Loading...
HomeMy WebLinkAboutDSHW-2024-005557 WASATCH ENVIRONMENTAL, INC. ENVIRONMENTAL SCIENCE AND ENGINEERING 2410 WEST CALIFORNIA AVENUE SALT LAKE CITY, UTAH 84104 PHONE (801) 972-8400 FAX (801) 972-8459 e-mail: wei@wasatch-environmental.com www.wasatch-environmental.com ADDITONAL INVESTIGATION WORK PLAN ARMS TECHNOLOGY MACHINE SHOP 2779 WEST DIRECTORS ROW SALT LAKE CITY, UTAH PROJECT NO. 2619-003C PREPARED FOR: MR. DOUG HANSEN UTAH DEPARTMENT OF ENVIRONMENTAL QUALITY DIVISION OF WASTE MANAGEMENT AND RADIATION CONTROL 195 NORTH 1950 WEST, 2ND FLOOR P.O. BOX 144880 SALT LAKE CITY, UTAH 84114-4880 PREPARED BY: WASATCH ENVIRONMENTAL, INC. 2410 WEST CALIFORNIA AVE SALT LAKE CITY, UTAH 84104 801-972-8400 FAX: 801-972-8459 MARCH 26, 2024 Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 1 TABLE OF CONTENTS Section Page No. 1. INTRODUCTION AND OBJECTIVES ............................................................................................. 2 2. SITE BACKGROUND ...................................................................................................................... 2 3. SITE INVESTIGATION ACTIVITIES ................................................................................................ 4 3.1 Groundwater Monitoring Well Installation, Development, Surveying, and Sampling ......... 4 3.2 Off-Site Groundwater Sampling .......................................................................................... 5 3.3 Indoor Air Sampling............................................................................................................. 5 4. SAMPLING METHODOLOGY ......................................................................................................... 5 4.1 Groundwater Monitoring Well Installation, Development, Surveying, and Sampling ......... 5 4.2 Off-Site Groundwater Sampling .......................................................................................... 6 4.3 Indoor Air Sampling............................................................................................................. 7 5. REPORTING .................................................................................................................................... 7 FIGURES Figure 1 – Site Location Map Figure 2 – Historical and Proposed Sample Location Map Figure 3 – TCE in Groundwater Concentration Map Figure 4 – TCE in Soil Gas Concentration Map Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 2 ADDITIONAL INVESTIGATION WORK PLAN ARMS TECHNOLOGY MACHINE SHOP 2779 WEST DIRECTORS ROW SALT LAKE CITY, UTAH 1. INTRODUCTION AND OBJECTIVES In accordance with the Utah Division of Waste Management and Radiation Control (DWMRC) request, we have prepared this work plan for conducting investigative activities at the Arms Technology machine shop (Site), owned by ATI Corporation, located at 2779 West Directors Row in Salt Lake City, Utah. See Figure 1 for a Site Location Map. This work plan has been prepared to evaluate groundwater flow direction, evaluate volatile organic compound (VOC) and semi-volatile organic compound (SVOC) impacts to groundwater at the Site, and evaluate indoor air at the Site. The objectives of this work plan are to:  Install, develop, survey, and sample groundwater monitoring wells at the Site to evaluate the groundwater flow direction, evaluate on-Site VOC and SVOC impacts to groundwater, and evaluate the potential for VOC impacts to be migrating onto the Site from an off-Site source; and  Collect indoor air samples to evaluate the potential for VOC impacts to on-Site commercial workers. This work plan describes the sampling and analytical procedures that will be used for sampling to be performed during investigation activities at the Site. 2. SITE BACKGROUND Wasatch completed a Phase I Environmental Site Assessment (ESA) dated September 21, 2023, for the Site on behalf of Buchalter (the legal representative for the potential purchaser). This report identified the following recognized environmental conditions (RECs) and recommended additional investigation be completed:  There is a potential for releases to the Site from the long-term use of the sump near the southwest corner of the Site.  