3 Identification of Biased Environmental Data Coincidence, error, studied ignorance, or junk science? 3.1 INTRODUCTION An expert opinion is worth no more than the factual data upon which it is based. The critical review of environmental data is therefore essential for judging the reliability of the factual information. Environmental data relied upon to form an opinion should be of a sufficient known quality to withstand the scientific and legal challenges relative to the purpose of the data collection. In most instances, only a small percentage (about 10 to 15%) of the data in an environmental investigation contains elements susceptible to bias. These elements are usually associated with the geologic investigation and sample collection, analyti- cal testing, and interpretation of the horizontal and vertical extent of soil and groundwater contamination. An important task in the forensic review of environmental data is the determina- tion of whether a pattern of bias (systematic error) exists. This bias can be due to factually incorrect information, errors, or intentional manipulation. Figure 3.1 illus- trates bias and data variability (random error) based on a sample population whose true concentration is about 20 parts per million (ppm). As depicted in Figure 3.1, data can be biased negatively or positively. Three specific types of biases and/or errors are defined as follows: 1. Positive bias: In a data sufficiency context, a positive bias arises when a test incorrectly indicates contamination or an increase in contamination when there is none. 2. Negative bias: In a data sufficiency context, a negative bias occurs when monitor- ing fails to detect contamination or an increase in the concentration of a hazardous material. 3. Erratic data: Erratic data are anomalous values which make it statistically impos- sible to develop meaningful trends and/or correlations. These biases result from investigative, sampling, analytical, and statistical errors. Ultimately, expert witness opinions based on incorrect information can result. ©2000 CRC Press LLC 3.2 GEOLOGIC CHARACTERIZATION The geologic characterization component of a site investigation provides insight regarding contaminant distribution and transport. Components of a geologic inves- tigation usually include: • Drilling and logging of the boreholes and/or trenches • Soil retrieval for textural classification and/or physical testing • Soil sampling for chemical analysis The first step is to acquire and review the original field borings and/or trench logs. Compare the information on the field logs and final logs in the report for consistency. If geologic cross-sections or fence diagrams are included in the report, examine them for consistency with the field log/trench descriptions. When reviewing boring logs, examine their placement relative to historical information, especially areas of known or suspected contamination. This review often provides insight as to whether additional borings and/or sampling are neces- sary. Given that site access agreements among multiple parties are usually required in order to perform additional sampling, the sooner the data sufficiency of the FIGURE 3.1 Graphical representation of sample bias and variability. (From Mishalanie, E., in Proc. of the National Environmental Forensic Conference: Chlorinated Solvents and Petroleum Hydrocarbons, August 27–28, College of Engineering and Engineering Profes- sional Development, University of Wisconsin, Madison, 1998, p. 27. With permission.) ©2000 CRC Press LLC geologic information is identified, the sooner the site access agreements and sam- pling can proceed. The sufficiency of existing geologic information can be deter- mined via the following steps: • Ascertain whether the drilling method employed allows an accurate description of the subsurface. • Determine whether the number of soil borings are sufficient to characterize the geologic environment relative to litigation allegations. • Decide whether the borings are sufficiently deep to characterize the geology of interest. • Decide whether the borings are spatially located so as not to preclude developing useful information for geologic characterization. The drilling technology impacts the geologist’s ability to describe the soil and/or geologic setting. Reliance solely on mixed drill cuttings from air or mud rotary drilling, for example, precludes the ability to provide detailed descriptions of strati- graphic changes. Continuous hollow stem augering and/or most push technologies that retrieve an in situ soil sample provide this level of detail. 