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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION II DATE: November 9, 1994 SUBJECT: Hydrogeologic Review of Draft RI Report, Tutu Wells Site, St. Thomas, dated August 1994, prepared by Geraghty & Miller, Inc. FROM: Linda Ross, Hydrogeologist Technical and Pre-Remedial Support Section TO: Mel Hauptman, Chief New York and Caribbean Superfund Branch II In response to your request for hydrogeologic review I have prepared the following comments. Please send me a copy of the final comment letter so that I can follow up. Also, if you can provide feedback on the usefulness of the various comments, this would be helpful. If you have any questions please contact me at extension 6324 or via LAN at ROSS-LINDAC. General Comments 1. Soil, shallow bedrock and groundwater source(s) of chlorinated VOCs at Laga Industries. The source(s) of chlorinated VOCs at Laga have not been delineated. Laga had the highest chlorinated VOCs in groundwater (MW-16) during the last sampling round by approximately an order of magnitude, yet the source(s) of the contamination has not been determined. This work should have been performed as part of this RI. Likely locations for the soil or shallow bedrock source(s) of chlorinated VOCs are the elevated soil-gas hits northwest of the building and under the building. In addition, well MW-16 should be turned into a cluster to determine concentrations at depth because the vertical extent of groundwater contamination at the site has not been determined. The deep well should be double cased because of the potential for DNAPL. 2. Groundwater elevation maps. Three of the four groundwater elevation maps do not include the water level elevations. This should be corrected. In addition both groundwater measuring rounds were taken in the same month, May 1994. At least another round of water level measurement should be produced for the Remedial Design taken under different climatic conditions. This will improve the final groundwater extraction design. As shown by Figure 4-7 water level conditions are variable in this area and were quite different between TUT OO6 O654 *64642* 64642 November 1992 and May 1994. 3. Downgradient extent of contamination is not delineated. This RI has not delineated the downgradient extent of contamination. If there are additional supply wells downgradient of the site, they should be sampled. 4. Perform an analysis of PCE and the breakdown products The RI does not attempt a site-specific analysis of PCE and the various breakdown products. This should be included in the text and illustrated by maps. This could be useful in determining where to place the extraction wells. 5. Preparation of additional groundwater concentration maps. Additional analysis is need for the groundwater concentration data. The two maps that are available (Figures 5-17 and 5-18) do not provide enough visual information about individual compounds, variation with depth and vertical distribution. The following additional maps should be prepared in a clearly presented manner, contoured and discussed. a. Maps showing chlorinated VOCs for both shallow and deep aquifers. These should be similar in format to the ones already prepared. b. Maps showing petroleum related compounds for both shallow and deep aquifers. These should be similar in format to the ones already prepared. c. Preparation of maps each showing the distribution of the following chlorinated VOCs: PCE, TCE, 1,2-DCE and vinyl chloride. Plot these for both shallow and deep aquifers. d. Preparation of a cross-section showing the distribution of total chlorinated VOCs. Show screen setting or length of open hole. e. Preparation of cross-sections showing the distribution of the following chlorinated VOCs: PCE, TCE, 1,2-DCE and vinyl chloride. Show screen setting or length of open hole. Specific Comments page 2-11, paragraph 3 - Plots of the eight rounds of supply well sampling from September 1990 through April 1993, should be included in this report as an Appendix. TUT 006 0655 page 3-1 - To assist in understanding the relative locations of the various PRPs, a large scale location map should be produced. The map should fit on a 8 1/2" x 11" or slightly larger sized paper. page 3-16, paragraph 3 - Change "including 21" to "consisting of 21". page 3-23, paragraph 2 - The groundwater samples were collected with bailers. Degassing of the VOCs can occur with the use of bailers, therefore, the concentrattionsof VOCs detected should be considered minimum values. In the future groundwater purging and sample collection should be done with a low flow pump in order to minimize degassing. Before any additional groundwater sampling contact EPA about the correct method of purging and sample collection using this low flow technology. page 3-25, paragraph 1 and page 3-28, paragraph 1 - The pumping tests should also yield values of hydraulic conductivity (K). Include this in the discussion. page 4-8, paragraph 3 - Because the geologic transitions are difficult to determine, include what criteria was used for deciding when the geologic material is unconsolidated, weathered bedrock or competent bedrock. page 4-21, paragraph 3 - Figure 4-6 does not show fracture traces. The reference should probably be to Figure 4-1. page 4-22, paragraph 2 - Figure 4-6 does not depict that the former stream channel of the Turpentine Run has been filled, and the surface drainage is channelized through a storm sewer under the area. page 4-22, paragraph 3 and page 4-23, top of page- The steep gradient may be indicative