Field Pilot Test Research Articles

Dynamic compaction of saturated sands and silty sands: design

Current practice for design, suitability assessment, and determination of the optimum field operation parameters for dynamic compaction rely mainly on field pilot tests, past experience, and empirical equations. At present there are no detailed analytical procedures available to determine the densification achievable, or to analyse the effects of various operational parameters on the degree of improvement achievable during dynamic compaction of sands and non-plastic silty soil deposits. This paper presents a set of simplified charts to determine the post-improvement penetration resistance of saturated sands and non-plastic silty sands, supplemented with pre-installed wick drains, due to improvement by dynamic compaction. The theoretical basis and the numerical schemes for simulation of dynamic compaction leading to these charts are presented elsewhere. The charts facilitate design choice of parameters such as grid spacing, number of impacts per grid point, energy per impact, time cycle between impacts, and drain spacing required to achieve a minimum specified post-improvement penetration resistance for a range of initial soil conditions. Simplified procedures for the use of these charts for liquefaction mitigation design are presented and illustrated using design examples.

Treatment of geothermal waters for production of industrial, agricultural or drinking water

A conceptual study has been carried out to convert geothermal water and condensate into a valuable industrial, agricultural or drinking water resource. Laboratory and field pilot test studies were used for the conceptual designs and preliminary cost estimates, referred to treatment facilities handling 750 kg/s of geothermal water and 350 kg/s of steam condensate. The experiments demonstrated that industrial, agricultural and drinking water standards could probably be met by adopting certain operating conditions. Six different treatments were examined. Unit processes for geothermal water/condensate treatment include desilication of the waters to produce marketable minerals, removal of dissolved solids by reverse osmosis or evaporation, removal of arsenic by oxidation/precipitation, and removal of boron by various methods including ion exchange. The total project cost estimates, with an accuracy of approximately ±25%, ranged from US$ 10 to 78 million in capital cost, with an operation and maintenance (or product) cost ranging from US$ 0.15 to 2.73 m −3 of treated water.

Concurrent bioremediation of perchlorate and 1,1,1-trichloroethane in an emulsified oil barrier

A detailed field pilot test was conducted to evaluate the use of edible oil emulsions for enhanced in situ biodegradation of perchlorate and chlorinated solvents in groundwater. Edible oil substrate (EOS®) was injected into a line of ten direct push injection wells over a 2-day period to form a 15-m-long biologically active permeable reactive barrier (bio-barrier). Field monitoring results over a 2.5-year period indicate the oil injection generated strongly reducing conditions in the oil-treated zone with depletion of dissolved oxygen, nitrate, and sulfate, and increases in dissolved iron, manganese and methane. Perchlorate was degraded from 3100 to 20,000 μg/L to below detection (< 4 μg/L) in the injection and nearby monitor wells within 5 days following the injection. Two years after the single emulsion injection, perchlorate was less than 6 μg/L in every downgradient well compared to an average upgradient concentration of 13,100 μg/L. Immediately after emulsion injection, there were large shifts in concentrations of chlorinated solvents and degradation products due to injection of clean water, sorption to the oil and adaptation of the in situ microbial community. Approximately 4 months after emulsion injection, concentrations of 1,1,1-trichloroethane (TCA), perchloroethene (PCE), trichloroethene (TCE) and their degradation products appeared to reach a quasi steady-state condition. During the period from 4 to 18 months, TCA was reduced from 30–70 μM to 0.2–4 μM during passage through the bio-barrier. However, 1–9 μM 1,1-dichloroethane (DCA) and 8–14 μM of chloroethane (CA) remained indicating significant amounts of incompletely degraded TCA were discharging from the oil-treated zone. During this same period, PCE and TCE were reduced with concurrent production of 1,2- cis-dichloroethene ( cis-DCE). However, very little VC or ethene was produced indicating reductive dechlorination slowed or stopped at cis-DCE. The incomplete removal of TCA, PCE and TCE is likely associated with the short (5–20 days) hydraulic retention time of contaminants in the oil-treated zone. The permeability of the injection wells declined by 39–91% (average = 68%) presumably due to biomass growth and/or gas production. However, non-reactive tracer tests and detailed monitoring of the perchlorate plume demonstrated that the permeability loss did not result in excessive flow bypassing around the bio-barrier. Contaminant transport and degradation within the bio-barrier was simulated using an advection–dispersion–reaction model where biodegradation rate was assumed to be linearly proportional to the residual oil concentration ( S oil) and the contaminant concentration. Using this approach, the calibrated model was able to closely match the observed contaminant distribution. The calibrated model was then used to design a full-scale barrier to treat both ClO 4 and chlorinated solvents.

