C • K. w & MILLER, INC. Environmental Services /""""N Ground Water Engineering Hydrocarbon Remediation Education July 1, 1993 Ana Gloria Ramos Designated Coordinator Tutu Environmental Investigation Committee P.O. Box 364269 San Juan, Puerto Rico 00936-4269 Re: Technical Rationale for Proposed Monitoring Well MW-15 at Ramsay Auto Property, Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands Dear Ms. Ramos: In response to the May 25,1993 letter to Andy Praschak, U.S. Environmental Protection Agency (USEPA) legal counsel, from Carol Ann Rich, legal counsel for Ramsay Auto, Geraghty & Miller, Inc. has prepared this letter to address Ms. Rich's concerns by describing the technical rationale for the installation of proposed Monitoring Well MW-15. This monitoring well was proposed to be installed south of the drum storage area and underground storage tank (UST) located at the Ramsay property (see enclosed Figure 1-1). Ms. Rich's May 25 letter raised three technical concerns: • technical justification for evaluation of the ground-water quality at Ramsay, • the potential influence of adjacent properties on ground-water quality, • location, depth, and purpose for proposed Monitoring Well MW-15. The technical justification or rationale for this proposed monitoring well and an assessment of influence of adjacent properties is based upon previous work, which is discussed below. The location, depth, and purpose of the proposed monitoring well is presented below with a detailed description of the proposed work. TUT 006 1429 201 West Passaic Street, 3rd Floor• Rochelle Park, New Jersey 07662*(201) 909-0700'FAX (201) 909-0567/0568 *64779* 64779 PREVIOUS WORK Geraghty & Miller has reviewed the Preliminary Assessment (PA) of Ramsay Motors dated March 24, 1989 which was prepared by NUS Corporation (NUS) for the U.S. Environmental Protection Agency (NUS Corporation 1989). Geraghty & Miller prepared Table 1 (attached), which summarizes this PA. Based on their February IS, 1989 site reconnaissance, NUS identified two waste management areas including: (1) twenty-five 55- gallon drums of waste oil, and (2) a UST used for waste oil storage. At the time of the NUS site reconnaissance, the 25 drums of waste oil were being stored in the maintenance garage. According to the NUS report (NUS Corporation 1989), the drums of waste oil were "...not properly stored or contained. Many of the drums are open and there is oil pooled on the floor." NUS also observed oil leaking into the soil around the maintenance garage "in a few areas" during the February 1989 reconnaissance of the Ramsay Property. It was also reported that soil samples analyzed by Cenref Labs indicated the presence of ethylbenzene, xylene, 2-hexane, and toluene in soil (NUS Corporation 1989). No other details regarding this soil sampling (i.e., location, concentration, methods, etc.) were provided by NUS. The waste oil UST at the Ramsay property is located beneath the maintenance garage (also referred to by NUS as the workshop area), which is used for automotive repairs and servicing (Figure 1-1). The age, volume, and construction of the UST is unknown. Although NUS (1989) stated "[tjhere is no information that indicates that the tank is leaking; therefore, there is little potential for contaminant migration...", NUS recommended "the tank should be tested to ensure that it is sound and not leaking" (NUS Corporation 1989). Considering that very little is known about the UST construction and integrity, Geraghty & Miller believes an assessment of the impact of this UST on ground-water quality is warranted. This assessment can be accomplished by installing a monitoring well (proposed Monitoring Well MW-15) downgradient of the UST (Figure 1-2), similar to the monitoring wells that have been installed downgradient of the USTs located at the Texaco and Esso Service Stations. Previous samples of waste oil, soil, and ground water have been collected by USEPA subcontractors for laboratory analysis (see Table 2 attached). On August 17, 1988, waste oil from the Ramsay UST was sampled by Roy F. Weston, Inc. (Weston) and U.S. Virgin Islands Department of Planning and Natural Resources (DPNR) personnel. The sample holding time was exceeded on the volatile organic compound (VOC) analysis, and the analytical results TUT 006 1430 GERAGHTY & MILLER, INC. obtained should be qualified as estimated. Detected VOCs included 2-butanone (also known as methyl ethyl ketone [MEK]) (150 milligrams per liter [mg/L]), benzene (210 mg/L), toluene (1,400 mg/L), ethylbenzene (290 mg/L), and total xylenes (1,700 mg/1) (Weston 1988). On June 8, 1989, Camp, Dresser and McKee (COM) Federal Programs personnel also sampled the waste oil