Evaluation of Extensive Secondary Maximum Contaminant Level Exceedances Following Remediation by In Situ Chemical Oxidation

In situ chemical oxidation (ISCO) with activated persulfate is commonly used for the remediation of petroleum impacted soil and groundwater because of its proven efficiency and the perception that reaction end products are completely innocuous. While the reaction products are less hazardous compared to the contaminants being treated, they may inadvertently prolong site closure in areas that have adopted the U.S. Environmental Protection Agency (EPA) Secondary Maximum Contaminant Levels (SMCLs) as enforceable standards. This study examines the occurrence and persistence of iron, manganese, sulfate, sodium, and total dissolved solids (TDS) in groundwater following persulfate ISCO. The concentrations of these chemicals were observed remaining above their respective regulatory criteria almost 3 years following the chemical application. Background concentrations and mobilization due to the petroleum contamination and ISCO application are also evaluated. Baseline sampling revealed substantially higher iron and manganese concentrations inside the plume area compared to the upgradient and downgradient wells suggesting mobilization due to redox reactions occurring inside of the plume. Iron was not a component in the applied chemical formula, yet the iron concentration spiked by 366% in the key monitoring well during the first post-remediation monitoring event. Ionic interactions between the ISCO amendment and native soils are believed to be responsible for displacing significant quantities of iron from the soil. Sulfate, sodium, and TDS exceedances are primarily associated with decomposition products of the ISCO amendments. The iron, manganese, sulfate, sodium, and TDS concentrations are trending downward over time, but still exceed regulatory criteria or pre-ISCO concentrations.     

Precipitation types in winter storms

The characteristics of and the evolution between snow, rain, ice pellets, and freezing rain are discussed. Precipitation type and the nature of its size distribution and extent are related to the melting behaviour of snow. Model calculations of this melting show the progression of precipitation type from freezing rain to ice pellets and finally to snow, as melting systematically erodes an upper level inversion within about 5 h for a precipitation rate of 1mm h^–1. The increase in temperature of the low level subfreezing region associated with ice pellet formation (up to 1°C) should furthermore be detectable. These phase transitions between the various precipitation types, as affected by atmospheric cooling by melting, are predicted to occur over mesoscale distances.     

Characteristics and distribution patterns of snow and meteoric ice in the Weddell Sea and their contribution to the mass balance of sea ice

Based on snow- and ice-thickness measurements at >11 000 points augmented by snow- and icecore studies during 4 expeditions from 1986 - 92 in the Weddell Sea, we describe characteristics and distribution patterns of snow and meteoric ice and assess their importance for the mass balance of sea ice. For first-year ice (FY) in the central and eastern Weddell Sea, mean snow depth amounts to 0.16 m (mean ice thickness 0.75 m) compared to 0.53 m (mean ice thickness 1.70 m) for second-year ice (SY) in the northwestern Weddell Sea. Ridged ice retains a thicker snow cover than level ice, with ice thickness and snow depth negatively correlated for the latter, most likely due to aeolian redistribution. During the different expeditions, 8, 15, 17 and 40% of all drill holes exhibited negative freeboard. As a result of flooding and brine seepage into the snow pack, snow salinities averaged 4‰. Through ¹⁸O measurements the distribution of meteoric ice (i.e. precipitation) in the sea-ice cover was assessed. Roughly 4% of the total ice thickness consist of meteoric ice (FY 3%, SY 5%). With a mean density of 290 kg/m³, the snow cover itself contributes 8% to total ice mass (7% FY, 11% SY). Analysis of ¹⁸O in snow indicates a local maximum in accumulation in the 65 to 75^S latitude zone. Hydrogen peroxide in the snow has proven useful as a temporal tracer and for identification of second-year floes. Drawing on accumulation data from stations at the Weddell Sea coast, it becomes clear that the onset of ice growth is important for the evolution of ice thickness and the interaction between ice and snow. Loss of snow to leads due to wind drift may be considerable, yet is reduced owing to metamorphic processes in the snow column. This is confirmed by a comparison of accumulation data from coastal stations and from snow depths over sea ice. Temporal and spatial accumulation patterns of snow are shown to be important in controlling the sea-ice cover evolution.     

