2007-12-19_REVISION - M1988112 ‎(17)‎

• Permit No: M1988112
• IBM Index Class Name: REVISION
• Doc Date: 12/19/2007
• Doc Name: Soil Profile Description
• From: TELESTO
• To: DRMS
• Type & Sequence: AM3
• Media Type: D
• Archive: No

Novemher 2007 Newmont * Salazar Ranch Fluoride Final- Report • 1
INTRODUCTION AND BACKGROUND
This report provides an assessment of a number of issues related to irrigating alfalfa at the
Salazar Ranch with ground water diverted from the San Luis Mine West Pit. Specifically,
this assessment has examined water use by alfalfa, uptake of fluoride (F) by alfalfa,
potential toxicity that increased concentrations of F may have on alfalfa, and the potential
toxicity that may exist for domestic livestock and wild ungulates that use irrigated alfalfa
as forage.
Water chemistry data from the West Pit ground water at Salazar Ranch were used in this
assessment. Fluoride concentrations of approximately 4.5 mg/L were reported for West
Pit ground water and used as the basis of our calculations. Fluorite saturation index
values for the West Pit ground water indicate that the water is initially near equilibrium
with respect to fluorite. However, upon reaction with the soils, the soil extractions
become consistently undersaturated with respect to fluorite. Fluorite undersaturation,
combined with rapid fluoride removal provides evidence that fluoride removal results
from adsorption rather than precipitation. Studies have also shown that the presence of
secondary carbonate minerals, such as calcium, in the soil will also act to precipitate
fluorite if the fluoride adsorption capacity of the soil is exceeded.
ALFALFA UPTAKE OF FLUORIDE
A thorough search of the literature did not reveal any studies that document the amount of
F that alfalfa bioconcentrates. However, fluoride studies conducted on clover, a species
that is functionally similar to alfalfa, reported F tissue concentrations at levels 4 to 5 times
greater than F concentrations in solution. Results from the study suggest that plants with
similar biomechanisms to clover, such as alfalfa, would have the capacity to accumulate
and store concentrations of fluoride in plant tissue at levels higher than the F
concentrations in the irrigation water applied at Salazar Ranch (Arnesen 1997).
If we assume a similar but conservative tissue bioaccumulation factor for alfalfa of 3, the
maximum amount of F that alfalfa could remove from irrigation water is approximately 3
MWH 1825 Sharp Point Drive, Suite 118 *Fort Collins, Colorado 80525 * [phone]