Permeable reactive barrier using atomized slag material for treatment of contaminants from landfills

This paper presented a permeable reactive barrier using atomized slag material for the treatment of landfill leachate and contaminated ground water. This study investigated the feasibility of using atomized slag and modified by products from iron and steel making industries as new reactive material for leachate treatment. Batch and column tests, and field pilot tests were performed as model systems to explore the effect of atomized slag as an alternative reactive material. From the evaluation of various atomized slag based PRB systems, a combination of an atomized slag and sand system was found to have a substantial reaction capacity for leachate and organics, thus it has the potential to be used in the permeable reactive barriers for a subsurface remediation. The test results showed that the adsorption capacity is high in the order of pH 7>pH 5>pH 9, the heavy metal removal rate is high in the order of Cd>Pb>Cr>Cu, and organic removal rate is high in the order of T-P>COD>T-N.

Value of Injection Testing as an Alternative to Conventional Well Testing: Field Experience in a Sour-Oil Reservoir

Summary Environmental constraints and high costs, especially offshore, are making conventional-well testing less and less feasible and accepted by the public administration. New options were thoroughly evaluated to find a viable alternative to standard production tests for characterizing the well productivity without surface production. An accurate investigation demonstrated that injection tests could provide all the information needed to calculate the well productivity at reasonably low costs and with a good degree of reliability. On the basis of the results of laboratory and field pilot tests, it was proved that injectivity tests could be applied successfully to a real sour-oil field. Laboratory tests proved that brine could be a suitable injection fluid because there were no compatibility problems with the oil and the reservoir rock. It was verified that the interpretation of the pressure transients should be referred to the falloff period rather than to the injection phase. The formation permeability-thickness product (kh) could be identified correctly from the pressure-derivative analysis only if multiphase flow was assumed. The total skin value could also be obtained from the test interpretation. The total skin comprises two components: a mechanical component resulting from permeability damage and a biphase component resulting from fluid interaction in the reservoir. Except for a limited number of cases, the biphase skin can be evaluated only with numerical well testing, provided that the fluid relative permeability curves are available. It was also demonstrated that the biphase component depends mainly on the injection rate but is independent of the formation permeability. Then, the well-known transient equation was applied to determine the well productivity index (PI) based on the kh and the mechanical skin. PI values calculated from injection tests compared satisfactorily with PI values measured from six drillstem tests (DSTs) performed on appraisal wells.

Seabed Ground Improvement in Coastal Reclamation Area by Heavy Tamping After Rockfilling Displacement

Considering the characteristics of seabed ground in coastal reclamation area, ultra soft clay improvement method by heavy tamping after rockfilling displacement was proposed combined with a case study. The improvement mechanisms of the method can primarily be attributed to rockfilling displacement (RD), dynamic compaction (DC), dynamic replacement (DR) and dynamic replacement and mixing (DRM). For the case study given in this article, heavy tamping construction program was proposed based on field pilot tests. Furthermore, the effectiveness of the proposed ground improvement method was verified through in situ plate load test, sand fill test and the analyses of observed settlement data. Thus, the method of heavy tamping after rockfilling displacement is applicable for the improvement of seabed ground in coastal reclamation area. It is proposed for similar projects that heavy tamping of fills may be performed by layers and correspondingly tamping energy increased to further enhance the improvement effect of DC, DR and DRM. In addition, delayed improvement effect or time effect of soil mass after heavy tamping is still an issue to be further studied.

