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In cooperation with the U.S. Army Corps of Engineers, Chicago District, the U.S. Geological Survey investigated the processes affecting water quality, geochemistry, and microbiology in representative extraction and monitoring wells at a confined disposal facility (CDF) in East Chicago, Indiana. The CDF is a 140-acre Federally-managed facility that was the former location of an oil refinery and is now used for the long-term disposal and storage of dredge material from the Indiana Harbor and Indiana Harbor Canal. Residual petroleum hydrocarbons and leachate from the CDF are contained within the facility by use of a groundwater cutoff wall. The wall consists of a soil-bentonite slurry and a gradient control system made up of an automated network of 96 extraction wells, 42 monitoring wells, and 2 ultrasonic sensors that maintain an inward hydraulic gradient at the site. The pumps in the extraction wells require vigilant maintenance and must be replaced when unable to withdraw water at a rate sufficient to maintain the required inward gradient. The wells are screened in the Calumet aquifer, a coarse-grained sand and gravel unit that extends approximately 35 feet below the land surface and is not utilized for drinking-water supply at the CDF or in the surrounding area. This study was initiated to identify the cause of decreased pump discharges and to identify potential mitigation strategies. For this study, the U.S. Geological Survey collected groundwater and solids from monitoring and extraction wells. Groundwater samples were collected during June 2014 for precautionary health screening and on four occasions during September 2014 through November 2014. Groundwater samples collected from two extraction wells during June 2014 were analyzed for concentrations of anthropogenic organic constituents. During September through November 2014, groundwater samples were collected from one additional extraction well, and samples from three monitoring wells were analyzed for concentrations of inorganic and organic constituents, dissolved gases, and bacterial abundance and diversity. Solid samples were collected during April 2014, during September 2014 through November 2014, and during November 2016. Solid samples were collected from the exterior of extraction-well pumps and as flocculent from water samples. Solid samples were collected from 10 wells, including 1 extraction well and 3 monitoring wells sampled for water quality. Solid samples were analyzed for mineralogy, solidphase habit, geochemistry, and organic composition. The following is a list of observations that were made during this study: (1) the water quality is substantially variable among the six well locations sampled as part of this study— lower (more negative) redox values and higher concentrations of many constituents (including calcium, magnesium, sodium, and sulfate) and properties (including dissolved solids, hardness, and turbidity) were detected in sampled wells located near the extraction wells with the highest frequency of failure; (2) water-level drawdown is variable between extraction wells—wells with the greatest drawdown may pull deeper groundwater into the borehole; (3) dissolved gas results indicate reducing oxidation-reduction processes in the aquifer material that can feasibly contribute iron, carbon dioxide, and other byproducts from hydrocarbon degradation to precipitates and solids that accumulate on and impair pump operation; (4) crystalline and amorphous solid-phase minerals are precipitating in the borehole; (5) several types of bacteria are present in water pumped from extraction wells and are likely responsible for bonding mineral and microbiologic matter to the pump (and other well components); and (6) bacteria may create microenvironments that facilitate precipitation of solids or inhibit dissolution of unstable minerals once the bacteria adhere to biofilm attached to the pump. Results of the study indicate that bacteria may be accumulating and entrapping solid material on the exterior of pumps. This accumulation reduces heat transfer and water discharge from the pump and may lead to decreased efficiency or mechanical failure. Observations could not be made on the well screen, gravel pack, or surrounding geologic formation; therefore, mitigating measures in the borehole may not solve well-productivity issues. 