from the Ramsay UST. Analytical results obtained by CDM included estimated concentrations of benzene (64 mg/L), toluene (450 mg/L), ethylbenzene (130 mg/L), total xylenes (1,200 mg/L), and 2-hexanone (also known as methyl butyl ketone [MBK]) (180 mg/L) (CDM Federal Programs 1989). On September 8, 1988, CDM Federal Programs personnel sampled the ground water from the Ramsay Supply Well, which was stored in the on-site holding tank (CDM Federal Programs 1989). Tetrachloroethane (PCE) was detected in this ground-water sample at 11 mg/L (see Table 2 attached). This reported PCE concentration is consistent with the results of seven sampling events conducted at the Ramsay Supply Well by Geraghty & Miller (1992b), which reported chlorinated VOC concentrations of PCE, as well as, 1,2-dichloroethene (1,2-DCE), and —^ trichloroethene (TCE). Ground-water samples collected at several supply wells indicate that . PCE and its breakdown products (i. e., 1,2-DCE, TCE and vinyl chloride) are present throughout the Tutu area (Geraghty & Miller, Inc. 1992b). At least two separate sources of ground-water contamination by chlorinated VOCs have been identified (Geraghty & Miller, Inc. 1993). On September 8, 1988, CDM also collected two soil samples (Samples eR-07s and eR-08s) near the southern portion of the Ramsay property (see Table 2 enclosed). These soil sampling locations were placed in the vicinity of a reported release of waste oil draining from what is currently the Antilles Auto Parts facility south of the Ramsay Property. The soil results (see Table 2 attached) reported by CDM are possibly indicative of the release from the Antilles (former Gassett) facility because petroleum compounds were detected (i.e., benzene, toluene, ethylbenzene, and propylbenzene). This area also receives drainage of surface water from the Curriculum Center (former Laga Building) during rainfall events. A grass-covered drainage ditch runs east to west, allowing drainage to enter a storm-sewer catchment located on the east side of Route 384. The Antilles facility was formerly known as Gassett Auto Parts, and prior to that it was known as Consolidated Auto Parts. Automotive servicing and repairs have been and are still //*"*N performed at this property south of Ramsay. Tlrr 006 GERAGHTY & MILLER, INC. More recently, during a site visit on June 5, 1991 Geraghty & Miller personnel observed drums of waste oil stored outside the Ramsay maintenance garage adjacent to the south wall of the garage. This is the area identified as the Drum Storage Area on Figure 1-1. An area of stained soil approximately 4 feet by 6 feet was observed around the drums. The stained soil area consisted of unvegetated soil (i.e., with no grass cover) with black oily stains. Thick grass cover was present throughout the area surrounding the stained soil area. Two drums were observed in the grass southeast of the Drum Storage Area. One of these drums (at the location of Soil Boring B-3; see Figure 1-1) was lying on its side with an open bunghole. This drum was approximately two-thirds full of a black oily liquid presumed to be waste oil. Near the open bunghole, a stained soil area approximately 0.5 foot by 1 foot was noted. Apparently during late 1991 or early 1992, Ramsay constructed a concrete slab with curbing over the area of stained soils noted at the Drum Storage Area, as described above. This concrete slab is currently used for the storage of 55-gallon drums containing waste oil. On August 3, 1992, Geraghty & Miller performed two soil borings (Borings B-2 and B-3 on Figure 1-1) near the Ramsay property as part of the Tutu Service Station Investigation, which --^ was conducted according to a USEPA-approved Work Plan (Geraghty & Miller, Inc. 1992a). At each boring, continuous soil samples were collected to refusal using decontaminated split spoons. Each 2-foot interval was screened in the field using a calibrated HNU photoionization detector (PID). Soil samples from each 2-foot interval were collected for headspace VOC analysis in the field using an on-site PhotoVac lOS-Plus Gas Chromatogram (GC). As specified in the Work Plan, the soil sample with the highest HNU reading from each boring was sent for laboratory analysis. If no HNU readings were detected above background concentrations, the soil sample immediately above bedrock (or the water table, whichever was encountered first) was to be collected for laboratory analysis. Laboratory analysis included Target Compound List (TCL) VOCs, TCL base neutral acid (BNA) extractable compounds (i.e., semi-volatile compounds), Target Analyte List (TAL) metals and cyanide. Laboratory analytical results and the accompanying data validation performed by Geraghty & Miller were presented in Technical Memorandum n (Geraghty & Miller, Inc. 1993). Copies of the sample/core logs for Borings B-2 and B-3 are enclosed. Table 4 presents a summary of the field GC analytical results. Boring B-2 was drilled at the Drum Storage Area. Because of the concrete slab and curbing at the Drum Storage Area, Boring B-2 was drilled immediately south of the stained soils noted during the June 5, 1991 site visit. Boring B-2 was advanced to refusal at 3.5 feet below /""""^ land surface (bis) without encountering HNU readings above background concentrations in the TUT OO6 14C GERAGHTY & MILLER, INC. two split-spoon samples collected. Since no HNU readings were recorded above background concentrations, the soil sample from 2.0 to 3.5 feet bis (above bedrock) was collected for laboratory analysis. Although the actual sampling interval was noted on the sample/core logs, soil sample intervals were rounded to 2-foot intervals for easier reference. Therefore, this sample was labeled as Sample B-2 (2-4'). Laboratory analysis of Soil Sample B-2 (2-4') reported VOC concentrations of methylene chloride at 17 micrograms per kilogram (ug/kg) (equivalent of parts per billion [ppb]) and acetone at 14 ug/kg. Both of these VOCs are common laboratory contaminants. BNA analysis reported estimated concentrations of benzo(a)pyrene at 270 ug/kg, benzo(g,h,i)perylene at 290 ug/kg, and pyrene at 220 ug/kg. Total petroleum hydrocarbon concentrations (TPH) of 110,000 ug/kg were also detected in Soil Sample B-2. Table 3 presents a summary of the laboratory analytical results for Soil Samples B-2 and B-3. Although the only petroleum compounds detected in the laboratory analyses were BNA compounds, other petroleum compounds may have also been released with the waste oil spilled _^ near the Drum Storage Area. VOC compounds detected in waste oil from the Ramsay UST included benzene, toluene, ethylbenzene, and total xylenes. These compounds have likely been released to soil, as well as the BNA compounds. These VOC compounds are more volatile, biodegradable, and soluble than BNA compounds. Therefore, these VOCs may have been dissolved with infiltration and migrated to the water table in the bedrock unit. Field GC analysis of the two soil samples collected at Soil Boring B-2 indicated the presence of PCE at concentrations of 2 ppb in Sample B-2 (0-2') and 4 ppb in Sample B-2 (2-4') (see Table 4 attached). Field GC analysis also indicated the presence of cis-l,2-DCE, benzene, and toluene at undetermined concentrations below the method detection limit (BMDL) of approximately 1 to 3 ppb for these parameters. Because all of the field GC results are equal to or less than 4 ppb, these reported results may be due to soil gas derived from contaminated ground water. VOC soil concentrations up to approximately 10 ppb may be derived from contaminated ground water. A comparison of the VOC analyses performed by the laboratory (Table 3) and by the field GC (Table 4) for soil samples collected near the Ramsay property demonstrates that the field GC analyses reported the presence of more VOC parameters than the laboratory analyses. /"""^ For instance, the field GC detected 1,2-DCE, benzene, toluene, and PCE, whereas the Tt IT 006 1433 GERAGHTY & MILLER, INC. laboratory analysis detected PCE, methylene chloride, and acetone. (Methylene chloride and acetone are common laboratory contaminants). This is consistent with analytical results for other sampling locations. This may be attributed to the shorter holding time of field GC samples (a few hours) versus the laboratory sample holding time (a few days), resulting in detection of trace concentrations by the field GC. Also, the different extraction methods and analytical instruments may cause these differences. The field GC analyzed a vapor extraction and the laboratory analysis was performed on a liquid extraction. Geraghty & Miller's review and assessment of the field GC data is still in progress; the results and conclusions regarding the field GC results are preliminary until this assessment is completed. A complete assessment of the field GC data will be presented in the Remedial Investigation (RI) report. Soil Boring B-3 was drilled approximately 75 feet west of Soil Boring B-2, near a 55- gallon drum that was lying on its side with an open bunghole. Boring B-3 was advanced until refusal at a total depth of 3.3 feet bis. Sample B-3 (0-2') had an HNU reading 0.2 ppm above background, so this sample was collected for laboratory analysis. The laboratory analysis of Soil Sample B-3 (0 to 2 feet) reported VOC concentrations of methylene chloride at 26 ug/kg, and acetone at 6 ug/kg. As mentioned previously, these two compounds