Numerical Simulation of a Steam-Injection Pilot Study for a PCP-Contaminated Aquifer

The following study was focused on the simulation of a steam-injection field pilottest conducted in our past research. The scope of research contained two main subjects: heat transfer and contaminant transport when steam was injected into a pentachlorophenol (PCP)-contaminated aquifer. Numerical simulation of the heat transfer during the field test showed that vertical permeability is more influential to the distribution of water temperature than the horizontal permeability. If the vertical permeability is relatively high, the steam in the aquifer has a higher tendency to migrate upward and cause the aquifer temperature to rise faster. The simulation results also showed that heat convection is very sensitive to the soil permeability. Therefore, high permeability media makes the effect of heat convection more important on applying the steam-injection method. Heat conduction dominates the heat transfer within the hot aqueous zone. However, the hot aqueous zone is relatively smaller than the steam zone when steam is injected into the aquifer. Therefore, heat conduction is not as important as heat convection within the steam zone, which is the same result observed in the field test. Specific heat of soil media is also a sensitive factor. A numerical simulator, T2VOC, was utilized to simulate the PCP transport in the aquifer when steam was injected into the aquifer. The results showed that the shape of PCP distribution was identical to that of steam. It illustrated thatthe steam carried PCP upward and laterally. The high vertical soil permeability causes the steam to migrate upward with PCP easily. A low partitioning coefficient allows PCP to be desorbed easier, also an important factor. A majority of the PCP in the soil was transferred to the aqueous phase as the water temperature increased, showing similar results to those observed in the field test. According to the sensitivity analysis, PCP transport is more sensitive to the vertical permeability than the partitioning coefficient. The steam-injection rate is also an important operation parameter and may determine the success of the remediation work.

BIOLOGICAL SOURCE TREATMENT OF ACID MINE DRAINAGE

Acid mine drainage (AMD) originates from mining operations with oxidation of metal sulfides. The oxidizing process releases protons and generates acidity. A biological source treatment (BST) technique has been developed to address AMD at its source. The BST technique utilizes sulfate-reducing bacteria (SRB) and substrate amendments to establish an intracellular and/or extracellular biogeochemical formation on the surface of metal sulfide, shielding them from being oxidized. SRB transfer electrons from organic substrates to sulfate and form sulfide. This process consumes protons and raises pH, while dissolved metals are precipitated with sulfide. Laboratory studies have shown that effluent/solids from wastewater treatment plants contain adequate populations of SRB as the inoculum for BST applications. In laboratory studies, the pH of AMD samples increased from 7.0 and stabilized in the neutral pH range for more than 20 months with one treatment. A field pilot study of the BST technique was conducted at a reclaimed coal mine in central Tennessee. Results to date indicate a significant increase in pH in the testing area, stabilizing in the pH range from 6.0 to 7.0, from the initial acidic readings. Decreases in sulfate and increases in sulfide concentrations confirm valid sulfate-reducing activity. Electromagnetic surveys were conducted in the field pilot test to identify AMD source and assist in monitoring the performance. Data from both the laboratory and field studies demonstrate that BST process is an innovative technology that can be applied in suitable sites and offer a cost-effective and long-term treatment of AMD.

