A Simple Analytical Model for Interpretation of Tracer Tests in Two-Domain Subsurface Flow Systems

Goebes, Marian D.; Younger, Paul L.

doi:10.1007/s10230-004-0054-y

Cited by 21 publications

(13 citation statements)

References 22 publications

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“…Cravotta et al 2004;Diaz-Goebes and Younger 2004). For example, Cravotta et al (2004) conducted a tracer test with sodium bromide that demonstrated detention time within a limestone drain was less than half of that computed on the basis of the measured flow rate and assumed saturated volume of the limestone bed (Eq.…”

Section: Discussion: Treatment-system Performancementioning

confidence: 99%

Downflow Limestone Beds for Treatment of Net-Acidic, Oxic, Iron-Laden Drainage from a Flooded Anthracite Mine, Pennsylvania, USA: 1. Field Evaluation

Cravotta¹,

Ward²

2008

Mine Water Environ

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Passive-treatment systems that route acidic mine drainage (AMD) through crushed limestone and/or organic-rich substrates have been used to remove the acidity and metals from various AMD sources, with a wide range of effects. This study evaluates treatment of net-acidic, oxic, iron-laden AMD with limestone alone, and with organicrich compost layered with the limestone. In the fall of 2003, a treatment system consisting of two parallel, 500-m 2 downflow cells followed by a 400-m 2 aerobic settling pond and wetland was installed to neutralize the AMD from the Bell Mine, a large source of AMD and baseflow to the Schuylkill River in the Southern Anthracite Coalfield, in east-central Pennsylvania. Each downflow cell consisted of a lower substrate layer of 1,090 metric tons (t) of dolomitic limestone (60 wt% CaCO 3 ) and an upper layer of 300 t of calcitic limestone (95 wt% CaCO 3 ); one of the downflow cells also included a 0.3 m thick layer of mushroom compost over the limestone. AMD with pH of 3.5-4.3, dissolved oxygen of 6.6-9.9 mg/L, iron of 1.9-5.4 mg/L, and aluminum of 0.8-1.9 mg/L flooded each cell to a depth 0.65 m above the treatment substrates, percolated through the substrates to underlying, perforated outflow pipes, and then flowed through the aerobic pond and wetland before discharging to the Schuylkill River. Data on the flow rates and chemistry of the effluent for the treatment system indicated substantial neutralization by the calcitic limestone but only marginal effects from the dolomitic limestone or compost. Because of its higher transmissivity, the treatment cell containing only limestone neutralized greater quantities of acidity than the cell containing compost and limestone. On average, the treatment system removed 62% of the influent acidity, 47% of the dissolved iron, 34% of the dissolved aluminum, and 8% of the dissolved manganese. Prior to treatment of the Bell Discharge, the Schuylkill River immediately below its confluence with the discharge had pH as low as 4.1 and supported few, if any, fish. However, within the first year of treatment, the pH was maintained at values of 5.0 or greater and native brook trout were documented immediately below the treatment system, though not above.

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Section: Discussion: Treatment-system Performancementioning

confidence: 99%

Downflow Limestone Beds for Treatment of Net-Acidic, Oxic, Iron-Laden Drainage from a Flooded Anthracite Mine, Pennsylvania, USA: 1. Field Evaluation

Cravotta¹,

Ward²

2008

Mine Water Environ

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“…at higher initial iron concentrations, it will occur faster) (Hedin et al 1994). However, no investigation has ever assessed the actual hydraulic residence time of the Coal Authority's mine water treatment systems, although some guidance can be drawn from studies conducted in the United States (Keefe et al 2004;Lin et al 2003), in U.K. RAPS systems (Wolkersdorfer et al 2005), and modelling studies (Goebes and Younger 2004). Much could be gained from such an investigation, since this would allow quantification of the actual rate of iron attenuation, and provide an indication of the hydraulic efficiency of these systems.…”

Section: Introductionmentioning

confidence: 98%

Determination of Hydraulic Residence Times in Several UK Mine Water Treatment Systems and their Relationship to Iron Removal

2009

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In the UK, the Coal Authority has more than 40 mine water treatment systems, most of which are wetland systems with settlement lagoon pretreatment. The purpose of treatment in wetlands is the oxidation of ferrous to ferric iron and the subsequent hydrolysis and precipitation of ferric hydroxide within the wetland. It is generally accepted (Hedin et al., Passive treatment of coal mine drainage, 1994, p 35; Skousen and Ziemkiewicz, Acid mine drainage control and treatment, 1996, p 362; Younger et al., Mine water: hydrology, pollution, remediation, 2002, p 442) that this process proceeds by a first-order rate law, although most systems are designed based on an areal removal rate (10 g/m 2 /day) developed by the U.S. Bureau of Mines (Hedin et al., Passive treatment of coal mine drainage, 1994, p 35); this design guideline inherently assumes a constant removal rate. Given the actual kinetics of iron removal in wetlands, it follows that residence time will control iron removal; given the wide range of system geometries and aspects, it is logical to ascertain the actual hydraulic residence time of wetlands and settlement lagoons and determine the effect this has on iron removal. To make a preliminary assessment of this link, hydraulic residence time of two Coal Authority wetlands (Lambley and Whittle) and two Coal Authority settlement lagoons (Acomb East, Acomb West and Whittle) were measured using bromide tracer tests. Water samples for iron analysis and flow measurements were taken during each tracer test. The Lambley wetland performs well in terms of residence time, and, as reeds become established and adsorptive processes increase, its iron removal performance (currently 58% removal) may improve, but the low influent iron concentration appears to be a significant impediment to meeting the original performance target. In contrast, the hydraulic performance of the Whittle wetland system is poor, which appears to be due to accumulation of dead plant material coupled with a high length to width ratio. However, performance in terms of iron removal is good (92% removal), which appears to be due to the higher influent iron concentration, and especially the fact that the iron enters the wetland largely in particulate form. The longer residence time of water within the Acomb lagoons (&12 h) resulted in far more effective iron removal (72% in the east lagoon and 85% in the west lagoon) than the shorter residence time at Whittle (24% iron removal, &5 h residence time). Performance (in terms of iron removal) of the settlement lagoon systems appears to be far more closely related to the hydraulic residence time (albeit this conclusion must be tentative, given that only three systems have been investigated, and the Acomb system receives chemical addition). Based on this study, treatment system sizing using 100 m 2 lagoon area per 1 L/s flow appears to be a more appropriate basis for design rather than an areal iron removal rate.

