•f; ISSN 1047-3289 J. Air Waste Manage. Assoc. 42: 277-283 SFUND RECORDS CTR 1751-00087 Soil-Gas Contamination and Entry of Volatile Organic Compounds into a House Near a Landfill SFUND RECORDS CTR 88111859 Alfred T. Hodgson, Karina Garbesi, Richard G. Sextro, and Joan M. Daisey Energy and Environment Division Lawrence Berkeley Laboratory University of California Berkeley, California
Toxic volatile organic compounds (VOC) are commonly found In landfills, Including landfills were sampled for total orgeuiic those accepting only municipal waste. These VOC can migrate away from the site gases measured as methane. Sixty- through the soil and result In contaminated off-site soil gas. This contaminated soil gas four percent of the landfills had perim eter concentrations of total organic can enter houses built near landfills and Is a potential source of human exposure to VOC. gases in excess of 5 ppmv, and 20 This study Investigated soll-gas contamination and the mechanisms of entry of VOC percent had concentrations in excess into a house with a basement sited adjacent to a municipal landfiil. The VOC were of five percent, the standard which Identified and quantified in the soil gas and In Indoor and outdoor air. Pressure coupling officisdly defines offsite migration. between the basement and the surrounding soli was measured. Using soll-gas tracers, If houses are situated in the near vicinity of a site with subsurface gas the pressure-driven advective entry of soli gas was quantified as a function of basement migration, it is possible under some depressurization. From the measurements, estimates were made for the diffusive and circumstances for soil-gas conteuni- advective entry rates of VOC Into the house. nants to enter the houses through A comparison of the chlorinated hydrocart>ons found In soli gas at the site and In the their substructures. Such entry will landfiii suggests that the landfill Is the source of the halogenated compounds In the result in elevated indoor concentra tions of the contaminants. vIclnKy of the house. At the conditions of the study, the diffusive and advective entry Evidence for the entry of landfill rates of VOC from soli Into the basement were estimated to be low and of similar contaminants into houses is provided magnitude. Advective entry of soli gas into the house was limited by the low soil air by Wood and Porter who detected permeability and the low beiow-grade leakage area of the basement. For this reason, methane at concentrations approach high Indoor concentrations due to the intrusion of VOC from soil gas are unlikely at this ing one percent in enclosed spaces of houses located near a landfill following house, even under conditions that would produce relatively large underpressures In the an incident of gas migration.^ In one basement. house 180 m from the lemdfill, chlori nated hydrocarbons, presumably origi Landfills, including municipsd facili detected in landfill gas in approxi nating from the landfill, were detected ties designated to accept only nonhaz- mately 70 percent of the 288 sites at the entry point for soil gas. ardous waste, have been found to con tested. ^ These VOC can migrate from The entry of soil-gas contaminants tain elevated concentrations of toxic the landfill site through the subsur into houses has been studied in rela volatile organic compounds (VOC). In face by advective transport in the gas tion to the issue of indoor radon. These a recent study of predominantly munic and aqueous phases or by diffusion. studies have demonstrated that radon ipal landfills mandated by the Califor The CARB study provides direct evi enters houses by diffusion and by ad nia Air Resources Board (CARB), one dence for the subsurface transport of vective transport from the surround or more of the ten toxic VOC selected gaseous contaminants away from land ing soil. In single-family residences as indicators of hazardous waste were fill sites. ^ Perimeter gas wells at 288 with elevated indoor concentrations, the dominant entry mechanism is the advective flow of radon-bearing soil gas into the buildings.^"^ The pressure differential which drives this flow is Implications caused by indoor-outdoor thermal dif ferences, wind loading on the building Since gas in landfills is commonly contaminated with toxic VOC and ofT-site shell and soil, and unbalanced ventila migration of landfill gas through the subsurface is also common, there may be tion systems.2'^'^ In extreme weather locations in the vicinity of landfills in which populations are being exposed to conditions, the depressurization of elevated levels of VOC in their homes. For the house in this study, the entry rate building substructures can approach of VOC was low due to the low soil-air permeability and the low below-grade -10 Pa.^ The resulting advective en leakage area of the btisement. However, in some circumstances, a large percentage try of soil gas can constitute a signifi of the ventilation air for a house may derive from the advective entry of soil gas. It is possible that locations with significant potential for elevated indoor exposures cant portion of the toted amount of air via this pathway may be identified from data on off-site migration of contami infiltrating into a house if the building nants, soil type and housing characteristics. substructure is sufficiently leaky and
