Robert L. Siegrist

In Situ Chemical Oxidation of Contaminated Soil and Groundwater Using Persulfate: A review

Persulfate is the newest oxidant that is being used for in situ chemical oxidation (ISCO) in the remediation of soil and groundwater. In this review, the fundamental reactions and governing factors of persulfate relevant to ISCO are discussed. The latest experiences for ISCO with persulfate are presented, with a focus on the different activation methods, the amenable contaminants, and the reactions of persulfate with porous media, based primarily on a critical review of the peer-reviewed scientific literature and to a lesser extent on non-reviewed professional journals and conference proceedings. The last sections are devoted to identifying the best practices based on current experience and suggesting the direction of future research.

Hydraulic and purification behaviors and their interactions during wastewater treatment in soil infiltration systems

Four three-dimensional lysimeters were established in a pilot laboratory with the same medium sand and either an aggregate-laden (AL) or aggregate-free (AF) infiltration surface and a 60- or 90-cm soil vadose zone depth to ground water. During 48 weeks of operation, each lysimeter was dosed 4 times daily with septic tank effluent (STE) at 5 cm/d (AL) or 8.4 cm/d (AF). Weekly monitoring was done to characterize the STE, percolate flow and composition, and water content distributions within the lysimeters. Bromide tracer tests were completed at weeks 0, 8, and 45 and during the latter two times, ice nucleating active (INA) bacteria and MS-2 and PRD-1 bacteriophages were used as bacterial and viral surrogates. After 48 weeks, soil cores were collected and analyzed for chemical and microbial properties. The observations made during this study revealed a dynamic, interactive behavior for hydraulic and purification processes that were similar for all four lysimeters. Media utilization and bromide retention times increased during the first two months of operation with the median bromide breakthrough exceeding one day at start-up and increasing to two days or more. Purification processes were gradually established over four months or longer, after which there were high removal efficiencies (>90%) for organic constituents, microorganisms, and virus, but only limited removal of nutrients. Soil core analyses revealed high biogeochemical activity within the infiltrative zone from 0 to 15 cm depth. All four lysimeters exhibited comparable behavior and there were no significant differences in performance attributable to infiltrative surface character or soil depth. It is speculated that the comparable performance is due to a similar and sufficient degree of soil clogging genesis coupled with bioprocesses that effectively purified the wastewater effluent given the adequate retention times and high volumetric utilizations of the sand media.

In situ chemical oxidation for groundwater remediation

Preface.- In Situ Chemical Oxidation: Technology Description and Status.- Fundamentals of ISCO using Hydrogen Peroxide.- Fundamentals of ISCO using Permanganate.- Fundamentals of ISCO using Persulfate.- Fundamentals of ISCO using Ozone.- Principles of ISCO Related Subsurface Transport and Modeling.- Principles of Combining ISCO with other In Situ Remedial Approaches.- Evaluation of ISCO Field Applications and Performance.- Systematic Approach for Site-Specific Engineering of ISCO.- Site Characterization and ISCO Treatment Goals.- Oxidant Delivery Approaches and Contingency Planning.- ISCO Performance Monitoring.- Project Cost and Sustainability Considerations.- ISCO Status and Future Directions.- Appendices.

Removal of E. coli during intermittent filtration of wastewater effluent as affected by dosing rate and media type

Wastewater effluent dosing rates of 25 and 50 mm/day were intermittently applied in eight daily doses of 3.125 or 6.25 mm each, to 15-cm diameter 80 cm high columns packed with two types of Light Weight Aggregates (LWA) and one type of activated carbon aggregates. After three months of wastewater effluent application at 25 mm/day to stabilize the filter systems, Escherichia coli was spiked once each day onto the surface of the columns and wastewater effluent was applied at 25 mm/day for the months. The same procedure was repeated for effluent application rate of 50 mm/day. During operation, hydraulic behavior was monitored by moisture tensiometers located 5, 10, 20 and 40 cm below the filter surface as well as by radiotracer studies. Removal behavior was assessed by sampling and analysis of the column percolate and media within the column. The removal of E. coli was decreased as a result of increasing the dosing rate for all three media. In all media, the highest removal rates were observed in the upper part of the columns. Sorption head measurements showed that each effluent dose rapidly penetrates through the upper part of the filters, until a steady state, unsaturated flow was established in the lower sections. Different flow patterns were observed for the two dosing rates. For the dosing rate of 50 mm/day, the flow was penetrating faster, and to a deeper level before establishing steady unsaturated flow. Fast flow through the upper part of the filter, where the bacterial removal is most effective, may explain the significantly lower removal for the dosing rate of 50 mm/day. The dynamic behavior of the filter columns showed that most of the water movement took place right after dose application, during intermittent dosing. This indicates that dose size may be just as important for bacterial removal as the daily dosing rate.