An examination of snow redistribution over smooth land‐fast sea ice

An understanding of temporal evolution of snow on sea ice at different spatial scales is essential for improvement of snow parameterization in sea ice models. One of the problems we face, however, is that long‐term climate data are routinely available for land and not for sea ice. In this paper, we examine the temporal evolution of snow over smooth land‐fast first‐year sea ice using observational and modelled data. Changes in probability density functions indicate that depositional and drifting events control the evolution of snow distribution. Geostatistical analysis suggests that snowdrifts increased over the study period, and the orientation was related to the meteorological conditions. At the microscale, the temporal evolution of the snowdrifts was a product of infilling in the valleys between drifts. Results using two shore‐based climate reporting stations (Paulatuk and Tuktoyuktuk, NWT) suggest that on‐ice air temperature and relative humidity can be estimated using air temperature recorded at either station. Wind speed, direction and precipitation on ice cannot be accurately estimated using meteorological data from either station. The temporal evolution of snow distribution over smooth land‐fast sea ice was modelled using SnowModel and four different forcing regimes. The results from these model runs indicate a lack of agreement between observed distribution and model outputs. The reasons for these results are lack of meteorological measurements prior to the end of January, lack of spatially adequate surface topography and discrepancies between meteorological variables on land and ice. Copyright © 2009 John Wiley & Sons, Ltd.     

Chemical stratification and stability of meromictic lakes in the Upper Romerike district

A number of lakes in Southeast Norway have developed biogenic meromixis and have typically also considerable concentrations of dissolved iron and manganese in the bottom waters. Eight such lakes are described. Products of biological decomposition like carbon dioxide, methane and some inorganic salts gave a difference in density between mixo- and monimolimnion and hence chemical stability to the lakes. The concentration of iron and manganese gave minor contributions to the density gradients, and these substances are regarded as less important for the stability because of their reduced solubility under oxic conditions. Quantitative expressions of wind influence on lake surfaces were obtained by calculation of the work of the wind during the heating season. These values were low compared with a more exposed lake in the same region. Water movements generated by the wind have eroding effects on the chemical stratification only during short periods of homothermy before icelaying. During the rest of the year the monimolimnion is protected by either thermal stratification or ice cover. During the autumnal partial circulation a substantial reduction in chemical stability took place. For some of the lakes it is assumed that full circulation may take place in years with favourable weather conditions.     

A note on the characteristics and possible origins of desert varnishes from southeast Morocco

Two substrate-controlled varnish types were identified from arid southeast Morocco: (1) patchy varnish interspersed with ‘silica glaze’ on silicified limestone and (2) a complete varnish cover on partially-silicified limestone. Electron probe microanalysis was used in conjunction with scanning electron microscopy to investigate their chemical composition. In both instances, varnishes are predominantly silica and iron-rich with localized concentrations of manganese. Inorganic fixation of iron and manganese is the preferred explanation, with manganese and iron derived predominantly from external sources—possibly wind-blown dust. Some iron and silica may also be derived by outward migration from within the substrate, particularly on partially silicified limestone.     

Ice‐cover variability on shallow lakes at high latitudes: model simulations and observations

A one‐dimensional thermodynamic model for simulating lake‐ice phenology is presented and evaluated. The model can be driven with observed daily or hourly atmospheric forcing of air temperature, relative humidity, wind speed, cloud amount and snowfall. In addition to computing the energy balance components, key model output includes the temperature profile at an arbitrary number of levels within the ice/snow (or the water temperature if there is no ice) and ice thickness (clear ice and snow‐ice) on a daily basis, as well as freeze‐up and break‐up dates. The lake‐ice model is used to simulate ice‐growth processes on shallow lakes in arctic, sub‐arctic, and high‐boreal forest environments. Model output is compared with field and remote sensing observations gathered over several ice seasons. Simulated ice thickness, including snow‐ice formation, compares favourably with field measurements. Ice‐on and ice‐off dates are also well simulated when compared with field and satellite observations, with a mean absolute difference of 2 days. Model simulations and observations illustrate the key role that snow cover plays on the seasonal evolution of ice thickness and the timing of spring break‐up. It is also shown that lake morphometry, depth in particular, is a determinant of ice‐off dates for shallow lakes at high latitudes. Copyright © 2003 John Wiley & Sons, Ltd.     

Trace element and major ion concentrations and dynamics in glacier snow and melt: Eliot Glacier,Oregon Cascades