Copyrifiht 1992—Air & Waate Manrtfiement Association
March 1992 Volume 42, No. 3 277 -.1 the soil is suthcientiy permeaoie to at iLs ciobebt pOiiiL. i tic lana UCL.^^JCI- *' soil-air flow.^ the berm and the house is flat. At the 4 and 11m from the west basement In this study, the mechanisms in time of the study, the region of the wall. Soil-air permeabilities were mea volved in the entry of VOC from soil landfill nearest the house was full and sured using 30 probes installed in the into a single-family residence -mth a capped with soil. A plan view of the soil around the house at distances of basement were investigated using tech study site is shown in Figure 1. 0.5 to 7 m from the basement wall and niques similar to those employed in The house is a single-story structure at depths of 1.5 and 3 m. The pVobes the radon studies cited above. The built over a basement and a garage. and the in-situ measurement of perme house was located in an area of contam The basement floor is ~2.5 m below ability have previously been described.'' inated soil adjacent to a municipal grade. The foundation and beisement The probes were also used to measure landfill. Volatile organic compounds of the house were constructed by exca pressure coupling between the soil and were identified and quantified in in vating the soil, pouring a cement slab the house and to collect seunples of soil door and outdoor air and in the soil gas with an integral footing, emd building gas for anedysis of VOC and tracer surrounding the house. Pressure cou up a wall of cement blocks on top of the gases. Probe locations are shown in pling between the basement and the slab. The cavities in the blocks were Figure 1. surrounding soil was measured to de back-filled with cement. The exterior The analysis of peirticle-size distribu termine the region of influence of the of the wall was coated with an asphalt tion, by a standard sieving and sedi house on the soil and to elucidate the sealant, and the interior of the wall mentation technique, revealed a range entry pathway for soil gas. Using soil- was painted, but otherwise bare. The of U.S. Department of Agriculture soil g£is tracers, the pressure-driven entry floor areas of the first floor and the t3T)es from loamy sand to silt loam.'-^ of soil gas was quantified by experimen basement are 183 and 103 m^, respec Horizontal layering was evident in the tally depressurizing the basement. tively. The respective volumes are 430 two profiles farthest from the house. From the field measurements, esti and 290 m^. The effective leakage area Above 2.4 m, the layers alternated mates were made for the diffusive and of the entire house, as measured by between loamy sand and seuidy loam, advective entry rates of VOC into the the technique of Sherman and Grim which has more fine particles. Be house at normal operating conditions. srud, is 0.125 m^, indicating that the tween a depth of 2.4 to 2.8 m, the soil In a previous report, the results of a structure is relatively tight. For sev was silt loam, which is predominantly numerical model were compared with eral months prior to the study and silt. The profile 0.8 m from the house the measurements of pressure cou throughout the study, the house was was relatively uniform loeuny sand, pling and the pressure-driven entry of unfurnished and unoccupied. probably because this region was exca soil-gas under experimental condi vated and refilled during construction. tions. 1° Investigations were conducted from late July through early November Moisture content, determined by 1987. Data on local wind speed and weighing before and after oven drying, was two to four percent by weight over Experimental direction, precipitation, and indoor and outdoor temperatures were continu a depth of 0.5 to 2 m and increased to The study was conducted at a single- ously collected throughout this period. approximately 12 percent in the sUt- family residence sited adjactent to the Precipitation w£is only 1.5 cm. loam layer. The mean in-situ soil air Geer Road Landfill in Stanislaus The soil surrounding the house was permeability at a depth of 1.5 m was County, Cedifornia. This is an active analyzed for particle-size distribution, 2.5 X 10-12 a j-ange of 0.3-20 landfill accepting only municipal waste. moisture content and permeabiUty, X 10-12 xt?. This range is consistent The landfill is contained by a perime Samples for particle-size and moisture with the particle-size composition of ter berm constructed of soil. The berm analyses were extracted by bucket au the soil.