Seasonal Water Table Research Articles

The relationship of fine-resolution, multi-proxy palaeoclimate records to meteorological data at Fågelmossen, Värmland, Sweden and the implications for the debate on climate drivers of the peat-based record

Fluctuations in bog surface wetness (BSW) over an 86-year period were reconstructed using fine-resolution analyses of testate amoebae, plant macrofossils and peat humification from Fågelmossen, an ombrotrophic bog in western Sweden. Results were compared with local instrumental temperature and precipitation data and reconstructed values of total seasonal water table deficit using an age–depth model based on spheroidal carbonaceous particle analysis and a historically dated, geochemically typed tephra layer. Statistically significant correlations between decadal means of the fine-resolution data and climate parameters lend support to the notion that a climate signal may be present in those data, enhancing confidence in the peat-based record to address pressing research questions on abrupt climate change. All three proxies were correlated most significantly with annual precipitation, plant macrofossils only when correlations were time-lagged by 10 years, suggesting that precipitation, rather than temperature, is the primary driver of the BSW record at Fågelmossen. However, plant macrofossils also correlated significantly with annual temperature when time-lagged by 10 years. The correlation of individual physical and biological proxies with climate parameters on different time-scales, coupled with the significant correlation of plant macrofossil results with annual temperature in addition to annual precipitation, may bring into question the use of composite curves of BSW that combine results from multi-proxy studies. The correlations reported here partly support those from other similar studies, but highlight that regional variability may be greater than previously hypothesised and that it may not be possible to apply a single explanation of climatic forcing where bog surface wetness reconstructions are concerned.

Evaluation of Soil Colors as Indicators of the Seasonal High Water Table in Coastal North Carolina

Evaluation of Soil Colors as Indicators of the Seasonal High Water Table in Coastal North Carolina

Evaluation of on-site wastewater system Escherichia coli contributions to shallow groundwater in coastal North Carolina

The study goal was to determine if on-site wastewater systems (OSWWS) installed in coastal areas were effective at reducing indicator bacteria densities before discharge to groundwater. Groundwater Escherichia coli (E. coli) densities and groundwater levels adjacent to 16 OSWWS in three different soil groups (sand, sandy loam, and sandy clay loam) were monitored and compared to background groundwater conditions on four occasions between March 2007 and February 2008 in coastal North Carolina. Groundwater beneath OSWWS had significantly (p≤0.05) lower densities of E. coli than septic tank effluent, but significantly higher densities of E. coli than background conditions for each soil type. Twenty three percent of all groundwater samples near OSWWS had E. coli densities that exceeded the EPA freshwater contact standards (single sample 235 cfu/100 mL) for surface waters. Groundwater E. coli densities near OSWWS were highest during shallow water table periods. The results indicate that increasing the required vertical separation distance from drainfield trenches to seasonal high water table could improve shallow groundwater quality.

Controls on groundwater nitrogen contributions from on-site wastewater systems in coastal North Carolina

The goal of this study was to evaluate the influence of soil type and separation distance to water table on dissolved inorganic nitrogen concentrations in groundwater adjacent to on-site wastewater systems. Groundwater nitrogen species (NO3--N and NH4+-N) and groundwater levels adjacent to 16 on-site systems in three different soil groups (group I- sand, group II- coarse loams and group III -sandy clay loams) were monitored for 15 months (January 2007-March 2008) in coastal North Carolina. On-site systems in soil group I had the highest concentrations of dissolved inorganic nitrogen (median of 18.9 mg/L) in groundwater, and most frequently (mean 61%) exceeded 10 mg/L, followed by systems in soil group II (11.0 mg/L, 50%) and soil group III (2.6 mg/L, 9%), respectively. Groundwater NH4+-N concentrations near on-site systems in soil groups I and II that maintained a 60+cm separation to the seasonal high water table were 4 mg/L lower in relation to systems that had <60 cm separation, but median NO3--N concentrations were 6.5 mg/L higher. On-site systems in group I and II soils are prone to groundwater nitrogen loading with separation distance often controlling the nitrogen speciation in groundwater near on-site systems.

