The results of a field experiment comparing water‐quality constituents, specific conductance, geophysical measurements, and well‐bore hydraulics in two long‐screen wells and adjacent vertical clusters of short‐screen wells show bias in ground‐water data caused by well‐bore flow in long‐screen wells. The well screen acts as a conduit for vertical flow because it connects zones of different head and transmissivity, even in a relatively homogeneous, unconfined, sand and gravel aquifer where such zones are almost indistinguishable. Flow in the well bore redistributes water and solutes in the aquifer adjacent to the well, increasing the risk of bias in water‐quality samples, failure of plume detection, and cross‐contamination of the aquifer. At one site, downward flow from a contaminated zone redistributes solutes over the entire length of the long‐screen well. At another site, upward flow from an uncontaminated zone masks the presence of a road salt plume. Borehole induction logs, conducted in a fully penetrating short‐screen well, can provide a profile of solutes in the aquifer that is not attainable in long‐screen wells. In this study, the induction‐log profiles show close correlation with data from analyses of water‐quality samples from the short‐screen wells; however, both of these data sets differ markedly from the biased water‐quality samples from the long‐screen wells. Therefore, use of induction logs in fully cased wells for plume detection and accurate placement of short‐screen wells is a viable alternative to use of long screen wells for water‐quality sampling.

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Knowledge of the characteristics of highway runoff (concentrations and loads of constituents and the physical and chemical processes that produce this runoff) is important for decision makers, planners, and highway engineers to assess and mitigate possible adverse impacts of highway runoff on the Nation's receiving waters. In October, 1996, the Federal Highway Administration and the U.S. Geological Survey began the National Highway Runoff Data and Methodology Synthesis to provide a catalog of the pertinent information available; to define the necessary documentation to determine if data are valid (useful for intended purposes), current, and technically supportable; and to evaluate available sources in terms of current and foreseeable information needs.

In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929. WATER-QUALITY INFORMATION Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (p,S/cm at 25°C). Concentration of chemical constituents in water are given in micrograms per liter (ng/L). Turbidity is given in nephelometric units.

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