FIELD DOCUMENTS AND WORK PLANS 1990

Home Browse Search

Marley Cooling Tower Co. 2 20 September 1990 3) EW-1 - to monitor changes near boundaries of capture zones Shallow wells 204 and 301. Intermediate wells 321 and 324. At our 17 September 1990 meeting, Mr. Austreng and I also discussed the need for additional monitoring wells to delineate the plume boundaries. The July quarterly monitoring report concluded that the limits of ground water contamination have not been determined (1) in the shallow zone southeast of the south yard, (2) in the 100-foot sand (eastern extent) , and (3) in the intermediate zone (southeastern extent). Marley should prepare a workplan for the installation of monitoring wells to delineate the extent of contamination within these areas. Water levels within the site' s monitoring wells continue to decline, from April to July 1990 water levels have declined approximately 3 feet in the shallow zone, 3 to 5 feet in the 100-foot sand, 3 to 6 feet in the intermediate zone, and 4 to 12 feet in the deep zone. All of the shallow zone piezometers and 10 out of the 18 existing shallow zone monitoring wells in the North Yard have gone dry. Three other shallow monitoring wells had water levels below their submersible pump inlets. Hence, the intermediate zone is quickly becomming the uppermost water-bearing zone in the North Yard. In addition, purportedly due to the drought conditions that have prevailed in this area since late 1987, a ground water divide in both the shallow and intermediate zones has developed within the North Yard. Shallow and intermediate ground water below the North Yard now flows to the east. The design of the existing ground water monitoring network within the North Yard was predicated upon pre-drought conditions that indicated that the water levels and hydraulic gradients in the vicinity of the site were influenced by recharge from the the Stockton Diverting Canal located to the north. Ground water flow was determined to be southerly, hence monitoring wells were installed to track the contaminant plume in this direction. However, current drought conditions have caused the ground water flow beneath the North Yard, within both the shallow and intermediate zones, to move eastward. Marley has begun to assess the implications of these changes in the ground water flow direction. Their July quarterly monitoring report includes water quality data from two new monitoring wells (June 1990) installed within the shallow and intermediate zones approximately 800 feet east of the North Yard. Total chromium concentrations in both of these wells were below the detection limit of 10 ppb, indicating that the chromium plume beneath the North Yard has not migrated this far east. Apparently, based upon this data, the July quarterly monitoring report concludes that the eastern extent of chromium contamination within the intermediate zone has been determined. There is no conclusion regarding the extent of shallow zone contamination to the east of the North Yard, nor any data demonstrating the water quality of the deep zone, east of the North Yard. Marley needs to assess the effectiveness of the North Yard's existing ground water monitoring network in all three water bearing zones, based upon (1) the changes (drought induced and/or seasonal ) in the ground water flow direction, (2) the drying up of the shallow zone monitoring wells and piezometers, and (3) the need to determine the 50 ppb aquifer cleanup boundary, and (4) the need to measure the effectiveness of