Design and Application of an Alkaline‐Surfactant‐Polymer Flooding System in Field Pilot Test

We have developed an inexpensive sort of flooding reagent whose major components are natural mixed carboxylates from proportionally mixed saponification residuals of cottonseed oil, tea oil, vegetable oil, and soybean oil. An orthogonal test design method was used to select one form of this flooding reagent (which is named SD) by measuring the phase behavior and another form of the flooding system: alkaline/surfactant/polymer (named SD‐ASP). The optimal composition was obtained by measuring the transient interfacial tension (IFT) at the crude oil/aqueous interface. Results of the tests show that the SD‐ASP flooding systems are tolerant to salt up to 1.5×105 mg/L and to Ca2+ and Mg2+ to 5.0×103 mg/L at 90°C, the IFTmin (the minimum of IFT) is 10−3 mN/m, and the oil recovery ratio reaches 22.77% by using the core flood experiment. The pilot tests, including a putting in and sending out in a single oil well, a group oil well and a larger well region, were all very successful, with an average input‐output ratio of 1∶4.15. All these results demonstrate that the SD‐ASP formulation is a new, very inexpensive, and highly effective flooding system.

石炭の国際的市況変化と新規環境技術の展開「二酸化炭素炭層固定化技術開発」における圧入予備実験について

The Japanese Ministry of Economy, Trade and Industry (METI) has undertook 5-Year project on CO2 sequestration in coal seams since 2002. This project consists of fundamental research into CH4-CO2-coal interaction, CO2 monitoring technologies, cost reduction of CO2 capture from flue gases, and the economics of sequestration. Another component of the project is a field pilot test. After preliminary screening of potential sites, the Ishikari coalfield in Hokkaido, Japan, was selected as the pilot test site. In 2003, a well was drilled in the South Oh-Yubari district within the Ishikari coalfield, and named IW-1. This was the first well drilled in Japan from the surface to a coal seam for purposes of CO2 sequestration and was designed for CO2 injection. In 2004, second well (called PW-1) was drilled at the surface location 195m away from IW-1 for the production purpose. The two wells were together intended to constitute a multi-well pilot test site. A multi well CO2 injection/CH4 production test was conducted using both IW-1 and PW-1. This paper introduces the overall coal seam CO2 sequestration project and presents the results of the multi well injection/production test.

DNAPL remediation with in situ chemical oxidation using potassium permanganate: II. Increasing removal efficiency by dissolving Mn oxide precipitates

In situ chemical oxidation (ISCO) schemes using MnO 4 − have been effective in destroying chlorinated organic solvents dissolved in ground water. Laboratory experiments and field pilot tests reveal that the precipitation of Mn oxide, one of the reaction products, causes a reduction of permeability, which can lead to flow bypassing and inefficiency of the scheme. Without a solution to this problem of plugging, it is difficult to remove DNAPL from the subsurface completely. In a companion paper, we showed with batch experiments that Mn oxide can be dissolved rapidly with certain organic acids. This study utilizes 2-D flow-tank experiments to examine the possibility of nearly complete DNAPL removal by ISCO with MnO 4 −, when organic acids are used to remove Mn oxide. The experiments were conducted in a small 2-D glass flow tank containing a lenticular silica-sand medium. Blue-dyed trichloroethylene (TCE) provided residual, the perched and pooled DNAPL. KMnO 4 at 200 mg/l was flushed through the DNAPL horizontally. Once plugging reduced permeability and prevented further delivery of the oxidant, citric or oxalic acids were pumped into the flow tank to dissolve the Mn oxide precipitates. Organic ligands removed the Mn oxide precipitates relatively quickly, and permitted another cycle of MnO 4 − flooding. Cycles of MnO 4 −/acid flooding continued until all of the visible DNAPL was removed. The experiments were monitored with chemical analysis and visualization. A mass-balance calculation indicated that by the end of the experiments, all the DNAPL was removed. The results show also how heterogeneity adds complexity to initial redistribution of DNAPL, and to the efficiency of the chemical flooding.

