EIS-0113_Section_11 - Hanford Site

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COMMENTS ON APPENDIX O
STATUS OF HYDROLOGIC AND GEOCHESRCAL MODELS USE TO
SIMULATE CONTAMINANT MIGRATION FROM HANFORD DEFENSE WASTES
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COMMENTS ON APPENDIX Q "a
APPLICATION OF GEOHYDROLOOIC MODELS TO POSTULATED
RELEASE SCENARIOS FOR THE HANFORD SITE
The following comments on Appendix O summarize the hydrogeelogie models used to
estimate travel Omer and peek concentrations from a release of contamination to Me
The. fallowing eommente on Append& Q discus the application of ,wbyd,o1.gic models
to the Hanford site:
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3.5.2.8
3.5.2.11
1. N the seduce zone, a simple, unit hydraulic gradient, ane-dimensional, arelytical
model was used to simulate edveative transport. Under the protective barrier,
where More would theoretically be no infiltration, molecular. diffusion was assumed
to the predominant transport mechanism and a diffusion model used. A version of
the TRUST model was. need to attempt a simulation of two-dimensional ground
water Row in the vedose zone, but evidently the writers were .able to operate the
model
2. A Mite difference model (VTT) was used to nlmulate saturated groundwater flow.
"In model has Been calibrated to the uneontimed aquifer at the Hanford site.
3. M snalfica4 one-dimensional Gems o t model wen used to simulate .nlaminenl
tremport through both the accelerated and saturated canes. The model is referred
to as e st.basti.-cor native model becouae. it tires the dispersion term of Ran
equation to simulate the random nature of travel time estimates along streamlines
of Dow. This section of App.dlx 0 is confusin,; on exasple calculation would aid
Me reader in interpreting exactly how Me model was need.
1. Generally aoreervetive m uman,tioaa were made throughout the appendix.. Based on
the models described In Appendix .O, travel times through the unsaturated zone are
much larger than travel Umes through the saturated zone.. Unfortunately, very
little information is given oa exactly now these compum6ons were performed and
the assumptions. Net were made.
2. The text correctly states that hydraulic conductivity In the unsaturated Zone Is a
very sensitive parameter. The Campbell equation was used to estimate hydraulic
conductivity an a function are not given in Me text. Since Me vedose Zone model
was .calibrated, the parameters used to the calculations are very important sad
should be discussed in the text.
3.5.2.6
3.5.2.27
4.2.55
3. Equation Q.1 oa page Q.3 is incorrect also; it is not known exactly what the 4.2.55
equation is supposed to be..
4. Assumptions used in the saturated came modeling are adequate, .1M.gb, as
mentioned above, travel itmes through the unsaturated... ere much longer Man
travel times borough Me saturated...
4. On page 0.33,. section 0.4.3.6, It is stated Mat a reactant dispersion coefficient
3.5.2.12 based on dispersion through the acculturated Zone Is need In both the unsaturated
and saturated zones, but nowhere in Appendices 0 or Q is Me method of calculating
the dispersion coefficient described.
S. Append ix O rentairm n good discuslm, of geoehemteal interactions and Me
limitations of fire models. applied, but reached no conclusions an the effectiveness
of Me models or an other potentially usable models.
5. Same additional saturated name modeling was performed to lack at Me
onre roamers of increased Irrigation N no Brea. h was ...ad that a maximum
of 20 percent of Me Irrigation water aaplied would become groundwater recharge. 3.5.3.1
This is hot a bed asumptioy but It is certainly not a worst a.. esumptlon. It is
Almost always necesery to ewxrapply hvigatiou water to flush Me setts through
Us root zone ro evoid Increasing soil salinity. With saline water, and saline. soils, it
I. not uncommon to have 50 pereent of applied[ irrigation water become gru.d
water recharge
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