Implementing RTS, XRF, and GIS-based Technology to Conduct Environmental Investigations

Transcription

1 Implementing RTS, XRF, and GIS-based Technology to Conduct Environmental Investigations By Leroy Leonard, Randy McBride, and James Bond, Shaw Environmental, Inc. Abstract Shaw Environmental Inc. (Shaw) integrated robotic total station (RTS) surveying techniques, x- ray fluorescence (XRF) analytical instrumentation, and geographical information system (GIS) software to guide the environmental site characterization of ranges at the former Fort McClellan U.S. Army Base. The RTS was used to establish a sample grid. Samples were then collected at the nodes of the sample grid and analyzed by XRF for lead and other metals. ArcGIS was used to manage the spatial database that housed coordinate and analytical data from the XRF evaluation, and ArcGIS Geostatistical Analyst was used to generate lead isoconcentration contours from the XRF data using two-dimensional interpolation. The contours were overlain onto site features and the sampling grid to aid in the spatial analysis of the data and to determine where additional sampling needed to take place. The RTS, XRF, and GIS-based approach proved to be an effective way to conduct site characterization. The RTS survey approach allowed sample grid nodes to be identified in a rugged, remote area, with minimal impact to the forest. The XRF provided consistent, accurate analytical service. The GIS-produced maps were critical for directing the field sampling efforts. Introduction The former Fort McClellan (FTMC) U.S. Army Base in Calhoun County, Alabama is a 23,400 acre installation under the control of the Army Training and Doctrine Command (Figure 1). It was established in 1917 as a National Guard camp and was closed under the Base Realignment and Closure program in September Most recently FTMC was the home of the U.S. Army Chemical School and Training Center Figure 1. Fort McClellan Location and the Military Police School. Beginning in 1998, the U.S. Army Corps of Engineers (USACE)-Mobile District contracted Shaw to

2 2 conduct a series of site investigations (SI) and remedial investigations (RI) at parcels on FTMC where site-related contamination was suspected. As of 2004, Shaw has performed investigations on over 300 sites and has used X-ray fluorescent (XRF) technology-based instruments to analyze over 1,600 soil and sediment samples. The XRF has been successfully used at FTMC to characterize the nature and extent of metals contamination in 26 weapons training and demonstration ranges covering 12,700 acres basewide. These ranges include small arms (pistol, rifle, and shotgun), light and heavy machine gun, mortar, grenade, rifle grenade, anti-tank rocket, explosives, and light and heavy artillery weapons firing and/or impact areas. Most recently, Shaw has integrated robotic total station (RTS) surveying techniques and geographical information system (GIS)-based software to collect and manage geospatial and XRF analytical data. This approach was used in 2003 to characterize surface soil contamination at the Choccolocco Corridor Ranges (CCR). The CCR encompasses a 250-acre complex of four, small arms training ranges (Figure 2). Figure 2. Choccolocco Corridor Ranges Location Shaw and the USACE decided to use a dynamic, multiphase sampling and analysis plan to conduct the RI at these ranges because the contamination was expected to be very widespread and not well-defined after the initial SI activities were complete. Several unique challenges had to be addressed in the planning stages of the RI for the CCR. The largest obstacle was dealing with the relatively unknown range history and usage. Historical aerial photographs indicated that this area had been initially developed during World War II for range training. At least four ranges were in use through 1976 when operations at the CCR ceased (Figure 3). Very little Figure Aerial Photograph

3 3 activity and no maintenance was performed by the Army in the 25 years between CCR closure and base closure which allowed the old range areas to be overgrown with a dense pine and hardwood forest. No documentation of the ranges during operation existed and few FTMC personnel were available to interview. From aerial photography it was determined that the direction of range fire was consistently to the east, towards the base of the Choccolocco Mountains. By base closure, few site features remained and the range firing lines, targets, and impact zone areas were undefined. In addition to the lack of information about the ranges, several other obstacles had to be overcome to complete the characterization of the ranges. These obstacles included the remoteness of the CCR from the rest of the FTMC Main Post, the rugged and steep topography especially in the large hillside potential impact zone, and the presence of a dense forest canopy that would certainly make satellite reception difficult for global positioning system (GPS) surveying. The forest undergrowth also included many mature Mountain Longleaf Pines which have been identified as an endangered species. In addition to the 250-acre area where the range activities actually occurred, the CCR also included a 3,700-acre area designated as the range safety fan. The range safety fan was an area set aside by the FTMC range control as a personnel exclusion zone during range training. Because the way the CCR area was defined for investigation, the range safety fan also had to be addressed using some sampling and analysis. CCR SI Summary An initial SI was conducted at the CCR from July to September This SI included the collection of 87 surface soil samples, 70 subsurface soil samples, and 3 surface water and sediment samples. In addition, 12 residuum groundwater monitoring wells were installed and sampled. The results of the SI indicated that metals contamination, specifically lead, with some elevated concentrations of copper, antimony, and zinc was prevalent in the CCR surface soils. Lead concentrations exceeding 400 mg/kg up to concentrations greater than 7,000 mg/kg were found in several hotspot locations near old bullet impact areas (Figure 4). Clearly a more definitive nature and extent evaluation was needed to complete the investigation picture. Figure 4. Lead in Surface Soil - CCR SI Results

