Seismic-refraction surveys were made across suspected buried, drift-filled bedrock valleys believed to underlie two sites of known ground-water contamination the Twin Cities Army Ammunition Plant (TCAAP) near New Brighton and the former Koppers Coke Plant in St. Paul, Ramsey County, Minnesota. Refraction data were collected along two lines at each site; each line traversed the axis of a suspected valley.
Drift-filled bedrock valleys were thought to incise the Prairie du Chien-Jordan aquifer to an altitude between 500 and 560 feet above sea level at the TCAAP site. The interpretation of one seismic profile indicates that a valley probably does not exist under the area surveyed; the modeled depth profile shows the bedrock surface ranging between altitudes of about 700 to 780 feet. Interpretation of a second seismic profile just south of the TCAAP indicates that a shallow valley may exist under the northern half of the line; the modeled depth profile shows that the bedrock surface declines from an altitude of about 780 feet to about 690 feet over a horizontal distance of 400 feet.
A drift-filled bedrock valley was thought to incise the St. Peter aquifer to an altitude between 770 and 800 feet above sea level at the Koppers site. The interpretation of a seismic profile just east of the Koppers site is not conclusive, but suggests that a bedrock valley may be present near the middle of the line. The interpretation of a second seismic profile across the westward extension of the same suspected valley also is not conclusive, but suggests that a bedrock valley may be present at the north end of the line. The optimal field layout for each line at the site (longer shot offsets) could not be obtained because of limited space available in the densely developed residential neighborhoods.