^ The permeability at a depth lies approximately 70 m from the house ger at sampling depths of 0.3 to 2.8 m of 3 m was simileu-. Pressure coupling between the house arid the soil at the probe locations was measured in an attempt to define both the region of influence of the house on the surrounding soil and the pathway for entry of soil gas .into the house. This measurement weis carried out using a previously described tech nique.^ With the door between the garage and outdoors open, the door between the basement and the upper floor closed, and the windows and doors on the upper floor open, the basement was held at 25 ± 2 Pa below atmo spheric pressure using a large exhaust fan installed in the doorway between
(290) the basement and the garage (Figure 940 » 1). During depressurization, the pres (••91 sure differences between the beisement no* •o ^ and the atmosphere, dP^, and the soil '§ '^^^--^ Probe Depths probes and the atmosphere, dPj, were -70 m to edge ol landliil \, ^^^^ • 1 .S m measured. The pressure coupling in ^ 3 0 m percent was calculated as 100 • (dPb- .SF6 •2- "^^P^ lil 3 .2 m Sciie (ml dPs)/dPb. \ Freon-12 0 1 ? 3 < On a number of occasions during the measurement of pressure coupling, the Figure 1. Plan view of the study site and the basement level of the house showing the exhaust fan was switched off or the locations of the soil probes and the concentrations of Freon-12 and SF6 tracer gas in soil gas exhaust flow rate was abruptly sampled from each probe in early November. changed. Pressures at the soil probes
278 J. Air Waste Manage. Assoc. it-'tipoiidea wittun a minute of the trations in September were generally There is a difference in the composi change in fan mode. This direct re very low. tion of VOC in the soil probes between sponse demonstrated that the depres Samples for qualitative and quanti the September and October sampling surization at the probes originated at tative analysis of VOC were collected periods. In September, three com the basement. In addition, pressures and analyzed using previously de pounds, Freon-12, Freon-11, and tetra at the probes were found to be linear scribed methods. In brief, samples chloroethylene, had average soil-gas with basement pressure. were collected on multisorbent sam concentrations in excess of 20 ppbv. In Soil-geis entry into the house weis plers containing Tenax-TA, Amber- October, dichloromethane, acetone, measured as a function of basement sorb XE-340 and activated charcoal in hexanal, 2-methylbutane, and toluene depressurization using sulfur hexa- series. Sampling flow rates of ~ 100 edso had concentrations in excess of fluoride (SF6) and dichlorodifluoro cm^ min-i (20°C, 760 torr) were regu this level. Even though two of the methane (Freon-12) as soil-gas trac lated with electronic meiss-flow control probe locations were common to both ers. In September, a total of490 cm^ (3 lers. Sample volumes for soil gas, out sampling periods, the concentration g) of pure SF6 was injected into five door eiir and indoor air were typically ranges for September and October do probes to the north and west of the 0.23, 5.6 and 2.5-5.6 L, respectively. not overlap for any of these five com house in approximately equal portions Single samples were collected for qual pounds. The reason for this apparent to provide a source of labeled soil gas. itative analysis. Duplicate samples temporal change in soil-gas composi were simultaneously collected for By early November, when the meeisure- tion is unknown. ment was conducted, the SF6 had dif quantitative analysis. A volume of air fused over much of the probe field. equal to two probe volumes was vented The soil-gas concentration of Freon- Freon-12 was found to be present from each soil probe before samples of 12, which was measured at edl probe throughout the probe field as a soil-gets soil gas were collected. locations by GC-ECD (Figure 1), is perhaps representative of the spatial conteiminant. For analysis, a sample was ther- variabihty in the distribution of VOC medly desorbed with a sample concen Immediately prior to the measure in soil gas at the site. The average trating and inletting system (UNA- ment of soil-gas entry, soil gas at each concentration of Freon-12 for the site CON Model 810A, Envirochem Inc.) of the probe locations was analyzed for was 450 ppbv with individued concen SF6 and Freon-12. First, a volume of and injected into a GC equipped