3.2.1 BORING LOG TERMINOLOGY Soil descriptions on a boring log are based on visual observations of drill cuttings or from physical testing (e.g., sieve analysis and hydrometer tests). The review of soil textural descriptions requires that a uniform soil classification scheme be used or that different classifications are standardized (ASTM, 1993). The use of multiple soil classification schemes is not uncommon where numerous environmental consultants have performed geologic investigations at the site. An illustration of the importance of a common classification scheme is a soil described as a silt based on the results of a grain size analysis. The particle size of the soil lies between 0.1 and 0.02 mm. Based on these grain size results, multiple particle size classifications are possible, as shown in Table 3.1 (Gee et al., 1986; Hillel, 1982; Wilson et al., 1998). According to the International Soil Science Society classification, the soil is a fine sand. Other schemes classify the soil as ranging from TABLE 3.1 Soil Classification Schemes Particle Size Classification Classification Scheme Used Very fine sand to silt U.S. Department of Agriculture Very fine sand to coarse silt Canada Soil Survey Committee Fine sand International Soil Science Society Fine sand to fines (silt and clay) American Society of Testing Materials Fine sand to fines (silt and clay) German Standards Fine sand to silt British Standards Institute ©2000 CRC Press LLC a silt to a fine sand. All are correct for their respective classification schemes. Without adjusting these interpretations to a common standard, however, subsequent geologic interpretations and associated diagrams can perpetuate this nonstandardized bias. In the United States, the Unified Soil Classification System developed by the Corps of Engineers (U.S. Corps of Engineers, 1960) is the most commonly used system (Figure 3.2). FIGURE 3.2 Unified Soil Classification System, grain size chart, and well construction symbols used on boring logs. ©2000 CRC Press LLC Soil color is usually recorded on a boring log. If a standardized color scheme is not used, the correlation value of this information should be considered qualitative. The most common color standard is the Munsell Soil Color Chart, which contains 196 different standard color chips (Kollmorgen Corp., 1975). The Munsell system is arranged by the following characteristics: • Hue is the color of the soil relative to red, yellow, green, blue, and purple. • Value indicates the lightness of the soil (0 for black and 10 for absolute white). • Chroma is the strength of the color (0, for neutral grays, to 20). For absolute achromatic colors (pure grays, white, and black) with zero chroma and no hue, the letter N (neutral) is used in place of the hue designation. A notation such as 5YR 5/6 on a boring log indicates use of the Munsell system. In “5YR”, 5 is the middle of the color value between yellow and red color hue (YR). The notation “5/6” is the chroma value between 5 and 6. Boring logs often contain soil terminology used by non-geologists (drillers or soil scientists). A driller’s log may qualitatively describe a soil as light or heavy. A sandy soil that is loose and well aerated is called light, while a clayey soil that tends to absorb and retain fluid when wet is termed heavy. If there is doubt about the meaning of such terms, ask the author of the boring log. When soil samples are collected at random depth intervals, ascertain whether there is an attempt to avoid collecting soil samples with a higher or lower probability of detecting contamination. An example is the consistent sampling of coarse sands and the avoidance of sample collection in finer grained materials (silty or clayey soils) through which a contaminant with a high sorption capacity has infiltrated. Conversely, soil samples collected at the interface of coarse, overlying, fine-grained sediments (i.e., a sand overlying a clay) can result in an overestimation of the concentration, volume, and (by extension) remediation costs for the contaminated soil. An extension of this manipulation is the use of small sample volumes for chemical analysis which biases the chemical results due to the soil particle size not being representative. This technique assumes that the association of a chemical in the soil is uniquely associated with a particular particle size. A proposed approach to quantify this potential particle size bias is to examine the sample size required for analysis relative to the particle size distribution of the soil sample. This method identifies the potential bias due to the grain size distribution between soil samples collected from similar soil textures. Ramsey (1996) defines this potential bias due to the particle size representativeness as: S = (22.5d 3 /m s ) 1/2 (Eq. 3.1) where S=sample mass. 22.5 = sampling constant, which is an approximation and is applicable to many, but not all, hazardous waste materials. d 3 = maximum particle diameter. m s = sample mass in grams. ©2000 CRC Press LLC In most cases, the larger the sample volume, the smaller the potential particle size bias. If a soil sample is homogenized or sieved by the laboratory and a particular particle size fraction is selected for extraction, a similar chemical bias can be introduced. Examination of laboratory documentation will provide this information. If a contaminant is migrating through the soil via unsaturated flow, it can preferentially circumvent a coarse-grained layer. As a result, systematic sampling of these coarse-grained sediments underestimates the extent of contamination. Con- versely, sampling consistently at the interface of a coarse and fine-grained sediment through which a contaminant has traveled in an unsaturated state