There is a potential for releases to the Site from the long-term use of chemicals, lubricants, and oils on the Site. The Client requested that investigations be completed to evaluate the identified RECs. On October 24, 2023, Wasatch completed four soil borings (GP-1 through GP-4) at the Site. Wasatch advanced borings GP-1, GP-2, and GP-3 in the areas hydraulically downgradient of the building to evaluate for impacts migrating away from the building, and boring GP-4 was advanced adjacent to the sump to evaluate for potential releases in this area. Additionally, Wasatch collected six sub-slab soil gas samples (SG-1 through SG-6) from beneath the on-Site building. Based on the data collected Wasatch concluded the following:  The suspected source area soil sample collected from boring GP-4 did not exhibit analyte concentrations that exceeded their applicable United States Environmental Protection Agency (U.S. EPA) Regional Screening Level (RSL) for Residential or Industrial Soil, except for arsenic. Based on Wasatch’s experience the detected arsenic concentration is within the typical Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 3 background range of 20 to 30 mg/kg for this area. Therefore, it is Wasatch’s opinion that the detected concentration of arsenic in soil is representative of background concentrations and is not considered to be a release.  Chloroform was detected in all soil gas samples at concentrations ranging from 1.2 micrograms per cubic meter (µg/m3) to 18 µg/m3. Chloroform is a common laboratory contaminant and is also a breakdown compound of chlorine which is commonly observed in soil gas samples due to the use of municipal water for irrigation or from leaking municipal water pipes in the area. Chloroform is not considered to be a constituent of concern resulting from the suspected release of chlorinated solvents, petroleum hydrocarbons, or metals at the Site.  Soil gas samples SG-4 and SG-5 exhibited trichloroethene (TCE) concentrations that exceed the applicable U.S. EPA Vapor Intrusion Screening Level (VISL) Residential and Commercial Target Sub-Slab and Near-Source Soil Gas Concentrations (TSSGCs). The TCE concentrations in soil gas indicate a release of TCE has likely occurred near soil gas samples SG-4 and SG-5. These samples were collected near the sand trap and the former paint booth features which may be the release point(s). Given the detected TCE in soil gas concentrations, there is a potential that the rate of vapor intrusion into the building may result in TCE indoor air concentrations that exceed the U.S. EPA RSL for Industrial Air.  The arsenic concentrations detected in groundwater exceed the U.S. EPA MCL; however, these concentrations are below the Utah Division of Water Quality (DWQ) Water Quality Standards (GQS) for arsenic. Given the elevated background concentrations of arsenic in soil, it is Wasatch’s opinion that the arsenic concentrations detected in groundwater are within the typical background concentration range for this area. No other metals were detected at concentrations that exceed their applicable U.S. EPA Maximum Contaminant Levels (MCLs).  TCE was detected in all groundwater samples analyzed for volatile organic compounds (VOCs) at concentrations ranging from 12.3 micrograms per liter (µg/L) to 75.4 µg/L. These concentrations exceed the U.S. EPA MCL for TCE. These samples were collected hydraulically downgradient of the on-Site building. Based on these data, it appears that a release of TCE may have originated from the on-Site building.  Based on the data obtained from boring GP-4, it does not appear that a release from the sump has occurred.  Given the totality of the data, it appears that a release of TCE has occurred at the Site and may be located near the sand trap/paint booth features. Wasatch recommended that this release be reported to the Utah Department of Environmental Quality (DEQ). Wasatch also recommended that additional investigation be completed to define the nature and extent of these impacts. On January 4, 2024, Wasatch completed eight additional borings (GP-5 through GP-12) at the Site to further evaluate the on-Site VOC impacts to soil and groundwater. Based on the data Wasatch concluded the following:  Several soil samples were collected above the water table in suspected source areas. Low concentrations of TCE were detected in the GP-11 (at 5 feet bgs) and GP-12 (at 6 feet bgs) borings above the water table. This indicates that a minor surface release has likely occurred in this area. However, these detected TCE concentrations are below the U.S. EPA RSL for Residential and Industrial Soil and the U.S. EPA Protection of Groundwater Soil Screening Level (PGWSSL).  No chlorinated solvents (including TCE and cis-1,2-dichloroethene [CIS]) were detected at concentrations exceeding their applicable U.S. EPA RSLs for Residential or Industrial Soil in the soil samples collected. However, soil samples GP-9-10, GP-10-10, GP-10-15, GP-11-10, GP-11- Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 4 15, and GP-12-12 (all collected at or below the water table) exhibited TCE concentrations that exceed the U.S. EPA PGWSSL. This indicates there are soil impacts below the water table at sufficient concentrations to result in impacts to groundwater at concentrations that exceed the U.S. EPA MCL.  