SITE INFORMATION AND CORRESPONDENCE

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Dallas Corporation -2- 15 November 1989 after a report interpreting a full year of monitoring data is submitted. Ground water monitoring well number 5 was installed on 1 June 1989. The well location was determined in the field jointly by Board staff and Mr. Harvey. This well was installed to make sure at least one monitoring well existed directly down gradient of the surface impoundment. The direction of the ground water gradient varied over 120 degrees according to monitoring reports from the past few years. Monitoring well number one is down gradient of the surface impoundment as determined by some of the gradient measurements. Monitoring well number 5 has been included in the monthly monitoring program. Ground water monitoring well number 6 was completed at a depth of 124 feet on 14 December 1988. This well is up gradient of the surface impoundment. It has been included in the monthly monitoring program. The deep monitoring well was completed to determine the nature of the interconnection between the deep and shallow aquifer. The NAR had hypothesized that a confining layer existed across the site. One conclusion of the investigation at well number 6 was, "The variability of the stratigraphic units encountered in the boring are such that the existence of a shallow, low permeability confining layer as originally suggested by previous investigators could not be confirmed. However, the initial well development monitoring indicates a strong possibility that the interbedded sediments may provide confining properties. " The field tasks proposed to fulfill the HAR requirement by Dallas Corporation have been successfully completed. We have received reports describing those tasks. Some uncertainty still exists regarding the interconnection of the most permeable zones in the subsurface. The results of sampling from existing monitoring wells on the site does not indicate that substantial ground water pollution occurred. Based on present knowledge of site conditions, no further field work towards hydrogeological characterization, other than monitoring of existing wells, seems warranted. Further interpretation of site conditions based on analysis of the data from recent subsurface exploration in conjunction with information from the original HAR should be completed. The following items, shortcomings identified in the HAR, should be discussed: 1. Nature of the interconnection between upper and lower water bearing zones. 2. Extent of uppermost water bearing zone. 3. Existence of any vertical gradients. 4. Extent of leachate migration. Cross sections across the site should be drawn which include the boring log data from monitoring wells 5 and 6 and observations in the surface impoundment excavation. The additional interpretation should be submitted with evaluation of the yearly monitoring results.