provides the greatest opportunity of detecting a contaminant. Plate 3.1 * illustrates a field experi- ment where dye moving through a medium-grained glacial sand in an unsaturated state preferentially migrates around the coarse-grained sediment. * Plate 3.1 appears behind page 242. FIGURE 3.3 Boring log with organic vapor analysis measurements. ©2000 CRC Press LLC Soil lithology descriptions, field measurements, and sampling locations re- corded on a boring log can provide insight regarding the intentional manipulation of sampling locations for the purpose of biasing the chemical results. Figure 3.3 is a portion of a boring log containing field organic vapor analysis (OVA) and HNu ™ measurements. The presence of a distinct layer of contamination between 45 and 50 ft is suggested by the HNu ™ readings of 200 ppm; if samples were not collected for chemical testing between this interval, this could suggest intentional biasing. This type of analysis is also useful for targeting subsequent evidentiary sampling. Figure 3.4 is a field boring log example that illustrates the presence of a volatile compound at about 5 ft (OVA = 1000 ppm) that was not sampled. Samples in Figure 3.4 with non-detect and near OVA and HNu ™ detection levels at 10 and 20 feet, however, were sampled. In this instance, the decision not to sample at 5 feet precludes the confirmation of a potential surface release indicated by the OVA reading of 1000 ppm. FIGURE 3.4 Boring log with field measurements (OVA and HNu ™ ). ©2000 CRC Press LLC Field measurements used to screen soil sampling locations are qualitative and sensitive to the compound detected and instrument calibration, but do not rely on field measurements beyond this qualitative, field-screening purpose. Figure 3.5 is a field log in which photoionization (PID), flame ionization (FID), and infrared (IR) detectors were used. Values for the three instruments for the same soil ranged from 0 to 841 ppm. 3.3 INTERPRETATION OF GEOLOGIC INFORMATION Information on a boring log is used to create geologic cross-sections or fence diagrams. Significant latitude is available in the extrapolation of boring log descriptions FIGURE 3.5 Boring log with PID, FID, and IR readings. ©2000 CRC Press LLC to create these diagrams. These interpretations are important when low permeability horizons, relative to vapor or liquid contaminant transport, are incorporated in the geologic cross-sections or fence diagrams. Geologic diagrams are created via manual interpretation (Figure 3.6) or interpo- lation by computer software. Areas of inquiry (A through D) on Figure 3.6 are framed and labeled. If the purpose of the cross-section is to represent the presence of a continuous layer of clayey soils that retards contaminant transport, potential areas for differing interpretation are possible as described in the following text. A. A contact between artificial fill (speckled fill) and a silt and clay (white space) is present midpoint between Boring 1 and MW-1. This interpretation extends the silt/ clay layer into an area where no data are available but which may be a logical assumption. B. The contact between the silty and clayey sand (dotted fill) and the silts and clays (white space) is interpreted to occur at a point that is not midpoint between MW- 1 and MW-B1. This interpretation is inconsistent with the midpoint methodology used in A. C. The extent of the silty and clayey sand (dotted fill) is interpreted to extend halfway between Boring 2 and VE-2 in one direction but only a short distance in the opposite direction between Boring 2 and VE-5. This interpretation creates a signifi- cant horizon of predominately silt and clays between C and D. Another interpre- tation is to create a contact between framed areas C and D. This alternative interpretation creates a thin layer of silt and clays that are less of an impediment to the vertical transport of contaminants. This interpretation is also inconsistent with examples A and B, where the soil contact between two wells is interpreted as the midway point. Furthermore, there is no boring located between Boring 2 and VE-4 to indicate the presence of a clay layer. D. The contact between the gravels at the bottom of VE-5 is extended toward Boring 2, where it is not encountered. This is inconsistent with the method used in A and B. E. The geologic interpretation between Boring 2 and VE-4 deviates from the pattern observed in frames A to C in that the contact between the silty and clayey sands in Boring 2 and gravels in VE-4 is not interpreted as occurring midpoint. The silty and clayey soils in VE-4 are portrayed as extending just short of Boring 2, although there are no intervening data to confirm this interpretation. Examine the horizontal and vertical scales used in cross-sections. In Figure 3.6, the vertical scale is 0.4¥ of the horizontal scale. If the scale is not 1:1, the viewer’s perception may be significantly skewed. The preparation of an alternate geologic cross-section that is scaled and presented as a rebuttal exhibit may be appropriate. A variation to the Figure 3.6 manual interpretation of the geologic data is assignment of numerical values that represent different soil properties. Computer software then spatially extrapolates between these values. Computer interpretations and their por- trayal in cross-sections, isopach maps, or fence diagrams can produce highly errone- ous interpretations. When reviewing a computer-generated geologic diagram em- ploying this technique, you will need to: ©2000 CRC Press LLC FIGURE 3.6 Example of manually created geologic cross-section. ©2000 CRC Press LLC [...]