TCE was detected in all groundwater samples at concentrations ranging from 4.88 to 47.3 µg/L. These concentrations exceed the U.S. EPA MCL for TCE, except for groundwater sample GP-7- 17 (4.88 µg/L). Additionally, TCE is the only VOC that has been detected at a concentration above the U.S. EPA MCL. Based on the groundwater data, TCE impacts to groundwater appear to be present across the Site.  Based on the totality of the groundwater data, TCE was detected along the northern, western, eastern, and southern boundaries of the Site. This indicates that TCE impacts may be migrating onto the Site, as the local groundwater flow direction is unknown but was assumed to be to the north or northwest.  Groundwater sample GP-11 exhibited the highest TCE concentration detected under the building. Given this and that TCE was detected in the soil above the water table in this boring, it is Wasatch’s opinion that this area likely represents a minor TCE source area under the building. Groundwater monitoring wells should be installed to verify the groundwater flow direction.  One groundwater sample (GP-9-30) was collected from a depth of 30 feet bgs. TCE was detected at a concentration of 20.1 µg/L, which exceeds the U.S. EPA MCL. This indicates that TCE impacts have migrated to at least 30 feet bgs at the Site.  Given the totality of the data, it appears that a release of TCE has occurred at the Site and may be located near the sand trap/paint booth features. Additionally, it appears that TCE impacts are migrating onto the Site from an off-Site source, likely resulting in co-mingled plumes. Wasatch recommends that this release be reported to the Utah DEQ. Wasatch also recommends that additional investigation be completed to define the nature and extent of these impacts under the guidance of the Utah DEQ. Wasatch submitted a DWMRC application to enter into regulatory oversight with the Utah DWRMC on February 20, 2024. The Site was accepted into the DWMRC Corrective Action program. DWMRC requested that additional environmental investigations be completed. Wasatch, DWMRC personnel, and the Client completed a virtual meeting on March 21, 2024, where several items of concern were discussed. In this meeting we discussed the sampling conducted at the sump located on the southwest corner of the Site and determined no further sampling was required to evaluate the sump. We also discussed the outside drum storage area and determined this area has only ever stored empty drums; therefore, it was determined that no additional evaluation of this area was required. Wasatch has provided DWMRC with the SDS sheets for the coolants and bluing agents used at the Site. Based on the SDS sheets, Wasatch did not identify a U.S. EPA RSL or MCL for any specific chemical that was listed on the SDS sheets provided. It is Wasatch’s opinion that the proposed groundwater monitoring wells below are sufficient to determine the Site groundwater flow direction and determine where groundwater is entering the Site. All other discussed items of the meeting are addressed in the sections below. 3. SITE INVESTIGATION ACTIVITIES 3.1 Groundwater Monitoring Well Installation, Development, Surveying, and Sampling Six groundwater monitoring wells (MW-1 through MW-6) will be installed at the Site to evaluate VOC and SVOC impacts to groundwater at the Site and to evaluate the potential for VOC and SVOC impacts that Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 5 may be migrating onto the Site from an off-Site source. The monitoring wells will be installed using the direct-push drilling methods. Soil core samples would be continuously collected from 5-foot long by 1.5- inch diameter discrete interval push samplers equipped with disposable polybutyrate liners. Soil samples would be collected continuously and field logged by an experienced geologist. The field logging would include a description of color, moisture content, consistency, odor, staining, and soil type based on the Unified Soil Classification System and screened in the field with a photoionization detector (PID). Monitoring well construction will consist of a 2.0-inch inner diameter (I.D.) polyvinyl chloride (PVC) well with a 10-foot screen to a depth of approximately 15 to 20 feet below ground surface. The monitoring wells will be developed to remove fines from the well screen prior to sampling using a pump or a disposable polyethylene bailer. In order to determine groundwater flow direction at the facility, top-of-casing elevations and the coordinates of the well locations will be professionally surveyed by Robinson, Biehn & Biehn, Inc. Wasatch will obtain groundwater elevation measurements from each monitoring well using an electronic water level probe. The probe will be decontaminated between each monitoring well with a phosphate- free soap, rinsed with potable water, and then rinsed with de-ionized water. Based on the measurements obtained, Wasatch will construct a potentiometric surface elevation contour map to determine groundwater flow direction. 