Transport and fate of Cryptosporidium parvum oocysts in intermittent sand filters.

The transport potential of Cryptosporidiim parvum (C. parvum) through intermittent. unsaturated, sand filters used for water and wastewater treatment was investigated using a duplicated. 2(3) factorial design experiment performed in bench-scale, sand columns. Sixteen columns (dia = 15 cm, L = 61 cm) were dosed eight times daily for up to 61 days with 65,000 C. parvum oocysts per liter at 15 degrees C. The effects of water quality, media grain size, and hydraulic loading rates were examined. Effluent samples were tested for pH, turbidity, and oocyst content. C. parvum effluent concentrations were determined by staining oocysts on polycarbonate filters and enumerating using epifluorescent microscopy. At completion, the columns were dismantled and sand samples were taken at discrete depths within the columns. These samples were washed in a surfactant solution and the oocysts were enumerated using immunomagnetic separation techniques. The fine-grained sand columns (d50 = 0.31 mm) effectively removed oocysts under the variety of conditions examined with low concentrations of oocysts infrequently detected in the effluent. Coarse-grained media columns (d = 1.40 mm) yielded larger numbers of oocysts which were commonly observed in the effluent regardless of operating conditions. Factorial design analysis indicated that grain size was the variable which most affected the oocyst effluent concentrations in these intermittent filters. Loading rate had a significant effect when coarse-grained media was used and lesser effect with fine-grained media while the effect of feed composition was inconclusive. No correlations between turbidity, pH, and effluent oocyst concentrations were found. Pore-sizc calculations indicated that adequate space for oocyst transport existed in the filters. It was therefore concluded that processes other than physical straining mechanisms are mainly responsible for the removal of C. pavum oocysts from aqueous fluids in intermittent sand filters used under the conditions Studied in this research.

Fate of trace organic compounds during vadose zone soil treatment in an onsite wastewater system

During onsite wastewater treatment, trace organic compounds are often present in the effluents applied to subsurface soils for advanced treatment during vadose zone percolation and groundwater recharge. The fate of the endocrine-disrupting surfactant metabolites 4-nonylphenol (NP), 4-nonylphenolmonoethoxylate (NP1EO), and 4-nonylphenolmonoethoxycarboxylate (NP1EC), metal-chelating agents ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA), antimicrobial agent triclosan, stimulant caffeine, and antibiotic sulfamethoxazole during transport through an unsaturated sandy loam soil was studied at a field-scale test site. To assess the effects of effluent quality and hydraulic loading rate (HLR) on compound fate in the soil profile, two effluents (septic tank or textile biofilter) were applied at two design HLRs (2 or 8 cm/d). Chemical concentrations were determined in the two effluents and soil pore water at 60, 120, and 240 cm below the soil infiltrative surface. Concentrations of trace organic compounds in septic tank effluent were reduced by more than 90% during transport through 240 cm (often within 60 cm) of soil, likely due to sorption and biotransformation. However, the concentration of NP increased with depth in the shallow soil profile. Additional treatment of anaerobic septic tank effluent with an aerobic textile biofilter reduced effluent concentrations of many compounds, but generally did not affect any changes in pore water concentrations. The soil profile receiving septic tank effluent (vs. textile biofilter effluent) generally had greater percent removal efficiencies. EDTA, NP, NP1EC, and sulfamethoxazole were measured in soil pore water, indicating the ability of some trace organic compounds to reach shallow groundwater. Risk is highly dependent on the degree of further treatment in the saturated zone and the types and proximity of uses for the receiving groundwater environment.

Measurement error and spatial variability effects on characterization of volatile organics in the subsurface.

The effects of measurement error and spatial variability on establishing subsurface contaminant distributions were demonstrated in a study described herein, where soil underlying a former land treatment facility was intensively sampled and analyzed for volatile organic compounds (VOCs). Concentrations of VOCs measured on-site using a heated headspace/gas chromatography method were typically 10 times higher than concentrations measured at an off-site laboratory using a purge-and-trap/gas chromatography/mass spectrometry method. This was attributed either to VOC losses during storage and preparation of off-site samples and/or inefficient VOC extraction in the off-site method. Three contaminant distribution models developed from the on-site VOC measurements were evaluated through cross-validation and subregion sampling methods. Order of magnitude discrepancies existed between predicted and measured concentrations. These results show that increasing sampling density with cost-effective field analyses can be more effective than using complex spatial models to overcome the lack of spatial information in sparse data sets comprised of off-site laboratory analyses. 25 refs., 8 figs., 2 tabs.

