Dames & Moore, 1999 - USDA Forest Service

concentrations, but statistically the two concentrations were equivalent because of the above-mentioned
uncertainties associated with the flow estimates.
Relative to measured incoming load in Reach 2 (tailings influenced stream segment from RC-4 to RC-7),
the additions of magnesium were less than the additions in Reach 1. The deficit was +I550 mg/s. The
calculated concentration using this deficit was 26.1 mg/L (Table 6.6-1) which was close to the range of
magnesium concenlrations of 30 mg/L to greater than 100 mg/L in seeps.
The deficit between RC-7 and RC-2 was 684 mg/s, which was close to the contribution fiom SP-4 (5 15
mg/s).
The May 1997 analysis for magnesium implies that there are no significant missing magnesium load
contributions in the spring. The deficits between surface water additions and measured loads in Railroad
Creek can be accounted for by reasonable groundwater flows and magnesium concentrations.
The September 1997 magnesium load calculation for Reach 1 (Table 6.6-2) indicates little change between
RC-1 and RC-4 (-19 m a). The load provided by the only measurable source (P-5) was not significant
relative to the load entering the Site at .RC-1, and represented only 1.1 percent of the load previously
measured in May 1997. The Reach 1 balance was shown as a negative load (-75 mg/s). This small negative
load was consistent with the apparent flow loss in the reach (Section 4.3.7). In Reach 2, the load balance
was 71 1 mg/s, which can be accounted for by a groundwater contribution similar to that observed in May
1997.
In summary, the magnesium balance is in agreement with the site-specific water balance. The magnesium
balance indicated that all major sources were identified and that the required flow balances were consistent
with magnesium concentrations observed in both surface water and groundwater.
Quasi-Conservative Parameters - Zinc and Cadmium
Zinc and cadmium are often observed to show almost conservative behavior because their solubility is not
influenced by pH within the pH range normally encountered on site. They can be adsorbed onto soil and
sediment particles; however, this may not be a strong effect in coarse gravelly soils and stream beds.
The loading calculation of zinc followed the sarne'approach as for magnesium. In May, the difference
between RC-1 and RC-4 was 850 mg/s. The majority of this difference can be accounted for by P-5 (849
mg/s). SP-23 provided 71 mg/s, hence the cumulative load at RC-4 from measured sources was 1 123 mg/s.
This load at RC-2 was greater than the load at RC-4 (1034 mg/s). The balance of -90 mg/s is small relative
to the inflow from P-5 and therefore is not significant. The data imply that all significant loads in Reach 1
have been identified.
In Reach 2, very little zinc was added compared to Reach 1. The Copper Creek diversion was the largest
source. The required balance was 146 mg/s, which was larger than the point sources along Reach 2. The
concentration required to produce this balance was 2.5 m&. This implies that groundwater originating in
Reach 1 (i.e., from the mine support areas) enters Railroad Creek in Reach 2. The total of the balances for
Reach 1 and Reach 2 is 56 mg/s. This is less than 5 percent of the total load in Railroad Creek and implies
overall that non-point sources contribute insignificantly to the load in Railroad Creek during May. P-5 is the
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17693-005-019Uuly 27,1999,4:11 PM;DRAFf FINAL Rl REPORT