Comments provided by Dave Kacheck, CENWO-ED-GG Dated: November 2, 2007

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1 Baker Environmental, Inc. A Unit of Michael Baker Corporation Airside Business Park 100 Airside Drive Moon Township, PA (412) FAX (412) U. S. Army Corps of Engineers Omaha District Attn: CENWO-PM-HD (Jeffery Skog) 106 South 15th Street Omaha, NE Subject: Response to Comments Draft LNAPL Investigation Pilot Study Report Former Atlas E Missile Site No. 12 Windsor, Colorado Mr. Skog: Provided herein are responses to comments on the Draft LNAPL Investigation Pilot Study Report for Former Atlas E Missile Site No. 12 located in Windsor, Colorado provided in your November 7, 2007 and subsequent s and our conference call of December 7, Comments provided by Dave Kacheck, CENWO-ED-GG Dated: November 2, I have reviewed the LNAPL Pilot study report and have the following comments. It should be remembered that this study was to determine what technologies are appropriate for the site, not to do a definitive delineation of soil and groundwater. The study overall appears to have only eliminated DPT and MIP as useful technologies for investigations. Soil gas appears to be useful, but I understood it to be a relative indication of contaminants, not definitive or a replacement for actual media analyses of the various media. Additional soil gas investigation for Diesel range hydrocarbons will need to be completed, especially to the east. Let me know if you have any questions. Agree. Per the phased approach for this project, the work plan states the pilot report will describe the success/failure of the pilot study and pilot study-related documentation. The Phase I Investigation work plan will address the methods to delineate the lateral boundaries of the plume, the thickness of the LNAPL, and the potential source of the LNAPL. 2. Pg. 2 Para. 2. Indicate if the DPT was driven again to see if the gravel piece was anomalous or an indication of a siltstone formation. This would indicate if the DPT was truly incapable of reaching groundwater. Since the topography slopes away from the DPT hole location, discuss whether DPT may have been effective in areas away from the Launch and Service Building where the groundwater may be at a shallower depth. Indicate if it remains as a possible option based on surrounding borehole logs.

2 Page 2 Based on the known site stratigraphy (see drill logs in the previous and draft reports), observed increasing hardness during DPT borehole advancement (DPT advancement speed and responsiveness), and the evaluation provided by the DPT representative (Mike Martin, Vironex Rocky Mountain Regional Manager), DPT is not a realistic drilling option for the site. 3. Pg. 2, Para. 3. Include a copy of the DPT log for comparison to the other included logs. The text states a comparison was made between the three logs and the DPT log is needed to confirm the Baker analysis. As this was a drilling evaluation, logs SB-2 and SB-16/MW-7 were used for comparison to the DPT soil cores. A drill evaluation test borehole log was not created as the DPT soil cores correlated well with the logs and no significant variations were observed. 4. Pg. 3, Table 1. The field screening results for all three boreholes indicate that there is virtually no VOC contaminants in the soil at any of the sampled depths. Indicate how these concentrations relate to actual potential contaminant concentrations in the vadose zone. Also indicate how these screening concentrations relate to the soil gas results. Indicate if significant contaminants above action levels are present or if the concentrations are low. Interpret the concentration values of the field screening in relation to the potential type of future investigation techniques that can be employed. During the SI (1996), TPH/DRO was detected in the subsurface sample (a depth of 32 feet) from boring SB-5 (located in the area of the former RP-1 UST) at a level of 260 mg/kg. The concentration was less than the Colorado cleanup standard of 500 mg/kg. Elevated levels of VOCs in soil gas were detected with the PID in soil samples collected above and below the water table within the fill and natural material near the wastewater drainage sump. Analytical results of soil samples were non-detect for VOCs. The soil gas survey detected VOCs related to the known fuel and TCE releases. The survey is being used as a tool to assist with the delineation of LNAPL and the identification of other possible source areas. The soil gas survey will assist in determining the placement of soil borings to verify and further characterize site conditions for comparison the state standards. 5. Pg. 3, Section 3.0. The 4 day exposure time for the Gore modules seems short to get optimum results. Verify that the time of exposure was sufficient. The work plan stated the exposure time of 3 days. Per conversations with representatives of Gore, the exposure time is sufficient to detect the presence of VOCs and to meet the objectives to determine if the technology would work at the site based on the geology and the contaminants present. The short