Intermediate-scale 2D experimental investigation of in situ chemical oxidation using potassium permanganate for remediation of complex DNAPL source zones

In situ chemical oxidation is a technology that has been applied to speed up remediation of a contaminant source zone by inducing increased mass transfer from DNAPL sources into the aqueous phase for subsequent destruction. The DNAPL source zone can consist of one or more individual sources that may be present as an interconnected pool of high saturation, as a region of disconnected ganglia at residual saturation, or as combinations of these two morphologies. Potassium permanganate (KMnO(4)) is a commonly employed oxidant that has been shown to rapidly destroy DNAPL compounds like PCE and TCE following second-order kinetics in an aqueous system. During the oxidation of a target DNAPL compound, or naturally occurring reduced species in the subsurface, manganese oxide (MnO(2)) solids are produced. Research has shown that these manganese oxide solids may result in permeability reductions in the porous media thus reducing the ability for oxidant to be transported to individual DNAPL sources. It can also occur at the DNAPL-water interface, decreasing contact of the oxidant with the DNAPL. Additionally, MnO(2) formation at the DNAPL-water interface, and/or flow-bypassing as a result of permeability reductions around the source, may alter the mass transfer from the DNAPL into the aqueous phase, potentially diminishing the magnitude of any DNAPL mass depletion rate increase induced by oxidation. An experiment was performed in a two-dimensional (2D) sand-filled tank that included several discrete DNAPL source zones. Spatial and temporal monitoring of aqueous PCE, chloride, and permanganate concentrations was used to relate changes in mass depletion of, and mass flux, from DNAPL residual and pool source zones to chemical oxidation performance and MnO(2) formation. During the experiment, permeability changes were monitored throughout the 2D tank and these were related to MnO(2) deposition as measured through post-oxidation soil coring. Under the conditions of this experiment, MnO(2) formation was found to reduce permeability in and around DNAPL source zones resulting in changes to the overall flow pattern, with the effects depending on source zone configuration. A pool with little or no residual around it, in a relatively homogeneous flow field, appeared to benefit from resulting MnO(2) pore-blocking that substantially reduced mass transfer from the pool even though there was relatively little PCE mass removed from the pool. In contrast, a pool with residual around it (in a more typical heterogeneous flow field) appeared to undergo increased mass transfer as MnO(2) reduced permeability, altering the water flow and increasing the mixing at the DNAPL-water interface. Further, the magnitude of increased PCE mass depletion during oxidation appeared to depend on the PCE source configuration (pool versus ganglia) and decreased as MnO(2) was formed and deposited at the DNAPL-water interface. Overall, the oxidation of PCE mass appeared to be rate-limited by the mass transfer from the DNAPL to aqueous phase.

Soil sampling and analysis for volatile organic compounds

AbstractConcerns over data quality have raised many questions related to sampling soils for volatile organic compounds (VOCs). This paper was prepared in response to some of these questions and concerns expressed by Remedial Project Managers (RPMs) and On-Scene Coordinators (OSCs). The following questions are frequently asked:1.Is there a specific device suggested for sampling soils for VOCs?2.Are there significant losses of VOCs when transferring a soil sample from a sampling device (e.g., split spoon) into the sample container?3.What is the best method for getting the sample from the split spoon (or other device) into the sample container?4.Are there smaller devices such as subcore samplers available for collecting aliquots from the larger core and efficiently transferring the sample into the sample container?5.Are certain containers better than others for shipping and storing soil samples for VOC analysis?6.Are there any reliable preservation procedures for reducing VOC losses from soil samples and for extending holding times? Guidance is provided for selecting the most effective sampling device for collecting samples from soil matrices. The techniques for sample collection, sample handling, containerizing, shipment, and storage described in this paper reduce VOC losses and generally provide more representative samples for volatile organic analyses (VOA) than techniques in current use. For a discussion on the proper use of sampling equipment the reader should refer to other sources (Acker, 1974; U.S. EPA, 1983; U.S. EPA, 1986a).Soil, as referred to in this report, encompasses the mass (surface and subsurface) of unconsolidated mantle of weathered rock and loose material lying above solid rock. Further, a distinction must be made as to what fraction of the unconsolidated material is soil and what fraction is not. The soil component here is defined as all mineral and naturally occurring organic material that is 2 mm or less in size. This is the size normally used to differentiate between soils (consisting of sands, silts, and clays) and gravels.Although numerous sampling situations may be encountered, this paper focuses on three broad categories of sites that might be sampled for VOCs:1.Open test pit or trench.2.Surface soils (<5 ft in depth).3.Subsurface soils (>5 ft in depth).

Microbial Diversity of Septic Tank Effluent and a Soil Biomat

ABSTRACT Microbial diversity of septic tank effluent (STE) and the biomat that is formed as a result of STE infiltration on soil were characterized by 16S rRNA gene sequence analysis. Results indicate that microbial communities are different within control soil, STE, and the biomat and that microbes found in STE are not found in the biomat. The development of a stable soil biomat appears to provide the best on-site water treatment or protection for subsequent groundwater interactions of STE.