Sites with parameter concentrations that have equaled or exceeded drinking water standard(s) (DWS), including location and parameter(s) are shown in Table 4.6-7A.  Impaired lakes and streams with site type, name, length of impaired stream reach, area of impaired lake, designated use standard and parameter(s) exceeded is shown in Table 4.6-7B.  Figure 4.6-9 shows the location of exceedences and impairment keyed to Table 4.6-7.  All community water systems are regulated under the Safe Drinking Water Act and treat water supplies to meet drinking water standards.  Not all parameters were measured at all sites; selective sampling for particular constituents is common.  A description of water quality data sources and methods is found in Volume 1, Appendix A. 

Well, Mine or Spring sites that have equaled or exceeded drinking water standards (DWS)

• Refer to Table 4.6-7A.
• Sixty-five measured sites have parameter concentrations that have equaled or exceeded drinking water standards.
• The parameter most frequently equaled or exceeded in the sites measured was arsenic.  Other parameters equaled or exceeded included cadmium, fluoride, lead, nitrate/nitrite, mercury and total dissolved solids.

Lakes and Streams with impaired waters

• Refer to Table 4.6-7B.
• Water quality standards for selenium were equaled or exceeded in one 40-mile reach of the Colorado River between Hoover Dam and Lake Mohave.
• The Colorado River between Hoover Dam and Lake Mohave is not part of the ADEQ water quality improvement effort called the Total Maximum Daily Load (TMDL) program at this time.