3 Page 3 exposure time was utilized to reduce field personnel costs. 6. Pg. 3, Section 3.0. Indicate if the act of pushing the DPT drive point would potentially smear the sidewalls of the hole to limit influx of vapors. This could be a problem in high clay content soils. Per Gore, pushing a DPT drive point and potentially smearing the sidewalls will not affect results. In fact, Gore s storage, installation and retrieval guidelines, provided in the work plan, state that a narrow diameter hole is drilled or driven to a depth of at least three feet. Hand tools such as a slam bar or rotary hammer drill will suffice ; Geoprobe type tools can also create the installation hole. 7. Pg. 4, Section 3.0. Discuss the relationship between the mass level results measured by Gore and actual VOC concentrations in the soil. Indicate how this relates to CDPHE action levels for soils for each contaminant. The issue is: do the results of the investigation also indicate moderate to high levels of contaminants as would be measured by traditional analyses of soils, or just relative to themselves. This is critical to potential future investigations and remediation. Per Gore, the results have a strong positive relative correlation between the soil gas data and what is observed during subsequent matrix sampling. In other words, at locations where the soil gas levels are high, there is a corresponding high probability that the compound is present in the subsurface. With lower soil gas levels, the probability of finding the compound decreases. In most site characterization programs, the soil gas data delineates the nature and extent of the subsurface impact by volatile and semivolatile organic compounds. The soil gas data at a sample location can be compared relative to the soil gas data reported from the other sample locations across the site. Even if the soil gas mass levels are fairly low, patterns in the spatial distribution will appear indicating the area(s) of greatest subsurface impact. It is in these areas, that subsequent matrix sampling should occur. On a standard basis, Gore reports air, soil gas, subslab vapor and water data, by target compound desorbed from the GORE TM Module, in units of micrograms (mass). Concentration data can be reported for modules deployed in any of these sampling environments. For soil gas, soil porosity and percent water saturation values are required. This survey reports soil gas mass levels present in the vapor phase. Vapors are subject to a variety of attenuation factors during migration away from the source concentration to the module. Thus, mass levels reported from the module will often be less than concentrations reported in soil and groundwater matrix data. In most instances, the soil gas masses reported on the modules compare favorably with concentrations reported in the soil or groundwater (e.g., where soil gas levels are reported at greater levels relative to other sampled locations on the site, matrix data should reveal the same pattern, and vice versa). However, due to a variety of factors, a perfect comparison between matrix data and soil gas levels can rarely be achieved. Soil gas signals reported by this method cannot be identified specifically to soil adsorbed, groundwater,

4 Page 4 and/or free-product contamination. The soil gas signal reported from each module can evolve from all of these sources. 8. Pg. 4, Section 4.0. It is unclear what is really occurring at the site in relation to LNAPL extent and thickness. Indicate if the sample collected and analyzed was degraded and how it compares to previous samples collected and analyzed. Is there an explanation for the observed LNAPL extent and thickness noted in this investigation and a relationship to groundwater elevation, new site conditions, recent precipitation, etc. Each time investigations are done on the LNAPL, results are dramatically different. Give an explanation or hypothesis for these discrepancies as it relates to this investigation. Baker agrees with this assessment. The inconsistencies in the data record of free product thickness, the nature of the free product and the location of the source area do not confirm a historical release of rocket fuel from the facility. It is possible that a more recent release of diesel fuel occurred near MW-7. The recorded thicknesses of product using an interface probe was measured to be less than 1 inch in MW-7 and MW-9 during the RI (1999) and during the pilot study (2007). In 2005, the free product in MW-7 was measured at 0.5 inches; in 2006, at approximately 16 inches in a bailer. The absence of periodic (e.g., quarterly or semi-annual) water elevation and free product thickness data and inconsistencies in measurement methods add to the site complexities. 9. Pg. 5, Section 5.0. The conclusions are pretty basic. The information included in the report hints that deeper analysis should be completed. Agree. See response to Comment Pg. 5, Section 5.0. One of the reasons for completing this pilot study was to identify what technologies may be optimum for future investigations of the soil and groundwater to delineate TCE concentrations and extent. The report does not discuss this, but merely indicates that DPT and MIP are not appropriate. Based on the results of this study and general knowledge, discuss what technologies could be employed in future investigations to meet the site contaminant delineation requirements for remedial action. See response to Comment Pg. 5, Section 5.0. Since there are so many discrepancies between all the investigations at the site, and the soil gas sampling was localized in one area, indicate if there could be a potential LNAPL source to the east of the old RP-1 tank in an area that has not been investigated by soil gas. The diesel range soil gas results hint at elevated concentrations to the east/southeast.

5 Page 5 RESONSE: Agree. See conclusions, third bullet (below). The GORE Modules results and associated contour maps show that moderate to high mass levels were observed for fuel-related compounds and TCE. The spatial patterns indicate fairly well-defined petroleum soil gas plumes with the suspected source being in the vicinity of the former RP-1 fuel and catch tanks and a TCE plume southwest of the wastewater drainage sump and wastewater drainage sump discharge headwall. Additional soil gas sampling is recommended to assist the delineation of the nature and extent of the fuel and TCE contamination. Note: additional soil gas data can be combined and mapped with these data. Comments provided by Kathie Englert, CENWO-ED-GS Dated: October 31, Subject line. Include the Site number. The Former Atlas E Missile Site No. 12 has been added to the subject line. 2. Page 1. Section 1.0. equipped with a GH62 The text was revised. 3. Page 2. Second paragraph. Note: MC sampler The text was revised. 4. General. Indicate on the figure that the MC and MIP were in the same location, or within the same location. The Figure 1 legend description for the test borings location symbol was revised as follows: Note: Test boring location represents both MC and MIP boreholes; advanced within approximately five feet of each other. The figure was not revised.

