THE VALUE OF AN ACCURATE CONCEPTUAL SITE MODEL (CSM) IS WORTH ITS WEIGHT IN GOLD, BUT LIMITATIONS IN FUNDING OR REGULATORY REQUIREMENTS OFTEN PERPETUATE DATA GAPS IN THE UNDERSTANDING OF A FACILITY’S CONTAMINANT FATE AND TRANSPORT. In addition, some data sets only include a speciated range of target analytes [e.g. Benzene, Toluene, Ethylbenzene, Xylenes (BTEX)]. AST’s approach to characterization and remediation is to obtain quantitative high-resolution soil analytical data to further define the distribution and intensity of contaminant mass within the subsurface. Soil samples from both the unsaturated and saturated zones are sent for speciated volatile organic compounds (VOCs) and total mass fraction [e.g. total petroleum hydrocarbons (TPH)] laboratory analysis. AST recommends collecting and analyzing soil samples from approximately every 500 ft2 to 1,000 ft2 aerially and 1 ft to 2 ft vertically. Paired with the no-cost analytical performed at the RPI Project Support Laboratory, the refined CSM results in a more efficient and cost-effective path to remediation and ultimately successful site closure.
Historical methodologies for installation and construction of monitoring wells were simple: make the well screens as long as you can to ensure they make water. Coupled with a general lack of high-density soil sampling above and below the water table, this standard practice has resulted in significant data gaps in the conceptual site model (CSM). AST utilizes discrete vertical profiling of overburden groundwater to determine contaminant gradients and variability in aquifer properties due to geologic heterogeneity. Vertical profiling can effectively be implemented during high-density soil sampling. Short-interval (typically <5 ft) screen lengths can be installed at selected intervals within a common borehole using ½ in to 1 in PVC screen and riser casing. Nested clusters of up to three separate casings with vertically offset screened intervals can be installed within the same borehole. Stainless steel screen-point samplers (a.k.a. hydropunch) can also be used in parallel to reduce material costs or increase on-site production time without sacrificing data quality. Groundwater samples from yielding intervals can then be collected and shipped to the RPI Project Support Laboratory in Golden, CO for speciated and total mass fraction laboratory analysis.