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Al Jesena - 9 - 1 March X000 <br /> Draft RI for OU#3 <br /> NCTS, Stockton <br /> 1. Page S-1, Section 2.0. It is unclear why a 30-year simulation period was chosen in the "no action <br /> alternative." Usually a simulation period is proposed once there are cleanup alternatives <br /> considered for comparison, such as pump and treat systems with an associated cleanup period <br /> (e.g., 10 years). What is the concentration of the leachate when it reaches groundwater and how <br /> does that value compare to established background water quality and water quality goals? <br /> 2. Page S-2, Section 3.2. Without knowing the character of the waste in the landfills how can the <br /> Navy assume that the "primary source of contamination no longer exists...and that all the wastes <br /> were released in the past?" Soil and/or the individual landfills may continue to leach contaminants <br /> as rainwater infiltrates the unsaturated zone, which is significantly less than 21 feet. Landfills that <br /> are seasonally inundated with groundwater may also continue to leach contaminants to <br /> groundwater and possibly to surface water depending upon whether there is a drainage channel <br /> adjacent to the trench(s). Moreover, groundwater samples were only analyzed for VOCs so we do <br /> not know the extent of groundwater impacts from leachable constituents in soil for other COPCs. <br /> Obviously, there are wells associated with each site, but often these wells are not downgradient <br /> from sample locations where the waste extraction tests showed leachable products or the sites's <br /> monitoring wells were contaminated with other COCs. Please clarify why these assumptions were <br /> made when they do not fit the site specific factors. <br /> 3. Page S-14. The modeler uses an attenuation zone (mixing zone) of 21 feet based on the thickness <br /> of Confining Unit 1 when the groundwater has been measured at 7 feet bgs (Figure 2-13). In this <br /> regard, there is no attenuative capacity available for any of the COPCs. Therefore, if the <br /> calculated degree of attenuation, using the generic designated level methodology(in this case x1), <br /> is not available between the base of the contaminated soil and highest groundwater, then the soil <br /> constituent threatens groundwater quality, and the soil must be remediated to the lowest level that <br /> is achievable, considering both technological and economic factors. If the same contaminant is <br /> present in both groundwater and in overlying soils, contaminant breakthrough has occurred and no <br /> attenuative capacity is available for that constituent within overlying soils. Discrete groundwater <br /> samples should be taken to verify whether groundwater has been impacted from COPCs other than <br /> VOCs (see Table K-9)based on WET extract results. <br /> 4. Page S-20. Please clarify what the Navy deems insignificant. What are the concentrations? <br /> Background for organics is 0 (zero). <br /> 5. Goal GM-2 for site IAS-07 states that the results of the groundwater modeling indicate that the <br /> VOC plume will not increase significantly in size over the 30-year time frame modeled. Without <br /> knowing the content of the landfills, how can the Navy make this assumption? <br /> The document continues to report that the lack of plume movement is due to the high organic <br /> carbon content of the water-bearing zone, low hydraulic gradient, low- soil permeability, and the <br /> assumption that the source is no longer releasing based on the age of the landfills. If this is so, <br /> how did VOC plumes reach Aquifer 4, which requires further investigation? How long will it be <br /> before aerobic/anerobic conditions prevail in this environment? Tetra-Tech project managers and <br /> Board staff observed trenching activities at Site IAS-07 and witnessed the exposure of glass <br /> bottles containing an unknown orange liquid. In fact, the groundwater was tinted orange. How <br />