Linking root production to aboveground plant characteristics and water table in a temperate bog

Fine root production and its relationships to aboveground plant components and environmental drivers such as water table have been poorly quantified in peatland ecosystems, despite being the primary input of labile carbon to peat soils. We studied the relationship between fine root (< 1 mm) production, aboveground biomass and growing season water table within an ombrotrophic peatland in eastern Ontario. We installed 80 in-growth bags (10 cm diameter) to measure fine root production over the full range of 40 cm in water table depth. The point-intersect method was used to estimate peak aboveground biomass components (total, leaf and stem) for the 0.36 m2 area surrounding each in-growth bag. Mean fine root production was 108 ± 71 g m-2 y-1 and was strongly related to both aboveground biomass and water table. Linear regression analysis showed strong allometric relationships between fine root production and aboveground biomass for shrubs (r 2 = 0.61, p < 0.001), suggesting that fine root production estimates can be approximated using aboveground biomass data. Water table had a significant effect on the allocation of biomass to fine roots, leaves and stems with a deeper water table significantly increasing both fine root production at depth and at each depth increment. Shrub biomass allocation to leaves and stems similarly shifted, with greater investment in stems relative to leaves with a deeper water table. As a result, greater fine root biomass was produced per unit leaf biomass in areas with a deeper water table, illustrating an important tradeoff between leaf and fine root tissues in drier conditions. Our results indicate that any drop in water table will likely increase aboveground biomass stocks and the influx of labile carbon to peat soils via fine roots and leaves.

Estimating Trace Element Availability in Soils with a Seasonal Water Table using Commercially Available Protocols

The soil accumulation of metals and other elements as a result of human activities is a global concern. This investigation involves the use of commercially available extractions to estimate elemental abundance and availability. The need exists, especially in poor nations, to have cost-effective analytical capabilities to perform an initial screening of a soil resource to determine if a problem exists. Three extraction protocols are proposed: (i) an aqua regia digestion to estimate a baseline geochemistry, (ii) a pyrophosphate extraction to estimate elemental abundances associated with the soil organic fraction, and (iii) a water extraction to estimate the most available fraction. If the soil resource is impacted, then more refined and traditional methods are required to document the extent of impact for possible remediation. The three extraction protocols were applied to soils with little impact to illustrate the assessment potential for selected metals and p-block elements.

Resupply mechanism to a contaminated aquifer: A laboratory study of U(VI) desorption from capillary fringe sediments

Contaminated capillary fringe sediments are believed to function as long-term source of U(VI) to Hanford’s 300 Area groundwater uranium plume that discharges to the Columbia River. The deep vadose zone at this site experiences seasonal water table elevation and water compositional changes in response to Columbia River stage. Batch and column desorption experiments of U(VI) were performed on two mildly contaminated sediments from this system that vary in hydrologic position to ascertain their U(VI) release behavior and factors controlling it. Solid phase characterization of the sediments was performed to identify mineralogic and chemical factors controlling U(VI) desorption. Low adsorbed U(VI) concentrations prevented spectroscopic analysis. The desorption behavior of U(VI) was different for the two sediments in spite of similar chemical and textural characteristics, and non-carbonate mineralogy. Adsorption strength and sorbed U(VI) lability was higher in the near-river sediment. The inland sediment displayed low sorbed U(VI) lability (∼10%) and measurable solid-phase carbonate content. Kinetic desorption was observed that was attributed to regeneration of labile U(VI) in the near river sediment, and carbonate mineral dissolution in the inland sediment. The desorption reaction was best described as an equilibrium surface complexation reaction. The noted differences in desorption behavior appear to result from U(VI) contamination and hydrologic history, as well as sediment carbonate content. Insights are provided on the dynamic adsorption/desorption behavior of contaminants in linked groundwater–river systems.

Primary sink and source of geogenic arsenic in sedimentary aquifers in the southern Choushui River alluvial fan, Taiwan

Abstract This work characterized the sink and source/mobility of As in the As-affected sedimentary aquifers of the southern Choushui River alluvial fan, central Taiwan. Major mineral phases and chemical components were determined by XRD and X-ray photoelectron spectroscopy (XPS). The partitioning of As and Fe among cores were determined by sequential extraction. Based on XPS results, the primary forms of Fe were hematite, goethite and magnetite. Sequential extraction data and the XRF analysis indicated that Fe oxyhydroxides and sulfides were likely to be the major sinks of As, particularly in the distal-fan. Furthermore, Fe oxyhydroxides retained higher As contents than As-bearing sulfides. The reductive dissolution of Fe oxyhydroxides, which accompanied high levels of HCO 3 - and NH 4 + concentrations, was likely the principal release mechanism of As into groundwater in this area. The dual roles of Fe oxyhydroxides which are governed by the local redox condition act as a sink and source in the aquifer. Ionic replacement by PO 4 3 - and HCO 3 - along with seasonal water table fluctuation, caused by monsoons and excessive pumping, contributed specific parts of As in the groundwater. The findings can be used to account for the inconsistency between Fe and As concentrations observed in groundwater.

