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dissolved fraction and the reported value is a "total recoverable" concentration and, consequently, <br />most likely biased high. Therefore, this single exceedence is not considered significant. <br />Effluent from Pond 004 exceeded the nitrite standard (0.05 mgll) on two occasions out of 18 samples <br />(concentrations ranged between 0.06 and 0.11 mgll), while Pond 008 effluent exceeded the nitrite <br />standard on three occasions out of 18 samples (concentration range of 0.07 to 0.14 mgll). As noted <br />above, nitrates are unstable in aerated water and will quickly oxidize to nitrate. Consequently, these <br />infrequent exceedences are not considered significant. <br />The chronic selenium standard (4.6 pgll) was just exceeded in Pond 004 effluent on two occasions out <br />of 18 samples (5.0 pg/l, mean of the exceedences of 5.0 pgll), while there have been five exceedences <br />out of 18 samples in Pond 008 effluent (concentration range from 5.0 to 10.0 pg/l, mean of the <br />exceedences of 6.0 Ng/i). The mean values of the exceedences indicate the observed concentrations <br />are generally just slightly elevated above the standard. The mean selenium value of all samples from <br />Pond 004 is 1.3 pg/l and 2.9 ugll for Pond 008. Since the standard is based on the dissolved fraction <br />and the reported value is a "total recoverable" concentration, the observed values may not be true <br />exceedences. The acute selenium standard (18.4 pgll) was not exceeded at either pond. In addition, <br />both Cow Camp Creok (the receiving stream for Pontl 004) and Bond Creek (the receiving stream for <br />Pond 008) are ephemeral streams that do not flow year round (see the 2004 Annual Hydrology Report <br />for the hydrograph record) and offer marginal aquatic life habitat. Consequently, these exceedences <br />are not considered significant. <br />Effluent from both ponds exceeded the sulfide standard (0.002 mg/l) on several occasions. Pond 004 <br />exceeded the standard on five dates (concentrations ranged from 0.003 to 0.02 mg/l, exceedence mean <br />of 0,008 mgll), and five excursions (range of 0.003 to 0.008 mg/l, exceedence mean of 0.004 mgll) <br />occurred in the Pond 008 effluent. The mean values of the excursions indicate that the observed <br />concentrations are generally just slightly elevated above the standard. Mean values for all samples are <br />0.002 mg/I and 0.001 mg/l for Pond 004 and 008, respectively. As noted above, sulfide is a very <br />unstable ionic compound that quickly oxidizes to sulfate. Consequently, these exceedences are not <br />considered significant. <br />Table 7-118, Comparison of Permanent Pond Effluent to Agricultural Standards, summarizes pond <br />effluent water quality to promulgated Colorado surface water agricultural standards (Regulation 31). <br />Manganese is the only constituent in pond effluent with concentrations elevated above the agricultural <br />standard (0.2 mg/l). All five ponds exceeded the standard at various times over the period from 1999 to <br />2004. In general, mean exceedence concentrations were slightly elevated above the standard. The <br />exceedence mean for Pond 003 was approximately 2.5 times greater than the standard (0.52 mg/I <br />versus 0.2 mg/l). CDPHE has recognized that the existing manganese agriculture standard is <br />problematic, Many high quality, and/or use-protected waters contain naturally occurring <br />concentrations of manganese elevated above 0.2 mg/l, In addition, the original EPA guidance indicated <br />that this standard is appropriate where irrigation water is applied to soils with a ph less than 6.0; <br />otherwise, the standard should be 10 mgll (EPA, 1976). Consequently, CDPHE has proposed a rule <br />TR-37 7-381 Revised 04/05 <br />