... phenolic cap 40-mL glass vial with Teflon®-backed silicon septum cap 1-L high-density polyethylene bottle with polyethylene-lined, white polyethylene cap 120-ml glass vial with Teflon®-lined, white polyethylene cap 16-oz wide-mouthed glass jar with Teflon®-lined, polylyethylene cap (water analysis) 8-oz wide-mouthed glass jar with Teflon®-lined, black polyethylene cap (water) 4-oz wide-mouthed glass... TABLE 3. 4 Summary of Sampling Results, Sampling Sequence, and Sampling Equipment for Site Shown in Figure 3. 15 Sampling Sequence Well PCE (mg/L) On-Site B3 B6 B14 B9 B10 MW1 MW9 MW5 MW4 MW7 MW3 ND ND 160 230 36 0 ND ND 30 70 130 250 1 2 3 4 5 — — — — — — a b Sampling Equipment Off-Site — — — — — 1 2 3 4 5 6 Purging Sampling Peristaltic Peristaltic Peristaltic Peristaltic Peristaltic Submersible Submersible... source, and the downgradient well with 1500 ppb The source and downgradient wells were short screened (10 ft) and completed in a silty sand The upgradient well (120 ppb) was completed with a 20-foot screen that intersected the silty sand and a highly permeable sand and gravel layer Concern about the longer screened, upgradient well diluting the TCE concentration via the uncontaminated sand and gravel... Teflon®-lined, black polyethylene cap (water) 1-L amber glass bottle with Teflon®-lined, black polyethylene cap 4-L amber glass bottle with Teflon®-lined, black phenolic cap 500-mL high-density polyethylene bottle with polyethylenelined, baked-polyethylene cap Extractable organics Volatile organics Metals, cyanide, and sulfide Volatile organic (soil) Extractable organics/metals Extractable organics and. .. the previous quarter and the sampling sequence were obtained from the chain of custody (see Table 3. 4) In addition, the sampling equipment and procedures were described in the work plan For on- and ©2000 CRC Press LLC FIGURE 3. 15 Map illustrating the impact of sampling equipment and sequence on groundwater chemistry results TABLE 3. 4 Summary of Sampling Results, Sampling Sequence, and Sampling Equipment... uncontaminated shallow water-bearing zone * Plate 3. 3 appears behind page 242 ©2000 CRC Press LLC FIGURE 3. 11 Cross-contamination of a shallow aquifer by a multiple-screened pumping well 3. 5.2 INSTALLATION OF GROUNDWATER MONITORING WELLS Contaminant distribution in groundwater is defined by the horizontal placement of the monitoring well as well as the screen length and interval While federal and state guidelines... dilution) and those farthest from the source are short screened, a pattern of sample chemistry manipulation and contaminant plume geometry via well screen length and proximity to the source may become apparent (Martin-Hayden and Robbins, 1997) The interpretation of the vertical distribution of a contaminant is especially sensitive to well screen length, interval, and placement (Robbins and Martin-Hayden,... scoops, split-spoon samplers, Hydropunches, bailers, and cone penetrometer testing tips Equipment rinsate blanks should be collected at a rate of FIGURE 3. 17 Decontamination of groundwater sampling equipment and rinsate troughs for cone penetrometer rods ©2000 CRC Press LLC TABLE 3. 6 Appropriate Sample Containers and Analysis Container Description Analysis 80-oz amber glass bottle with Teflon®-lined black... should be examined in total and a judgment made concerning the reliability of the chemical data 3. 5 .3 SAMPLING PLAN Environmental reports often include soil and groundwater sampling plans Review the sampling plan and compare it with the field notes describing the actual field ©2000 CRC Press LLC FIGURE 3. 13 Impact of well screen length on source identification practice This review can identify whether... cross-contamination originating from the sampling equipment Federal, state, and American Society for Testing Materials (ASTM) standards are available which describe decontamination procedures for contact and non-contact equipment used for soil and groundwater sampling (ASTM, 1990) In general, sampling equipment is washed with a detergent solution followed by a series of water, desorbing agents, and . contact between the silty and clayey sand (dotted fill) and the silts and clays (white space) is interpreted to occur at a point that is not midpoint between MW- 1 and MW-B1. This interpretation. experi- ment where dye moving through a medium-grained glacial sand in an unsaturated state preferentially migrates around the coarse-grained sediment. * Plate 3. 1 appears behind page 242. FIGURE 3. 3. investigation and sample collection, analyti- cal testing, and interpretation of the horizontal and vertical extent of soil and groundwater contamination. An important task in the forensic review of environmental