magnitude of air injection rate, related to the operational cost of air barriers, does not increases significantly given the progressively decreasing change rate. Compared to the workability of air barriers in the confined aquifer under similar conditions, the reduction in intruded seawater at 365.0 d in the unconfined aquifer reaches only about 0.45 times that in the confined aquifer, which indicates the significance of the boundary condition of aquifer top. The sensitivity analysis of the overlying unsaturated zone reveals that with its permeability decreasing or its thickness increasing, the performance of air barriers is enhanced owing to the blocking effect of the overlying layer on the escape of generated airflow and tends progressively to be stable. Particularly, the efficacy of air barriers in the confined aquifer, including the reduction in intruded seawater and the air injection rate, also can be achieved in an unconfined aquifer with an overlaying sufficient-semipermeable layer.

Utilization of pit lake on the cleaning process of residual saltwater in unconfined coastal aquifers

Subsurface dams are widely used to prevent saltwater intrusion. Once a subsurface dam is established, a large amount of residual saltwater (RSW) may trap behind the dam and negatively affect the groundwater exploitation over the long term. Based on monitoring hydrological information and field-scale numerical models, we proposed three kinds of RSW clean-up strategy coupling the applications of a pit lake and wells in a coastal aquifer. We firstly investigated the spontaneous natural removal of RSW in an actual coastal aquifer affected by a pit lake, assessed the impact of pit lake drainage on the removal of RSW, and designed a feasible strategy for reducing residual saltwater utilizing both pit lake and wells. Our results indicated that RSW remediation is a slow process under natural conditions. The area of the RSW decreased from 15.17 to 11.62 km2 after 20 years, and the Cl− concentration of RSW around the pit lake increased to 1750 mg/L. The RSW cleaning efficiency can be significantly enhanced by the pit lake drainage process. With the pit lake drainage rate of 1.6E5 m3/d, the area of the RSW decreased by 10.14 km2 in five years being 17-times larger than that of the natural restoration scheme (0.58 km2). With the combined well-lake drainage system, the total residual saltwater area decreased by more than 90% within five years, and the Cl− concentration of RSW almost reached WHO standards for drinking-water quality (250 mg/L). RSW upstream the subsurface dam was thoroughly cleaned up adopting the well–lake drainage strategy. Therefore, a well–lake drainage strategy can be strongly recommended for removing the RSW in coastal aquifers.

Contamination Transport in the Coastal Unconfined Aquifer under the Influences of Seawater Intrusion and Inland Freshwater Recharge-Laboratory Experiments and Numerical Simulations.

The coupled effect of seawater intrusion and inland freshwater recharge plays an important role in contamination transport in coastal heterogeneous aquifer. In this study, the effects of seawater intrusion and inland recharge on contamination transport were investigated by conducting laboratory experiments and numerical simulations. The laboratory tests were conducted in a sand tank considering two scenarios, namely the conditions of landward and seaward hydraulic gradients. The SEAWAT software was applied for validating the contaminant transport in coastal heterogeneous aquifer. The results indicated that the simulated seawater wedge and contours of the saltwater contaminant matched the observed ones well. The length of the seawater wedge in the scenario of seaward hydraulic gradient was smaller than that in the scenario of landward hydraulic gradient, which reflected that the large quantity of inland recharge have a negative effect on the invasion process of seawater. The plume moved mainly downward in the heterogeneous unconfined aquifer for both scenarios. The pollution plume became concave at the interface between each two layers, which was because the velocity of contaminant plume migration increased gradually from the upper layer to lower layer. The migration direction of the front of the plume was consistent with the direction of hydraulic gradient, which indicated that it was influenced by the water flowing. The maximum area of plume in the scenario of seaward hydraulic gradient was slightly smaller than that in the scenario of landward hydraulic gradient. The maximum area and vertical depth of the pollutant plume were sensitive to the hydraulic conductivity, dispersivity and contamination concentration. This study was of great significance to the controlling of pollution and utilization of freshwater resources in coastal areas.