Bottomland Forests in the Lower Mississippi Alluvial Valley Associated with the Endangered Lindera melissifolia

Forest canopy and subcanopy data were collected from and compared among five disjunct bottomland hardwood forests in the Lower Mississippi Alluvial Valley, each with known occurrence of a population of the federally endangered shrub Lindera melissifolia. All study sites are cut-over forests, underlain by hydric soils, and have a seasonal high water table. Canopy and subcanopy species are similar among sites, but species differ in relative importance, and flood tolerant tree species exceed that of flood intolerant species. Distribution of L. melissifolia colonies within each study site was not associated with mean tree density or d.b.h. Forest composition and structure at each study site reflect hydrologic regime, topography, historical disturbance, and an absence of recent disturbance. Results of this study provide a quantitative description of bottomland forests that currently sustain L. melissifolia populations. This information may be utilized for development of forest management plans aimed at ensuring continued sustainability of existing L. melissifolia populations and assessing other bottomland hardwood forests for potential reintroduction of this endangered species.

Evaluation of Water Quality Impacts of On-site Treatment and Disposal Systems on Urban Coastal Waters

Questions have been raised about the impact of onsite sewage treatment and disposal systems (OSTDS) on adjacent water bodies, particularly in coastal areas. If OSTDS are not properly sited and maintained, they pose a potential risk to public health and may contribute toward degradation of the receiving water body. To quantify the pollutant loading contributions from OSTDS located adjacent to coastal canals, two similar single-family residential neighborhoods were evaluated. One was connected to the sanitary sewer network (Hollywood, FL) and the other was served exclusively by septic tanks (Dania Beach, FL). Water quality sampling, focusing on nutrient and pathogen indicators, was conducted at the paired sites during the seasonal high water table (SHWT) and seasonal low water table (SLWT) events. During the SHWT, measured canal water quality, in terms of nutrient (i.e. nitrate) and microbial pathogen indicators in the adjacent areas appeared to be impacted by OSTDS. However, during the SLWT, no obvious impacts attributable to the septic tanks were detected. This suggests that the OSTDS may operate properly when the water table is low, but that the contributions by OSTDS to coastal pollutant loading may be quantifiable during certain portions of the calendar year when the ground water table elevation is relatively high, although the impact on the downstream marine environment is uncertain as a result of tidal dilution and lack of offshore study.

Linking fragipans, perched water tables, and catchment-scale hydrological processes

Abstract Soils with very slowly permeable fragipans and fragipan-like argillic horizons are extensive throughout the Palouse Region of northern Idaho and eastern Washington, USA. These soils develop seasonal perched water tables (PWTs) under the xeric moisture regime of the region. The objective of this study was to utilize a hydropedology approach to examine the linkages between fragipans, PWTs, and catchment-scale hydrological processes such as soil water storage, runoff, and lateral throughflow. A 1.7-ha catchment dominated by Fragixeralfs (Fragic Luvisols) was instrumented with 135 automated shallow wells to monitor PWTs. Soil water content was measured with water content reflectometry probes, and catchment outflow was measured with a flume. A 35 m × 18 m plot was isolated hydrologically from the surrounding hillslope using tile drains and plastic sheeting to measure perched water outflow. Results show that during the wet winter and spring months, the transition from unsaturated to saturated conditions is accompanied by changes in volumetric water storage of only 4–5%. PWT levels are at the surface of ∼ 26–45% of the catchment soils during periods of high rainfall and snowmelt, thereby generating saturation-excess surface runoff from hillslopes. Observed solute movement via subsurface flow is very rapid and ranges between 2.9 and 18.7 m d − 1 when PWTs are maintained in more-permeable Ap and Bw horizons. Subsurface lateral flow accounts for as much as 90% of the incident precipitation and snowmelt during early spring. Data indicate that the relatively shallow depth to the fragipans and high K sat in surface soil layers combine to create a very flashy hydrological system characterized by considerable temporal and spatial variation in patterns of saturation-excess runoff.