are common laboratory contaminants. TCE was detected in Soil Sample B-3 at an estimated concentration of 6 ug/kg. This reported TCE value may be due to volatilization of TCE from contaminated ground water. No other chlorinated VOCs, BTEX VOCs, BNAs, or TPH concentrations were detected in Soil Sample B-3 (Table 3). The field GC analysis of the two soil samples collected at Soil Boring B-3 indicated the presence of PCE at a concentration of 2 ppb in both the shallow (0 to 2 feet) and deeper (2 to 4 feet) sample. Field GC analysis also indicated the presence of trans-l,2-DCE, cis-l,2-DCE, benzene, and toluene. These reported trace amounts (1 to 3 ppb) may be due to soil gas derived from contaminated ground water. The Ramsay Supply Well is located approximately 165 feet north of the proposed location for Monitoring Well MW-15 (see Figure 1-1). Based on the reported non-potable usage (i.e., car washing), Ramsay's consultant, Cooper Environmental, has estimated that this supply well is currently pumped at a rate of approximately 7 to 100 gallons per day (gpd). This well is permitted by DPNR to withdraw up to 500 gpd. GERAGHTY & MILLER, INC. TUT °°6 l434 Based on the existing ground-water contour map for the site (Geraghty & Miller, Inc. 1993), shallow ground-water flow is generally from north to south at the Ramsay property (see Figure 1-2 enclosed). The water levels measured in existing shallow monitoring wells near the Ramsay property appear to be unaffected by the operation of the Ramsay Supply Well, which is reported to be 105 feet in depth. Based on the existing ground-water flow data (see Figure 1-2), Monitoring Well MW-1S is proposed at a location downgradient of the Drum Storage Area and the Waste Oil UST. Water-level measurements obtained from proposed Monitoring Well MW-1S will improve the definition of shallow ground-water flow conditions at the southern portion of the Ramsay property. PROPOSED WORK The main objective of the proposed work at the Ramsay property is to determine the impact of the Drum Storage Area and the Waste Oil UST on ground-water quality. The soil sampling at Boring B-2 indicates that a release of petroleum compounds (i.e., BNA compounds) has occurred, which has impacted soil quality. The proposed scope of work is intended to determine the distribution of petroleum contaminants in ground water. The proposed scope of work for the investigation is presented in detail below. INSTALLATION OF MONITORING WELL MW-15 To evaluate the ground-water elevation and ground-water quality in the bedrock unit, Geraghty & Miller proposes to install Monitoring Well MW-15 (see Figure 1-1). This monitoring well should be located near Boring B-2, where detectable concentrations of BNAs were encountered. After a 10-inch diameter boring is advanced to bedrock using the hollow-stem auger method, approximately 4 to 5 feet of 6-inch diameter steel casing will be grouted in the borehole to seal off the unconsolidated soils from the bedrock unit during further drilling. After allowing the grout to set for 24 hours, drilling will proceed into bedrock through the steel casing using an 8-inch diameter down the hole-hammer bit. Drilling will be continued to approximately 15 feet below the water table, and proposed shallow Monitoring Well MW-15 will be completed with an open borehole approximately 20 feet long. This is consistent with construction of other shallow monitoring wells that will be installed during the upcoming phase of the Tutu Service Station Investigation. TUT OOfa 1435 GERAGHTY & MILLER, INC. SAMPLING AND ANALYSIS No soil samples are recommended for laboratory analysis from the boring for proposed Monitoring Well MW-15 because soil quality has been sufficiently characterized by Soil Boring B-2. After allowing the ground water to equilibrate for at least 2 weeks following well development, ground-water sampling at this monitoring well will be performed during the second ground-water sampling event for the Tutu Service Station Investigation. Analysis will include TCL VOCs, TCL BNA compounds, TAL metals, cyanide, and TPH, as specified in the Tutu Service Station Investigation Work Plan (Geraghty & Miller, Inc. 1992a). At least two rounds of water-level measurements will be collected from this monitoring well after well development. We hope this has addressed all of Ms. Rich's concerns. If you have any questions, or if we can provide you with any additional information, please call. Sincerely, GERAGHTY & MILLER, INC. c: Andy Praschak, Esq. USEPA Leonard Reed, DPNR Clifford Crooke, DPNR Francis Torres, Esq. GAC&A Steve Kirkland, Esq. TEXACO Jose Agrelot, SOIL TECH PR01301-WP4/60*93.LTR/df Jeffrey S. Burdick Scientist v| x*" W /~