The use of zero‐valent iron injection to remediate groundwater: Results of a pilot test at the Marshall Space Flight Center

AbstractIn situ treatability studies are being conducted to evaluate various in situ technologies to manage groundwater contamination at the NASA Marshall Space Flight Center in Huntsville, Alabama. The focus of these studies is to evaluate remediation options for contaminated (mostly aerobic) groundwater occurring within the basal portion of a clayey residuum called the rubble zone. The tension‐saturated media and unsaturated media lying above the rubble zone are also being treated where they make up a significant component of the contaminant mass. An in situ chemical reduction field pilot test was implemented (following bench‐scale tests) during July and August 2000. The test involved the injection of zero‐valent iron powder in slurry form, using the FeroxSM process patented by ARS Technologies, Inc. The pilot test focused on trichloroethene (TCE)‐contaminated groundwater within the rubble zone. Maximum pre‐injection concentrations of about 72,800 micrograms per liter (μg/l) were observed and no secondary sources are believed to exist beneath the area. The potential presence of unexploded ordnance forced an implementation strategy where source area injections were completed, as feasible, followed by overlapping injections in a down gradient alignment to create a permeable reactive zone for groundwater migration. Eight post‐injection rounds of groundwater performance monitoring were completed. The results are encouraging, in terms of predicted responses and decreasing trends in contaminant levels. © 2003 Wiley Periodicals, Inc.

A case study of bioremediation of petroleum-hydrocarbon contaminated soil at a crude oil spill site

Laboratory and field pilot studies were carried out on the bioremediation of soil contaminated with petroleum hydrocarbons in the Borhola oil fields, Assam, India. The effects of aeration, nutrients (i.e. nitrogen and phosphorus) and inoculation of extraneous microbial consortia on the bioremediation process were investigated. The beneficial effects of these parameters on the bioremediation rate were realised equally in laboratory and field pilot tests. The field tests revealed that up to 75% of the hydrocarbon contaminants were degraded within 1 year, indicating the feasibility of developing a bioremediation protocol. A complementary computer simulation study was carried out to enhance the understanding of the basic processes and the rate determining factors for bioremediation under the practically relevant conditions of Borhola oil fields. The simulations indicated that due to the high initial contaminant concentrations, the bioremediation process was restricted mostly to the macropores of the system within the period of 1 year and had not penetrated into the soil aggregates sufficiently. Certain shortcomings of the model have been identified and possible refinements suggested.

Investigations of organic inhibitors for silica scale control in geothermal brines

Organic inhibitors, primarily in the form of dispersants, have been examined in laboratory screening and field pilot tests for silica scale control activity. Over 25 inhibitor formulations obtained from four different manufacturers were screened for scale control in a laboratory pressure reactor using a simple brine solution. Only a single inhibitor achieved >50% reduction in scale deposition compared to control (no inhibitor) experiments. This inhibitor proved to be effective at a dosage of about 1 ppm; however, above that dosage, scale inhibition decreased and significant deposition was observed. It is postulated that overdosing the dispersants leads to flocculation. A few inhibitors yielded positive results, but scale reduction compared to control tests was <35%. In contrast, progressive acidification of brine decreased scaling significantly. Several inhibitors were examined for scale control in a pilot test apparatus at a geothermal field. Two inhibitors decreased scale deposition by >50%. The majority of inhibitors tested in the field exacerbated scaling. Similar to the laboratory tests, brine acidification inhibited scaling by 97%. From these results it appears that the use of organic silica scale inhibitors in geothermal operations is limited to only a few applications. Until the drawbacks of high inhibitor cost, generally poor effectiveness, exacerbation of scaling upon overdosing, and the long-term effect of dispersing silica colloid particles into injection formations are resolved, organic inhibitors will likely continue to see limited use in the industry.