with a capillary column (DB-1701, J&W trations ranging from 100 to 2,100 soil gas equal to two probe volumes ppbv. As shown in the figure, the 3-m was vented from a probe; then, dupli Scientific, Inc.). The GC was con nected via a direct capillary interface deep probes had concentrations consid cate samples were collected using plas erably higher than the average, and tic sjrringes. Analyses were conducted to a Mass Selective Detector (MSD, concentrations on the north and east on-site with a geis chromatograph (GC) Series 5970B, Hewlett-Packard Co.). sides of the house were higher than on equipped with an electron-capture de For qualitative analyses, the MSD weis the west side, which averaged 250 tector (ECD) and a molecular sieve 5A scanned over a mass range of 33-250 ppbv. It is probable that the spatial column. Meanwhile, the basement was m/z. Compounds were identified using thoroughly ventilated to reduce indoor mass spectral data bases, and identifi variations of Freon-12 and of the other concentrations of the soil-gas tracers cations were confirmed, in most cases, VOC in Table I eu-ose from a combina to outdoor levels by running the ex by analyses of authentic standards. tion of interrelated factors, such as the haust fan at high speed for an ex For quantitative analyses, the MSD degree of coupling with the source tended period with the interior door to weis operated in the selected-ion-moni (presumed to be the lemdfill), the pres the upper floor, and all windows and toring mode. Multi-point calibration ence of relatively impermeable layers doors on the upper floor, open. The curves were constructed using authen in the soil as discussed in Reference 10 door to the upper floor and all of the tic standards. and other boundaries limiting trans heating ducts in the basement were port to the surface, spatial variations then closed, emd the GC-ECD weis set Results in the sorptive capacity of the soil for up to automatically sample and ana VOC, emd the degree of protection lyze basenient air for SF6 and Freon-12 from the wind. at one-minute intervals. The exhaust Volatile Organic Compounds Thirteen of the 14 compounds quan fan was operated to depressurize the Twenty-six individual VOC were tified in soil gas in September emd basement in stages by 20, 30, 40 and identified in samples of soil gas col October were also detected in indoor 50 Pa relative to atmospheric pres lected in July and September. In gen air (Table I). With the exception of sure. Each stage of depressurization eral, halogenated hydrocarbons and acetone, the concentrations of VOC in was maintained long enough to achieve oxidized compounds were the domi the house were low (6 ppbv or less) and near steady-state concentrations of the nant classes, both in terms of the did not chemge appreciably between analytes in the basement. numbers of compounds and the rela the samphng periods. The high concen Samples for analysis of VOC were tive chromatographic (toted-ion-cur- tration of acetone in October was at collected on three occeisions during the rent) peak areas of the compounds. tributed to a source of this compound study. A preliminary queditative sur Based on the qualitative results for brought into the house by the investi vey of soil gas, outdoor air, and base these samples, 14 individued VOC were gators. In October, concentrations of ment air was conducted in July. In selected for quantitative anedysis in VOC in the basement were compared September, samples for both quedita samples of soil gas and indoor and to concentrations in a bedroom on the tive and quantitative analyses were outdoor air collected in September and upper floor. All of the compounds had obtained from several soil probes and October. These compounds are repre nearly equivalent concentrations in the from outdoor and basement air. In sentative of the m^jor hydrocarbons, basement and the bedroom. This simi October, samples for quantitative anal halogenated hydrocarbons and oxi larity in concentrations of VOC be ysis only were collected from four soil dized compounds found in soil gas at tween floors suggests that the air in probes and from indoor air in both the the site. The concentrations of the the house is well-mixed when the house basement and the upper floor. Sam compounds are summarized in Table is in a closed condition, at least during ples of outdoor air were omitted in I. It is notable that the range of soil- periods of low infiltration. Concentra October since the number of samples gas concentrations for many of the tions measured in outdoor air in Sep that could be collected and analyzed dominant compounds was relatively tember, with the exception of acetone, was limited and outdoor VOC concen broad in both sampling periods. were all less than 1 ppbv.