of the low permeability of the zone penetrated by the shallow well, and conversely, the less steep gradient may be indicative of a high permeability zone. Replace the word "is" with "may" because there could be other factors contributing to these observations, such as topographic controls. page 4-23, paragraph 2, last sentence - Add that the gentle gradient may indicate a more permeable zone. Sections 4.6.2.4 and 4.6.2.5 - Analyze all the bedrock pumping test data using a method that was designed for fractured rock. The methods used assume homogenous and isotropic conditions. A suggestion for a analysis method is the "Double-porosity model for fractured aquifer with fracture skin" that is included in AQTESOLV (Moench, 1984). A sensitivity analysis should be done for the thickness of slab blocks (aquifer matrix) and the results should be compared with the Cooper-Jacob and Theis results. The TUT OO6 O656 double porosity method may be preferable because the assumptions are closer to what is observed in the field. In addition, the double porosity method yields aquifer characteristics for both the matrix and the fractures. Sections 4.6.2.4 and 4.6.2.5 - Include what the assumed aquifer thickness is for each analysis. Sections 4.6.2.4 and 4.6.2.5 - For every transmissivity value calculated, determine what the hydraulic conductivity (K) is. This information may be needed in the future, in particular, for the capture zone analysis which will be performed as part of the Feasibility Study. page 4-28, paragraph 3, last sentence - In reference to Figure 4- 18, confirm that this sentence is correct as written. page 4-29, paragraph 3 - Provide more information on how the contour spacing was calculated using the Cooper-Jacob equation to approximate the logarithmic decrease in drawdown with increasing distance from the pumping well. page 5-3, last bullet and page 5-4, first complete bullet - Clarify whether a site is considered impacted if the soil-gas survey detected VOCs, but a soil boring was never done at the location. EPA believes that an area with high soil-gas readings may constitute an impact to soil and/or groundwater, although it never has been confirmed by sampling. An example of this is the high soil-gas survey readings on the northwest portion of the Laga property, which never had confirmatory borings. Yet, a well installed directly downgradient to the high soil-gas high, yielded the highest groundwater concentrations at the Tutu Wells Site. There is also evidence that this location may have been the site of a sludge pit for dry cleaning waste while Laga was operational. Therefore, this particular soil-gas location must be considered impacted and should be included in the FS as a location which warrants remediation. An area with high soil-gas readings should be considered a potential source even without confirmatory sampling. page 5-5, bullet 3 - EPA does not agree with the criteria that an impacted sample surrounded by non-detects should not be considered an impact to soil. For example, at the Curiculum Center (Laga Industries) soil sample SS-12 (0-0.5 ft) yielded high concentrations of BTEX compounds and the adjacent samples showed non-detect. However, during an EPA site investigation on 11/3/94, it was noted that there was a active discharge pipe from the Curriculum Center at the approximate location of SS-12. This criteria should be removed. page 5-5, bullet 5 - EPA does not agree that the lack of data validation is sufficient to totally disqualify the data. The TUT OO6 O657 data can still be used qualitatively. page 5-6, paragraph 2 - EPA believes that a statistically based background concentration should be to used for subsurface soils. The maximum background soil concentration is unacceptable and it does not take into account that the background samples collected could be impacted. page 5-9, last paragraph, sentences 1 and 2 - Remove these two sentences because they do not agree with the available data. The highest soil gas survey levels are not in the same location as the soil boring locations. These sentences are misleading. page 5-31, bullet 1 - EPA generally agrees with this statement except at the Laga property where the soils were not adequately investigated, both at the soil-gas hot spot and under the building. This criteria should be modified to reflect conditions at Laga. page 5-47, paragraph 2 , sentence 4 - Remove this sentence because the source(s) of VOCs from the Curriculum Center building have not been located. page 5-50, paragraph 1, Curriculum Center - Remove the last phrase of the last sentence because the source(s) of the VOCs from the curriculum Center building have not been located. Table 3-4 - Key the sources of the data to the actual data. Table 4-1 and 4-2 - Provide a complete reference for the source of data. Table 4-4 - State what type of geophysical techniques were used to assemble this information. Table 4-8 - Provide hydraulic conductivity values (K) and aquifer thicknesses (b). Tables 5-1, 5-2, 5-3, 5-4, 5-5, 5-7, 5-8, 5-9, 5-10, 5-11 and 5- 12 - List the ARARs on the Tables and flag the exceedances. Table 5-6 - Modify this Table so a statistically valid concentration is used for background soil sampling. Table 6-1 - Key the sources of the properties to the listed properties. Table 6-1 - Provide information on the subscripts in the vapor pressure column. Figure 4-9, 4-10 and 4-12 - Plot the actual groundwater elevations on the Figures. The Figures are not useful in their TUT OO6 O658 present form. cc Dennis Santella, PRTS Carolyn Kwan, NYCSB2 TUT OO6 0659