Analysis of historical data (arsenic concentrations and site locations, and in most cases, well depths) from regional ground-water investigations was the starting point for evaluation of distribution of arsenic in the Willamette Basin. Some wells were sampled more than once; in these cases, the first-in-time sample was selected. Four sets of historical data included in table D2 are described below.
These data were collected between 1971 and 1997 as parts of various USGS projects. Many of these projects were regional in scope, and thus these data cover large areas in the Willamette Basin. In addition to arsenic concentrations, depth data also were retrieved. Data from both unfiltered and filtered samples were found in NWIS. Some of these NWIS data are discussed in the following reports: Frank and Collins, 1978; Gonthier, 1983; Leonard and Collins, 1983; Hinkle, 1997. Project data, although stored in NWIS, are discussed separately (see section "Sampling Design for Project Data").
These data, also from regional-scale projects, encompass large areas in the southern part of the basin. The data were collected between 1964 and 1973 by USGS personnel. Well depths were obtained from tables in the reports. Techniques used to process these samples (in particular, filtering or a lack thereof) are not known.
These data were collected during 1962-63, and summarized by Goldblatt and others (1963). Many of these wells withdraw water from the arsenic-rich Fisher Formation (Goldblatt and others, 1963). Arsenic concentrations and well depths were compiled from original project notes from USGS files. Samples were collected and analyzed as unfiltered samples (A.S. Van Denburgh, U.S. Geological Survey, oral commun., 1997).
More than 100 wells were sampled for arsenic by the Environmental Health Program in 1987. Most of these wells were located near Sweet Home, an area that received little coverage in the three regional data sets listed above. Drillers' logs were on file with the Environmental Health Program for many of these wells. In 1996, USGS personnel were able to locate 65 homes corresponding to addresses from well drillers' logs for sampled wells. Arsenic concentrations from Environmental Health Program files and well depths from well drillers' logs were matched with the home locations to create a data coverage. Samples were probably collected and analyzed as unfiltered samples.
Frank, F.J., 1973, Ground water in the Eugene-Springfield area, southern Willamette Valley, Oregon: U.S. Geological Survey Water-Supply Paper 2018, 65 p.
______, 1974, Ground water in the Corvallis-Albany area, central Willamette Valley, Oregon: U.S. Geological Survey Water-Supply Paper 2032, 48 p.
______, 1976, Ground water in the Harrisburg-Halsey area, southern Willamette Valley, Oregon: U.S. Geological Survey Water-Supply Paper 2040, 45 p.
Frank, F.J., and Collins, C.A., 1978, Ground water in the Newberg area, northern Willamette Valley, Oregon: Oregon Water Resources Department Ground-Water Report Number 27, 77 p.
Goldblatt, E.L., Vandenburgh, A.S., and Marsland, R.A., 1963, The unusual and widespread occurrence of arsenic in well waters of Lane County, Oregon: Eugene, Oregon, Lane County Department of Public Health, 24 p.
Gonthier, J.B., 1983, Ground-water resources of the Dallas-Monmouth area, Polk, Benton, and Marion Counties, Oregon: Oregon Water Resources Department Ground-Water Report Number 28, 50 p.
Helm, D.C., and Leonard, A.R., 1977, Ground-water resources of the lower Santiam River Basin, middle Willamette Valley, Oregon: Oregon Water Resources Department Ground-Water Report Number 25, 75 p.
Hinkle, S.R., 1997, Quality of shallow ground water in alluvial aquifers of the Willamette Basin, Oregon, 1993-95: U.S. Geological Survey Water-Resources Investigations Report 97-4082-B, 48 p.
Leonard, A.R., and Collins, C.A., 1983, Ground water in the northern part of Clackamas County, Oregon: Oregon Water Resources Department Ground-Water Report Number 29, 85 p.
Report: Ground-Water and Water-Chemistry Data for the Willamette Basin, Oregon
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