EXPERIMENTAL AND THEORETICAL INVESTIGATION OF LNAPL MOVEMENT IN STRATIFIED MEDIA DURING SOIL REMEDIATION

The saturation distribution and clean up efficiency of light non-aqueous phase liquid (LNAPL) in the strata beneath the earth has been the subject of many studies. Better understanding of LNAPL infiltration into layered soil is important for the effective design of remediation strategies. The objective of this study was to simulate LNAPL movement in homogenous and stratified porous media using gravity assisted inert gas injection (GAIGI) process as a cleaning technique. We used homogeneous and layered sandpacked transparent models that allows for visual observation of LNAPL movement in order to study LNAPL redistribution in a layered porous medium. Pore volume, porosity, absolute permeability, connate water saturation, and oil saturation of the models were determined experimentally. Seasonal water table movement and contaminated zone were established and then, under GAIGI process, clean up efficiency was determined. The downward displacement of LNAPL by gas drive resulted in very high LNAPL clean up efficiency. Using the contaminant production history in the homogeneous model, the LNAPL relative permeability was calculated and the results were extended to layered media. The numerical multi-phase flow model in porous media was validated with regard to the experimental results. This model is able to adequately reproduce the experimental LNAPL saturation profile and clean up efficiency.

Groundwater noble gas, age, and temperature signatures in an Alpine watershed: Valuable tools in conceptual model development

Bedrock groundwater in alpine watersheds is poorly understood, mainly because of a scarcity of wells in alpine settings. Groundwater noble gas, age, and temperature data were collected from springs and wells with depths of 3–342 m in Handcart Gulch, an alpine watershed in Colorado. Temperature profiles indicate active groundwater circulation to a maximum depth (aquifer thickness) of about 200 m, or about 150 m below the water table. Dissolved noble gas data show unusually high excess air concentrations (&gt;0.02 cm3 STP/g, ΔNe &gt; 170%) in the bedrock, consistent with unusually large seasonal water table fluctuations (up to 50 m) observed in the upper part of the watershed. Apparent 3H/3He ages are positively correlated with sample depth and excess air concentrations. Integrated samples were collected from artesian bedrock wells near the trunk stream and are assumed to approximate flow‐weighted samples reflecting bedrock aquifer mean residence times. Exponential mean ages for these integrated samples are remarkably consistent along the stream, four of five being from 8 to 11 years. The tracer data in combination with other hydrologic and geologic data support a relatively simple conceptual model of groundwater flow in the watershed in which (1) permeability is primarily a function of depth; (2) water table fluctuations increase with distance from the stream; and (3) recharge, aquifer thickness, and porosity are relatively uniform throughout the watershed in spite of the geological complexity of the Proterozoic crystalline rocks that underlie it.

Hydrological changes following restoration of the Bois-des-Bel Peatland, Quebec, 1999–2002

Restoration efforts at peatlands drained for peat extraction attempt to return the hydrological conditions necessary for Sphagnum moss regeneration. One year of pre-restoration monitoring (1999) and three years of post restoration monitoring were done at the Bois-des-Bel peatland near Riviere-du-Loup, Quebec, to evaluate hydrological changes that occurred at a managed section (restored site) relative to an adjacent abandoned section of the same peatland (unrestored site). Restored site evaporation was 74%, 74%, and 98% of unrestored site evaporation in 2000, 2001, and 2002, while runoff at the restored site was 83%, 30%, and 12% of unrestored site runoff over the same period. Seasonal soil volume change (swelling and shrinking of the peat) was evident at the restored site indicating rewetting of the peat profile despite the prolonged period between site abandonment and the initiation of the restoration measures (19 years). Site rewetting may have benefited from the relatively deep layer of residual peat (around 1.5 m). Higher seasonal mean water table and soil moisture were observed at the restored site relative to the unrestored site in 2000 through 2002 along with increased seasonal variability at the former location. Mean soil–water pressure was also higher than at the unrestored site and the range decreased, both spatially and on a seasonal and daily basis. The restoration techniques contributed to the recovery of hydrological conditions necessary for Sphagnum recolonization, though successful application at different sites may be limited by specific peat and climate characteristics.