Optimal Utilization of Coastal Unonfined Aquifers.(Dept.C)

This research concerns with optimal utilization of unconfined coastal aquifers under different constraints. This problem is a complicated, nonlinear, and constrained one. Therefore, the Genetic Algorithm nonlinear optimization method was selected to handle the present problem. Analytical solution was applied for the groundwater flow equation under assumption of steady sharp interface in homogenous aquifer. Image theory and the superposition principle were the main tools used through the analytical procedure. A Fortran program was written to apply the mathematical concepts of the problem. The method was applied to aquifer system underlain the City of Miami Beach at north of Spain.

Modelling groundwater level fluctuation in an Indian coastal aquifer

Estimating groundwater level (GWL) fluctuations is a vital requirement in hydrology and hydraulic engineering, and is commonly addressed through artificial intelligence (AI) models. The purpose of this research was to estimate groundwater levels using new modelling methods. The implementation of two separate soft computing techniques, a multilayer perceptron neural network (MLPNN) and an M5 model tree (M5-MT), was examined. The models are used in the estimation of monthly GWLs observed in a shallow unconfined coastal aquifer. Data for the water level were collected from observation wells located near Ganjimatta, India, and used to estimate GWL fluctuation. To do this, two scenarios were provided to achieve optimal input variables for modelling the GWL at the present time. The input parameters applied for developing the proposed models were a monthly time-series of summed rainfall, the mean temperature (within its lag times that have an effect on groundwater), and historical GWL observations throughout the period 1996–2006. The efficiency of each proposed model for Ganjimatt was investigated in stages of trial and error. A performance evaluation showed that the M5-MT outperformed the MLPNN model in estimating the GWL in the aquifer case study. Based on the M5-MT approach, the development of this model gives acceptable results for the Indian coastal aquifers. It is recommended that water managers and decision makers apply these new methods to monitor groundwater conditions and inform future planning.

Underground Barrier Wall Evaluation for Controlling Saltwater Intrusion in Sloping Unconfined Coastal Aquifers

Barrier walls are considered one of the most effective methods for facilitating the retreat of saltwater intrusion (SWI). This research plans to examine the effect of using barrier walls for controlling of SWI in sloped unconfined aquifers. The sloping unconfined aquifer is considered with three different bed slopes. The SEAWAT model is implemented to simulate the SWI. For model validation, the numerical results of the seawater wedge at steady state were compared with the analytical solution. Increasing the ratio of flow barrier depth (db/d) forced the saltwater interface to move seaward and increased the repulsion ratio (R). With a positive sloping bed, further embedding the barrier wall from 0.2 to 0.7 caused R to increase from 0.3% to 59%, while it increased from 1.8% to 41.7% and from 3.4% to 46.9% in the case of negative and horizontal slopes, respectively. Embedding the barrier wall to a db/d value of more than 0.4 achieved a greater R value in the three bed-sloping cases. Installing the barrier wall near the saltwater side with greater depth contributed to the retreat of the SWI. With a negative bed slope, moving the barrier wall from Xb/Lo = 1.0 toward the saltwater side (Xb/Lo = 0.2) increased R from 7.21% to 68.75%, whereas R increased from 5.3% to 67% for the horizontal sloping bed and from 5.1% to 64% for the positive sloping bed. The numerical results for the Akrotiri coastal aquifer confirm that the embedment of the barrier wall significantly affects the controlling of SWI by increasing the repulsion ratio (R) and decreasing the SWI length ratio (L/La). Cost-benefit analysis is recommended to determine the optimal design of barrier walls for increasing the cost-effectiveness of the application of barrier walls as a countermeasure for controlling and preventing SWI in sloped unconfined aquifers.

Improved Flower Pollination Algorithm for Optimal Groundwater Management

Groundwater management problems are typically of a large-scale nature, involving complex nonlinear objective functions and constraints, which are commonly evaluated through the use of numerical simulation models. Given these complexities, metaheuristic optimization algorithms have recently become popular choice for solving such complex problems which are difficult to solve by traditional methods. However, the practical applications of metaheuristics are severely challenged by the requirement of large number of function evaluations to achieve convergence. To overcome this shortcoming, many new metaheuristics and different variants of existing ones have been proposed in recent years. In this study, a recently developed algorithm called flower pollination algorithm (FPA) is investigated for optimal groundwater management. The FPA is improved, combined with the widely used groundwater flow simulation model MODFLOW, and applied to solve two groundwater management problems. The proposed algorithm, denoted as IFPA, is first tested on a hypothetical aquifer system, to minimize the total pumping to contain contaminated groundwater within a capture zone. IFPA is then applied to maximize the total annual pumping from existing wells in Rhis-Nekor unconfined coastal aquifer on the northern of Morocco. The obtained results indicate that IFPA is a promising method for solving groundwater management problems as it outperforms the standard FPA and other algorithms applied to the case studies considered, both in terms of convergence rate and solution quality.