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“…Tracer tests have previously been successfully used to elucidate hydraulic conditions and modal and mean residence times in mine systems and RAPS (Aldous and Smart, 1988;Diaz-Goebes and Younger 2004;Wolkersdorfer, 2002;Wolkersdorfer et al 2005, in press;Watson et al 2009) ) n e = effective porosity of the RAPS The above assumes that the RAPS medium is relatively homogenous and that T p represents a mean conservative tracer travel time. We should note that T p for a conservative tracer actually corresponds to a modal or dominant residence time of the system, which may not be the same as a mean residence time (Kusin et al, 2012), especially if there are significant matrix diffusion effects or a multi-modal porosity distribution.…”

Section: Previous Tracer Testsmentioning

confidence: 99%

“…Thus, the original Diaz-Goebes and Younger (2004) was modified slightly to incorporate a mixing tank effect to the model input. The number of parameters that are potentially adjustable in this model are considerable and therefore, a unique "best fit" solution could not unambiguously be identified.…”

Section: Diaz-goebes and Younger (2004) Model With Mixing Tankmentioning

confidence: 99%

Characterisation of hydraulic and hydrogeochemical processes in a reducing and alkalinity-producing system (RAPS) treating mine drainage, South Wales, UK

Taylor

Banks

Watson

2016

International Journal of Coal Geology

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A series of tracer tests has been carried out in the compost and limestoneTan-y-Garn Reducing and Alkalinity-Producing System (RAPS), designed to treat iron-rich net acidic mine water (mean pH 6.18, Fe = 47 mg L . Electrical conductivity and major ion chemistry were monitored for a 170 hour period.Sodium exhibited a retardation of 1.15 to 1.2 in the RAPS medium relative to chloride, due to cation exchange. Simple 1-D advection-diffusion analytical modelling succeeded in simulating the early portion of tracer breakthrough in the RAPS effluent. More complex analytical modelling, accounting for (i) mixing and dilution effects in the supernatant water input signature and (ii) matrix diffusion effects, was found to be required to adequately simulate the later-stage tail of the breakthrough curve in the RAPS effluent. 2 KeywordsTracer test, alkalinity, mine water, artificial wetland, matrix diffusion, ion exchange 3 Introduction What is a Reducing and Alkalinity-Producing System (RAPS)?It is common and cost-effective to treat iron-rich mine waters (Banks and Banks, 2001; PIRAMID Consortium, 2003;Sapsford and Watson, 2011) by passive, aerobic methods, such as aerobic sedimentation basins or wetlands.These function by the oxidation of ferrous to ferric iron, followed by the hydrolysis and precipitation of ferric iron from the water. This net process can be described by equation (1) The overall oxidation and hydrolysis reaction is thus acid-producing (2 moles of protons released for every mole of ferrous iron oxidised and precipitated).However, the hydrolysis and precipitation reaction is strongly pH-dependent: if the pH becomes too low, the hydroxide precipitate will not form. Thus, it is important that sufficient alkalinity is available in the water to absorb the protons produced and to buffer the pH at a reasonably high level (Hedin et al., 1994a;Younger et al., 2002). Alkalinity can be added actively, by dosing the influent mine water with hydroxide or carbonate. However, it can also be released passively by allowing the mine water to flow through limestone drains before entering the aerobic treatment lagoons or wetlands (PIRAMID Consortium, 2003). The limestone slowly dissolves, releasing bicarbonate alkalinity to the water. If the water contains oxygen, however, ferric hydroxide may precipitate out in the limestone drains, "armouring" the limestone clasts and inhibiting further dissolution (Hedin et al., 1994b;Cravotta and Trahan, 1999;Watzlaf et al., 2000a;Bernier et al., 2001). Thus, it is important to strip oxygen from the water before it enters the limestone drain, ensuring that iron remains in its ferrous form (Equation 2). This is most effectively done by a layer with a high organic content and thus a high oxygen demand -for example, a compost layer (represented by CH 2 O in equation (2)). On exiting a RAPS, the mine water will typically:(i) pass through a re-aeration system, such as an aeration cascade, before entering(ii) a system of aerobic treatment lagoons and/or wetlands, where the iron conte...

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A Simple Analytical Model for Interpretation of Tracer Tests in Two-Domain Subsurface Flow Systems

Cited by 21 publications

References 22 publications

Downflow Limestone Beds for Treatment of Net-Acidic, Oxic, Iron-Laden Drainage from a Flooded Anthracite Mine, Pennsylvania, USA: 1. Field Evaluation

Downflow Limestone Beds for Treatment of Net-Acidic, Oxic, Iron-Laden Drainage from a Flooded Anthracite Mine, Pennsylvania, USA: 1. Field Evaluation

Determination of Hydraulic Residence Times in Several UK Mine Water Treatment Systems and their Relationship to Iron Removal

Characterisation of hydraulic and hydrogeochemical processes in a reducing and alkalinity-producing system (RAPS) treating mine drainage, South Wales, UK

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