2011-12-28_HYDROLOGY - M1977300

• Permit No: M1977300
• IBM Index Class Name: HYDROLOGY
• Doc Date: 12/28/2011
• Doc Name: Notice of Violation, Amendment 3
• From: Cotter
• To: CDPHE-WQCD
• Permit Index Doc Type: Hydrology Report
• Email Name: AJW
• Email Name: TAK
• Media Type: D
• Archive: No

Remedial Assessment
Cleanup Criterion for Alluvial Fill Source Term Materials
The goal of remedial measures to address solid source term materials residing in the alluvial fill is to
permanently isolate this material from contact with alluvial groundwater, greatly reducing or eliminating
the potential for groundwater leaching at concentrations in excess of the in- stream uranium standard for
Ralston Creek. Remedial measures will include excavation and removal of any source term material
having the potential to leach uranium in concentrations in excess of 0.03 mg/L.
The first approach for assessing a cleanup level that might achieve the remedial objective was to plot
results of Synthetic Precipitation Leaching Procedure (SPLP) testing (EPA Method 1312) for evaluation
of the relationship between U -nat concentrations in solid source term material and leachate generated
from the SPLP testing (Figure 8). A non - linear logarithmic function provided the best statistical fit to
these data, though the statistical significance of this curve is weak. Despite the statistically weak
relationship (R = 0.50), a correlative trend is nevertheless apparent and the fitted curve suggests that on
average, solid source term concentrations in excess of about 39 mg/kg could result in alluvial
groundwater concentrations in excess of 0.03 mg/L.
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
•
y= 0.03Ln(x) - 0.06
R -0.50
0 500 1000 1500 2000 2500 3000 3500
Solid Source Term U -nat ( mglkg)
11
0.12
0.09
0.06
0.03
0.00
Solid Source Term U-nat (mglkg)
Figure 8: Left: "best fit" non - linear curve fitted to SPLP data. Right: curve with axes truncated
to highlight the lowest values and a solid source term concentration that on average can be
expected to produce a leachate concentration of about 0.03 mg /L when subject to SPLP
testing.
Potential reasons for high variability in SPLP testing results include significant heterogeneity in rock/soil
particle size distributions and associated variability in the amount of oxidation and soluble salts present
on the surfaces of these source term materials. These samples were collected at different locations and
depths within the alluvial fill pad and variable degrees of prior oxidation and leaching are thus expected.
Because these data lacked a strong statistical correlation, further analysis was necessary to develop a
cleanup criterion that provides high confidence that remedial objectives will be achieved.
The second approach for assessing a potential cleanup level involved using SPLP data to evaluate ratios
of U -nat concentrations in solid source term materials to those in the leachate. This ratio is known as a