A field test and analysis method has been developed to estimate the vertical distribution of hydraulic conductivity in shallow unconsolidated aquifers. The field method uses fluid injection ports and pressure transducers in a hollow auger that measure the hydraulic head outside the auger at several distances from the injection point. A constant injection rate is maintained for a duration time sufficient for the system to become steady state. Exploiting the analogy between electrical resistivity in geophysics and hydraulic flow two methods are used to estimate conductivity with depth: a half-space model based on spherical flow from a point injection at each measurement site, and a one-dimensional inversion of an entire dataset.
The injection methodology, conducted in three separate drilling operations, was investigated for repeatability, reproducibility, linearity, and for different injection sources. Repeatability tests, conducted at 10 levels, demonstrated standard deviations of generally less than 10%. Reproducibility tests conducted in three, closely spaced drilling operations generally showed a standard deviation of less than 20%, which is probably due to lateral variations in hydraulic conductivity. Linearity tests, made to determine dependency on flow rates, showed no indication of a flow rate bias. In order to obtain estimates of the hydraulic conductivity by an independent means, a series of measurements were made by injecting water through screens installed at two separate depths in a monitoring pipe near the measurement site. These estimates differed from the corresponding estimates obtained by injection in the hollow auger by a factor of less than 3.5, which can be attributed to variations in geology and the inaccurate estimates of the distance between the measurement and the injection sites at depth. 相似文献
We observed the onshore migration (3.5 m/day) of a nearshore sandbar at Tairua Beach, New Zealand during 4 days of low-energy wave conditions. The morphological observations, together with concurrent measurements of waves and suspended sediment concentrations, were used to test a coupled, wave-averaged, cross-shore model. Because of the coarse bed material and the relatively low-energy conditions, the contribution of the suspended transport to the total transport was predicted and observed to be negligible. The model predicted the bar to move onshore because of the feedback between near-bed wave skewness, bedload, and the sandbar under weakly to non-breaking conditions at high tide. The predicted bathymetric evolution contrasts, however, with the observations that the bar migrated onshore predominantly at low tide. Also, the model flattened the bar, while in the observations the sandbar retained its steep landward-facing flank. A comparison between available observations and numerical simulations suggests that onshore propagating surf zone bores in very shallow water (< 0.25 m) may have been responsible for most of the observed bar behaviour. These processes are missing from the applied model and, given that the observed conditions can be considered typical of very shallow sandbars, highlight a priority for further field study and model development. The possibility that the excess water transported by the bores across the bar was channelled alongshore to near-by rip-channels further implies that traditional cross-shore measures to judge the applicability of a cross-shore morphodynamic model may be misleading. 相似文献
Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m3/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms. 相似文献
Macroalgal blooms of Hypnea musciformis and Ulvafasciata in coastal waters of Maui only occur in areas of substantial anthropogenic nutrient input, sources of which include wastewater effluent via injection wells, leaking cesspools and agricultural fertilizers. Algal δ15N signatures were used to map anthropogenic nitrogen through coastal surveys (island-wide and fine-scale) and algal deployments along nearshore and offshore gradients. Algal δ15N values of 9.8‰ and 2.0-3.5‰ in Waiehu and across the north-central coast, respectively, suggest that cesspool and agricultural nitrogen reached the respective adjacent coastlines. Effluent was detected in areas proximal to the Wastewater Reclamation Facilities (WWRF) operating Class V injection wells in Lahaina, Kihei and Kahului through elevated algal δ15N values (17.8-50.1‰). From 1997 to 2008, the three WWRFs injected an estimated total volume of 193 million cubic meters (51 billion gallons) of effluent with a nitrogen mass of 1.74 million kilograms (3.84 million pounds). 相似文献
A new methodology is developed in assessing environmental impacts of desalination plants discharging brine into the ground.
The main environmental problem of the desalination of seawater is the brine disposal. The brine is commonly discharged into
the sea or injected into a saline aquifer. In the case of injection into the ground, it is necessary to design a disposal
system in a way that respects the environment and is sustainable. Laboratory and computational methods have been utilized
to simulate the unsteady three-dimensional (3D) phenomena of subsurface brine disposal. The computational software used is
SEAWAT, which is a 3D unsteady variable-density flow simulation model. The model is first used to simulate the laboratory
results, and good agreement is achieved. Then, hypothetical problems are designed and simulated of groundwater extraction
and brine disposal by desalination stations. The major purpose of these hypothetical problems is to delineate a methodology
and to create design charts for design and management of production and injection well fields for coastal desalination plants.
Several design charts have been developed with 36 scenarios for two well configurations created by four design parameters:
relative salt concentration (RSC), production and injection rates (Qd, Qr), well spacing (S), and simulation period (T). 相似文献
The Salalah central sewage treatment plant has been designed to treat 20,000 m3/day at the first stage and two further stages to double the initial capacity. The plant currently (2005) treats more than
15,000 m3/day effluents to a tertiary level, and after chlorination phase, the effluents are recharged into tube wells in a line parallel
to the coast. The process aims to help stabilize the seawater interface and a part to be recovered from hand-dug wells/boreholes
further inland and downstream. A three-dimensional flow and solute advection transport model was developed to assess the effectiveness
of the proposed recharge scheme and to track the solute transport with respect to the design system. The advection transport
model predicted that in 2020 the maximum pathlines of the injection fluids would reach the abstraction wells that are located
600 m, southward of the injection bores in about 1-year travel time in the case of the no-management interference and more
than that southward under management interference. The developed flow predicted the wedge of the saline intrusion in 2019
is tracked up to 2.7 and 3.4 km from the shoreline with the injection and without the injection, respectively under constant
underflow. The injection scheme is effective in pushing back the saline zone front by 700 m. This study argues that the treated
wastewater would help to increase the water levels at the vicinity of the injection line and to reduce the influence of saline
inflows from the coast. The reclaimed sewage recharge scheme is examined in the case of the Salalah coastal aquifer using
groundwater simulation, which can also be applied to other regions with similar conditions. 相似文献