3.2 Off-Site Groundwater Sampling Wasatch will request that two soil borings be completed on the adjoining west, assumed hydraulically upgradient, property. Groundwater samples will be collected from these borings to evaluate VOC and SVOC impacts to groundwater that may be migrating onto the Site from an off-Site source. The borings will be installed using the direct-push drilling methods. Soil core samples would be continuously collected from 5-foot long by 1.5-inch diameter discrete interval push samplers equipped with disposable polybutyrate liners. Soil samples would be collected continuously and field logged by an experienced geologist. The field logging would include a description of color, moisture content, consistency, odor, staining, and soil type based on the Unified Soil Classification System and screened in the field with a PID. 3.3 Indoor Air Sampling To evaluate the potential risk to indoor air for commercial workers, Wasatch will collect indoor air samples within the on-Site building. To evaluate current background VOC concentrations present in ambient air in the vicinity of the Site so that comparisons can be made to indoor air concentrations present at the on-Site building, Wasatch will collect an outdoor air sample from the roof or an upwind area of the building. 4. SAMPLING METHODOLOGY 4.1 Groundwater Monitoring Well Installation, Development, Surveying, and Sampling Chlorinated solvents have been identified at concentrations exceeding its U.S. EPA MCL within the groundwater beneath the Site. Additionally, DWMRC requested that SVOC groundwater samples be collected at the Site. Therefore, Wasatch proposes installing six groundwater monitoring wells to achieve the stated objectives. The monitoring wells will be installed using the direct-push drill rig (GeoProbe 7822 or equivalent), using hollow-stem auger or direct-push drilling techniques. Wasatch proposes installing the following monitoring wells as depicted in Figure 2. Each well will be installed to a depth ranging between 15 and 20 feet below ground surface (bgs) depending on measured depth to groundwater. Each well will be completed with 10 feet of 2-inch 0.010- Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 6 slot schedule 40 polyvinyl chloride (PVC) wells screen with 2-inch PVC well casing attached to the top of the well screen and extending to approximately 0.5 feet bgs. 10/20 silica sand will be placed as a filter pack material around the screen interval and extending at least 2 feet above the top of the screen interval. Bentonite chips will be placed from the top of the filter pack material up to ground surface and hydrated to form a well seal. Each well will be completed with a flush-mount surface completion consisting of an 8-inch steel well vault cemented in place. Once each well is installed, each well will be properly developed using over pumping well development techniques. A minimum of five well casing volumes of groundwater will be evacuated from each well; however, additional volume will be removed to sufficiently remove additional fines from the wells based on Wasatch’s discretion. All evacuated groundwater will be placed within a steel 55-gallon drum(s) labeled as pending analysis to facilitate proper disposal. All soil cuttings will also be placed within a steel 55-gallon drum and labeled as pending analysis to facilitate proper disposal. In order to determine groundwater flow direction at the Site, top-of-casing elevations and coordinate locations will be professionally surveyed by Robinson, Biehn & Biehn, Inc. Wasatch will obtain groundwater elevation measurements from each monitoring well using an electronic water level probe. The probe will be decontaminated between each monitoring well with a phosphate-free soap, rinsed with potable water, and then rinsed with de-ionized water. Based on the measurements obtained, Wasatch will construct a potentiometric surface elevation contour map to determine groundwater flow direction. The monitoring wells will be sampled using low-flow sampling