ArcView was used to identify which wells were common to two or more vintages. Of the over 1,600 wells: 87 wells had both EPA & IDEM locations; 59 wells had both EPA & USGS locations; 7 wells had IDEM & USGS locations; and, 5 wells had locations from all three efforts. The EPA set was used as a standard for preliminary comparisons because of the number of wells common to either the IDEM or USGS data sets.
The locations were compared between EPA & IDEM and EPA & USGS efforts, resulting in two sets. Distances between locations in respective sets were calculated and then compared statistically. Distances greater than one kilometer were attributed to typographical errors and dropped from each set. The average distance between EPA & IDEM locations was 15m, and 48m for the EPA & USGS efforts. The average difference in distances calculated for both sets is statistically significant at the 99% level. A confirmation survey by IDEM was done in spring 1997.
All vintages of locations were compared to high-quality locations obtained directly using survey quality equipment and methods in a confirmation survey. Neither IDEM, USGS or EPA method consistently achieved better than 5m accuracy. Both EPA and IDEM locations exceeded the EPA 25m goal for accuracy. The USGS locations though surprisingly accurate for the methods used, did not meet the EPA 25m goal.
This paper summarizes aspects of GIS development in the Hazardous Waste Geology Section, Office of Solid and Hazardous Waste Management, Indiana Department of Environmental Management. However, the views presented in this paper do not necessarily reflect the views of the agency. This project is funded annually by the US EPA to facilitate the clean-up of Northwest Indiana, which is designated as one of 43 Areas Of Concern around the Great Lakes by the International Joint Commission pursuant to the Great Lakes Water Quality Agreement between the US and Canada. Designation as an area of concern facilitates the interaction between all involved to design long term consensus-based plans to minimize an area's impact on the Great Lakes. Funding for the project is through the Great Lakes Initiative Program Element of EPA's annual Resource Conservation and Recovery Act 3011 grant to the Indiana Department of Environmental Management.
The United States Geological Survey has a network of over 160 wells in Northwestern Indiana. Locations for wells in the regional network were usually scaled form from 7.5 minute quads and occasionally surveyed with conventional methods. The locations were suitable for 1:120,000 scale maps in various reports for which the wells were installed. The wells were installed over decades to determine regional "ambient" water quality and flow; but not to define contamination "hot spots" (Rosenshein, 1961; Rosenshein & Hunn, 1962; Crawford & Wangsness, 1987; Watson & others, 1989; Fenelon & Watson, 1993; Shedlock & others, 1994; Greeman, 1995; Duwelius & others, 1996). Therefore, the USGS wells generally are outside of industrial sites. Of the 160 USGS wells, 59 also had locations determined by the EPA in another regional effort.
The EPA located 268 wells in Indiana directly, using hand-held mapping grade GPS receivers adjusted through undisclosed post-processing. The EPA collected the locations over several years, as part of a regional groundwater flow and quality study to document the extent and concentration of groundwater contamination (Kay & others, 1996). The results of the study were displayed as 1:120,000 scale maps. Wells in EPA's network are mostly on regulated industrial sites, with 59 USGS wells and 87 IDEM wells.
IDEM's locations for the wells were digitized from various types of site maps provided by the regulated concerns. Facility maps were transformed into real-world coordinates obtained from IDEM GPS surveys. The IDEM GPS surveys used first and second order monuments with survey grade static GPS methods. The transformed maps were digitized through either AUTOCAD or ARCINFO to obtain well locations. The IDEM methods for conversions are further discussed by Murray & others (1997).
The IDEM data set has over 1,600 located wells. The IDEM data is comprised of "all" wells for 58 regulated sites includes some USGS wells, and is updated regularly. This data set is one part of an effort to build a quantitative environmental data management system using GIS (Koelpin & Goldblatt, 1996). The 1,600 wells were not surveyed directly because of costs.
