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February 1998 Hayden Gulch Mine • Phase 2 & 3 Bond Release Application ~ Pape 14 <br />Ground Water <br />Ground water data collected since 1987 indicates that constituent concentrations detected in <br />ground water were generally less than corresponding baseline concentrations measured prior to <br />mine development. Minor exceptions include total iron concentrations in recent monitoring <br />well HG-2 samples which frequently exceeded baseline concentrations. The source of the <br />elevated iron is believed to be an algal or bacterial growth and not representative of ground <br />water quality. Total aluminum, iron and manganese concentrations reported for both HG-1 <br />and HG-2 in the 1997 samples also exceeded baseline concentrations. However, these <br />exceedances are assumed to be related to the observed increase in total suspended solids. It is <br />important to note that seep/spring and surface water samples did not have any corresponding <br />constituent increase. <br />A comparison of the ground water data indicates that with the exception of total iron, no <br />constiruent concentrations exceeded Colorado ground water standards. Total iron values in <br />HG-2 were frequently greater than the secondary drinking water standard for iron. However, <br />as indicated in the existing permit, there aze no domestic-use ground water wells in the vicinity <br />of the mine site. [n addition, a review of the baseline data indicates that the baseline ground <br />water also typically exceeded the secondary drinking water standard. <br />The ground water data also indicate that in general, constituent concentrations, with the <br />possible exceptions of sulfate and total dissolved solids (TDS) at HG-1, have remained relatively <br />constant since 1987. Both sulfate and TDS concentrations ac HGl could have decreased <br />slightly over the reclamation liability period. <br />The ground water elevation data indicates that there has been some variability in water levels. <br />Average ground water levels in HG-2 have increased approximately 25 feet since 1987. This <br />increase and appazent trend towards pre-mine levels is conststent with predictions m the <br />existing PHC. Water levels in monitoring wells HGl and UC-2 have remained fairly constant <br />since 1987. <br />Seep/Springy <br /> <br />Seep/spring data collected since 1987 indicates that some seep flows have several constituents, <br />including calcium, conductivity, iron (total), sodium, sulfate and TDS which frequently <br />exceeded maximum baseline values. The data also indicates that seep waters monitored at RSP- <br />4 were the most heavily impacted which is consistent wick the predictions in the approved <br />PHC. However, with the exception of TDS at RSPB, none of the constituent concentrations <br />exceeded Colorado ground water agricultural standazds. None of the seep/spring samples had <br />constituent concentrations greater than WDEQ agricultural use guidelines. WDEQ guidelines <br />were used in the HIA to evaluate use-suitability of surface waters at the mine site and further <br />downstream in Hayden Gulch because Colorado does not have surface water agriculrural <br />standards. The WDEQ guidelines are widely used throughout the industry and are accepted <br />values for assessing potential impacts. <br />Trend analyses indicate that seep/spring constiruent concentrations, with the possible <br />exception of calcium and sulfate at RSP~F, have remained relatively constant during the <br />reclamation liability period. However, data collected in 1996 and 1997 indicate that the <br />Montgomery Watson Americas ~dba TerraMatnzJ • P.O. Boz 774018 <br />Steamboat Springs, Colorado 80477 ' (970J 8796260 <br />{r~ \d n \M.e 16 ] Rod Rdue Arylrum \Tm \pv ] b J GoM Rdue Ary(ra,m <br />