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U.S. Environmental Protection Agency

Missouri Water Science Center


Expanded Site Investigation/Remedial Investigation (ESI/RI)

The following is a brief description of the Expanded Site Investigation/Remedial Investigation (ESI/RI); a report of the findings is available in printed form at the Riverfront site data repository at the New Haven Public Library. In addition, the document also is available online [ESI/RI investigations].

INTRODUCTION

At the request of the U.S. Environmental Protection Agency (U.S. EPA), the U.S. Geological Survey (USGS) conducted an Expanded Site Investigation/Remedial Investigation (ESI/RI). The primary objectives of the ESI/RI were to determine:

  1. The attitude of the alluvial water table and shallow bedrock water table in the New Haven area,
  2. If the Missouri River alluvial aquifer beneath the Riverfront site was contaminated by tetrachloroethene (PCE), and
  3. If substantial quantities of PCE containing waste were present at the closed old city dump.

Because the Riverfront Site was identified in the ESI as the most probable source of the PCE contamination in city wells W1 and W2, the scope of the ESI/RI investigation focused on the Riverfront Site with only a cursory evaluation of other potential sites. The ESI/RI also included an inventory of private and public wells in the New Haven area to assess the ground-water flow and quality, the collection of core samples from trees growing near the downtown Riverfront site and the City Dump, the collection of water samples from seeps at the City Dump, and the installation and sampling of alluvial monitoring wells in downtown New Haven near the Riverfront Site. At the request of the U.S. EPA, additional efforts performed as amendments to the original ESI/RI work plan included the evaluation of a contaminated water-supply service line and assistance during a removal action of contaminated soils near that water line, the installation and sampling of five bedrock-monitoring wells in the New Haven area, and the sampling of soils, seeps, and trees at an industrial dump site southeast of New Haven.

RESULTS

Objective I

The attitude of the bedrock water table was determined using data collected during a well inventory in the New Haven area. During the well inventory the depth to water in more the 60 water wells in the vicinity of New Haven was measured, and well construction information, and the altitude of the wellhead were obtained. Using this information, a map of the water table in the bedrock was constructed. Ground water flows perpendicular to contour lines on the water-table map, which shows a east-west trending shallow ground-water divide beneath New Haven in the vicinity of State Highway 100 {image}. The water-table map was later used to determine the location of monitoring wells.

The attitude of the alluvial water table beneath the Riverfront Site was determined using water levels measured in four monitoring wells installed in 1999 and an existing hand-dug well near the site. The measured water levels indicate that under normal stages of the Missouri River, ground water in the alluvium beneath the site flows to the northeast toward the river {image}.

Objective II

The ESI/RI detected PCE contamination in the Missouri River alluvium near the Riverfront site in downtown New Haven. The contamination was first detected in tree-core samples and later confirmed by the installation and sampling of alluvial monitoring wells [image of suspected plume from tree-core analysis].

Objective III

Substantial quantities of PCE were not detected during a reconnaissance of the old city dump located along State Highway 100 in the east part of New Haven {image}. Analysis of tree-core and ground-water samples from seeps along the northern face of the dump and streams downgradient from the dump indicated trace quantities [less than 1 mg/L (microgram per liter] of PCE.

Additional data

During the ESI/RI, three bedrock monitoring wells were installed in New Haven to assist the U.S. EPA in evaluating the extent of PCE contamination in the bedrock aquifer in the vicinity of city well W2 and the city dump. The wells ranged from 230 to 465 ft (feet) deep. No PCE was detected in the monitoring well near the city dump. Moderate quantities of PCE (less than 20 mg/L) were detected in a monitoring well between city well W2 and the Riverfront site, and large quantities of PCE (greater than 200 mg/L) were detected in a monitoring well south of city well W2. During the sampling of these bedrock monitoring wells, PCE was detected in water from a faucet in downtown New Haven adjacent to the Riverfront Site and in water from a sink in a nearby public restroom. Both locations were served by the same plastic water line that was adjacent to the Riverfront site. Analysis of samples collected from other locations on the city distribution system and active supply wells (wells W3 and W4) confirmed that the PCE contamination was restricted to the two locations on the plastic line. The U.S. EPA conducted an emergency removal action to replace the contaminated plastic waterline and remove nearby PCE contaminated soils.

SUMMARY

Based on the results of the ESI/RI and previous studies, the U.S. EPA determined that a Remedial Investigation (RI) was needed to define the nature and extent of PCE contamination in the New Haven area. After discussions with community leaders and citizens during several public meetings, the Riverfront Site was proposed for the National Priorities List (NPL), more commonly known as the Superfund.

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