|
RULE 2 - PERMITS
<br />Surface water in the proposed PSCM area is consistently alkaline, as evidenced by a laboratory pH
<br />• range (all stations) of 8.2 to 8.8 s.u., and a field pH range of 7.8 to 8.5. Impoundment samples were
<br />slightly less alkaline, with one near - neutral field sample (range 7.9 to 8.6 lab / 7.1 to 8.5 field). Grassy
<br />Creek, Pond 002, and Pond 003 had similar alkalinity, averaging 252 mg/L to 288 mg/L total alkalinity
<br />(as calcium carbonate). Pond 004 and Little Grassy Creek (SSLG5), had lower values, averaging 220
<br />mg/L and 180 mg/L, respectively. Stream alkalinity averaged approximately 150 mg/L lower than that
<br />of alluvial wells (392 mg/L), while stream pH was higher than that in the alluvial wells, which
<br />averaged 7.86 (laboratory).
<br />Total dissolved solids varied seasonally, with a reduction during spring via dilution from snowmelt
<br />runoff contributions, and according to the influence of spoil water and discharges from Pond 002,
<br />which was high in TDS (3,912 mg/L average) due to contributions from the Seneca II spoil aquifer and
<br />spoil springs. Sites SSG1 and YSGF5, both on Grassy Creek upstream of the Little Grassy Creek
<br />confluence, had similarly moderate levels of TDS, averaging 839 mg/L and 843 mg/L, respectively,
<br />and ranging in the 600's to 900's (mg/L). Site SSLG5, on Little Grassy Creek upstream of Pond 002
<br />(NPDES2), had elevated TDS relative to the first two stations, averaging 1,056 mg/L, and ranging
<br />from 300 to 2,270 mg/L. Sites SSG2 and YSG5, both on Grassy Creek downstream of the Little
<br />Grassy Creek confluence, reflect the mixing of contributions from Little Grassy Creek, including Pond
<br />002, and the Grassy Creek mainstem above the confluence. Both sites were high in TDS, respectively
<br />averaging 2,768 and 2,701 mg/L, but showed the influence of dilution of Pond 002 outflows (3,912
<br />mg/L) by Grassy Creek mainstem flows. The average TDS in the alluvial wells approximated that of
<br />Pond 002 outflows.
<br />is Suspended solids were moderate, and highest at YSGF5 (68 mg/L average) and SSLG5 (107 mg/L
<br />average), both located above mining and largely uncontrolled by surface impoundments. The lowest
<br />TSS values, averaging 11 mg/L or less, were reported for the impoundments, as would be expected.
<br />Total recoverable iron concentrations tracked those of TSS, with peak concentrations exceeding the
<br />Colorado Department of Public Health and Environment (CDPHE) Yampa River Segment 13e (Grassy
<br />Creek) aquatic life standard of 1.0 mg/L at all stream stations and average concentrations exceeding
<br />the standard at SSG1, YSGF5, and SSLG5. The standard is normally not exceeded at any of the
<br />NPDES outfalls due to settling in the impoundments. Seneca Coal Company has been granted, by the
<br />CDPHE, a `temporary modification' of this iron standard until Seneca Coal Company can provide data
<br />to determine a proper ambient -based standard. A comparison of the iron concentration at YSGF5
<br />(2.09 mg/L) with that at SSG1 (1.91 mg/L) and YSG5 (0.72 mg/L) suggests three conditions:
<br />1. Present (pre- mining) conditions in the Grassy Creek mainstream lead to natural iron
<br />concentrations of approximately 2 mg/L.
<br />2. Pond 002 effectively removes iron from Little Grassy Creek flows via settling.
<br />3. Iron from the Grassy Creek mainstream is diluted by presumably lower concentrations in
<br />runoff from Scotchman's Gulch, which enters Grassy Creek between stations SSG2 and YSG5.
<br />Note that Scotchman's Gulch and its tributary Armand Draw each have in -line water reservoirs
<br />in which ancillary settling may be achieved.
<br />No surface water samples exceeded the CDPHE Yampa River Segment 13e (Grassy Creek) aquatic life
<br />chronic manganese standard of 2.618 mg/L, though several exceeded the agricultural use standard of
<br />• 0.2 mg/L. The agricultural use standard is only appropriate where water is applied to soils with pH
<br />values lower than 6.0, and so is unlikely to be applicable at PSCM, as the affected water is not used
<br />directly for irrigation. Average manganese concentrations in Grassy Creek slightly exceeded the
<br />PSCM Permit App. 2.04 -75 Revision 12/17/09
<br />
|