March 1992 Volume 42, No. 3 279 Table I. Concentrations of VOC in soil gas, mdoor air and outdoor air in bepiemot;! ariu uciuuei. Concentration (ppbv) September October Soil gas' Soil gas*" Compound Range Avg Basement Outdoor air Range Avg Basement Bedroom Halogenated Hydrocarbons Freon-12 230-920 550 2.3 0.2 110-340 190 3.5 2.3 Freon-11 7.6-110 46 0.8 0.3 42-230 140 0.8 1.3 Dichloromethane <0.1-2.1 0.7 1.2 0.1 50-200 120 3.9 5.4 1,1,1-Trichloroethane 1.4-11 4.9 0.7 0.3 2.8-9.4 6.1 0.6 0.7 Tetrachloroethylene 23-150 70 0.7 0.1 26-79 56 0.8 0.8 Oxidized Compounds Acetone 16-27 20 12 4.9 190-370 250 82 15 Hexanal 3.3-7.9 6.1 1.0 ND<= 37-52 42 1.5 1.9 4-Methyl-3-penten-2-one < 0.1-10 3.4 ND ND ND — ND ND 3-Heptanone <0.1-6.8 4.2 0.6 ND 7.8-15 9.9 ND ND Hydrocarbons 2-Methylbutane ND — 5.2 0.3 14-74 36 4.4 5.0 Toluene 2.1-3.6 14 4.4 1.1 40-92 70 4.8 4.4 Ethylbenzene ND — 0.6 ND 2.8-3.6 3.3 0.8 0.7 m-,p-Xylene ND — 1.9 ND 9.3-12 11 2.7 2.3 o-Xylene 0.2-1.7 0.7 1.0 0.2 3.4-7.2 5.8 1.6 1.2 "SoU probes AW2, CW2 and B2. '•Soil probes AW2, CW2, DEI and DE2. 'Not present above detection limit of ~ 0.1 ppbv.
