Source Zone Delineation Demonstration Report - Triad Resource ...

and the three-dimensional numerical modeling of soil contamination generated during the investigation,data gaps are identified prior to demobilizing from the site. Based on the experience from the OU 12Source Zone Delineation Demonstration, it is feasible to update/refine the soil contamination model withthe analytical data obtained from the most recent boring prior to mobilizing the CPT rig to the nextsampling location. In addition, the WS/DSITMS investigation eliminates the data evaluation andreporting task typically required during a conventional investigation.The total cost for a single phase of fieldwork and sample analyses in the WS/DSITMS investigation is$90,620, compared with $120,790 and $111,750 for two phases in the HSA investigation and DPTinvestigation, respectively. An additional cost of $14,760 is incurred during the conventionalinvestigative approaches for data evaluation and reporting following the first phase of fieldwork. Thedata evaluation and reporting task is required to identify data gaps associated with the initial phase ofsampling and develop a sampling and analysis plan to fill those gaps in order to adequate characterize thesuspected source zone. By eliminating the need for a second phase of field investigation, the overalltimeframe for making subsequent decisions is reduced. This results in a shorter timeframe by which tomake investigative and/or remediation decisions and ultimately can reduce the lifecycle costs associatewith a site.Although the WS/DSITMS investigation does not require a separate data evaluation and reporting taskbetween field sampling events, it does require the development of a site model to guide sample collection.For the WS/DSITMS investigation, it is assumed that $3,680 (32 hours of a seniorhydrogeologist/engineer) is required to refine the site model from the work plan prior to the start offieldwork. During field activities, it is assume that an additional $4,140 (4 hours per day for 9 days of asenior hydrogeologist/engineer) is required to continuously update/refine the site model with the mostrecently collected site data. Because the site model is built and continuously updated in the field, lesstime is required during the RI reporting stage to generate the final version of the CSM, thus reducing theoverall cost of the RI report. In addition to a reduction in cost, one of the main advantages of theWS/DSITMS investigative approach is data density and the consequent improvement in the model ofVOC contamination in the vadose zone. The nominal vertical spacing between soil samples is 1 foot forthe WS/DSITMS investigation, compared to 2 feet for the conventional investigative techniques.Ultimately, the higher data density achieved in the WS/DSITMS investigation results in a very detailedmodel of vadose zone contamination. Decreasing the spacing to 1 foot during the conventionalinvestigations doubles the analytical expense, significantly increasing total project costs.In spite of its advantages, the WS/DSITMS investigation has some limitations. Flexibility in selecting asoil sample is lost, because a sample can only be collected from either end of the 1-inch diameter and 1-foot long stainless steel sampling tube. A related drawback is the inability to continuously log soilstratigraphy. At best, a one-foot composite soil type can be identified, based on the material removedfrom the sampling tube when it is cleaned. Moreover, none of the traditional CPT logging data iscollected with the Wireline CPT sampler, precluding the inference of soil stratigraphy from CPT logs.The method is also constrained by the ability of the CPT rig to push, making the method difficult to applyin gravelly and cobbly soils, and also limiting the method to relatively shallow (