Impact of Recharge Through Residual Oil Upon Sampling of Underlying Ground Water

At an aviation gasoline spill site in Traverse City, Michigan, historical records indicate a positive correlation between significant rainfall events and increased concentrations of slightly soluble organic compounds in the monitoring wells of the site. To investigate the recharge effect on ground water quality due to infiltrating, water percolating past residual oil and into the saturated zone, an in situ infiltration experiment was performed at the site. Sampling cones were set at various depths below a circular test area, 13 feet (4 meters) in diameter. Rainfall was simulated by sprinkling the test area at a rate sufficiently low to prevent runoff. The sampling cones for soil-gas and ground water quality were installed in the unsaturated and saturated zones to observe the effects of the recharge process. At the time of the test, the water table was below the residual oil layer. The responses of the soil-gas and ground water quality were monitored during the recharge and drainage periods, which resulted from the sprinkling.
Infiltrated water was determined to have transported organic constituents of the residual oil, specifically benzene, toluene, ethylbenzene, and ortho-xylene (BTEX), into the ground water beneath the water table, elevating the aqueous concentrations of these constituents in the saturated zone. Soil-gas concentrations of the organic compounds in the unsaturated zone increased with depth and time after the commencement of infiltration. Reaeration of the unconfined aquifer via the infiltrated water was observed. It is concluded that water quality measurements are directly coupled to recharge events for the sandy type of aquifer with an overlying oil phase, which was studied in this work. Ground water sampling strategies and data analysis need to reflect the effect of recharge from precipitation on shallow, unconfined aquifers where an oil phase may be present.     

Ground Water Remediation Using an Extraction, Treatment, and Recharge System

Ground water remediation of volatile organic compound (VOC) contamination at a site in Michigan was initiated as a result of a consent agreement between the Michigan Department of Natural Resources (MDNR) and the responsible party. Under the direction of the MDNR, the responsible party conducted a remedial investigation/feasibility study using federal guidelines to define the extent of contamination at the site and to select a response action for site remediation. The selected alternative included a combination of ground water extraction, treatment, and recharge, and soil flushing. The extraction system withdraws ground water from various depths in heavily contaminated areas. The ground water is treated using an air stripper. A spray distribution system spreads effluent from the stripper over a recharge basin constructed over the most contaminated areas. Additional contaminant removal is achieved by volatilization from the spray and percolation through the gravel bed. Recharge water moves downward through the contaminated soils, thus flushing residual soil contaminants. The initial operating data demonstrated that the system can effectively remove trichloroethylene (TCE) from ground water (approximately 95 percent overall removal efficiency). The annualized capital and operation and maintenance (O & M) costs of the remedial action were estimated for several operating periods (15, 20, and 30 years).     

Planning Urban Growth in Ground Water Recharge Areas: Central Valley, Costa Rica

Nitrate levels in the ground water of the Central Valley of Costa Rica have increased in relation to the past. Previous studies determined that the unseweved sanitation systems in the recharge areas are the main source of nitrogen. Calculations are made in this study to estimate the maximum population density allowable without improved sewage systems in order to keep the nitrogen levels in ground water below the World Health Organization (WHO) criteria. Results were achieved employing a mass balance that involved the concentration and rate of domestic effluents and the flow rate in the aquifer, as well as an estimation of the effects caused by the agricultural activity. It was concluded that, in general terms, the population density must not exceed 45 inhabitants per hectare. Otherwise, sewage systems and treatment plants are necessary. These conclusions provide a basis for urban growth planning, which will protect ground water quality. The method used in this case should apply to similar situations.     

The Ground Water Recharge and Pollution Potential of Dry Wells in Pima County, Arizona

This paper summarizes a study to estimate the potential for dry-well drainage of urban runoff to recharge and pollute ground water in Tucson, Arizona. We selected three candidate dry wells for study. At each site we collected samples of runoff, dry-well sediment, vadose-zone sediment, perched ground water, and ground water. Water content data from vadose-zone samples suggest that dry-well drainage has created a transmission zone for water movement at each site. Volatile organic compounds, while undetected in runoff samples, were present in dry-well sediment, perched ground water at one site, and ground water at two sites. The concentrations of volatile organics (toluene and ethylbenzene) in the water samples were less than the corresponding EPA human health criteria. Pesticides were detected only in runoff and dry-well sediment. Lead and chromium occurred in runoff samples at concentrations above drinking water standards. Nickel, chromium, and zinc concentrations were elevated in vadose-zone samples at the commercial site. Of the metals, only manganese, detected at the residential site, exceeded Secondary Drinking Water Standards in ground water. It is concluded that the three dry wells examined during this study are currently not a major source of ground water pollution.     

Coproduced Ground Water Treatment and Disposal Options During Hydrocarbon Recovery Operations

Reinjection of untreated ground water during hydrocarbon recovery operations provides for economical water handling and can accelerate the recovery of the free hydrocarbons. However, considering current regulatory trends, water containing dissolved hydrocarbon constituents would require treatment prior to reinjection into the aquifer. The disposal of coproduced ground water is dependent on several factors, including the volume of water, level of treatment required, and availability of disposal options. Disposal options include reinjection, discharge to surface water, and beneficial use. This paper presents treatment and disposal options for coproduced water during hydrocarbon recovery operations including cost comparisons for a particular case study.
Treatment technologies for oil/water separation, inorganics and heavy metals removal, and dissolved hydrocarbon removal are presented. The primary technologies discussed for dissolved hydrocarbon removal include air stripping, activated carbon adsorption, biological treatment, and combinations of these technologies. Consideration of the use of existing refinery waste water treatment facilities for ground water treatment should be encouraged where applicable. However, separate treatment facilities are usually required because the use of existing on-site treatment facilities is usually not feasible because of the volume of water produced during large recovery projects and the effectiveness of existing treatment facilities. A specific case example is presented with costs for applying different technologies including the use of existing on-site facilities. Treatment costs ranged between 44 cents to $2.82 per thousand gallons (11 cents to 75 cents per thousand liters) of water treated for the specific technologies examined herein.     

Ground Water Recharge and Chemical Contaminants: Challenges in Communicating the Connections and Collisions of Two Disparate Worlds

Our knowledge base regarding the presence and significance of chemicals foreign to the subsurface environment is large and growing — the papers in this volume serving as testament. However, complex questions with few answers surround the unknowns regarding the potential for environmental or human health effects from trace levels of xenobiotics in ground water, especially ground water augmented with treated waste water. Public acceptance for direct or indirect ground water recharge using treated municipal waste water (especially sewage) spans the spectrum from unquestioned embrace to outright rejection. In this paper, I detour around the issues most commonly discussed regarding ground water recharge and instead focus on some of the less-recognized issues—those that emanate from the mysteries created at the many literal and virtual interfaces involved with the subsurface world. My major objective is to catalyze discussion that advances our understanding of the barriers to public acceptance of waste water reuse with its ultimate culmination in direct reuse for drinking. I pose what could be a key question as to whether much of the public's frustration or ambivalence in its decision-making process for accepting, or rejecting, water reuse (for various purposes including personal use) emanates from fundamental inaccuracies, misrepresentation, or oversimplification of what water is and how it functions in the environment—just exactly what the water cycle is. These questions suggest it might behoove us to revisit some very elementary aspects of our science and how we are conveying them to the public.