13.01.2013 Views

Dames & Moore, 1999 - USDA Forest Service

Dames & Moore, 1999 - USDA Forest Service

Dames & Moore, 1999 - USDA Forest Service

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

The chemistry of these monitoring wells is compatible with a groundwater flow pattern that includes<br />

natural groundwater from upslope and affected groundwater originating from the east waste rock pile<br />

andtor the mill buildings area. Further, these groundwater concentrations may be influenced by<br />

groundwater flowing within the former creek channel which underlies the tailings. 'Ihis relatively<br />

permeable unit may control and channel the flow of affected groundwater from the weathered source<br />

areas, including the portal drainage, lagoon, waste rock piles, and mill area towards the SP-2 seep.<br />

Tailings Pile 2 and 3<br />

Groundwaters sampled from the underlying surf~cial material in the central areas of tailings piles 2 and 3<br />

(e.g., wells PZ-lA, TP2-5A, TP3-6A) generally had low metal concentrations (e.g., Cu: -Q to 67 pgL; Zn:<br />

32 to 400 pg/L; Cd: 0.2 to 2.2 p&), although an occasional elevated iron level (5,710 CLgn iron) was<br />

observed in PZ-1A. This elevated level is probably the result of groundwaters leaching natural materials or<br />

minor incursions of tailings waters infiltrating the substrate.<br />

The metals load discharged by the seeps (SP-3, SP-4, SP-5 and SP-18) appears to be the result of oxidation<br />

of tailings, possibly due to the interaction with groundwaters derived hm Railroad Creek. Groundwater<br />

wells in the substrate near the tailings pile edges (e-g., TP2-4A, PZ-6A, TP3-8) had higher concentrations of<br />

iron (7,040 to 58,300 fl), sulfate (340 to 1,500 mg/L) and total dissolved solids (500 to 2,400 mgL).<br />

~irnited data on groundwaters in saturated tailings (e.g., PZ-IB) report elev&ed iron (69,000pgL) and<br />

elevated sulfate concentrations (850 mg/L). These values are similar in magnitude to the concentrations<br />

recorded for the seeps (Fe: 23,900 to 154,000 p&; SO,: 530 to 880 ma). 6.5.2.2 Metal Removal<br />

Metal removal mechanisms are described below and are summarized in Figures 6.5-1 7 to 6.5- 19.<br />

Tailings Pile 1 Area<br />

Seepage emerges from the base of tailings pile 1 at SP-I and SP-2 and enters Railroad Creek. The seeps<br />

are strongly acidic @H2000 mgL) and iron (-1000<br />

mgL). As the acidic seepage mixes with Railroad Creek water, it goes through several rapid chemical<br />

changes including:<br />

Conversion of unoxidized ferrous iron to ferric iron by atmospheric and dissolved oxygen<br />

Increasing pH due to dilution and stream water alkalinity allowing additional ferric iron<br />

to precipitate as flocculent (in surface water) or goethite (in groundwater)<br />

Co-precipitationlsorption of copper with flocculent or ferricrete<br />

Further pH increase due to dilution and stream water alkalinity resulting in precipitation<br />

of aluminum as flocculent or aluminum hydroxide precipitate<br />

Formation of copper carbonate flocculent<br />

Attenuation occurs by precipitation of ferricrete, aluminum hydroxide, copper carbonate and co-<br />

precipitation of copper with ferricrete.<br />

\U)M-SMI\VOLI\COMMOMWP\~W)~Ulo~2\nW.doc<br />

6-38<br />

176934054l9Wuly 27.<strong>1999</strong>;4:11 PMDRAFT FINAL RI REPORT

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!