Groundwater Contamination Risk from Hazardous Waste Injection Wells in Houston, TX, Study Guides, Projects, Research of Geography

Download Groundwater Contamination Risk from Hazardous Waste Injection Wells in Houston, TX and more Study Guides, Projects, Research Geography in PDF only on Docsity! Identifying Potential Risk to Groundwater from Hazardous Waste Injection Wells : A case study of seven counties in the Houston, Texas Area Kelly Sims GEOG 4520 - Intermediate Geographic Information Systems Dr. Minhe Ji May 7th 2002 Introduction Groundwater is a precious resource. It is the largest source of drinking water available, but only about 0.62% of the total amount of water on Earth. (Hudak 3) Contamination of this supply of water could be detrimental to areas that rely on groundwater as their primary source. Groundwater contamination can happen in many different ways and at many different levels. Figure 1, obtained from The Groundwater Foundation, shows some of the many ways groundwater can be contaminated. Many industries create hazardous wastes. Some industries dispose of these wastes by injecting them into wells under high pressure. Some drilling wastes, like brine, are injected back into the ground at the drilling site, while others are taken to another location. This is a reasonable method of disposal, in most cases. However, if injection wells do not follow strict adherence to their rules and regulations, the result could be contaminated water supplies. Therefore, certain groundwater supplies could be at-risk to contamination from these hazardous wastes. Sims, Page 2 of 15 Figure 1. Sources of Contamination Geographic Information Systems technology was used in order to assess the potential pollution risks associated with these hazardous waste injection sites within the Gulf Coast Aquifer of Texas. With this project, the questions asked were: is there a spatial relationship between the location of the hazardous waste injection sites and the public water supply and what areas of the aquifer are at-risk to contamination from these injection sites. Review of Literature Groundwater contamination: Sims, Page 5 of 15 facilities. Other industrial and municipal waste disposal wells which inject fluid beneath the lowermost formation containing an aquifer within one-quarter mile of the well bore. This includes injection wells operated in conjunction with uranium mining activities. This class is regulated by the TNRCC through the use of permits. Class II Wells used to inject “oil and gas waste”, a term that is defined to include waste arising out of or incidental to drilling for or production of oil, gas, or geothermal resources, the underground storage of hydrocarbons other then storage in artificial tanks or containers, or operation of gasoline plants, natural gas processing plants, or pressure maintenance or repressurizing plants. The injected waste fluid (usually salt water) may be combined with wastewaters from gas plants, unless those waters are classified as hazardous waste at the time of injection. Wells used for the enhanced recovery (secondary recovery) of oil or natural gas. Wells used for the underground storage of hydrocarbons which are liquid at standard temperature and pressure. Class III Wells used to inject fluids for extraction of minera ls, exclusive of oil and natural gas. Brine injection wells are regulated by the RCT through permits. The TNRCC has full authority for regulating all other Class III injection wells, all of which are regulated by permit except uranium injection wells, which are regulated by a permit and production area authorization process. Class IV Wells used by generators of hazardous wastes or of radioactive wastes, by owners or operators of hazardous waste management facilities, or by owners or operators of radioactive waste disposal sites to dispose of hazardous wastes or radioactive wastes into or above a formation which contains an underground source of drinking water within one-quarter mile of the well bore. Class V Wells used for miscellaneous injection that are not included in the other class descriptions or are single family residential cesspools or septic system disposal wells. Remediation of Contaminated Groundwater: If groundwater contamination is found in a location, various methods may be used to clean up the polluted area. While digging up soil and trucking it to a landfill might be a relatively easy approach, it is not always the correct choice of action. Sometimes contamination may occur under buildings or to a much greater extent than can be excava ted. Some of the alternative methods include: In Situ Physical or Chemical Treatment, Biological Treatment, and Electrokinetics. A common method is an In Situ method called air sparging. This consists of Sims, Page 6 of 15 injecting gas (usually oxygen) under pressure into saturation zone wells to volatilize contaminants dissolved in groundwater, present as non-aqueous phase liquid, or sorbed to the soil matrix. These contaminants migrate upward and are removed upon reaching the vadose zone, typically through soil vapor extraction. (GWRTAC) Methodology The study area for this paper was first selected due to the location of the Gulf Coast Aquifer in Texas (Figure 3.) However, due to the size of this aquifer, the study area was scaled down to comprise of seven counties in the Houston area of Texas (Figure 5., see inset) These seven counties were chosen due to the high population density of the area, high density of industry, number of injection wells in the area, and the Gulf Coast Aquifer stretches underneath each of these counties. After defining the study area, the next step was to obtain the data on the public water supply wells and the hazardous waste injection wells in Texas. Data were acquired from the Texas Natural Resource Conservation Commission (TNRCC) and the Texas Natural Resource Information System (TNRIS). Once data were obtained, the layers were defined and projected into the same coordinates: UTM zone 14. They consisted of polygon and point layers. The polygons included: Texas counties and the Gulf Coast aquifer. The points included: Texas public water supply wells and Texas hazardous waste injection sites. Sims, Page 7 of 15 Figure 3. Gulf Coast Aquifer Region of Texas The overlay of layers on the map was based on their new coordinate system. The point data was geocoded by latitude and longitude which allowed for the analysis of the sites by geographic location. Portions of the layers were selected based on whether they were within the study area. These selections were saved as new layers and named with the prefix “ha” for Houston Area. Buffers were created around the Houston Area public water supply wells. The hazardous waste injection sites that were within the buffers were saved into a new layer. While Sims, Page 10 of 15 A straight- line-distance correlation was executed to determine the areas of close distance to the public water supply wells. The concentrations of both the public water supply wells and the hazardous waste injection wells are shown by Figure 7. The hazardous waste injection sites that are within the 0.5-mile buffer are depicted in red and the remainder is green. This figure shows the high concentration of the hazardous waste injection wells near the city of Houston and near public water supply wells. The greatest at-risk water wells within the study area were found to be those that are the deepest. This conclusion was reached for two reasons. One reason is that most contaminants flow in a down gradient direction. Therefore, as long as the contaminant does not react with the aquifer medium, it will follow the groundwater flow direction. The second reason is, since the hazardous wastes are being injected into deep-wells, contaminants will be closer to the deeper areas of the aquifer than to the near-surface areas. Figure 5. Sims, Page 11 of 15 Public Water Supply Wells that are within 0.5 miles of a Hazardous Waste Injection Well_in_ counties surrounding the Houston Area. MONTGOMgRY LIBERTY CHAMBERS Counties: ® Hazardous Waste Injection Wells ® Public Water Supply Wells By: Kelly Sims 140,000 May 3rd 2002 Meters Sims, Page 12 of 15 Figure 6, Estimated Surface of the Gulf Coast Aquifer in counties surrounding the Houston Area By: Kelly Sims May 3rd 2002 Value Re High : 6432.33 120,000 Conrad CI Mee ters