Entry of Volatile Organic Compounds obtedned by first averaging the concen its diffusion coefficient in the cement- Into the Basement trations of SF6 and Freon-12 in the block wall be meeisured or estimated. probes nearest each of three wedls that Since no measurements were avedl- The meeisurements of pressure cou are acljoined by soil. For the west and able, the diffusion coefficient for pling, described in detail in Reference north walls, the concentrations in the Freon-12 in the cement-block wall was 10, were used to estimate the distribu 1.5-m deep probes 0.5 m from the approximated based on data for radon. tion of the leed^age area over the beise walls were averaged. For the east wall, The diffusion coefficients of radon in ment shell. An average pressure cou the concentrations in the 1.5-m deep poured cement emd in soil have been pling of 30 percent was measured in probes next to the patio were averaged reported to be 7 x 10"^ and 7 x 10"^ the probes 0.5 m from the west and since the presence of the patio prohib m2 h-i, respectively.^'!^ It weis pre north beisement walls, with a range of ited measurements adjacent to the sumed that cement blocks are consider 4—44 percent. Pressure coupbng weis fairly evenly distributed along the two wall. These values were then weighted ably more permissive of air flow than walls. This indicates that the entry of by the lengths of their respective walls poured cement but less permissive than soil gas was probably not localized at and averaged. This yielded weighted- typical soils. Adjusting for the differ only a few points as was observed in average tracer-geis concentrations con ence in the molecular diffusivities of earlier studies.^-^ Instead, entry was tributing to entry by diffusion and radon and Freon-12 in air, the diffii- probably more evenly distributed over advective transport of 74 ppbv for SF6 sion coefficient for Freon-12 in the the basement shell, at leeist in the and 620 ppbv for Freon-12. The spatial cement block was approximated to be horizontal plane. This conclusion is heterogeneity of the tracer-gas concen in the range of 10-3-10-4 m^ h-^. supported by numerical modeling, i" trations in the soil and the possibility Using this range, thejveighted average The results of this modeling demon that the pathway for entry of gases is soil-gas concentration of Freon-12 of strated that entry probably occurred not entirely uniform over the beise 620 ppbv, an indoor concentration of 3 through the semi-permeable cement- ment walls introduce considerable un- ppbv, a cross-sectional area of 99 m^ block basement wedls, distributed over certednty into these estimates. (the area of the three sides of the their area, rather than through a gap . During the study period, the average basement wall), and a diffusion path at the wall-floor interface, as is as indoor-outdoor temperature differen length of 15 cm (the thickness of the sumed in other models.^^'^^ The floor tial was approximately 6° C, and the cement-block wall), the diffusive flux would not contribute significantly to average wind speed weis 2 m s"!. At of Freon-12 into the basement was entry because of the lack of penetra these moderate natural conditions, the estimated to be approximately 200- tions and the very low air permeability maximum underpressurization of the 2000 ug h-i. This is equivalent to 8ui of a poured concrete slab. beisement would be expected to be on advective entry rate of soil gas conteun- The soil tracer gases, SF6 and Freon- the order of only several Pa. Due to ing the same concentration of Freon 12, were used eis surrogates for VOC to this lack of a strong driving force for 12ofabout0.1tolm3h-i. assess the magnitude of VOC entry advective transport and the appar The advective entry rate of soil gas into the basement. The concentrations ently low effective leedtage area be into the house as a function of beise of both tracers in the soil gas at all of tween the basement and the soil, it is ment underpressure was determined the probes are shown in Figure 1. reasonable to eissume that entry of from the depressurization experiment. Since the pathway for the entry of soil VOC into the basement from the soil Immediately prior to initiating this gEises into the house is appeirently dis would be dominated by diffusion un experiment, the measured background tributed over the basement walls, the der the natural conditions at the time concentrations of the tracers SF6 and concentrations of the tracer gases for of the study. Freon-12 were below detection and 1 use in estimating the entry of VOC by The calculation of the diffusive en ppbv, respectively, in the basement, diffusion and advective transport were try rate for a compound requires that the open upper floor of the house, and