English

Upward migration of either acidity or sodium is often cited as a concern when soil covers are placed over mine wastes. Regulatory concerns associated with upward migration are commonly used to justify capillary barriers or increased cover thickness. Upward migration of soluble salts is known to occur in soils with permanent or seasonal water tables near the soil surface and is a common problem in agricultural contexts. Short-term studies conducted at mine reclamation sites where changes in pH or salinity occurred at the contact between the soil cover and waste have been used to infer that upward migration would ultimately degrade cover quality. Thus, we investigated the potential for upward migration in soil covers overlying acid mill tailing and coal spoils 20 to 25 years after cover placement and revegetation. The soils were sampled and analyzed at discreet intervals above the soil-waste contact to assess upward migration. Changes in soil pH and/or extractable constituents were inconsistent among sites and varied from about 2 to 10 cm above the soil cover-waste contact. Field observations suggest that physical mixing of the cover and tailing during construction, rather than advection, accounted for acidification of the basal soil cover. Based on evidence from our investigations and an understanding of soil developmental processes in arid-regions, we conclude that upward migration of constituents from wastes is not a time-transgressive process that will result in cover degradation in arid and semi-arid regions where permanent or seasonal water tables occur well below the soil surface. Finally, we consider the changes in chemistry at the soil cover above the waste interface to be biologically insignificant.

Combined estimation of specific yield and natural recharge in a semi-arid groundwater basin with irrigated agriculture

A water budget approach is developed to jointly estimate specific yield and natural recharge in an unconfined aquifer with significant seasonal water table fluctuations. Water table fluctuations are due to distinct seasonality in groundwater recharge. The separation of the hydrologic year into two (or more) extended seasons of recharge (wet season) and no-recharge (dry season) with accompanying changes in water table allows for a split use of the water table fluctuation (WTF) method, first to estimate specific yield from the water table drop during the dry season (no recharge) and, second, to estimate recharge from the water table rise during the wet season, after considering all other water budget components explicitly. The latter includes explicit computation of groundwater storage with the WTF method. The application of the WTF method requires a large number of water level measurements throughout the unconfined aquifer before and after each season. The advantage of the method is that specific yield and recharge are estimated at the scale of interest to basin hydrologic studies and that the method requires no extensive in situ instrumentation network. Here, the method is demonstrated through a case study in a fractured hard-rock aquifer subject to intensive groundwater pumping for irrigation purposes.

Soil Morphology‐Water Table Cumulative Duration Relationships in Southern New England

Although redoximorphic features (RMFs) are commonly used in place of direct observation to estimate the depth of the seasonal high water table (SHWT), little is known about the relationships between RMFs and the duration of the water table. The objective of this study was to gain a better understanding of how the expression of RMFs relates to the depth and duration of the water table in moderately well‐drained soils of southern New England. The 20 soils studied included Dystrudepts, Quartzipsamments, and Psammaquents; of these, 17 met the criteria for Oxyaquic (8) or Aquic (9) subgroup classification. Water table levels were monitored for 18 mo from February to July of the following year to compare the depth and cumulative duration of the water table (cumulative saturation) to RMFs within soil horizons. Average seasonal high water table level (ASHWT) was correlated (p &lt; 0.05) to the depth of the first loamy horizon with &gt;2% RMFs (r2 = 0.65–0.72). Water table levels occurred within horizons with no RMFs for as much as 13% of the 18 mo study period. Mean cumulative saturation for soils with textures finer than loamy sand ranged from 3% for horizons with no RMFs to 36% for horizons with a depleted matrix. For horizons with textures of loamy sand and coarser, the mean cumulative saturation ranged from 8% for horizons with no RMFs to 45% for horizons with &gt;2% depletions. (Percentage of cumulative saturation would have likely been less if we monitored for a full 2 yr, as the late summer and fall of the second year were not monitored.) Our results suggest that the abundance of RMFs increases as the percentage of time the water table is present within a horizon increases. Additionally, coarse‐textured horizons are less expressive in regards to RMF abundance than are loamy‐textured horizons with similar cumulative saturation. For land‐use decisions, soil morphology should be used to provide both an estimate of the depths of a defined SHWT and cumulative saturation.

