EHsS support Davis Liquid Waste Superfund Site Smithfield, Rhode Island Prepared for: Davis Site Performing Party Group September 21, 2017 Prepared by: EHS Support, LLC Groundwater Geochemical and ESS Group, Inc. Evaluation Technical Memorandum consider done it MASSACHUSETTS RHODE ISLAND VIRGINIA 100 Fifth Avenue, 5th Floor 10 Hemingway Drive, 2nd Floor 999 Waterside Drive, Suite 2525 Waltham, Massachusetts 02451 East Providence, Rhode Island 02915 Norfolk, Virginia 23510 p +1 781.419.7696 p +1 401.434.5560 p +1 757.777.3777 September 21, 2017 Mr. Darryl Luce EPA New England Office of Site Remediation and Restoration 5 Post Office Square, Suite 100 Mail Code OSRR07-1 Boston, Massachusetts 02109-3912 Re: Groundwater Geochemical Evaluation Technical Memorandum Davis Liquid Waste Superfund Site Smithfield, Rhode Island ESS Project No. D164-007 Dear Darryl, On behalf of the Davis Site Group and pursuant to the RD/RA Consent Decree, Section X (Reporting Requirements), and Appendix B (Statement of Work) Section V.B (Pre-Design Investigation Plan), enclosed is the final Groundwater Geochemical Evaluation Technical Memorandum. This memorandum documents the evaluation of the additional analyte data (major and minor cations and anions and stable isotopes) from the Fall 2015 Site-wide Monitoring Event. Electronic copies of the final document are also enclosed. Sincerely, ESS GROUP, INC. EHS SUPPORT CORP. / ,/ //-' / / / ;)'v\./ .re:. / / ,,-,/. L -- Jeffrey G. Hershberger, P.G. Nigel Goulding Project Manager Project Director Enclosure (2 copies) C: Gary Jablonski (RIDEM) (1 copy) Liyang Chu (Nobis) (1 copy) Nigel Goulding (EHS) (electronic only) Joe Biss (EHS) (electronic only) www.essg rou p,com environmental consulting & engineering services TECHNICAL MEMO To: Davis Site Performing Party Group From: John Bartos, EHS Support LLC Jeff Hershberger, ESS Group, Inc. CC: Joe Biss, EHS Support LLC Date: September 21, 2017 Re: Groundwater Geochemical Evaluation Fall 2015 Groundwater Monitoring Event Davis Liquid Waste Superfund Site Smithfield, Rhode Island ABSTRACT EHS Support, LLC (EHS Support) and ESS Group, Inc. (ESS) have performed a groundwater geochemical evaluation using samples collected during the Fall 2015 Groundwater Sampling Event. The objective was to identify the different groundwater flow paths at the Davis Liquid Waste Superfund Site (the Site) through the use of groundwater geochemistry. The results of this evaluation support the following conclusions. 1. The evaluation has identified that there are three different geochemical types of groundwater at the Site: a. Calcium-Bicarbonate – unimpacted, native groundwater (overburden and bedrock) b. Calcium-Chloride – impacted by anthropogenic organic compounds i. Elevated chloride concentrations are the result of historic and ongoing reductive dechlorination of chlorinated volatile organic compounds (CVOCs) c. Sodium-Bicarbonate (and Calcium-Sodium-Bicarbonate) – minimally-impacted and unimpacted groundwater associated with the dike structure 2. The locations of wells exhibiting the unimpacted, native geochemical type (Calcium-Bicarbonate) groundwater is in agreement with the bedrock plume delineations as presented in the recently submitted Draft Conceptual Site Model submittal (Draft CSM). a. This conclusion is also supported by the distribution of chloride at the Site, particularly within the bedrock. 3. The geochemical type groundwater within the dike structure (Sodium Bicarbonate and Calcium- Sodium-Bicarbonate) is different from the other Site groundwaters and is related to the different Davis Site Performing Party Group Groundwater Geochemical Evaluation September 21, 2017 mineralogy of the bedrock within the dike and suggests the potential for a longer residence time within the dike based on the limited areal extent of this feature. a. The shift in the geochemical type for the groundwater in the dike structure relative to the other bedrock wells sampled is clearly evidenced on Figure 12 based on the analytical results for the three dike monitoring wells (OW-111-R, OW-80, OW-111-RD). b. The geochemical type for the groundwater at dike well OW-111-RD is further shifted due to the higher concentration of chloride at this location. This appears related to the detections of Site contaminants in this well. 4. Surface waters display a different geochemical type (Calcium-Sulfate) and variability in isotopic signature likely due to variable evaporative losses (ponded vs. flowing) and variability in the influence of contributions from groundwater discharges, which typically have a heavier isotopic signature. a. Sulfate may be coming from the wetland areas within and upstream of the Site as a result of sulfate reduction of sulfide compounds (e.g., hydrogen sulfide, iron sulfide) within the anaerobic sediments of the wetlands and also potential contribution from atmospheric deposition, as well b. At the time of sampling, the stable isotope data suggest that there might be groundwater discharging into the surface water possibly at Latham Brook surface water station and within the Northern Wetlands. 