Field Evaluation of In Situ Chemical Oxidation Through Vertical Well‐to‐Well Recirculation of NaMnO4

AbstractA field pilot test was conducted at a U. S. Department of Energy site to evaluate in situ chemical oxidation of trichloroethene (TCE) in a silty‐sandy gravel aquifer located at 26 to 30 feet (8 to 9 m) below ground surface. A vertical well‐to‐well recirculation system was designed and implemented by placing four corner extraction wells in a square grid, with each well 45 feet (13.7 m) from a center injection well. Ground water was extracted from the four perimeter wells, combined aboveground in a piping network, and then amended inline with sodium permanganate (NaMnO4) before reinjection into the aquifer through a center injection well. During the pilot test, oxidant amended ground water (250 mg/L NaMnO4) was injected at 18 gpm (68.1 L/m) for 10 days, during which time‐354 pounds (160.6 kg) of NaMnO4 were delivered and approximately 240,660 gallons (911 kL) of ground water were recirculated and treated. NaMnO4 injection using vertical wells in a five‐spot pattern was capable of providing sufficient hydraulic control to deliver oxidant throughout the permeable zones of the 4100 ft2 (380 m2) test area within three days. TCE concentrations were reduced, from 2,000 μg/L to &lt;10 μg/L, throughout all but the lower permeable eastern edge of the test region, indicating an apparent reduction in contaminant levels of 92% within three days and 97% within 10 days (two hours after the end of active recirculation). One month after system shut down, residual oxidant concentrations in the ground water had declined to &lt;1 mg/L, while a gradual increase in TCE concentrations was observed. Oxidant consumption over time is expected due to a combination of factors, including oxidation of the natural organic material present, oxidation of TCE that diffused out from the finer‐grained and less permeable zones, and advection of TCE into the test area from the upgradient plume. No adverse effects to system toxicity, generation of reaction intermediates and products (e.g., chlorinated organic acids or partially degraded chlorocarbons), or reduction in formation permeability were observed.

Vacuum preloading consolidation of Yaoqiang Airport runway

Yaoqiang Airport is an international airport serving the city of Jinan, China. The soil on the site consists of alternate layers of silty sand, silty clay, silt and clay. An under-consolidated soft clay layer approximately 4 m thick is located at between 7·5 m and 11·5 m depth above a silty clay layer. Soil improvement was proposed to consolidate the site prior to the construction of a runway to eliminate excessive settlement under static and dynamic loads on the runway. The results from field pilot tests for both surcharge preloading and vacuum preloading under the same consolidation pressure of 80 kPa are presented. Soil settlement in the range 20–30 cm was achieved in 80–90 days. For the vacuum treatment, in-situ deep mixing slurry cut-off walls were installed to control vacuum loss in a shallow silty sand layer. Data from the successful full-scale vacuum treatment of the site are also presented

Field-Scale Demonstration of Enhanced MTBE Bioremediation through Aquifer Bioaugmentation and Oxygenation

In situ bioaugmentation and biostimulation experiments were conducted at the USN Hydrocarbon National Environmental Test Site at Port Hueneme, CA (PH), where the dissolved MTBE groundwater plume is over 1500 m long. Laboratory microcosm experiments prepared with PH groundwater showed that MTBE was rapidly metabolized (t1/2 ≤ 2 weeks) after inoculation with a high-activity MTBE-degrading bacterial consortium (MC-100). Microcosm studies also showed that natural ether degraders were present at PH; however, the rates were 3−5 times slower than with the bioaugmented treatment. The field pilot test was conducted to assess the efficacy of creating an MTBE biobarrier by inoculating with MC-100 and maintaining well-oxygenated conditions. Three test plots located in the MTBE-only portion of the plume included control (no treatment), O2-only (intermittent O2 gas injection), and O2 + bioaugmented (MC-100) zones. Initial MTBE and dissolved oxygen (DO) concentrations in the plots prior to treatment varied from 2 to 9 m...