280 J. Air Waste Manage. Assoc. outdoors near the basement sill plate. During depressurization, eiir flow into 4 Freon* 12 the basement was detected at the elec • SF6 trical outlet boxes, which were re n E, cessed into cavities cut into the cement £ 15 blocks near the bottom of the weJl. The CO average concentrations of SF6 emd Freon-12 in air samples collected from the cavities on the west wall were about 90 and 200 ppbv, respectively. These concentrations were similar to the average concentrations measured in the soil adjacent to this wall (Figure 0 5 10 15 20 25 30 35 40 45 50 1), indicating that air entering the Basement underpressure (Pa) basement from the walls had its origin Rgure 2. Advective entry rates of soil gas Into the basement as a function of in the soil and that the induced flow basement depressurization relative to atmospheric pressure. The entry rates probably did not significantly dilute were estimated using a mass-balance model and concentrations of Freon-12 the soil-gas concentrations. and SF6 tracer gas. The best estimate of the entry rate is given by the region of overlap for the two compounds (shaded area). A simple meiss-balance model assum ing steady-state conditions was ap plied to the concentrations of SF6 and demonstrates that the minor under and advective entry rates that were Freon-12 measured at the end of each pressures of several Pa that would be estimated above. For the other com depressurization stage. Setting the expected to develop in the basement pounds, this approach generally pre mass flow of a tracer gas in the exhaust relative to the surrounding soil at the dicted entry rates that were one to two eur equed to the mass flow of the gas in moderate conditions of the study would orders of magnitude higher. This re the air entering the basement gives: result in a probable entry rate of soil sult was interpreted as indicating the gas of less than 0.5 m^ h'^. Therefore, existence of indoor sources for these Q,C, = Q.C. + Q„C„ (1) the advective entry of soil gas contami compounds. The Cf is the steady-state concentra nants would be approximately equiva tion of the tracer geis in the basement, lent to diffusive entry at these condi Discussion and Cg and C„ are the concentrations tions. in the soil gas and outdoor air, respec For comparison, em effective soil-gas Data on the subsurface gas concen tively. The corresponding flow rates of entry rate (Qg) at the natural condi trations of selected toxic VOC in the soil gas and outdoor air are Qg and QQ. tions of the study weis estimated from (Jeer Road Landfill are available from The ventUation rate of the basement, the concentrations of VOC measured the Landfill Gas Testing Progreim of Qf, is simply the calibrated flow rate of in September and October. The total the Califomia Air Resources Board. ^ the exhaust fan. Solving for Qg, and house infiltration rate at these condi Samples collected in 1987, just prior to letting Qf = Qs -I- Qo yields: tions was predicted to be about 200 m^ the present study, from five gas-sam (0.2 air changes per hour).ii This pling wells within the landfill were Cf - C, infiltration rate was substituted for Qf analyzed for ten VOC plus methane. (2) in Equation 2. For each compound The targeted compounds and their con detected in the house, the equation centration ranges in the landfill gas Soil-gas entry rates (Qg) at each was solved for Qg assuming the whole- are shown in Table II. The compounds applied basement underpressure were house concentration equaled the base with the highest concentrations in calculated from Equation 2 for both ment concentration in September and landfill gas are dichloromethane, 1,1,1- SF6 and Freon-12 using the weighted- using a weighted whole-house concen trichloroetheme, tetrachloroethylene, average soil-gas concentrations. The tration in October. The average value and vinyl chloride. With the exception results are shown in Figure 2. Al of Qs for Freon-12, Freon-11 and tetra of vinyl chloride, which was not quan though the relationship between entry chloroethylene weis 1.5 m^ h-! with a tified by the present study, these chlo rate and pressure is approximately lin relative standard deviation of 50 per rinated compounds also occurred as ear for both compounds, the underly cent (n = 6). This average is within contaminants in soil gas near the ing uncertainties discussed above sig the range of the combined diffusive house. The maximum soil-gas concen- nificantly Umit the precisions of the estimated entry rates. These uncertain ties are represented in the figure by Table II. Concentrations of methane and ten toxic VOC in landliil gas compared with assuming that the effective concentra concentrations of methane in soil gas at the perimeter of the landfiU and with tions of the tracer gases in the soil geis concentrations of VOC in soil gas near the house. near the basement wedls have preci sions of plus or minus one half the M{tx. soil calculated weighted-average concentra Cone, range Cone, range gas/max. tions. Within the resulting confidence Compound landfill gas" (ppbv) soil gas (ppbv) landfill gas intervals, there is a region of overlap Methane 180,000-500,000ppmv 2-1000 ppmv (Perimeter) 0.002 between the two compounds that de Dichloromethane 2,500-51,000 < 0.1-2000 0.004 fines the best estimate of the soil-gas 1,1,1-Trichloroethane < 10-13,000 1.4-11 0.001 entry rate. The fact that the estimated Tetrachloroethylene 620-18,000 23-150 0.008 entry rates based on Freon-12 are Vinyl chloride < 500-19,000 NM'' — higher than those based on SF6 sug 1,2-Dichloroethane <20-850 NM — 1,2-Dibromoethane <1 NM — gest that entry might be somewhat Trichloromethane < 2-980 NM — higher on the north side of the house Tetrachloromethane <5 • NM — where Freon-12 concentrations are Trichloroethylene 1,600-8,300 NM — higher than their average, and SF6 Benzene 890-4,500 NM — concentrations are lower. 'Landfill gas and perimeter soil gas concentrations are from Reference 1. The relationship shown in Figure 2 ''Either not measured or not present above limit of detection of ~0.1 ppbv at study site.
