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• • source. In general, the bedrock aquifers have dissolved solids concentrations of less than 1,000 mg/L, while the springs and alluvium generally have dissolved solids concentrations of approximately 1,000 mg/L. The surface water usually has dissolved solids concentrations of 200 to 400 mg/L. The ground water present in the bedrock aquifers, surface water, most of the springs, and half of the alluvial wells has as the predominant anion bicarbonate (sometimes with carbonate). The predominant anion far the remaining ground waer is sulfate. The high concentration of sulfate in many of the alluvial wells may be due to the affects of agricultural irrigation. Chloride is found in only small quantities. Sodium is the predominant cation for many of the bedrock and alluvial wells and a majority of the springs. Calcium is the predominant cation for the surface water. Magnesium was found to be a predominant cation in one bedrock well and one alluvial well. Because of the generally mixed water types and high variability of concentrations within the water sources, it is difficult to discreetly characterize water sources by their water type. Bedrock Aquifers-WaterQualiry Trout Creek Sandstone. Ground water samples have been collected from two (2) wells completed in the Trout Creek Sandstone. These wells were/are the water supply well serving Okie Plaza and the water supply well at the No. 5 mine. The Okie Plaza well was undermined and is no longer supplying Trout Creek water. Samples have been taken quarterly since March 1981. A statistical summary of the ground water chemistry for the Trout Creek Sandstone is presented in Table 14, Summary of Water Quality Data- Trout Creek Sandstone. Ground water from the No. 5 Mine well is the sodium-bicarbonate type and proportions of the major ions appear to be relatively constant. Ground water from the Okie Plaza supply well is the sodium-magnesium bicarbonate type. The recommended secondary drinking water standard for total dissolved solids (500 mg/L) is exceeded by the averages for these two (2) wells. The total dissolved solids concentrations for the Okie Plaza well averaged 890 mg/L with a maximum of 1030 mg/L measured. The total dissolved concentration for the No. 5 Mine well averaged 639 mg/L with a maximum of 805 mg/L, Middle Sandstone. Ground water samples have been collected from six (6) wells completed in the Middle Sandstone. These wells are I) TR-4, 2) TR-7a, 3) 81-O1, 4) 83-O1, 5) 83-02, and 6) 83-03. Samples have been collected quarterly since March 1981. Wells 83-O1, 83-02, and 83-03 have been sampled primarily for field parameters and since 1985 for water levels only. A statistical summary of [he ground water chemistry for the three Middle Sandstone is presented in Table 15, Summary of Water Quality Data -Middle Sandstone. There have been three (3) distinct water types recognized on the basis of major ion concentrations. Water from well TR-4 is of the calcium- bicarbonate type. Water from well TR-7a is of the sodium-bicarbonate type. Major ion concentrations in well 81-01 are variable; however, the main water type appears to be calcium-bicarbonate. Tota] dissolved solids averaged 251 mg/L in well TR-4, 245 mgJL, in well TR-7a, and 430 mg/L in well 81-01. The maximum dissolved solid measured was 720 mg/L in well 81-O1. Generally, the concentrations of parameters analyzed compared favorably with EPA primary and secondary drinking water standards. However, primary and secondary parameter concentrations are often exceeded for boron, chromium, dissolved solids, fluoride, iron, lead, maganese, sulfate, and selenium. Twentymile Sandstone. Ground water samples have been collected from two (2) wells completed in the Twentymile Sandstone. These wells are 1) well 259 and 2) No. 9 mine well. Samples have been collected quarterly since March 1981. A statistical summary of [he ground water chemistry for the Twentymile Sandstone is presented in Table 16, Summary of Water Quality Data -Twentymile Sandstone. Groundwater present in the Twentymile Sandstone is generally ofthe calcium- bicarbonate type. Total dissolved solids average 264 mg/L in well 259 and 391 mg/L in No. 9 mine well. The maximum measured value of 490 mg/L in No. 9 mine well is still below the secondary standard. EPA drinking water standards are exceeded by average measured concentrations for iron and occasionally exceed standards for other metals and sulfate.. There are no major differences in chemistry between wells 259 and the No. 9 mine well in terms of major ion concentrations, suggesting the groundwater chemistry in [he Twentymile Sandstone Permit Renewal No. 3 2.04-17 Revised 7/10/00