2 Geochemistry and Microbiology of Groundwater and Solids from Extraction and Monitoring Wells, East Chicago, Indiana Remedies for the pump fouling problems were derived from the review and interpretation of data collected during this study and from information documented in other sources about groundwater well fouling. Potential remedies to problems associated with pump fouling at the CDF may include the following: (1) reducing attractiveness of the extraction wells for microbiological growth by modifying the chemical or physical environment of the well, (2) modifying the pump exterior to decrease microbiological adherence, (3) changing the pumping regime to control the chemistry of water entering the well from the surrounding aquifer material, (4) modifying the pumps to be less physically and thermally attractive, and (5) removing hydrocarbons from groundwater and the aquifer material surrounding the wells or adding surfactants to make them more mobile. Pilot scale testing may be necessary to identify the most effective treatment or combination of treatments. Introduction The U.S. Geological Survey (USGS), in cooperation with the U.S. Army Corps of Engineers (USACE), led a study during June 2014 through November 2014 to specifically identify the hydrologic, chemical, and microbiologic processes affecting declining pump efficiency and frequent pump failure at a confined disposal facility (CDF) in East Chicago, Ind. (fig. 1). A decline in groundwater pump efficiency through time is common and can be attributed to biofouling (Sterrett, 2007). To better understand the causes behind declining pump efficiency, data were collected to describe the geochemistry and microbiology of groundwater and solids collected from extraction and monitoring wells at the CDF. Site History The efficiency of groundwater-extraction wells used to maintain an inward hydraulic gradient at the CDF site near East Chicago, Ind., is of necessary operational concern for the site operator, the USACE, Chicago District. The inward hydraulic gradient is maintained by use of a network of monitoring and extraction wells (fig. 2). The site was formerly the home of oil-refining operations. In 1981, the property owner filed for bankruptcy; therefore, all aboveground materials and structures related to refinery operations were removed, and the site was covered with a layer of clean soil. Groundwater monitoring began in 1991 following the detection of hydrocarbon contamination, and a groundwater-recovery system was installed in 1992 along the southern boundary of the CDF property on the north side of the Lake George Branch (fig. 1). Organic compounds have been identified in soil and water samples since monitoring began and were observed during installation of the extraction and monitoring wells that currently regulate water levels at the CDF (Cohen and others, 2002) (fig. 3). Hydrocarbon seepage along the south margin of the property and into the Lake George Branch also was described in Cohen and others (2002). The location of hydrocarbons at the site differs through time. The Lake George Branch is a segment of the Indiana Harbor Canal (fig. 1). The Lake George Branch and Indiana Harbor Canal are connected to Lake Michigan (fig. 1) and water levels in the Indiana Harbor Canal vary continually in response to water levels in Lake Michigan and discharges from the Grand Calumet River (fig. 1), another tributary of the Indiana Harbor Canal. The gradient-control system at the CDF automatically responds to changing water levels in groundwater adjacent to the Indiana Harbor Canal. The study area is underlain by the Calumet aquifer and wells at the CDF are completed in that geologic unit. The Calumet aquifer is a coarse-grained sand and gravel unit that extends approximately 35 feet (ft) below the land surface. The Calumet aquifer is not utilized for drinking-water supply at the CDF or in the surrounding area and for purposes of this study, is referred to as “aquifer material”. Maintenance of inward, horizontal hydraulic gradients on all sides of the CDF is a critical operating feature of the site that enables isolation and control of residual hydrocarbons and leachate from the dredged sediment as well as control of existing site issues. The 22 nests of 4 extraction wells were installed in the permeable aquifer material, surficial sand and gravel deposits inside a groundwater cutoff wall. The groundwater cutoff wall consists of an impermeable bentonite slurry that extends from land surface to at least 3 ft below the interface between the fine-grained deposit and the surficial aquifer material. An additional eight extraction wells were added to three well nests along the southern perimeter of the CDF in 2015. Two monitoring wells are collocated with each nest of extraction wells. One monitoring well is located inside the slurry wall, and one monitoring well is outside the slurry wall. Pumps within the extraction wells are periodically activated to maintain an inward gradient between the monitoring wells. Extraction wells are about 30 ft with 5-ft screens at their base to limit the possibility for drawdown to reach the well screen. The wells were screened below occasional residual petroleum contamination from prior site activities. A strong hydraulic connection between wells and aquifer materials surrounding the well screen is necessary to allow accurate monitoring of water levels in the subsurface and to maintain withdrawal rates required to establish the inward gradient. A poor connection between the well and the surrounding materials can increase drawdown in the extraction well and

scientific investigations report

Geochemistry and microbiology of groundwater and solids from extraction and monitoring wells and their relation to well efficiency at a Federally operated confined disposal facility, East Chicago, Indiana