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• Selected water quality data obtained by the U. S. Geological Survey (USGS) and IVECC were reviewed to estimate the water quality of the North Fork during low flow periods. The data reviewed consisted of 15 sampling events conducted by the USGS during the October 1981 -September 1982 water year (provided in Attachment 1), the most recent quarterly sampling conducted by WECC on October Il, 1985 (provided in Attachment 2) and graphical representations of data for 1983 produced by IVECC (provided in Attachment 3). The data reviewed are summarized in Table L The lowest flow volume in the North fork normally occurs during the months of October through February. Water quality data obtained for the remaining months during which flows are generally in excess of 100 efs were not reviewed for the purpose of this analysis, nor are they presented in Table 1. Water quality for most parameters in the North Fork is generally better during periods of low flow than during high flow because of much lower turbidity during low tlow. Typical values approximately the average of the low flow data reviewed were estimated and are shown n Table I. Most parameters are well below tl~e ISS during low flow periods. Ammonia is typically found at a concentration of about 0.15 mg/1 in comparison with the ISS of 0.2 mg/1. The measured concentration of ammonia • occasionally exceeds the ISS both upstream and downstream of the refuse pile. Cadmium and mercury are parameters which also have existing concentrations near the ISS. The ISS for mercury has been set at a concentration below the detectable measurement ability of most analytical laboratories. Detection limits reported in the data reviewed for this analysis ranged from 4 to 200 times greater than the ISS. For this reason, it is not possible to accurately estimate the existing background concentration of mercury in the North Fork in relation to the ISS. Data for some o[ the parameters which have ISS were not available. These included residual chlorine, hexavalent chromium, cyanide, dissolved manganese, nitrite, silver and sulfide. Residual chlorine is set to regulate the discharge of treated sewage effluent and is not a parameter of concern when considering the impacts of the refuse leachate. Discussions with CIIILRD indicate cyanide is not expected to be a parameter of concern based on their experience at other sites. Silver is very insoluble and is not expected to leach at significant concentration from the refuse. Sulfide and nitrite, which are reduced chemical species, are expected to convert to oxidized ionic forms after mixing with the North Fork water which is high in • dissolved oxygen. Hexavalent chromium and dissolved manganese were assumed to be at the same concentration as trivalent chromium and total manganese respectively, adding to the already high degree of conservatism incorporated in the analysis. ,.