We present concentrations of environmentally available (unfiltered acidified 2% v/v HNO₃) As, Cu, Cd, Pb, V, Sr, and major ions including Ca²⁺, Cl^?, and SO₄^2? in a July 2005 and a March 2006 shallow snow profile from the lower Eliot Glacier, Mount Hood, Oregon, and its proglacial stream, Eliot Creek. Low enrichment factors (EF) with respect to crustal averages suggests that in fresh March 2006 snow environmentally available elements are derived primarily from lithogenic sources. Soluble salts occurred in lower and less variable concentrations in July 2005 snow than March 2006. Conversely, environmentally available trace elements occurred in greater and more variable concentrations in July 2005 than March 2006 snow. Unlike major solutes, particulate‐associated trace elements are not readily eluted during the melt season. Additionally, elevated surface concentrations suggest that they are likely added throughout the year via dry deposition. In a 1‐h stream sampling, ratios of dissolved (<0·45 µm) V:Cl^?, Sr:Cl^?, and Cu:Cl^? are enriched in the Eliot Stream with respect to their environmentally available trace element to Cl^? ratios in Eliot Glacier snow, suggesting chemical weathering additions in the stream waters. Dissolved Pb:Cl^? is depleted in the Eliot Stream with respect to the ratio of environmentally available Pb to Cl^? in snow, corresponding to greater adsorption onto particles at greater pH values. Copyright © 2009 John Wiley & Sons, Ltd.     

Characteristics of water stable isotopes and hydrograph separation in Baishui catchment during the wet season in Mt.Yulong region,south western China

Glaciers are of crucial importance for the livelihood of the local populations, which depend on their meltwater for water and energy supplies. For this reason, seasonal variations of oxygen‐18 of glacial stream water and their sources within a small glacial catchment in south western China were investigated during the wet season. The results showed significant difference of oxygen‐18 existed among meltwater, rainwater, ground water and stream water, and significantly seasonal variation of precipitation occurred during the observed period. The streamflow of Baishui catchment was separated into components of ice‐snowmelt and precipitation using oxygen‐18. As shown by the result of the two‐component mixing model, on average, 53.4% of the runoff came from ice‐snowmelt during the wet season, whereas the remaining 46.6% were contributed by precipitation in the catchment. According to monthly hydrograph, the contribution of snow and glacier meltwater varied from 40.7% to 62.2%, and that of precipitation varied from 37.8% to 59.3% in wet season. Uncertainties for this separation were mainly caused by the variation of tracer concentrations. The roles of glacier and snow meltwater should be noticed in water resource management in those glacial regions in south western China. Copyright © 2012 John Wiley & Sons, Ltd.     

Snow disappearance timing is dominated by forest effects on snow accumulation in warm winter climates of the Pacific Northwest,United States

Forests modify snow processes and affect snow water storage as well as snow disappearance timing. However, forest influences on snow accumulation and ablation vary with climate and topography and are therefore subject to temporal and spatial variability. We utilize multiple years of snow observations from across the Pacific Northwest, United States, to assess forest–snow interactions in the relatively warm winter conditions characteristic of maritime and transitional maritime–continental climates. We (a) quantify the difference in snow magnitude and disappearance timing between forests and open areas and (b) assess how forest modifications of snow accumulation and ablation combine to determine whether snow disappears later in the forest or in the open. We find that snow disappearance timing at 12 (out of 14) sites ranges from synchronous in the forest and open to snow persisting up to 13 weeks longer in the open relative to a forested area. By analyzing accumulation and ablation rates up to the day when snow first disappears from the forest, we find that the difference between accumulation rates in the open and forest is larger than the difference between ablation rates. Thus, canopy snow interception and subsequent loss, rather than ablation, set up longer snow duration in the open. However, at two relatively windy sites (hourly average wind speeds up to 8 and 17 m/s), differential snow disappearance timing is reversed: Snow persists 2–5 weeks longer in the forest. At the windiest sites, accumulation rates in the forest and open are similar. Ablation rates are higher in the open, but the difference between ablation rates in the forest and open at these sites is approximately equivalent to the difference at less windy sites. Thus, longer snow retention in the forest at the windiest sites is controlled by depositional differences rather than by reduced ablation rates. These findings suggest that improved quantification of forest effects on snow accumulation processes is needed to accurately predict the effect of forest management or natural disturbance on snow water resources.     

Relative influence upon microwave emissivity of fine-scale stratigraphy,internal scattering,and dielectric properties

Summary The microwave emissivity of relatively low-loss media such as snow, ice, frozen ground, and lunar soil is strongly influenced by fine-scale layering and by internal scattering. Radiometric data, however, are commonly interpreted using a model of emission from a homogeneous, dielectric halfspace whose emissivity derives exclusively from dielectric properties. Conclusions based upon these simple interpretations can be erroneous. Examples are presented showing that the emission from fresh or hardpacked snow over either frozen or moist soil is governed dominantly by the size distribution of ice grains in the snowpack. Similarly, the thickness of seasonally frozen soil and the concentration of rock clasts in lunar soil noticeably affect, respectively, the emissivities of northern latitude soils in winter and of the lunar regolith. Petrophysical data accumulated in support of the geophysical interpretation of microwave data must include measurements of not only dielectric properties, but also of geometric factors such as finescale layering and size distributions of grains, inclusions, and voids.     

