Environ. Sci. Technol. 1997, 31, 632-638
Cultural and Hydrogeological Factors That Influence Well Water Quality R. PETER RICHARDS Water Quality Laboratory, Heidelberg College, 310 East Market Street, Tiffin, Ohio 44883
A large database on chemicals in midwestern private rural wells was evaluated using analysis of covariance (ANCOVA) to determine which of 19 cultural, geological, and structural factors are statistically associated with concentrations of nitrate, triazine herbicides, and/or acetanilide herbicides. Well depth is negatively correlated with concentrations of all three parameters. Drilled wells have lower concentrations than dug or driven wells. Wells that have gone dry in the past have higher concentrations. Domestic wells are less likely to contain herbicides than others, and those closer to dealer sites are more likely to contain herbicides. Proximity to a river correlates negatively with nitrate and triazines. Proximity to barnyards or feedlots is positively correlated with all three parameters; proximity to an animal waste holding tank is not. Age of the well is negatively related to acetanilide concentration but positively related to nitrate concentration. Sandy soils have higher acetanilide concentrations than clays. Adjusted R 2 values were 10.5% for the nitrate ANCOVA , 6.7% for triazines, and 16.0% for acetanilides. These low values probably reflect the difficulty of obtaining reliable information by well owner surveys and the importance of types of information not available from such surveys, plus the random impact on well concentrations of accidents and practices at the well site.
Introduction In 1987, the Water Quality Laboratory (WQL) of Heidelberg College initiated the Cooperative Private Well Testing Program (1), which is operated on a county-by-county basis with help from local sponsoring organizations. Well owners participate voluntarily and pay a low fee to have their wells tested. They also complete a questionnaire about their well that provides information on many of the factors that are thought to be associated with rural well contamination. Well owners receive a confidential report on their well, and the sponsoring organizations receive summaries and maps of the results. Since 1987, over 43 000 rural residents from 372 counties and 17 states have submitted water samples as part of this program. This paper presents an analysis of results from the geographically contiguous midwestern region of Ohio, Indiana, Illinois, Kentucky, and West Virginia, from which most of the samples have been obtained. Additional criteria for inclusion of samples in the analysis were that samples be from wells or springs not surface water sources; that only one sample from a given well be included; and that the wellowner survey contain answers to all relevant questions. These restrictions reduced the sample size considerably, but still left between 4500 and 7600 records available for statistical analysis, depending on the parameter. * Telephone: (419) 448-2198; fax:
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 3, 1997
Comparisons of the data set before and after excluding samples with incomplete questionnaires show that the reduced set is not completely unbiased. Some differences are highly significant statistically because of the power conferred by the large sample sizes, but all are sufficiently small in magnitude so that the results from the reduced data set can be considered adequately representative of the entire data set. The wells tested in this program were not randomly selected and are not necessarily a representative sample of all private wells in any particular area. Nonetheless, the large sample sizes obtained allow much useful information to be gleaned from these studies when the data are interpreted in appropriate ways. This paper focuses on a multivariate analysis of the relationships of nitrate concentrations to factors that are generally believed to reflect vulnerability of a well to contamination; relationships of triazine and acetanilide herbicides to these factors will be discussed briefly. A fuller treatment of the herbicides is available from the author on request. Preliminary analyses of portions of the data (2, 3) and a more detailed description of the data and results of univariate analysis of the influence of factors on well water quality (4) have been presented elsewhere.
Methods Program Design and Sampling Procedures. The Cooperative Private Well Testing Program is operated as a collaborative effort between the WQL and local organizations, usually at the county level. Sampling kits and questionnaires are distributed to participants, samples are taken on a specified day, the kits and questionnaires are returned the same day to a specified collection point, and they are then immediately delivered to the WQL with as little holding time as possible. Participants are instructed to sample a point as close to the well as possible and to run the water for 2-3 min before taking the sample. Each participant receives a report of analytical results and their relationship to human health guidelines. Sponsoring organizations receive a tabular summary of the results and maps of parameter distributions. Further details about the sampling program are provided elsewhere (1, 4). Analytical Methods. Nitrate is analyzed on a dedicated TRAACS 800 autoanalyzer system, using Standard Methods 4500-NO3 (5), which measures nitrate plus nitrite. Results are reported as nitrogen in (mg/L). The method detection limit (MDL) is 0.05 mg/L, but data are not censored; for this paper, all analytical values were used as reported. Since nitrite concentrations in these samples are very low, the analyses essentially reflect the nitrate concentrations. In the following, nitrate plus nitrite will simply be referred to as nitrate. Atrazine and related triazine herbicides were measured with the EnviroGard Triazine Plate Kit following the manufacturer’s instructions. The kits are calibrated for atrazine, although they also respond less strongly to simazine (Princep) and weakly to cyanazine (Bladex) and several breakdown products including hydroxyatrazine and de-ethylated atrazine. Alachlor (Lasso) and related acetanilide herbicides are measured with the EnviroGard Alachlor Plate Kit, calibrated for alachlor following the manufacturer’s instructions. This assay also reacts with some alachlor breakdown products, especially ethane sulfonate, to which the kit responds about 20% as sensitively as to alachlor (6), and to a much lesser degree with metolachlor (Dual). The MDL for triazines is 0.04 µg/L as atrazine and that for acetanilides is 0.05 µg/L as alachlor; as with nitrate, no censoring was imposed on the data. Because of the cross-reactivity of these tests, the results will be referred to as triazines and acetanilides rather than
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1997 American Chemical Society
TABLE 1. Categorical Variables Used in the Study and Their Permissible Statesa variable WELL CASING GONE DRY USE:D USE:Lb USE:I CROPLAND BARNYARD POOPTANK DEALER LAWNCHEM SEPTIC LANDFILL HAZARD RIVERb MIX CHEM SOIL
states drilled (DL) driven (DV) dug (DG) spring (SP) in pit (P) pitless (T) above (A) level (L) below (B) none (N) no (N) yes (Y) only (O) yes (Y) no (N) only (O) yes (Y) no (N) no (N) yes (Y) only (O) no (N) in sight (Y)
