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TECHNICAL MEMORANDUM AmerAlia, Inc. October 19, 1999 Page 4 the two aquifers and is up to 200 feet thick. Later studies redefined the bedrock aquifer system to include the upper aquifer as defined in earlier studies, the lower aquifer as the zone between the Mahogany zone and L-5 zone, and the Dissolution Surface. The thickness of the lower aquifer is about 30D feet. The primary water-bearing zones in the upper and lower aquifers are the "A Groove" and "B Groove" respectively. The "A Groove" is located directly above the Mahogany zone, with a thickness of about 15 feet. The "B Groove" is located directly below the Mahogany zone with a thickness of about 20 feet. The strata immediately above the Dissolution Surface is a significant water-bearing zone above the saline portion of the Parachute Creek member (zones R-5 to R-2) and is part of the tower aquifer. However, based on limited water quality data, the water quality of the strata immediately above the Dissolution Surface does not meet the drinking, agricultural, livestock, or wildlife water quality standards, because of its elevated levels of TDS and other constituents. A general hydrostratigraphic column for the Project area is shown on Figure 2. 2.2 Existing Data A large amount of water quality information is available for wells from the WRN site. Data from one well in the A-Groove section of the upper aquifer, four wells in the B-Groove section of the lower aquifer, and two wells in the Dissolution Surface zone have been analyzed. Several of these wells have been sampled monthly for a large number of constituents since 1989. A presentation of median and first and third quartile has been selected to summarize the White River Nahcolite data in Table 1. This has the advantage of being more resistant towards outliers. The data has been analyzed initially and it was found that the data is fairly consistent except for some outliers. These outliers have a large influence on the mean, but little influence on the median (Helsel and Hirsch, 1992). The spread of data can also be better estimated by the interquartile range, as it measures the range of the central 50 percent of data and is not influenced by the 25 percent on either end (Helsel and Hirsch, 1992). Some electronic data is available on wells from the C-a Tract. Data exists for bedrock wells GS-2M, GS-3M and GS-SM, and alluvial wells 522, 524, and 528. The data available is generally annual mean values for selected components for the some years between 1975 and 1985. Two USGS wells exist on the Project site (TH 75-7A and 7B), and water quality data exist for samples collected in 1975. A short summary of the data is presented in Table 1, and a summary for each well is presented in Appendix A. 2ndFinalTecMicalMemodoc 10/19/99 TRC HYDRO-GEO CONSULTANTS