PERMFILE53867

• Permit No: M1977004
• IBM Index Class Name: Permit File
• Doc Date: 8/31/1984
• Doc Name: Response to Adequacy
• From: Homestake
• To: DMG
• Media Type: D
• Archive: No

-6-
In the event the topographic patter
Supplemental Report S-1 is substantially
the time the final configuration is met,
for Division review. In accord with our
mass in the North Pit, Exhibit L has been
topographic monitoring.
The following items were raised by
concerning the hvdrologic aspects
n shown in Drawing 01001-2 of
different than that achieved at
Homestake would revise the drawing
plan for monitoring the landslide
revised to include a line item for
27, 1984
Item: The validity of the assumption of a linear relationship for predicting
leachate concentrations of the reclaimed low grade ore stockpiles, and how
this assumption affects the conservative nature of the prediction.
Res onset As is explained in Supplemental Report S-4, the effect of
leaching low-grade ore piles was examined from the perspective of the
long-term or "annualized" aspect and the single infiltration event
(Section 5 of S-4). Data from experimental measurements were used to
provide accurate and supportable simulations of future field conditions.
Experimental leachate data were generated by Rocky Mountain Analytical
Lab (16.4 of S-4). These data were used to develop "estimated leach
fractions" for the 10-day ]eaching period, as shown in Table S-2 of SR-4.
The annualized calculation was based on data collected for Saguache,
Colorado by Thornwaite (1955) in order to provide some perspective of the
annual potential for water to flow through the pile. In fact, this
calculation is not particularly important to the analysis at hand. Rather,
the analysis should focus on the effect of the individual precipitation
event that generally results in infiltration of water into the ground
water system.
Based on permeability measurements of waste rock piles at the Pitch
site, it was determined that the flow velocity through the pile would be
about 0.5 ft./min. Thus the flow time through the 50 foot deep pile would
be about 100 minutes, rather than the 10-day contact period used to develop
the laboratory data and the "estimated leach fractions." Based on various
laboratory leaching experiments, it has been demonstrated that leachate
concentrations increase, at least to a point of leachate saturation, with
increasing residence time in the waste rock. Many laboratory data suggest
the changes in concentration with increasing residence follow a pattern of
(1) slow rise in the very early stages of contact; (2) a rapid increase for
a longer period of time followed by; (3) a very slow increase to the maximum;
and, (4) finally a steady, slow to moderate decrease. (There are, of course,
variations to this pattern, not all of which have been explained.) The
initial stages of the pattern could be explained by (1) the time required
to react with leachable materials; (2) the removal of many of the leachable
materials located on the surfaces of the primary flow paths; and, (3)
a change to conditions where the smaller paths and discontinuous process
channels, with longer residence times, contribute leachates to the larger,
less concentrated, flows through the primary flow paths. Compensating against
the increase in concentrations with residence time can also be the decrease in
oxygen in the infiltrating water which could decrease the oxidation and
dissolution of metals.