California EPA Department of Toxic Substance Control Uses Geospatial Analysis to Target Site Remediation
Need to get that stain out of your favorite business suit? Surely the local dry cleaning shop can remove it. For years, dry cleaners have used perchloroethylene (PERC) to efficiently remove spots from garments. But what is good for your clothes is not good for your health, because PERC is a carcinogen. The offal produced in dry cleaning processes is classified as hazardous waste that contaminates soil and gets into the drinking water. The California Environmental Protection Agency's (Cal/EPA) Department of Toxic Substance Control (DTSC) has been using GIS to locate and prioritize community sites that have been contaminated by dry cleaning chemicals and need remediation.
In 2007, California legislators banned the use of PERC because it endangers the environment and public health. PERC is a volatile compound and can migrate from the groundwater through the soil and into the air, where it may be trapped within homes and businesses. PERC vapors may also contribute to toxic smog. Federal environmental protection and state health officials warn that either inhaling PERC vapors or ingesting PERC in drinking water causes esophageal cancer, lymphoma, and cervical and bladder cancer and may affect the central nervous system. Now, many dry cleaners have adopted different practices, such as using silicone or carbon-based cleaning substances. But the dry cleaner industry has left its legacy of PERC in the soil, threatening water and air resources.
With a grant from the Cal/EPA in 2005, DTSC staff developed a dry cleaner discovery process that uses data from the California Department of Public Health's drinking water well database and ArcGIS technology to spatially analyze at-risk sites in California's Central Valley. Two years later, DTSC launched its initial discovery project, focused on a community of 123,000 people located in the San Joaquin Valley at the base of the Sierra Nevada Mountains.
In the initial phase of the project, DTSC sampled the soil and shallow groundwater and analyzed the results. "GIS is an incredible tool to use for analysis of sampling data," notes Rick Fears, DTSC project manager and engineering geologist. "We used the Department of Public Health's database to generate a map of PERC-impacted public supply wells and their proximity to current and former dry cleaning operations. We then examined existing land-use and landownership data to determine potential areas of concern. With GIS, we were able to use this information to guide our sampling program, record the data, and analyze the results."
To detect the impact of dry cleaning contamination, the team first samples wells and tests them for halogenated hydrocarbons—most predominantly, PERC. Field-workers, such as licensed land surveyors, use GPS to attach latitude and longitude coordinates to the samples at the site. This location data makes it possible for the GIS team to create a well sample data layer in ArcGIS and generate a map that shows the proximity of dry cleaners to public water supply wells.
This map is used to direct the next phase, wherein field-workers perform soil borings to collect passive soil gas samples in shallow soil. Once again, they use GPS to attach coordinates, capturing sample record data at submeter levels. Because the sample data layer includes laboratory results, health risk assessors can query the geodatabase, requesting to see all the wells containing a certain level of PERC. They can also see specific sample data about the PERC concentration of trichloroethylene (TCE) in soil gas. Moreover, they can run screening models on this data and determine potential health risks for people occupying buildings around those areas, prioritize remedial action, and determine areas where additional analysis is needed.
The strength of ArcGIS is its ability to show geospatial relationships between different information sources. To create a comprehensive view of the project, toxic sample data can be correlated with other brownfield cleanup project data, such as underground storage tank or other environmental project information. The data is useful for identifying potential contamination sources and risks to public health. In addition to the Department of Public Health's public water supply data, DTSC also accesses U.S. Geological Survey (USGS) maps and data from the California Air Resources Board, which is responsible for licensing dry cleaners. Another valuable data resource is DTSC's Hazardous Waste Tracking System.
Generators of hazardous wastes that dispose of solvents off-site are required to complete a manifest for shipping to a disposal facility. This information enables the government to attach a business name to a hazardous waste generator or contractor removing wastes from a contaminated site. This data makes it possible for analysts to identify a time frame for when the pollutant was generated or may have been released into the ground. All this data is used to coax a picture of an area's potential threats to groundwater and public health. Combining this data with their own expertise, DTSC staff members assigned prioritization to site cleanup projects.