Observation and estimation of evaporation from the ground surface of the cryosphere in eastern Asia

The characteristics of evaporation from the ground surface of Asian cryosphere sites are presented, as estimated by the lysimeter method, a profile method, and a heat budget method. The observation sites were located on the eastern Tibetan Plateau, in the Qilian and Tianshan Mountains of China, and in eastern Siberia. The lysimeter method has been demonstrated to be a reliable observation technique for estimating daily evaporation from the land surface, given suitable experiment design and operation. Daily mean evaporation varied within the range of 0·3 to 3·5 mm on the permafrost surface, and regional differences in evaporation were strongly related to surface soil moisture. Locally, topography, by way of its influence on surface soil moisture, was found to control evaporation systematically. Seasonality of ground evaporation in permafrost regions is dominated by thaw–freeze cycles at the surface; evaporation from the melting permafrost surface is up to four to seven times greater than that from frozen ground. In forested terrain, the interception of precipitation can reduce daily evaporation by 60 to 70%. Sublimation from the snow surface was observed at some sites in the range of 0·2 to 1·0 mm daily; atmospheric conditions, such as wind speed and saturation deficit, were dominant factors in determining snow sublimation. Copyright © 2003 John Wiley & Sons, Ltd.     

Hydrothermal manganese crusts from two sites near the Galapagos spreading axis

Manganese oxide crusts similar to those reported from the Mid-Atlantic Ridge rift valley by Scott et al. (1974) were dredged at two sites near the Galapagos spreading axis on ocean floor estimated from magnetic anomalies to be 2.4 and 0.3 m.y. old. Compared to the typical ocean-floor manganese deposits attributed to precipitation from seawater, the 2–6 cm thick manganese crusts reported here exhibit very low Fe/Mn and low²³²Th/²³⁸U ratios, as well as lower transition metal and higher manganese concentrations. The manganese crusts were deposited several orders of magnitude faster than the more common hydrogenous nodules; this fact together with other geochemical characteristics and the geophysical environment suggests the manganese deposits reported here are of hydrothermal origin.     

Ionic and stable isotope chemistry as indicators of water sources to the Upper Mendoza River basin,Central Andes of Argentina

The Mendoza River is mainly dependent on the melting of snow and ice in the Upper Andes. Since predicted changes in climate would modify snow accumulation and glacial melting, it is important to understand the relative contributions of various water sources to river discharge. The two main mountain ranges in the basin, Cordillera Principal and Cordillera Frontal, present differences in geology and receive differing proportions of precipitation from Atlantic and Pacific moisture sources. We propose that differences in the origin of precipitation, geology and sediment contact times across the basin generate ionic and stable isotopic signatures in the water, allowing the differentiation of water sources. Waters from the Cordillera Principal had higher salinity and were more isotopically depleted than those from the Cordillera Frontal. Stable isotope composition and salinity differed among different water sources. The chemical temporal evolution of rivers and streams indicated changes in the relative contributions of different sources, pointing to the importance of glacier melting and groundwater in the river discharge.     

Estimation of snow water equivalent using microwave radiometry over Arctic first‐year sea ice

The magnitude and spatial distribution of snow on sea ice are both integral components of the ocean–sea‐ice–atmosphere system. Although there exists a number of algorithms to estimate the snow water equivalent (SWE) on terrestrial surfaces, to date there is no precise method to estimate SWE on sea ice. Physical snow properties and in situ microwave radiometry at 19, 37 and 85 GHz, V and H polarization were collected for a 10‐day period over 20 first‐year sea ice sites. We present and compare the in situ physical, electrical and microwave emission properties of snow over smooth Arctic first‐year sea ice for 19 of the 20 sites sampled. Physical processes creating the observed vertical patterns in the physical and electrical properties are discussed. An algorithm is then developed from the relationship between the SWE and the brightness temperature measured at 37 GHz (55°) H polarization and the air temperature. The multiple regression between these variables is able to account for over 90% of the variability in the measured SWE. This algorithm is validated with a small in situ data set collected during the 1999 field experiment. We then compare our data against the NASA snow thickness algorithm, designed as part of the NASA Earth Enterprise Program. The results indicated a lack of agreement between the NASA algorithm and the algorithm developed here. This lack of agreement is attributed to differences in scale between the Special Sensor Microwave/Imager and surface radiometers and to differences in the Antarctic versus Arctic snow physical and electrical properties. Copyright © 2003 John Wiley & Sons, Ltd.     