Groundwater Circulation Well for Controlling Saltwater Intrusion in Coastal aquifers: Numerical study with Experimental Validation

Saltwater intrusion into coastal aquifers has become a prominent environmental concern worldwide. As such, there is a need to prepare and implement proper remediation techniques with careful planning of freshwater withdrawal systems for controlling saltwater intrusion in coastal marine and estuarine environments. This paper investigates the performance of groundwater circulation well (GCW) in controlling saltwater intrusion problems in unconfined coastal aquifers. The GCWs have been established as a promising in-situ remedial technique of contaminated groundwater. The GCW system creates vertical circulation flow by extracting groundwater from an aquifer through a screen in a single well and injecting back into the aquifer through another screen. The circulation flow induced by GCW force water in a circular pattern between abstraction and recharge screens and can be as a hydraulic barrier for controlling saltwater intrusion problem in coastal aquifers. In this study, an effort has been made to investigate the behavior of saltwater intrusion dynamics under a GCW. An experiment has been conducted in a laboratory-scale flow tank model under constant water head boundary conditions, and the variable-density flow and transport model FEMWATER is used to simulate the flow and transport processes for the experimental setup. The evaluation of the results indicates that there is no further movement of saltwater intrusion wedge towards the inland side upon implementation of GCW, and the GCW acts as a hydraulic barrier in controlling saltwater intrusion in coastal aquifers. The present study reveals the GCWs system can effectively mitigate the saltwater intrusion problem in coastal regions and could be considered as one of the most efficient management strategies for controlling the problem.

Behaviour of contaminant transport in unconfined coastal aquifer: An experimental evaluation

Contamination of groundwater in coastal aquifers is a significant environmental concern for coastal populations across the world. As it not only leads to the depletion of available freshwater resources, but also threatens the ecology and economy of the coastal zones. A quantitative understanding of contaminant transport processes within coastal aquifer systems is, therefore, essential for efficient planning and management of coastal environments. The overarching aim of this research is to investigate the behaviour of contaminant transport patterns for various contaminant transport scenarios in a coastal unconfined aquifer. For this purpose, a series of laboratory-scale experiments have been carried out in the setup of a rectangular flow tank using dye to trace the movement of contaminant plume patterns with homogeneous soil formations. The experimental data indicate that the contaminant travels upward towards the seaward boundary when it approaches the saltwater wedge and then exits around the coastline. Upon installation of the pump, the saltwater intrusion wedge was moving rapidly towards the freshwater aquifer, and the contaminant was also moving along with the saltwater wedge towards the pump location. Experimental results also clearly show that the contaminant plume formed an elongated shape as it approached the saltwater–freshwater interface due to dispersion effects. The findings from this experimental study helped us to have a better understanding of the contaminant transport processes occurring in a coastal unconfined aquifer.

Effects of Temperature on Tidally Influenced Coastal Unconfined Aquifers

AbstractAquifer‐ocean temperature contrasts are common worldwide. Their effects on flow and salinity distributions in unconfined coastal aquifers are, however, poorly understood. Based on laboratory experiments and numerical simulations, we examined the responses of flow processes in tidally influenced aquifers to aquifer‐ocean temperature differences. The extent of seawater intrusion and seawater circulation were found to vary with the aquifer‐ocean temperature contrast. Compared with the isothermal case, an increase of up to 40% of the tide‐induced seawater circulation rate in the intertidal zone was observed when seawater is warmer than groundwater. In contrast, saltwater circulation in the lower saltwater wedge declines notably no matter whether the seawater is warmer or colder than groundwater. As the seawater temperature rises, the contribution of tide‐induced circulation to the overall increase of submarine groundwater discharge becomes more important compared with that of density‐driven seawater circulation. Both the upper saline plume and the freshwater discharge zone expand significantly with warmer seawater whereas the lower saltwater wedge contracts.