4 4 RI Overview Based on the widespread nature of the metals contamination evidenced by the results of the SI, the follow-up RI was designed with two distinct phases. The first phase included a field survey featuring onsite analysis using XRF followed by sampling with definitive offsite laboratory analysis. Phase I would be directed towards the 250-acre range study area where firing and training were conducted and also included the investigation of the range safety fan. At the end of Phase I, an assessment would be made of the collected XRF data and then a Phase II RI work plan would be prepared that would identify sample locations within and around the defined hotspots for laboratory analysis. The Phase I survey would help define extent of the hotspot contamination and the Phase II sampling and analysis would provide the data needed for risk assessment. Accordingly, the Phase II analyses would be performed on samples that met established concentration criteria therefore maximizing the value of the analysis. RI Phase I Survey Phase I of the RI consisted of establishing an initial 200-foot by 200-foot grid sampling pattern over the entire CCR area using the RTS. Surface soil samples were collected at the grid nodes and analyzed with the XRF. In areas where lead hotspots over 400 mg/kg were measured, the 200-foot by 200-foot grid was further broken down into a 100-foot by 100-foot pattern to better resolve the contaminant distribution. Likewise, when the survey crew was operating in a perimeter area with more than two nodes in any one direction (a total of 400 feet) and lead concentrations near background (less than 50 mg/kg) were recorded, further delineation in that direction was not required and the survey team was redirected. This way the XRF and RTS worked together to perform the survey in the most efficient manner possible, increasing coverage in the hotspot areas while eliminating the non-impacted areas from further study. RTS. RTS was selected as the land surveying system during the CCR RI Phase I due to the remoteness of the site, the canopy of trees, and the presence of the Mountain Longleaf Pine that inhibited tree clearing. The RTS system requires a two-man survey team, one that uses a laser-producing base station and another that moves the reflecting, pole-mounted prism around until the proper distance and direction are measured from the base station (Figures 5 and 6). The base station was setup over an existing grid node or placed over and existing monitoring well that Figure 5. RTS Base Station

5 5 had known surveyed coordinates to establish a grid origin. The RTS base sends out a laser signal that is reflected off the prism and the return signal is received. The onboard microprocessor then computes the distance and the compass bearing of the prism relative to its location. The base operator relays instructions to the pole man who relocates the prism and the position is measured again. This process is repeated until all of the grid node locations around a central point are found. The base is then relocated to one of the newly surveyed locations and the process is repeated. At the end of the day, the electronic data from the base station data logger was downloaded for transfer to an Excel spreadsheet. The RTS system proved to be both rugged and transportable. The team members traversed topographically challenging areas of the CCR to complete the grid with the RTS. Some areas of the CCR had over 900 feet of elevation gain in less than one quarter of a mile. The RTS was able to perform surveying in dense woods Figure 6. RTS Rod-Mounted Prism with minimal tree clearing. Because the system was laser based, clearing usually consisted of using hand tools to selectively remove a small tree or an offending branch. In this manner, minimal impact to the forest was maintained. XRF. Because the CCR were used for small arms training, lead was anticipated to be the contaminant with the largest spatial distribution and its XRF-measured concentrations were used primarily to define the areas of contamination. In addition to lead, concentrations of copper, nickel, and zinc were also monitored and recorded with the XRF (Figure 7). The shallow surface soil (0 to 4-inches) at each grid node was sampled just below the root zone using a hand trowel and the analyst was careful not to include rock or vegetative debris. The collected sample was then placed in an aluminum loaf pan for homogenization and inspected for bullets or fragments. If bullets or fragments were found, these were removed from the sample by hand and comments recorded on Figure 7. XRF Instrument

