sign in sign up
<<
Home , Groundwater, Soil contamination

ESTIMATING RESIDENTIAL INDOOR AIR IMPACTS DUE TO CONTAMINATION D.W. Kurz, P.E. Associate, EnviroGroup Limited, 7208 S. Tucson Way, Suite 125, Englewood, CO 80112; Phone: (303) 790-1340; Fax: (303) 790-1347. ABSTRACT The reliability of making risk-based corrective action (RBCA) decisions using ASTM methods was evaluated. (IAQ) testing results for 153 residential homes in 1998 at a site in Denver, Colo., were evaluated in this study. Decisions regarding and indoor air mitigation in resi- dences located over a shallow groundwater plume contaminated with chlorinated compounds were made based on actual test results. These decisions could have been based on the predicted concentrations of the com- pounds in indoor air using the Standard Guide for Risk-Based Corrective Action Applied at Release Sites (ASTM E1739-95). Risk-based screening levels may be useful to guide general project decisions. However, variance of results from house to house is significant due to site-specific geological, building, and ventilation factors. Based on the results of this evaluation, indoor air quality testing should be used, rather than RBCA predictive modeling, to establish the extent of impacts and determine the need for mitigation. Key words: chlorinated, decisions, groundwater, residential, risk

INTRODUCTION testing of indoor air in buildings over contami- At a number of industrial sites, volatile nated groundwater. organic compounds (VOCs) have seeped into A few states have recently developed groundwater beneath the site and then migrated indoor air pathway criteria for groundwater; off site. These plumes often flow below other however, these may underestimate the occur- commercial or residential buildings. VOCs in rence of indoor air impacts (Fitzpatrick and the groundwater can volatilize and migrate into Fitzgerald, 1996) and are based on models that the overlying structures. Depending on site have not been validated (Altshuler and conditions, building purpose, and the constitu- Burmaster, 1997). For example, Massachusetts ents present and their , individual VOCs groundwater-to-indoor air criteria may be present in the structures at concentra- (310CMR40.0932) are not applied to ground- tions above action levels for indoor air. more than 4.6 m (15 ft) below ground Although the groundwater-to-indoor air surface. Experience at the site in this study pathway for migration of and exposure to indicates groundwater at depths greater than 6 VOCs has been recognized for some time (e.g., m can significantly impact indoor air quality Johnson and Ettinger, 1991; ASTM, 1995), based on current toxicity criteria for 1,1 there is little information in the literature con- dichloroethene (1,1 DCE). cerning the potential for chlorinated compounds Although has generally received in groundwater to impact indoor air more attention than other VOCs in groundwater (Richardson, 1997). One reason for this may (e.g., Fischer et al., 1996), 1,1 DCE is more be the limited number of regulations requiring likely to cause indoor air impacts. The relative

220 Proceedings of the 2000 Conference on Hazardous Research risk to indoor air posed by volatile compounds The RBCA process provides a means for in groundwater is a function of the product of quantifying risk that site conditions pose to human the Henry’s Law Constant and the cancer slope health at sites that vary greatly in complexity, and factor for each compound (ASTM, 1995). On physical and chemical characteristics. this basis, risks posed by 1,1 DCE are approxi- In practice, a site-specific risk-based mately 28 times greater than benzene. screening level (RBSL) or target level concen- This paper evaluates the reliability of tration would be developed for a chemical of making corrective-action decisions using ASTM concern in groundwater based on a particular methods to determine the need for groundwater health-based action level for the compound in remediation and indoor air mitigation in resi- indoor air. These site-specific RBSLs in dences located over a shallow groundwater groundwater could be used to determine what plume contaminated with chlorinated com- homes receive indoor air mitigation systems to pounds based on the predicted concentrations alleviate potential health concerns due to indoor of 1,1 DCE in indoor air. If the ASTM method air quality. The RBSLs have the follow- is reasonably accurate, it would provide a ing relationship: straightforward, cost-effective method for RBSL(air) RBSL(water)= making mitigation decisions without the need for VF testing of individual homes. A reliable method The “volatilization factor” (VF) considers would minimize the false prediction of indoor air depth to groundwater and effective diffusion concentrations above the action level where the coefficients for the progressive movement of a actual result would be below the action level. VOC from the groundwater surface to the This would minimize installation of mitigation capillary fringe, to the , through systems in homes where a system is not needed. foundation/slab cracks, and into the residential structure. This factor can be calculated for each THEORY location using the peer-reviewed equations in The ASTM Standard Guide for Risk- the ASTM standard. The same equations can Based Corrective Action Applied at Petroleum be used to predict an expected concentration in Release Sites (ASTM E1739-95) provides a indoor air for a given concentration in ground- method for evaluating the site-specific condi- water: tions and risks. While the guide focuses on C(air) examples of petroleum product releases, the C(water)= VF RBCA process is not limited to a particular or, rearranging: class of compounds. The purpose of the RBCA process is to evaluate appropriate action C(air)=C(water)xVF levels based on the potential risk to human In evaluating indoor air risks, an advantage health. Limited can then be used to of the RBCA process is a method for making remediate sites associated with greater risks.