ARCVIEW was used to identify which wells were common to two or more vintages. The number of wells of interest were pared down through selection of wells within specified distances of wells in the other ARCVIEW themes. Result sets were converted to shapefiles. Dbase tables included well "ownership" and x-y coordinates in NAD83, UTM. Owners of wells (IDEM, EPA or USGS) were used to relate the tables and attach locations of differing vintages to respective wells. These tables were checked by hand to assure one-to-one correspondence between well names in the different vintages of locations. Of 1,600 monitoring wells in the region: 87 wells had both EPA & IDEM locations; 59 wells had both EPA & USGS locations; 7 wells had IDEM & USGS locations; and, 5 wells had locations from EPA, USGS and IDEM.
A confirmation survey was done by IDEM in March, 1997. An effort was made to confirm locations for at least ten percent of the wells from each set. Eleven of the 87 EPA-IDEM wells and ten of the 59 EPA-USGS wells were selected for confirmation. The five wells with locations from all three vintages were included in the confirmation survey, resulting in a 16 well total for the confirmation survey. Again, survey quality equipment and static GPS methods were used, incorporating first and second order NGS control.
For final comparisons the wells were grouped by IDEM/EPA locations, and USGS/EPA locations. The differences between vintage and confirmation locations were calculated for each well and then averaged within each vintage. The number of samples (wells) needed to have a 90% confidence level that the calculated average for the confirmation wells is within 2.5m of the "true" average was also calculated and was always less than the confirmation sample size. These values were calculated to allow for the small confirmation survey sample size (Dr. P. de Caprariis, 1986, unpublished lecture notes) as follows:
Calculation of the required number of samples does two things: first, it suggests that the number of wells in the confirmation survey was adequate; and secondly, all three methods of locating wells may had a reasonable likelihood of meeting EPA's goal of a 25m range of accuracy for locational data.
The IDEM wells used in the confirmation survey were censored, making that set most like the parent population of wells. Two wells were omitted (censored) from the IDEM/EPA confirmation set because in one case the incorrect well was surveyed during the confirmation survey (incorrectly identified in the field) and in the second case the source maps used to derive the IDEM locations were of unacceptable quality. Student's t-tests of differences between the IDEM/EPA locations suggest that without censoring some wells, the set of IDEM wells selected for the confirmation survey does not resemble the whole population of the IDEM/EPA wells.
Censoring the USGS/EPA confirmation wells adversely affected the average values in comparisons. Three wells were dropped from the confirmation set because it is believed that incorrect locations for the wells were reported in the source tables from the USGS - namely that the wells reported were confused with similar wells in the vicinity. However, deleting three wells from the confirmation set causes the set to become significantly different from the parent population of wells when compared with a Student's t-test. Censoring the wells reduced the average difference to an acceptable range, but that apparent "acceptable" accuracy cannot be applied the whole population of USGS wells in the region. Using all the USGS/EPA wells in the confirmation set raises the average difference to 44m.
The USGS method of deriving locations were surprisingly accurate. Even though the USGS well locations were scaled from 7.5 minute quads having a stated accuracy of plus or minus 40m, over half (four of seven) of the censored USGS locations are within 25m of the confirmation survey locations. However, further review of censored and uncensored USGS well sets challenges the ability of the method to meet the EPA 25m goal.
The IDEM approach to locating wells meets the 25m EPA goal for locational accuracy, economically and in a timely manner. Accuracy is directly related to the quality of the source maps used to generate locations. Highest accuracies were realized at sites submitting digital maps. Costs per well and per site range from one quarter to three fourths that of a similar efforts we are contracting out, depending on how IDEM equipment and fixed staff costs are treated. The method is also timely in that we located six times as many wells as EPA contractors in three years compared to their two years, and on a per site basis, we tied our current contractors.
The IDEM locations were compared to locations for some of the same wells obtained by either the USGS and/or EPA, and to high-quality locations obtained directly using survey quality equipment and methods in a confirmation survey. Neither IDEM, USGS or EPA method consistently provided better than 5m accuracy. Both EPA and IDEM locations exceeded the EPA 25m goal for accuracy. The USGS locations though surprisingly accurate for the methods used, did not meet the EPA 25m goal.
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