6 Page 6 5. Page 3. Table 1. Notes. Change rotosocic to rotosonic. The table text was revised. 6. Page 4. First paragraph. This is the first mention of the product fingerprint; provide a source for or clarify/elaborate. The fingerprint analysis was conducted by Evergreen Analytical, Inc. for USACE for the MW-07 Sampling and Analysis Report (2006). The text was revised to include (USACE, 2006). 7. Page 4. Section 4.0. Last paragraph. program would require change to program requires. The text was revised. 8. Page 5. Section 5.0. General. Clarify the source as the RP-1 tank. The fuel stored in this tank was not diesel fuel. Clarify in the last bullet if the age of the fuel has any meaning to its use at the site. The suspected source area is the southwest portion/corner of the facility where the RP-1 and Fuel Catch tanks were located. Although the USAF used these tanks for RP-1 fuel storage, someone, post USAF may have stored diesel fuel in one or both tanks even though it has/can not be documented. The tank closure/remediation sampling did not distinguish the type(s) of petroleum hydrocarbon. However; the fuel sample fingerprint analysis, conducted by Evergreen Analytical, Inc. for USACE for the MW-07 Sampling and Analysis Report (2006), states the LNAPL present in MW-7 was diesel fuel. Last bullet issue the age of the fuel based on the sulfur analysis suggests that diesel fuel possibly was stored in the USTs prior to their removal in See above. 9. Page 5. First sentence. the sites fuel was most likely This text and the first bullet were revised as follows:, the fuel collected from MW-7 was most likely

7 Page 7 Comments provided by Danielle Talkington, CENWO-ED-GS Dated: November 6, Baker should propose other investigative methods for delineating the lateral boundaries of the plume, the thickness of the LNAPL, and the source of the LNAPL. Of the methods used in the pilot study, there was limited success in achieving the objectives. Per the phased approach for this project, the work plan states the pilot report will describe the success/failure of the pilot study and pilot study-related documentation. The Phase I Investigation work plan will address the delineating the lateral boundaries of the plume, the thickness of the LNAPL (if present), and the potential source of the LNAPL. 2. DPT would not work so the Contractor needs to determine in what way HSA or other methods can obtain needed data. See response to Comment Field headspace screening appears to only indicate presence or absence of VOCs. Field headspace screening is a tool used to assist the onsite drilling/sampling programs by providing real time relative data. 4. For the soil gas survey, I would suggest that for indicating higher levels of mass of contaminant, that the shading would go from yellow to orange to red, instead of to purple, because that might be difficult to distinguish from the dark blue, which is a very low level of contamination. The Gore reports were presented in their standard format. For future surveys, Gore can present all the data (including this data) in any color/contour format. 5. Concur with the recommendation that several more soil gas points are needed to delineate the plume. Agree.

8 Page 8 6. The Contractor needs to suggest methods for determining the depth and thickness of the LNAPL across the site. See response to Comment The analytical results for TPH-gasoline (Total GRPH) show a maximum of 2.15 ug, a mean of 1.44 ug, and a standard deviation of 0.45 ug. The lack of variation in the color of the GRPH is because of the small range in mass. I question where there really is any significant amount of DRPH at the site, especially since background levels of GRPH were found in the trip blanks and method blanks. The trip blank concentration for GRPH was 0.04 ug, an order of magnitude less than the lowest detected concentration. The trip blank concentration for DRPH was 0.01 ug, far below the detected concentrations. Per Gore s report background levels of DRPH and GRPH were observed on the trip blanks/or the methods blanks. Target analyte levels reported for the field-installed modules that exceed trip and method blank levels, and the analyte method detection limit, are more likely to have originated from on-site sources. We agree that the GRPH concentrations were minimal and that mapping concentrations is not necessary. DRPH results are more indicative of site conditions, based on the historical presence of diesel/kerosene in the groundwater and soil. Baker is pleased to be involved with completion of this pilot study project for USACE. Should you have any questions or require clarification of the comment responses, or any other issues related to this project, please do not hesitate to contact me by phone at or by at sfrund@mbakercorp.com. In my absence, please contact Mr. Robert Roselius at or rroselius@mbakercorp.com. Sincerely, BAKER ENVIRONMENTAL, INC. Susan R. Frund, P.G. Project Manager

October 9, U. S. Army Corps of Engineers Omaha District Attn: CENWO-ED-ED (Jeffery Skog) 215 North 17 th Street Omaha, NE

October 9, U. S. Army Corps of Engineers Omaha District Attn: CENWO-ED-ED (Jeffery Skog) 215 North 17 th Street Omaha, NE Baker Environmental, Inc. A Unit of Michael Baker Corporation Airside Business Park 100 Airside Drive Moon Township, PA 15108 October 9, 2007 (412)-269-6300 FAX (412) 375-3996 U. S. Army Corps of Engineers