Proceedings of the 2000 Conference on Research 221 LEGEND

1,1 DCE RANGE IN GW (ug/L)

1 - 10

10 - 100

100 - 1000

> 1000

GROUNDWATER FLOW DIRECTION

SITE

Figure 1. 1,1 DCE plume in groundwater.

risk-based corrective action decisions using PROCEDURES VOC data from groundwater plumes without Indoor air quality testing results in 1998 for testing individual buildings over a plume. In this 153 residential homes at a site in Denver, Colo., study, indoor air concentrations were calculated were evaluated in this study. The homes overlie considering the 1,1 DCE concentration in groundwater with 1,1 DCE concentrations groundwater and the associated volatilization ranging up to approximately 1,000 ug/l, resulting factors for the progressive movement of 1,1 from the degradation of both 1,1,1 DCE from the groundwater surface into the trichloroethane (TCA) and trichloroethene residential structure at each location of 153 (TCE). Groundwater is at a depth of approxi- homes in the study. The 1,1 DCE concentration mately 20 to 30 feet below the ground surface, in groundwater beneath each home was esti- flowing primarily in weathered and mated using concentration contours that were siltstone. Measured concentrations of 1,1 DCE developed based on 1,1 DCE concentrations in in indoor air ranged up to 91 ug/m3 in resi- a series of groundwater monitoring (Figure dences located over the plume and were 1). Depth to groundwater was adjusted based generally below detection in homes beyond the on the depth of the basement or crawl space of detectable groundwater plume. Variance of the associated structure. The series of calcula- results from house to house is significant (plus or tions associated with the volatilization factor and minus an order of magnitude in some cases), the default , building, surface, and subsurface due to site-specific geological, building, and parameters presented in the ASTM guidelines ventilation factors. (ASTM E1739-95) were used to relate the Indoor air samples were collected over a VOC concentration in groundwater to the 24-hour period using an inert stainless steel predicted concentration in indoor air. container (SUMMA canister). Each canister

222 Proceedings of the 2000 Conference on Hazardous Waste Research SEAL

FAN FAN SEAL CRAWL SPACE BASEMENT WITH MEMBRANE SUCTION PIT

VAPORS

WATER TABLE

SUB-SLAB DEPRESSURIZATION SUB-MEMBRANE DEPRESSURIZATION Figure 2. Mitigation systems. was laboratory cleaned, evacuated to a nominal 1998, equipment tuning procedures met the vacuum of 0.01 torr, sealed, and shipped to the requirements of CDPHE (1999) guidelines. site under chain-of-custody documentation. The SIM mode monitors a few compounds The canister pressure was noted and recorded instead of the entire mass spectra, allowing a in the field at the beginning and end of the 1,1 DCE reporting limit of 0.04 ug/m3. sampling event. Sample collection commenced In this study, homes with 1,1 DCE con- with opening of the canister valve, which re- centrations in indoor air above the health-based sulted in flow of air into the canister at a steady action level were mitigated with sub-slab rate controlled by a regulator attached to the depressurization (SSD) or sub-membrane canister. Sample collection ceased approxi- depressurization (SMD) systems in homes with mately 24 hours afterwards by closing the valve. basements or crawl spaces, respectively (Figure In some cases, the canisters had equilibrated 2). Mitigated homes have been tested quarterly with ambient atmospheric pressures when the to monitor the effectiveness of these systems canisters were retrieved, indicating that the (Folkes and Kurz, 2000). sample collection period was less than 24 hours. RESULTS The SUMMA canisters were shipped to the The predicted 1,1 DCE concentrations in laboratory in batches under chain-of-custody indoor air were compared to the actual indoor protocols. Duplicate samples were collected at air results from the homes in the study. In a rate of approximately 1 in 20. approximately three out of five cases, the actual SUMMA canister samples were analyzed 1,1 DCE concentrations were within an order of at the laboratory in accordance with EPA Test magnitude of the predicted value. However, the Method TO-15, using a mass spectrometer RBCA calculations under-predicted 1,1 DCE operated in the selective ion monitoring (SIM) concentrations in indoor air in four out of five mode. For tests conducted after October

Proceedings of the 2000 Conference on Hazardous Waste Research 223 Figure 3. 1,1, DCE prediction ratio and groundwater concentration.