techniques. Monitoring well sampling will involve inserting ¼-inch outside diameter, low-density polyethylene tubing into the newly installed monitoring well. The tubing will be run through a peristaltic pump, then to a flow cell to which a multi- parameter AquaTroll 500 meter will be attached, and finally to a 5-gallon bucket to collect the purge water. The initial water level would be measured in the monitoring well only and recorded prior to the initiation of pumping. Once pumping is initiated, water levels, pumping rate, cumulative volume purged, water temperature, specific conductivity, pH, oxygen reduction potential (ORP), dissolved oxygen (DO), and turbidity will be recorded at three to five-minute intervals until either stabilization is achieved or the monitoring well pumps dry. Pumping rates will be maintained at rates of 50 to 200 milliliters per minute to minimize drawdown. Stabilization is defined as three consecutive measurement intervals where temperature and specific conductivity were +/- 3%, pH was +/- 0.1, DO was +/-10% (or less than 0.5 mg/L), and turbidity was +/- 10% (or less than 5 nephelometric turbidity units [NTUs]). If the monitoring well pumps dry, it will be allowed to recharge to a minimum of at least 90% of its static water level prior to sampling. After stabilization is achieved, the tubing would be disconnected from the flow cell and the groundwater sample would be dispensed into appropriate laboratory prepared containers. Groundwater samples would be collected into appropriate containers with gloved hands and transported under chain-of-custody, in an iced cooler to Chemtech-Ford Laboratories (CF) for analysis of VOCs using U.S. EPA Method 8260D and SVOCs using U.S. EPA Method 8270E. 4.2 Off-Site Groundwater Sampling These borings will be installed using the direct-push drilling methods. Soil core samples would be continuously collected from 5-foot long by 1.5-inch diameter discrete interval push samplers equipped with disposable polybutyrate liners. Soil samples would be collected continuously and field logged by an experienced geologist. The field logging would include a description of color, moisture content, consistency, odor, staining, and soil type based on the Unified Soil Classification System and screened in the field with a PID. Subsequent to the borings, a stainless-steel temporary well screen will be placed within the groundwater to collect a groundwater sample. Groundwater would be purged from the boring in an attempt to reduce the turbidity of the groundwater sample. Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 7 Groundwater samples would be collected into appropriate containers with gloved hands and transported under chain-of-custody, in an iced cooler to CF for analysis of VOCs using U.S. EPA Method 8260D and SVOCs using U.S. EPA Method 8270E. Given that the adjoining west property owners may reject our request to collect groundwater samples from their property. These borings may not be collected. Wasatch will provide proof of acceptance or rejection of our request to sample the adjoining west property. 4.3 Indoor Air Sampling To evaluate potential soil vapor intrusion impacts in the on-Site building, Wasatch would collect six indoor air samples, four within the warehouse/manufacturing area (IA-1 through IA-4) on the ground floor level and two in the office areas (IA-5 and IA-6), and one outdoor air sample (OA-1) to be used as a background sample. Proposed sample locations are shown in Figure 2. Prior to collecting any indoor or outdoor air samples, Wasatch would complete a chemical inventory of the interior of the building space at the Site. This would be done to verify that no products within the structure contain any chemicals of concern. If products are found that contain the same chemicals of concern we will be analyzing for, those products will be removed from the building for at least 7 days prior to sampling. This will be completed to reduce the potential for false positives within the indoor air samples. Wasatch would also interview the appropriate personnel to ascertain if potential activities within the beginning have been conducted that may result in false positives (i.e. recent remodeling, floor stripping, etc.) The technique for collecting the indoor/outdoor air samples would begin by checking for a vacuum in each 6-liter Summa canister supplied by the laboratory. The initial vacuum would be recorded on the chain-of- custody form. A 6-liter Summa canister would then be placed at an appropriate height for each sample location. The sampling location height will generally be placed at breathing space height. A sample regulator