Assessing the Effectiveness of Using Recharge Wells for Controlling the Saltwater Intrusion in Unconfined Coastal Aquifers with Sloping Beds: Numerical Study

Groundwater systems are considered major freshwater sources for many coastal aquifers worldwide. Seawater intrusion (SWI) inland into freshwater coastal aquifers is a common environmental problem that causes deterioration of the groundwater quality. This research investigates the effectiveness of using an injection through a well to mitigate the SWI in sloping beds of unconfined coastal aquifers. The interface was simulated using SEAWAT code. The repulsion ratios due to the length of the SWI wedge (RL) and the area of the saltwater wedge (RA) were computed. A sensitivity analysis was conducted to recognize the change in the confining layer bed slope (horizontal, positive, and negative) and hydraulic parameters of the value of the SWI repulsion ratio. Injection at the toe itself achieved higher repulsion ratios. RL and RA declined if the injection point was located remotely and higher than the toe of the seawater wedge. Installation at the toe achieved a higher RL in positive sloping followed by horizontal and negative slopes. Moreover, the highest value of RA could be reached by injecting at the toe itself with a horizontal bed aquifer, followed by negative and positive slopes. The recharge well is confirmed as one of the most effective applications for the mitigation of SWI in sloping bed aquifers. The Akrotiri case study shows that the proposed recharging water method has a significant impact on controlling SWI and declines in both SWI wedge length and area.

Assessment of the impact of sea-level rise on seawater intrusion in sloping confined coastal aquifers

Previous studies of the impact of sea-level rise on seawater intrusion (SLR-SWI) are mostly based on horizontal coastal aquifers, despite that most coastal aquifers are sloping. A recent study has shown that the effect of aquifer slope can not be neglected when assessing SLR-SWI in unconfined coastal aquifers. However, the effect of slope in confined aquifers has not been evaluated. In this study, we apply existing analytical solutions to quantify the effect of the slope of both upper and lower confining layers on SLR-SWI. The results show that for flux-controlled sloping confined coastal aquifer systems, SLR does not change the steady-state interface location, consistent with previous findings for horizontal aquifers. Therefore, our analysis focuses on head-controlled sloping confined coastal aquifer systems, for which we find the assumption of horizontal confining units causes significant errors. We demonstrate this by assessing the sensitivities of the seawater toe location and seawater volume to SLR for various combinations of sloping confining layers. The results indicate that the influence of the slope on SLR-SWI is small in thin confined aquifers. However, the slope is an important factor in thick confined aquifers. The influence of the slope in the lower confining layer on SLR-SWI is much greater than that of the upper confining layer. Aquifers that thin towards the sea are most susceptible to SLR-SWI, whereas those that thin towards inland are least susceptible. The assessment of SLR-SWI in sloping confined coastal aquifers in the current study demonstrates application of a rapid, first-order assessment tool that can be applied to a wide range of other sloping coastal confined-aquifer problems.

Pumping optimization of coastal aquifers using probabilistic search – case study: Quaternary aquifer of El-Arish Rafah, Egypt

Abstract The increased pumping of freshwater from coastal aquifers, to meet growing demands, causes an environmental problem called saltwater intrusion. Consequently, proper management schemes are necessary to tackle such a situation and permit the optimal development of coastal groundwater basins. In this research, a probabilistic search algorithm, namely Probabilistic Global Search Lausanne (PGSL), is used to calculate optimal pumping rates of unconfined coastal aquifer. The results of using PGSL are compared with a stochastic search optimization technique, Shuffled Frog Leaping Algorithm (SFLA). The finite element method is applied to simulate the hydraulic response of the steady state homogenous aquifer. The lower and upper (LU) decomposition method is adapted to invert the conductance matrix, which noticeably decreases the computation time. The results of both the PGSL and the SFLA are verified through the application on the aquifer system underlying the City of Miami Beach in the north of Spain. Multiple independent optimization runs are carried out to provide more insightful comparison outcomes. Consequently, a statistical analysis is performed to assess the performance of each algorithm. The two optimization algorithms are then applied on the Quaternary aquifer of El-Arish Rafah area, Egypt. The results show that both algorithms can effectively be used to obtain nearly global solutions compared with other previous published results.