6 6 the sample collection documentation by the analyst. Once homogenized, the sample was ready for analysis. The XRF uses radioactive sources within the instrument to produce x-rays that are directed towards the sample in such a way as to excite the atoms of certain elements that are present in the sample. The excited atoms then fluoresce and release energy of a certain wavelength. Each element has a characteristic wavelength that can be identified by the instrument detector and the quantity of energy at that wavelength can be measured. In this manner, the XRF determines which elements are present and their respective concentrations in the sample. The results can be read directly from the instrument display. XRF data were also stored in the onboard data logger and were transferred electronically to an Excel spreadsheet at the end of the day. The XRF analytical program included several elements of quality control (QC). These included the daily analysis of blanks and certified reference materials of known metals concentrations purchased from the National Institute of Standards and Technology. This calibration check was performed at the beginning of each day s analysis, and the results indicated that the XRF measurements were within 10 to 20% relative percent difference (RPD) of the certified value. Duplicate analysis was performed on selected samples for precision estimation and ten percent of all the XRF analyzed samples were also selected for offsite laboratory confirmation analysis. Regardless of the minimal amount of sample preparation typically performed for the XRF survey samples, the RPDs of these measurements showed good agreement. In the majority of cases, the percent difference measured between either the original and the duplicate XRF analysis or the original XRF and offsite laboratory analysis agreed within an acceptable range (typically less than 25% RPD). GIS. Using a simple Excel spreadsheet, the XRF data were matched to the grid node coordinates surveyed with RTS. The spreadsheet was then uploaded into an ArcView 8 compatible, geospatial database. ArcGIS Geostatistical Analyst was used in conjunction with ArcView 8 to generate isoconcentration maps in near real-time to summarize the sample team s progress. In this manner, over 580 survey nodes coordinates were recorded, XRF data Figure 8. XRF Survey Results - Phase I CCR RI

7 7 was analyzed, and mapped during Phase I (Figure 8). The GIS maps displayed lead isoconcentration contours (from the XRF data) that were overlaid onto the site features and the grid sampling pattern. These maps assisted in the geospatial evaluation of the extent of elevated lead concentrations. These isoconcentration maps were useful to provide a real-time quality control check of the incoming RTS and XRF data. As these data were matched and mapped, the GIS analyst could compare the results to the existing data to ensure that the data fit. The maps were key in directing the field sampling efforts to efficiently perform Phase I of the RI and the team was now able to determine where to extend or retract the sampling grids over those originally planned and where to further subsample potential hotspot areas. The maps were also a useful communication tool for Shaw project management to update the USACE and the FTMC installation environmental personnel on the progress of the CCR investigation. Phase I Safety Fan Sampling Immediately after the completion of the survey in the CCR range study area, a series of 40 surface soil samples in the range safety fan were collected and analyzed using XRF technology. This sampling event was conducted to determine if any impact to the safety fan was evident. These samples were collected from locations pre-selected in the Phase I RI work plan. Some locations were on the highest hilltop elevations while others were in associated drainage basins. For the most part, very little Army activity was observed in the sampled part of the 3,700-acre area. Safety fan areas that overlapped other existing ranges or areas investigated separately by Shaw were excluded from the safety fan survey. Lead concentrations in the safety fan samples were within the range of established FTMC background values (less than 109 mg/kg). Phase II Sampling and Definitive Laboratory Analysis When the Phase I survey was complete, the final lead-isoconcentration contour map was used by Shaw to plan and justify the Phase II RI sample locations (Figure 8). Phase II included sampling at additional surface soil locations, boring locations for subsurface soils, and eight additional monitoring wells were installed for groundwater samples. Continuing the Phase I field analysis approach, the XRF was used and a total of 177 surface and subsurface soil samples were screened during Phase II. XRF data were used in real-time by the sampling team to select sub-samples for offsite laboratory analysis. These RI samples were analyzed for an extensive list of parameters including volatile and semivolatile organics, pesticides, herbicides, PCBs, explosives, and full target analyte list of metals. Samples from

8 8 areas and from depths that showed both extensive and little lead contamination were selected for laboratory analysis to fully assess the risks to human health and sensitive ecological receptors. Summary Shaw s unique approach of dynamic planning coupled with field analysis and advanced data management and reporting was an effective and useful tool during the CCR RI. During Phase I, this approach provided the data needed for further delineation efforts, often the same day the samples were collected. In this way, the surface soil survey was conducted more efficiently. The Phase I safety fan sampling event documented that no contamination in this area was present and eliminated the need for additional sampling. The overall focus then remained on the RI effort to characterize and delineate the CCR impacted areas. Phase I data established the extent of contamination and identified range hotspots so the Phase II investigation could be efficiently planned and implemented. The Phase II screening used the XRF to select samples for laboratory analysis thereby optimizing the usefulness of that data set to address potential risk. The USACE-Mobile District estimated that by using Shaw s sampling approach, the Army saved over $270,000 when compared to traditional sampling and offsite analysis. Overall the RTS, XRF, and GIS-based approach was proven to be a very beneficial and cost effective way to conduct this RI for Shaw, the USACE, and the Army.