Environmental Site Assessment, Characterization, and Modeling

Trihydro’s data validation team uses proven in-house data validation procedures and quality assurance standards that meet or exceed the most recent United States Environmental Protection Agency (EPA) guidelines and requirements for data quality and data validation. Our staff has provided training to regulatory agencies and clients on performing and reviewing validations, as well as developing quality assurance project plans (QAPPs) for collecting and assessing defensible data. Trihydro’s chemical data evaluation staff have worked on some of the most complex sites across the country and have been recognized as "best in class" by a Fortune 100 company. Our team provides project planning and chemical data review, providing data end-users confidence that their data will be usable for its intended purposes.

Data quality also relies heavily on statistical understanding of the analytical process. For example, QAPPs and data quality objectives (DQOs) are developed to determine the amount and type of data necessary to make informed statistical decisions about a site. Understanding the data analysis techniques and statistical methods regulatory agencies use to plan and interpret analytical data and draw conclusions about environmental impacts helps organizations comply with environmental regulations. Trihydro regularly designs and implements sophisticated, project-tailored statistical approaches and data visualization solutions to help clients address complex data problems. Statistical methodologies employed include traditional, agency-required methods such as outlier analysis, trend analysis, two-sample tests, parametric and nonparametric analysis of variance, and the use of prediction, tolerance, and confidence intervals in various settings, but also more advanced statistical methods such as spatially-weighted analyses, multivariate analyses, ridge and nonlinear regressions, machine learning, and diverse geostatistical techniques (e.g., kriging and hierarchical Bayesian approaches). In addition to the plethora of statistical methods at our clients’ disposal. Trihydro’s experience in sampling design can be critical to successful and cost-effective site remediation.

Laboratory quality assurance programs are frequently regulated and verified by governing agencies. Trihydro's laboratory auditing team includes former laboratory personnel who have analyzed complex environmental samples in large and small commercial laboratories. With this experience, Trihydro is well-versed in the commonly used and promulgated EPA analytical methods, other standard laboratory methods, and various laboratory quality assurance requirements under EPA, National Environmental Monitoring Conference Institute (NEMC), The NELAC Institute (TNI), American Association for Laboratory Accreditation (A2LA), International Organization for Standardization (ISO), good laboratory practices (GLP), and other published guidance. Trihydro's laboratory experience, understanding of the various quality assurance programs, and familiarity with the analytical test methods provide an effective quantitative and qualitative assessment of laboratory performance and adherence to quality and safety standards.

Trihydro’s chemistry and statistical staff also routinely contribute to regulatory guidance and policy development. In one state, the regulatory agency adopted Trihydro's data validation guidelines as its standard. Trihydro team members are active in the environmental chemistry community, the Interstate Technology Regulatory Council (ITRC), NEMC. and TNI.

Groundwater models allow stakeholders to evaluate aquifer response and behavior, assess surface water-groundwater interactions, optimize well fields, and understand contaminant transport and mobility. Environmental models can simulate contaminant flow and transport, including dissolved and/or nonaqueous phase contaminants. Trihydro uses innovative methods to evaluate dissolved organic and inorganic constituent chemical interactions and source depletion mechanisms. Trihydro can also evaluate complex chemical reactions using PHREEQC and Geochemist Workbench packages.

Environmental Sequence Stratigraphy (ESS), an environmental forensics technique that improves conceptual site models (CSMs), has become a best practice in defining groundwater contaminant migration pathways, particularly in areas with complex geology and hydrogeology. In many cases, existing data can be evaluated at a finer scale to better understand preferential contaminant flow pathways, with no new data collection required. ESS is centered on pattern recognition, to identify depositional sequences and distinctive grain size distributions (i.e., preferential flow pathways that may or may not align with general potentiometric gradients) and can be used to develop detailed hydrostratigraphic units to generate groundwater fate and transport modeling grids.

Modeling efforts, whether simple analytic projects or complex numerical models, should begin with an understanding of site conditions and available data sets. Trihydro integrates the latest database and mapping capabilities to ensure modeling problems have a solid conceptual development. Trihydro employs numerous modeling methods and a suite of sophisticated, established software. Numerical models include MODFLOW, MT3D, PEST, ART3D, and MODFLOW-SURFACT, which are included in the Groundwater Vistas and GMS platforms. In addition, Trihydro uses state-of-the-art pre- and post-processing software packages that include MVS, Leapfrog Hydro, and the ESRI ArcMap-based GIS software suite.

Trihydro has the experience and background to review large existing datasets, compile comprehensive databases, and develop detailed CSMs for complex sites. CSMs use databases to synthesize the regional setting with site-specific geology, hydrology, hydrogeology, and geochemistry data to develop a comprehensive understanding of complex site conditions and improve site-related decision-making.

Trihydro has been a leader in vapor intrusion assessment since the early 2000s. Our specialists have carried out vapor intrusion studies in 17 states across the United States and have been involved in developing state and Interstate Technology and Regulatory Council (ITRC) vapor intrusion guidance documents. Trihydro has given multiple presentations on emerging vapor intrusion issues such as preferential sewer pathways and short-term trichlororethene (TCE) exposure.

We routinely assist municipalities, state and federal agencies, and the private sector with vapor intrusion-related projects. Our vapor intrusion experience includes a range of project sizes, from Phase I Environmental Site Assessment (ESA) vapor encroachment assessments, small-scale worker safety assessments, and rapid mitigation system installation, to serving as the technical lead for multiple regional vapor plume assessments, including collecting vapor data to support local, neighborhood-wide, and regional evaluation of residential vapor intrusion risk assessment.

When vapor intrusion is suspected, technicians may collect various samples to assess the presence of VOCs. Soil gas and groundwater samples may be taken from areas around a site and compared to samples taken on-site, such as sub-slab samples or indoor air samples. This comparison helps identify a chemical's source and determine whether vapors have migrated indoors. However, a building's makeup may contain the same chemicals being assessed, making it difficult to determine the source of various chemicals. If vapor intrusion is confirmed, a mitigation system can be installed to address concerns.

Trihydro’s common sense approach to vapor intrusion projects involves the application of multiple lines-of-evidence methods to determine the potential sources and account for background sources and to identify potentially complete exposure pathways and receptors. This information is then distilled into a vapor conceptual site model (CSM), which is used to design a strategy that includes input from multiple stakeholders. If the cost to mitigate the vapor hazard is lower than the assessment costs, Trihydro works with clients to determine if proactive mitigation is the more appropriate path to closure based on evaluation of the potential liability associated with each option, long-term operation and maintenance costs, and site access concerns.

In addition to evaluating vapor data as a direct media of concern, Trihydro has worked with clients to integrate routine vapor monitoring to natural source zone depletion (NSZD) assessments at petroleum-impacted sites. Specifically, soil gas data can be used to characterize the natural attenuation processes in the vadose zone and to quantify the biodegradation rates of a petroleum plume. Evaluating NSZD as part of vapor assessments can provide clients with a remedial alternative in lieu of active mitigation and/or remediation. At sites where NSZD biodegradation rates are appreciable, these data have been used to establish new remedial system endpoints, track progress towards remedial goals, and alleviate public concerns regarding contaminant longevity.

Trihydro has decades of experience conducting human health risk assessments and has integrated this expertise into vapor intrusion assessments. Using our risk assessment experience, Trihydro provides an accurate evaluation of actual health risk from the vapor intrusion pathway. Assessing vapor intrusion from this perspective can be valuable in achieving no further action that is effective and cost-conscious.