Borehole time domain reflectometry in layered sandstone: Impact of measurement technique on vadose zone process identification

The hydraulic behaviour of the vadose zone of a layered sandstone aquifer has been investigated using borehole-based Time Domain Reflectometry (TDR). Both a commercially available portable packer TDR system (TRIME-B3L Borehole Packer Probe) and specially designed borehole-emplaced TDR probes were used to monitor seasonal fluctuations in water content in the vadose zone of a layered sandstone over 1 year under natural rainfall loading. The data show that the vadose zone contains seasonal perched water tables that form when downward percolating water reaches layers of fine grained sandstone and siltstone and causes local saturation. The formation of perched water tables is likely to lead to lateral flow bypassing the less permeable, finer layers. This contrasts with behaviour inferred from previous studies of the same aquifer that used borehole radar and resistivity, which suggested its vadose zone behaviour was characterized by uniform downwards migration of wetting fronts. To investigate the impact of measurement technique on observed response, the TDR data reported here were used to produce simulated zero offset profile (ZOP) borehole radar responses. This simulation confirmed the limited ability of ZOP borehole radar to detect key vadose zone processes, because the phenomenon of critical refraction minimizes the sensitivity of the results to high water content layers. The ability of the resistivity method to detect perched water table responses is also limited, because of the relatively large sampling volume of the technique. The study illustrates that inappropriate technique selection results in hydrological process mis-identification, with serious consequences for the usefulness of data in hydrological modeling.

Groundwater quality under the influence of spent mushroom substrate weathering

Nitrate and other solutes resulting from field-weathering of spent mushroom substrate (SMS) percolate into underlying soils and may migrate to groundwater. A field trial was conducted to investigate the potential influences of SMS weathering on groundwater quality. Spent mushroom substrate was deposited at 90 and 150 cm pile depths over a Typic Hapludult and weathered for 2 years. Eight casing wells were installed around the SMS piles to monitor the quality changes of groundwater with a high seasonal water table of 760 cm below the surface. Although leachate solutes had moved more than 200 cm deep in soil from the surface, no significant changes of groundwater quality caused by SMS weathering were observed even one year after removal of the SMS piles (3 years total). The groundwater had pH, electrical conductivity (EC) and dissolved organic carbon (DOC) of 4.3-5.7, 0.2-0.3 dS m(-1) and 0.7-2.2 mg L(-1), respectively. The major inorganic ions were Mg(2+), Ca(2+), Na(+), Cl(-), SO(4)(2-) and NO(3)(-), with a concentration range of 2.5-68.3 mg L(-1). The results suggest that SMS leachate solutes migrated fairly slow in deep subsurface soils of the experimental field. Considering that leachate solutes may move several meters in soil through preferential flow channels, weathering of SMS in fields with a high seasonal groundwater table >or=5 m below the ground is recommended. Conservatively, SMS weathering should be conducted on compact surfaces and leachate be collected and reused as liquid fertilizers.

04/03063 Evaluation of bioventing on a gasoline—ethanolcontaminated undisturbed residual soil: Österreicher-Cunha, P. et al. Journal of Hazardous Materials, 2004,110, (1–3), 63–76

Several in-well aeration (IWA) technologies have been used since the early 1990s, but few field studies have been performed to evaluate the extent of water circulation around IWA systems. In this study, 27 discrete monitoring points (MPs) were installed at a gasoline-contaminated site to assess the efficacy of IWA. Pressure transducers and dissolved oxygen (DO) probes were sealed into the MPs, allowing them to be used to characterize subsurface changes in total head and DO with depth, distance and orientation from a central injection well. No change in DO or in hydrocarbon total mass or distribution occurred across the site during two trials (41 and 20 days) of the system. Water level fluctuations during the trials were similar in all MPs, and were due to seasonal water table changes and rainfall events. No circulation cell was established around the IWA well after 41 days of operation, and the impact of the well extended less than 90 cm from it. Groundwater only circulated through the sand pack around the well. Little, if any, recharge occurred through the lower screen. Silt accumulated in the well, limiting its operation time, even with a fabric filter sock over the lower screen. Obviously, IWA was ineffective at this site, probably because the horizontal hydraulic conductivity (Kh) of the soil opposite the lower screen was low (0.09 cm per day) and because the distance between the two screens was short relative to the borehole radius. Long remediation times would likely make IWA unattractive at this or other sites where the Kh of the soil is so low that the air injection rate would have to be low to prevent blowing the well dry.