"We initiated this dry cleaner discovery project in consultation with the Regional Water Quality Control Board for the Sacramento and San Joaquin valleys," explains Steve Becker, DTSC supervisor. "Performing a statewide investigation of PERC detections in public water supply wells, the team noted clusters of impacted public supply wells."
The first step of the dry cleaner discovery project was to develop a process to locate potential problems associated with dry cleaner operations, and the second step was to apply the process in consultation with the local community and government. Through this process, 35 cleaners in one city were identified as potential PERC sources. Of these, 20 sites were designated as candidates for possible remediation.
A subsequent 2008 study of active soil gas and water samples in the community revealed contamination in shallow soil and groundwater at 80 to 90 feet below ground surface. In general, DTSC determined that the overall level of contamination would not present a short-term risk of health effects. But DTSC did decide to evaluate potential vapors that may have moved into nearby buildings. It determined that additional sampling needs to be performed in seven other areas in the vicinity where elevated levels of PERC have been discovered. The locations and remediation status were posted on DTSC's EnviroStor database, a map-based Web site (envirostor.dtsc.ca.gov).
"We have a two-tiered technique of putting GIS to work," explains Mike Vivas, hazardous substances engineer and project manager for DTSC's site cleanup program. "One is to use GIS to build our project-specific shapefile library and generate composite maps of relevant features that can be combined with municipal and county data such as shapefiles for the local sewer system and local parcel maps. The maps display relevant features that we can click on and off for a clear view of the spatial relationships that can guide site remediation activities. The second is to use a server for general record keeping and publishing information via our online tool EnviroStor."
EnviroStor is a map-based information system that allows the public to search for properties regulated by DTSC, where extensive investigation and/or cleanup actions are planned or have been completed at permitted facilities and cleanup sites. Citizens can type in their own addresses and see if cleanup sites and permitted hazardous waste facilities are near where they work or live. Site visitors type in the city or county, and the tool offers them a list of cleanup projects, a report and map, the cleanup status (active, inactive, complete), facility type, and site address. Users can click data layers such as Federal Superfund, Voluntary Cleanup, Corrective Action, and Hazardous Waste Permit. The GIS-generated dynamic data files are laid over a static Google basemap.
This information provides transparency to the community. "School districts are particularly interested in this data," notes Bud Duke, a DTSC project manager and senior engineering geologist in its schools program. "In California, any school district that is going to use state funds to either build a new school or expand an existing school is required to go through DTSC to ensure that the site is safe for students and staff." Duke and Fears used ArcGIS to create maps that helped project managers screen school sites for environmental health risks.
Different types of data can be input into a GIS to better understand a site's geographic context. DTSC uses GIS to run a predictive model that shows where naturally occurring asbestos and other contaminants may be. Researchers identified ultramafic formations, which are rock formations that potentially contain asbestos, throughout the state. They also obtained data about radon gas locations from the California Geological Survey and USGS along with the locations of soil samples collected for arsenic content. Comparing these data layers with the locations of schools provides insight needed about contamination that may endanger schoolchildren.
GIS shapefiles can also be shared with other government agencies. For example, California's State Water Resources Control Board (SWRCB) hosts the map-based Web site GeoTracker, which has the same look and feel as EnviroStor and shows data about water quality monitoring. DTSC can overlay data layers from EnviroStor with those from SWRCB for publication on the Web. SWRCB has established regulations for reporting data to GeoTracker. DTSC is working on a regulation package that will require DTSC, responsible parties, and hazardous waste facility operators to submit environmental data and reports electronically to EnviroStor. These Web sites allow this data to be easily added to the databases so that it can be dynamically mapped with GIS.
ArcGIS also provides visualization of surface and subsurface in 3D so that users have a clear understanding of their data. Maps that show potential health risks, soil porosity, mineralogy, types of substances, slopes, groundwater flow, groundwater proximity, and a host of other attributes help brownfield cleanup project managers direct site remediation efforts.