with a flow restrictor would be provided by the laboratory. A sample regulator would be attached to each 6-liter Summa canister. The vacuum gauge on the flow restrictor would be monitored, with decreasing vacuum indicating that ambient indoor air is being collected into the sample canister. The samples would be collected for approximately 8 hours to represent a standard workday. The final vacuums would be recorded on the chain-of-custody form provided. The valve on each Summa canister would then be closed, the sample regulator would be removed, and a brass cap tightened to the inlets of the Summa canisters. The Summa canisters would be labeled with the appropriate sample location, as well as initial and final vacuum reading. Chain-of-custody documentation would be completed and the samples would be delivered to Pace for the analysis of the standard list of VOCs using U.S. EPA Method TO-15. The laboratory will use level 3 quality assurance/quality control (QA/QC) reporting. A Data Validation Report will be completed by an independent third-party for the groundwater, indoor air, and outdoor air sample samples. 5. REPORTING All data generated during the sampling will be documented in a final report. This report will include the following:  Narrative text,  Data tables,  Boring/well construction logs,  Applicable maps, Arms Technology Machine Shop Additional Investigation Work Plan Project No. 2619-003C Wasatch Environmental, Inc. Page 8  Chain of custody forms,  Laboratory analytical results, and  Third-party data validation report. The results of the sampling and analysis will be summarized in the report. Data will be presented in table format. Conclusions based on the data as well as field observations will be included in the report. After the laboratory data has been received, and reviewed, the report will be completed and submitted to ATI Corporation prior to submission to the Utah DWMRC. Sincerely, WASATCH ENVIRONMENTAL, INC. Blake Downey, P.G. Vice President and Senior Project Hydrogeologist Distribution: (1) Electronic - Addressee (1) Electronic – Scott Farber (ATI Corporation) The use or reuse of this information is restricted to the referenced document unless otherwise authorized. Wasatch Environmental Copyright 2006 ARMS TECHNOLOGY MACHINE SHOP WEI 2619-003C Figure 1 Site Location Map Approximate Location of Site The use or reuse of this information is restricted to the referenced document unless otherwise authorized. Wasatch Environmental Copyright 2006 ARMS TECHNOLOGY MACHINE SHOP WEI 2619-003C Historical and Proposed Sample Location Map Figure 2 Directors Row Cell Tower Compressor Compressor Filter House Filter HouseCoolant Drain Sump Transformer Closed-loop heated parking area Shed w/ Drums Floor drain Capped floor drain Paint Booth Coolant Totes Previous Boring Location Previous Soil Gas Sample Location Approximate Location of Site SG-1 SG-3 SG-4 SG-2 SG-5 SG-6 GP-2 GP-1 GP-3 GP-4 Proposed Indoor/Outdoor Air Sample Location LEGEND GP-10GP-9 GP-5 GP-12 GP-11 GP-8 GP-7 GP-6 Fence Sand Trap w/ Discharge Electrical Line Proposed Monitoring Well Location MW-3 MW-1 MW-2 MW-5 MW-4 IA-3 OA-1 IA-1 IA-2 IA-6IA-5 IA-4 Scale: 1-inch equals approximately 54 feet Assumed Groundwater Flow Direction Proposed Off-Site Soil Boring GP-13 GP-14 MW-6 The use or reuse of this information is restricted to the referenced document unless otherwise authorized. Wasatch Environmental Copyright 2006 ARMS TECHNOLOGY MACHINE SHOP WEI 2619-003C TCE in Groundwater Concentration Map Figure 3 Directors Row Sand Trap w/ Discharge Floor drain Capped floor drain Paint Booth Boring Location Approximate Location of Site GP-4 GP-1 TCE - 33.3 GP-2 TCE - 12.3 GP-3 TCE - 75.4 *All concentrations are reported in micrograms per liter. **All concentrations in exceed the U.S. EPA MCL.red Assumed Groundwater Flow Direction GP-7 TCE - 4.88 GP-12 TCE - 22.1 GP-11 TCE - 47.3 GP-5 TCE - 9.44 GP-6 TCE - 7.52 GP-10 TCE - 38.9GP-9-15 TCE - 43.3 GP-9-30 20.1TCE - GP-8 TCE - 32.7 The use or reuse of this information is restricted to the referenced document unless otherwise authorized. Wasatch Environmental Copyright 2006 ARMS TECHNOLOGY MACHINE SHOP WEI 2619-003C TCE in Soil Gas Concentration Map Figure 4 Directors Row Sand Trap w/ Discharge Floor drain Capped floor drain Paint Booth Soil Gas Sample Location Approximate Location of Site *All concentrations are reported in micrograms per cubic meter. **All concentrations in exceed the U.S. EPA Vapor Intrusionred Screening Level Commercial Target Sub-SLab and Near-Source Soil Gas Concentration. SG-1 TCE - <0.95 SG-2 TCE - 2.0 SG-4 TCE - 230 SG-3 TCE - 1.8 SG-5 TCE - 690 SG-6 TCE - 4.0