Linkage of liquid conductivity of glacier ice with its alkalinity over the north Qinghai-Xizang (Tibet) Plateau--Implication to the past dust recovery

Liquid conductivity (EC) measurement was conducted for the samples collected from several snow pits and ice cores over the Qinghai-Xizang (Tibet) Plateau, with their time range covering seasonal, decadal and centennial scales. Unlike the previous attention mostly focused on the acidity (H+) responding to the solid conductance (ECM) of glacial ice, we introduce the alkalinity (OH?) of snow and ice to show how it responds to EC. Strong linear relationship was established between EC and OH? for these snow pits and ice cores. Positive correlation is also established between EC and major cations (Ca2+, Mg2+, Na+ and K+). Since the cations are known as the proxies for the intensity of mineral dust influx onto glaciers of the northern Qinghai-Xizang Plateau, we believe that EC could be used as an indicator for the history of dust input in deep ice core study. In fact, records in Guliya ice core since the Little Ice Age (LIA) indicate that dust load in glacier may depend on the combination of temperature and humidity. "Cold-dry" combination favors the dust arising, and results in higher EC and OH- values, while "warm-wet" combination prevents dust form and EC and OH- values are lower. In the past century, with the atmospheric warming and precipitation increasing over the northern plateau, which means an atmospheric condition of dust decreasing, both EC and OH- displayed rapid decline.     

Natural Buffering of Groundwater Contaminants Related to Development in Fractured Rock

In rural areas of New England groundwater from fractured crystalline and sedimentary bedrock is a critical water resource. Increasingly, studies have shown that development occurring in rural areas is resulting in the impairment of water quality in fractured rock aquifers. The objective of this study was to evaluate the spatial and temporal variations in groundwater quality associated with development and evaluate the extent to which common groundwater contaminants associated with rural development may be naturally buffered. The study entailed a compilation and synthesis of over 2500 reports on domestic water quality that spanned a 30 year period. Focus was placed on the spatial distribution and temporal variations in sodium, chloride, iron, manganese, nitrate, and nitrite. Results indicate that despite significant levels of development, the amount of contamination to the bedrock has been minimal. Of the constituents examined, only the chloride concentration exhibits a systematic increase over time, but the level of chloride remained relatively low. The flux of chloride to the bedrock from deicing appears minimal despite the significant amounts of road salt used in the study area. Sodium concentrations in the bedrock remained relatively constant and appear to be buffered by ion exchange with calcium as suggested by the increase in hardness with time. Iron and manganese were present at relatively low levels but did not show any systematic trends over time. Nitrate and nitrite concentrations were very low and found to be inversely correlated with manganese and iron concentrations. This suggests that the presence of iron and manganese contribute to denitrification. This study indicated that both geochemical and biogeochemical processes are active buffering mechanisms that help shield the bedrock from contaminants associated with development.     

Ferromanganese rock varnish in north Norway: A subglacial origin

A thin, dark brown rock varnish is described from ice-smoothed bedrock on the forefield of a glacier in North Norway. It occurs only in narrow strips (ca 100 mm or less wide) which run roughly parallel to the ice front and along the top edges of small treads of a series of bedrock steps. The varnish is hard, thin (< 10 μm) and consists of an iron/manganese deposit, greatly enriched in these elements compared with the composition of the underlying gabbroic bedrock. It is suggested that the varnish formation is due to localized changes in Eh/pH conditions in subglacial regelation ice and meltwater at the top of the bedrock steps. These changes may be due to CO₂ and/or O₂ degassing from water held at higher pressures under the ice than in cavities downstream where the ice is decoupled from the bedrock. Glacier retreat rates indicate that the varnish has remained exposed subaerially at the surface for about twenty years, and its restricted occurrence suggests that it is not of biological origin but rather is essentially authigenic. Possible subglacial origins for associated iron and silica precipitates are also suggested.     

The influence of global and local atmospheric pollution on the chemistry of Antarctic snow and ice

The Antarctic ice sheet is the main sink for atmospheric pollution reaching the Antarctic atmosphere from other continents. The ice preserves a historical record of the atmosphere that can be recovered in ice cores. No increasing trend is observed over recent decades for nitrate and sulphate. There appears to have been an increase of perhaps eight-fold in lead concentrations in Antarctic snow, but the details of when the increase occurred have still to be defined. Many other species could be measured, but analytical problems have hampered such work. These studies would be impaired if emissions due to human activity in Antarctica became significant. The effect on snow concentrations of emissions from fuel and waste burning at Antarctic stations and from vehicles is still mainly confined to small areas around stations.     

A precise monitoring of snow surface height in the region of Lambert Glacier basin-Amery Ice Shelf,East Antarctica

The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04'E, 1850 m a.s.l.). east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between October and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G