Combined effect of cutoff wall and tides on groundwater flow and salinity distribution in coastal unconfined aquifers

Cutoff walls are widely used to alter groundwater flow and mitigate seawater intrusion in coastal areas. While their behavior and performance in aquifers under static oceanic conditions are well established, how do they combine with tides to affect groundwater flow and salinity distribution in coastal aquifers remains unclear. Here we addressed this research question based on physical experiments and numerical simulations. Cutoff walls were showed to regulate the inland freshwater flow and thus form a sharp waterlevel change in the landside of the cutoff wall. As such, inland groundwater flow was concentrated in the lower aquifer that inhibited seawater intrusion in the unconfined aquifer subjected to a static sea level (under the non-tidal condition). This modification was enhanced as the cutoff wall went deeper or seaward. However, the tide pushed the saltwater wedge seaward in comparison with the case under the non-tidal condition. Under this tidal condition, the modification of the cutoff wall on saltwater intrusion was no longer evident. In both cases under non-tidal and tidal conditions, the cutoff wall was found to alter the path and travel time of the inland fresh groundwater and seawater, and total freshwater storage in the aquifer. These results offer significant implications for designing engineering measures to mitigate seawater intrusion and managing groundwater resources in coastal zones.

Future Risks of Tsunami‐Induced Seawater Intrusion Into Unconfined Coastal Aquifers: Insights From Numerical Simulations at Niijima Island, Japan

AbstractTsunami‐induced seawater inundation causes vertical seawater infiltration into coastal aquifers and induces unexpected salinization of fresh groundwater resources. Assessing future risks of seawater intrusion in tsunami‐prone areas can provide essential information supporting disaster preparedness. In this study, we investigated seawater intrusion and aquifer recovery processes under the future Nankai earthquake and tsunami scenarios at Niijima Island, Japan. A groundwater model with a 2‐D vertical cross section was developed to solve variable‐density flow and salt transport in unsaturated‐saturated media using the numerical code, FEFLOW. Our simulation results indicate that the unsaturated zone behaves as an initial storage of the infiltrated seawater and controls the maximum amount of seawater infiltration during the anticipated tsunami inundation. The bedrock structures affect the direction of seawater movement in the saturated zone and the flushing time of the polluted aquifer. Our analysis suggests that the tsunami inundation height, the rainfall recharge rate, and hydraulic conductivity are the primary sources of uncertainties in the simulation results. These findings have implications for other tsunami‐prone zones with respect to the understanding of the relevant physical processes and model uncertainties.

Combined Effect of Tides and Varying Inland Groundwater Input on Flow and Salinity Distribution in Unconfined Coastal Aquifers

AbstractTides and seasonally varying inland freshwater input, with different fluctuation periods, are important factors affecting flow and salt transport in coastal unconfined aquifers. These processes affect submarine groundwater discharge (SGD) and associated chemical transport to the sea. While the individual effects of these forcings have previously been studied, here we conducted physical experiments and numerical simulations to evaluate the interactions between varying inland freshwater input and tidal oscillations. Varying inland freshwater input was shown to induce significant water exchange across the aquifer‐sea interface as the saltwater wedge shifted landward and seaward over the fluctuation cycle. Tidal oscillations led to seawater circulations through the intertidal zone that also enhanced the density‐driven circulation, resulting in a significant increase in the total SGD. The combination of the tide and varying inland freshwater input, however, decreased the SGD components driven by the separate forcings (e.g., tides and density). Tides restricted the landward and seaward movement of the saltwater wedge in response to the varying inland freshwater input in addition to reducing the time delay between the varying freshwater input signal and landward‐seaward movement in the saltwater wedge interface. This study revealed the nonlinear interaction between tidal fluctuations and varying inland freshwater input will help to improve our understanding of SGD, seawater intrusion, and chemical transport in coastal unconfined aquifers.