homes (Figure 3). Although a large number of (i.e., homes below the action level being pre- results were under-predicted, the predicted and dicted to be above the action level) was ap- actual concentrations may both be below or proximately 15%. both be above the action level. The primary Although the results at the extremes of the concern in evaluating the reliability of a predic- range may be acceptable, it is in the middle of tive method that has a tendency to under predict the range where a reliable predictive method for results is the probability of false negatives (i.e., decision making would be most useful. In the homes predicted to be below the action level range of 1,1 DCE concentrations in groundwa- testing above the action level). ter between 1 to 100 ug/L, there is a significant The overall false negative rate was ap- potential for predicting indoor air results below proximately 10%. However, this rate was not the action level in individual homes with actual consistent across the range of 1,1 DCE concen- results above the action level. Several mecha- trations in the groundwater plume (Figure 4). nisms may be responsible for actual test results The rate of the false-negative decisions ap- exceeding predicted results. Site-specific peared to be correlated to the concentrations of characteristics in individual houses are the most 1,1 DCE in the groundwater. Testing demon- likely cause of this variance between predicted strated that the estimates yielded false-negative and actual results (e.g., underlying soil condi- rates varying from 5%, in homes above ground- tions, presence or absence of open joints or water with 1,1 DCE concentrations below 10 cracks in foundations, and heating and ventilat- ug/L, to over 50%, in homes above groundwa- ing system conditions). In addition, the proxim- ter with 1,1 DCE concentrations of 50 ug/L. At ity of homes to nearby groundwater with higher 1,1 DCE concentrations greater than 100 ug/L concentrations may cause higher actual results in groundwater, there would have been no false- than predicted. negative decisions; but the false positive rate

224 Proceedings of the 2000 Conference on Hazardous Waste Research Figure 4. Actual and predicted concentrations of 1,1 DCE in indoor air (1,1, DCE concentration in groundwater).

Inherent in any predictive model is the months had test results exceeding the action attempt to include factors with a significant level during winter months. Cold weather, high effect on results. One, seemingly significant, winds, and furnace operation all tend to reduce factor in the ASTM equations is the depth to the air pressure in houses compared to ambient groundwater at the location. Logically, the pressures, creating additional forces for migra- closer the groundwater to the basement or tion of vapors from the subsurface into a home. crawl space of the home, the higher the ex- The test results for this study were collected pected concentrations in indoor air. In this during the summer months of 1998. Therefore, study, the depth to groundwater did not have a the tendency of the predictive methods to significant effect on the ability to predict the under-predict actual results would be expected actual 1,1 DCE concentration in indoor air. At to be more significant during winter months. groundwater depths below the structure ranging CONCLUSIONS from 3 m (10 ft) to 9 m (30 ft), the predictions Based on the results of this evaluation, were as likely to under-predict or over-predict indoor air quality (IAQ) testing should be used, at one depth as another (Figure 5). rather than RBCA predictive modeling, to A factor that has proven to be significant in establish the extent of impacts and determine the actual results but is not included in the predictive need for mitigation. methods is the seasonality effect. In several At very low and high contaminant concen- homes that did not initially exceed the action trations in groundwater, use of the RBCA level (i.e., were not mitigated), indoor air test equations may be an economical method for results were higher in the winter than in the making mitigation decisions. The high false- summer months. Some homes that had test negative rate at moderate concentrations in results below the action level during summer

Proceedings of the 2000 Conference on Hazardous Waste Research 225 Figure 5. 1,1 DCE prediction ratio and depth to groundwater.

groundwater indicates testing is needed in of Subsurface Gasoline Contamination.” homes that are predicted to be below the action & Technology. 30(10): 2948-2957. level, to minimize the false-negative rate. This need for testing individual homes is further Fitzpatrick, N.A., and J.J. Fitzgerald, 1996. “An Evaluation of Intrusion into supported to avoid the seasonal influence Buildings Through a Study of Field on results. Data.” Presented at the 11th Annual Conference on Contaminated , REFERENCES University of Massachusetts at Amherst. Altshuler, K.B., and D.E. Burmaster, 1997. “ Modeling: The Need for New Folkes, D.J., and D.W. Kurz, 2000. Techniques and Better Information.” “Remediation of Indoor Air Impacts Journal of . 6(1):3-8. Due to 1,1 DCE Groundwater Con- tamination.” Presented at the Second American Society for Testing and Materials, International Conference on 1995. Standard Guide for Risk-Based Remediation of Chlorinated and Recal- Corrective Action Applied at Petroleum citrant Compounds, Monterey Califor- Release Sites. E 1739-95. nia, May 2000. Colorado Department of and Johnson, P.C., and R.A. Ettinger, 1991. Environment, 1999. Guidance for “Hueristic Model for Predicting the Analysis of Indoor Air Samples. Haz- Intrusion Rate of Contaminant Vapors ardous Materials and Waste Manage- into Buildings.” Environmental Science ment Division. & Technology. 25(8): 1445-1452. Fischer, M.L., A.J. Bentley, K.A. Dunkin, A.T. Richardson, G.M., 1997. “What Research is Hodgson, W.W. Nazaroff, R.G. Sextro, Needed on Indoor of Volatile and J.M. Daisey, 1996. “Factors Organic Contaminants?” Journal of Soil Affecting Indoor Air Concentrations of Contamination. 6(1): 1-2. Volatile Organic Compounds at a Site

226 Proceedings of the 2000 Conference on Hazardous Waste Research