5. Both the geochemical data and the stable isotope of hydrogen and oxygen data suggest mixing between lighter isotopic signature groundwater found in the unconsolidated deposits and heavier isotopic signature bedrock groundwater and that the degree of mixing varies across the Site. a. Similarity between the native geochemical type for both the overburden and bedrock groundwaters supports mixing between the two units which is consistent with current Site conceptualizations and the location of the Site within a groundwater discharge area dominated by upward vertical gradients. b. Stable isotope results suggest that the unconsolidated deposit groundwater and bedrock groundwater are both mixing between two different water sources within distinct isotopic signatures [recent groundwater derived principally from precipitation (approximately -7.3‰ δ18O) and deeper, regional groundwater influenced by recent Wisconsinan-aged glaciation (postulated to be between -10 and -14‰ δ18O) from scientific literature]. c. Overburden monitoring wells exhibiting the highest chloride concentrations (OW-43, OW-409-D), excluding well OW-200-O, are located in an area of suspected preferential upwelling from the underlying bedrock, likely related to key bedrock structural features. 6. The isotopic signature of the impacted groundwater varies spatially depending on the area of the Site and with respect to certain key geologic features, such as the East-West Fracture Trace. The similarity in the ionic signature between the unimpacted groundwater within both the unconsolidated deposits and the bedrock is a strong indicator of mixing between the two units. This is supported by the prevalence of upward vertical hydraulic gradients within the bedrock and the location of the Site within a 2 Davis Site Performing Party Group Groundw ater Geochemical Evaluation September 21, 2017 discharge area where groundwater would be expected to be upwelling into the unconsolidated deposits and surface water. The isotopic data also indicates a deeper, older groundwater probably representing the “regional” groundwater flow path that appears to be mixing with more recent groundwater of the local groundwater flow system. The isotopic data also supports that the degree of mixing is highly variable. This variability in mixing is likely due to variability in groundwater recharge derived from precipitation, complexity of the bedrock groundwater flow regime and associated variability in the flux of groundwater from the underlying bedrock into the unconsolidated deposits. 1.0 INTRODUCTION EHS Support, LLC (EHS Support) and ESS Group, Inc. (ESS) submit this technical memorandum on behalf of the Davis Site Performing Party Group (Davis Site Group) to summarize the findings of an geochemical evaluation of groundwater samples that were collected from both the unconsolidated deposits (overburden) and the bedrock during the 2015 Site-wide Groundwater Monitoring Program (Fall 2015) at the Davis Liquid Waste Superfund Site in Smithfield, Rhode Island (the Site). The regional location of the Site is provided on Figure 1 and a general Site Plan and the monitoring well network are shown on Figure 2. 1.1 Site Collected Data The Fall 2015 Site-wide Groundwater Monitoring Program consisted of the following analytes that were used in this evaluation: • Analysis of samples from select monitoring wells (30 wells) for major and minor cations/anions and stable isotopes of oxygen and hydrogen. • Analysis of samples from select surface water sampling locations (3 locations) for cations/anions and stable isotopes. The sampling methodologies and analytical results of the analyses for target compounds are detailed in the Fall 2015 Site-wide Groundwater Sampling Report (ESS, 2016). 1.2 Background Data A review of groundwater geochemical data available from the United States Geological Survey (USGS) and the State of Rhode Island Department of Environmental Management (RIDEM) was performed to develop background conditions for the Site area. Analytical data for nineteen groundwater monitoring wells and thirteen surface water sampling locations were available within ten miles of the Site using the National Water Information System (NWIS) database from the USGS. No geochemical data was found from RIDEM. The majority of the background wells are under 60 feet in depth with three wells having a depth between 100 and 300 feet. Based on the limited available information from