Development and Evaluation of The Michigan Occupational Health and Safety Management System Assessment Instrument: A Universal OHSMS Performance Measurement Tool

A universal Occupational Health and Safety Management System (OHSMS) Assessment Instrument has been developed to measure the effectiveness of a wide range of OHSMSs. The development and evaluation of the instrument's overall structure, its OHSMS principles, and its measurement criteria are presented in this article. Thirteen OHSMS and environmental management system (EMS) models were reviewed in an effort to define the OHSMS universe. Four of these models were selected as instrument input models. These models are (1) the Occupational Safety and Health Administration's Voluntary Protection Programs (VPP); (2) the British Standards Institute's OHSMS, BS 8800:1996; (3) the American Industrial Hygiene Association's OHSMS; and (4) the International Organization for Standardization's (ISO) EMS ISO 14001:1996. The instrument in its final form contains 27 sections, 118 OHSMS principles, and 486 measurement criteria. Evaluation of the instruments principles and measurement criteria was conducted by a 16-member panel of occupational health and safety experts. The expert review revealed that there was good correspondence between the input model clauses and the OHSMS principles, and between the principles and their associated measurement criteria. It is concluded that (1) the OHSMS principles and measurement criteria present a sound foundation from which the effectiveness of a wide range of OHSMSs can be determined; (2) the instrument is sufficiently developed to use in field-pilot tests; and, (3) the instrument provides a framework that can contribute to the identification and measurement of occupational safety and health performance variables.

Development and Evaluation of The Michigan Occupational Health and Safety Management System Assessment Instrument: A Universal OHSMS Performance Measurement Tool

A universal Occupational Health and Safety Management System (OHSMS) Assessment Instrument has been developed to measure the effectiveness of a wide range of OHSMSs. The development and evaluation of the instrument's overall structure, its OHSMS principles, and its measurement criteria are presented in this article. Thirteen OHSMS and environmental management system (EMS) models were reviewed in an effort to define the OHSMS universe. Four of these models were selected as instrument input models. These models are (1) the Occupational Safety and Health Administration's Voluntary Protection Programs (VPP); (2) the British Standards Institute's OHSMS, BS 8800:1996; (3) the American Industrial Hygiene Association's OHSMS; and (4) the International Organization for Standardization's (ISO) EMS ISO 14001:1996. The instrument in its final form contains 27 sections, 118 OHSMS principles, and 486 measurement criteria. Evaluation of the instruments principles and measurement criteria was conducted by a 16-member panel of occupational health and safety experts. The expert review revealed that there was good correspondence between the input model clauses and the OHSMS principles, and between the principles and their associated measurement criteria. It is concluded that (1) the OHSMS principles and measurement criteria present a sound foundation from which the effectiveness of a wide range of OHSMSs can be determined; (2) the instrument is sufficiently developed to use in field-pilot tests; and, (3) the instrument provides a framework that can contribute to the identification and measurement of occupational safety and health performance variables.

Aluminum silicate scale formation and inhibition (2): scale solubilities and laboratory and field inhibition tests

The solubilities of pure silica, iron-silicate and aluminum-silicate scales were measured in water from 25–250°C in a laboratory pressure reactor. Iron- and aluminum-silicate scales are significantly less soluble than pure amorphous silica. Aluminum- and iron-rich silica scales at equilibrium conditions are predicted to deposit from near-neutral, low salinity brines at temperatures that are 25 and 75°C above the saturation point for pure amorphous silica, respectively. This laboratory study demonstrates that higher brine injection temperatures are required to mitigate aluminum- and iron-rich silica scaling compared with pure amorphous silica. In a laboratory scale test, pure amorphous silica and aluminum-rich silica deposition rates have been measured at high degrees of supersaturation in the presence of potential inhibitors. Scale deposition was best inhibited by brine pH modification techniques. A commercially available dispersant successfully inhibited amorphous silica scaling, but exacerbated aluminum silicate scaling. Scale inhibition was also achieved in the presence of aluminum complexing\\sequestering agents in a patent-pending process. Screening of these potential silica- and aluminum-silicate scale inhibitors in the laboratory will focus the efforts of ongoing field pilot scale testing. The effect of complexing\\sequestering agents on scale inhibition was monitored in preliminary field pilot tests. These complexing agents achieved 25% to 80% aluminum silicate scale inhibition.