THE IOWA STATE-WIDE RURAL WELL-WATER SURVEY DESIGN REPORT: A SYSTEMATIC SAMPLE OF DOMESTIC DRINKING WATER QUALITY
G.R. Hallberg, B.C. Kross, R.D. Libra, L.F. Burmeister, L.M.B. Weih, C.F. Lynch, D.R. Bruner, M.Q. Lewis, K.L. Cherryholmes, J.K. Johnson, M.A. Culp
Iowa Department of Natural Resources, Geological Survey Bureau,
Technical Information Series 17, 1990, 135 p.
The Iowa Department of Natural Resources and the University of Iowa (UI) Center for Health Effects of Environmental Contamination conducted a survey (a one-time sampling) of the quality of private drinking-water supplies used by rural Iowans. The State-Wide Rural Well-Water Survey (SWRL) was carried out between April 1988 and June 1989. The two primary objectives were to address: 1. What proportion of private rural wells in Iowa are affected by various environmental contaminants? and 2. What proportion of rural Iowa residents are utilizing well water containing these environmental contaminants?
To provide a statistically valid framework to answer these questions, a systematic sample, stratified by rural population density, was designed. A target of 698 sites was defined, based on statistical considerations, available funds and logistical constraints. The systematic framework was defined using every 5-minute intersection of latitude and longitude in the state; the intersections chosen for sampling sites, were distributed proportionally through the population, based on rural-population density strata, defined at the county level. The drinking-water well closest to each chosen intersection was selected for sampling. Iowa State University Cooperative Extension Service county staff identified eligible participants, based on design criteria.
The effect of temporal variability in groundwater quality during the survey was addressed in two ways: 1. 10% of all sites were sampled a second time, but during a different season; 2. all sites within a county (or counties), typifying six general hydrogeologic regions in Iowa, were sampled quarterly. In addition, routine sampling was dispersed across the state seasonally.
Standardized procedures for field activities were employed during SWRL. An appointment was arranged for each site, so that a resident was available to interview. Information was compiled on items such as well construction, agricultural practices, water treatment, past water-quality problems, waste disposal practices, and the general health status of rural residents. The drinking water wells' construction/placement characteristics and proximity to point-sources of contamination were inventoried by field staff. Sampling points were chosen as close to the well as possible; the water-system was purged until tracking measurements were stable. Samples for laboratory analysis were collected in pre-treated containers supplied by the laboratories. Field quality assurance and quality control (QA/QC) included blank, spiked, and duplicate samples. Custody forms tracked the movement of all sample containers.
All primary well-water samples collected were analyzed for total coliform bacteria; nitrate (+nitrite)-N, ammonia-N, and organic-N; major inorganic ions; 27 commonly-used pesticides; and selected pesticide metabolites. Analyses were performed by three laboratories: the University Hygienic Laboratory; the Analytical Toxicology Laboratory, with the UI Department of Preventive Medicine and Environmental Health; and the Environmental Engineering Laboratory, with the UI Department of Civil and Environmental Engineering. The labs had U.S. EPA QA/QC plans in place, and the SWRL plan utilized and verified their implementation. The method detection limits (MDL) for pesticide analyses were set as the minimum practical concentration quantitation limit for each analyte in a groundwater matrix, established through QA/QC procedures. Groundwater-matrix effects necessitated an increase in some SWRL MDLs, relative to a reagent water matrix. This may cause an increase in false negative detections, but should minimize false positive detections.
Overall completion criteria were established for the survey and were met successfully. For 1. site-inventory, sample collection and analysis, and 2. return of voluntary health questionnaires, criteria of 95% and 60%, respectively, were set. These criteria were met, at 98% and 85%. The final SWRL well-water sample was 686 sites (of 698). Sample and analysis completeness were also set for each county. County criteria were met with one exception, for one analyte; 92 counties (of 99) were sampled at 100% of the design. Ninety-four percent of the 10% repeat sites were resampled, and 93% of the quarterly sites were sampled four times. In total 1,048 well water samples were collected and analyzed during SWRL. Of the 686 SWRL sites, 47% were the primary rural-residence site selected (i.e., closest to the 5-minute intersection), and 79% were among the first three choices. The most common reason a selected residence was not sampled was the inability to contact a resident (70%). Less than 8% of persons contacted were unwilling to participate; nearly 23% of those contacted did not use a well on the premise as their primary source of drinking water.