A Rapid Assessment Method to Identify Potential Groundwater Flooding Hotspots as Sea Levels Rise in Coastal Cities

Sea level rise (SLR) will cause shallow unconfined coastal aquifers to rise. Rising groundwater can emerge as surface flooding and impact buried infrastructure, soil behavior, human health, and nearshore ecosystems. Higher groundwater can also reduce infiltration rates for stormwater, adding to surface flooding problems. Levees and seawalls may not prevent these impacts. Pumping may accelerate land subsidence rates, thereby exacerbating flooding problems associated with SLR. Public agencies at all jurisdiction levels will need information regarding where groundwater impacts are likely to occur for development and infrastructure planning, as extreme precipitation events combine with SLR to drive more frequent flooding. We used empirical depth-to-water data and a digital elevation model of the San Francisco Bay Area to construct an interpolated surface of estimated minimum depth-to-water for 489 square kilometers along the San Francisco Bay shoreline. This rapid assessment approach identified key locations where more rigorous data collection and dynamic modeling is needed to identify risks and prevent impacts to health, buildings, and infrastructure, and develop adaptation strategies for SLR.

Decision tree as a tool for the management of coastal aquifers of limited saturated thickness

In this paper, a decision tree is presented, constructed on the basis of hydrogeological characteristics (water table depth, freshwater thickness, surface area required and distance between wells), to choose the optimal groundwater extraction method in the case of a coastal unconfined aquifer. A comparison is made of the groundwater extraction methods in a freshwater aquifer of limited thickness occurring in coastal dunes in the eastern region of the Province of Buenos Aires (Argentina). The negative effects brought about by the wrong use of the groundwater extraction methods are analysed, because, as a result of excessive extraction, such methods lead to the dramatic decrease of the freshwater reserves. The decision tree is a useful tool to assist decision-makers as it suggests the most suitable groundwater extraction method options (vertical wells or wellpoints), as well as identifying areas that are unsuitable for sustainable groundwater extraction.

Potential of mixed hydraulic barriers to remediate seawater intrusion.

Remediation measures are crucial to prevent or reverse seawater intrusion deteriorating coastal fresh groundwater resources. The mixed hydraulic barrier approach, as a combination of positive and negative hydraulic barriers, holds promising advantages especially for arid areas because extracted water provides a resource for injection after treatment. However, transient remediation mechanisms and impact of parameters are still unsatisfyingly understood. Therefore, the feasibility and optimal management of mixed hydraulic barriers as well as a comparison to single positive and negative barriers are explored with a synthetic 2D variable-density model of an already salinated, unconfined coastal aquifer using SEAWAT and FloPy. The hydraulic conductivity, porosity, injection and extraction rate, barrier locations, injection salt concentration, and reduction of pumping stress are varied jointly to determine the parameters' impact and interdependencies. The hydraulic conductivity controls the overall remediation potential as a hydrogeological component. Reduced inland abstractions of supply wells and the injection rates of the positive barrier show the largest remediation effects. However, locating the positive barrier within the salt wedge poses the risk of trapping salt landside. A sole negative barrier did not improve remediation substantially. This study thus shows that remediation with mixed hydraulic barriers can be feasible if implemented according to local conditions.

Hydrogeological vulnerability in Jacó coastal aquifers, Central Pacific, Costa Rica

In the last two decades, the Central Pacific of Costa Rica experienced a strong growth in urban and tourism development. If not regulated, this development can result in a pressure to groundwater resources and, therefore, a threat in terms of quality and quantity. In this study, a hydrogeological vulnerability map of Jacó aquifers was performed, by the GOD method. Geological profiles were elaborated, and field verification was performed. It is confirmed that, in the study area, two aquifers are found: a) a detritic, porous, unconfined coastal aquifer, settled in the Jacó alluvial plain and, b) an aquifer in the basaltic fractured rocks of the Nicoya Complex, unconfined in the mountainous zone and underlying the detritic formation in the central area, where the groundwater is integrated to that of the detrital aquifer. The zone of the alluvial aquifer resulted in a medium vulnerability index, whereas the mountainous areas in a low vulnerability. Management recommendations were proposed.