March 1992 Volume 42, No. 3 281 trations of the three compounds are low conceiiuiaciofib aiiu i-ne dinuai. 1
282 J. Air Waste Manage. Assoc. iiotii . t...iinLj Ui coiiuiuiiiiULOu lariu- zi, i9o/, oeiiei i, b., el al., has., Insti 13. Hodgson, A. T.; Girman, J. R. "Applica tute for Water, Soil and Air Hygiene, tion of a Multisorbent Sampling Tech fiUs and waste sites on a site-by-site Berlin, Vol. 2, pp. 338-392, 1987. nique for Investigations of Volatile Or basis. If high-risk areas are identified, 5. Sextro, R. G.; Moed, B. A.; Nazaroff, W. ganic Compounds in Buildings," in studies could be conducted in these W.; Revzan, K. L.; Nero, A. V. "Investi Design and Protocol for Monitoring areas to determine if the advective gations of Soil as a Source of Indoor Indoor Air Quality, ASTM STP 1002, Radon," in Radon and Its Decay Prod Nagda, N. L.; Harper, J., Eds., Ameri entry of soil gas into substructures is ucts: Occurrences, Properties, and can Society for Testing and Materials, resulting in significantly elevated in Health Effects, Hopke, P., Ed., ACS Philadelphia, PA, pp. 244-256, 1989. door exposures to VOC. Symposium Series 331, American 14. Mowris, R. J.; Fisk, W. J. "ModeUng Chemical Society, Washington D.C, pp. the effects of exhaust ventilation on 10-29,1987. 2^^Rn entry rates and indoor ^^^Rn Acknowledgment 6. Na^arofT, W. W.; Moed, B. A.; Sextro, concentrations," Health Physics 64: R. G. "Soil as a Source of Indoor Ra 491 (1986). This work weis supported by the don: Generation, Migration and Entry," 15. Loureiro, C. O.; Abriola, L. M.; Martin, Occidental Chemical Corporation un in Radon and Its Decay Products In J. E.; Sextro, R. G., "Three-dimen der Agreement No. BG 8602A and by doors, Nazaroff, W. W.; Nero, A. V., sion2d simulation of radon transport Eds., John Wiley & Sons, New York, into houses with basements under con^ the Assistant Secretary for Conserva NY, pp. 57-112, 1988. stant negative pressure," Environ. Sci tion and Renewable Energy, Office of 7. Turk, B. H.; Prill, R. J.; Grimsrud, Technol. 24: 1338 (1990). ' Building Technologies, Building Sys D. R.; Moed, B. A; Sextro, R. G. "Char 16. Nero, A V.; Nazaroff, W. W. "Charac tems emd Materials Division of the acterizing the occurrence, sources, and terizing the source of radon indoors. variability of radon in Pacific North Radiation Protection Dosimetry 7: 23 U.S. Department of Energy under Con west homes," J. Air Waste Manage. (1984). tract No. DE-AC03-76SF00098. The Assoc. 40:498(1990). 17. Shah, J. J.; Singh, H. B. "Distribution authors thcmk the owners of the house 8. Nazaroff, W. W.; Lewis, S. R.; Doyle, of volatile organic chemicals in outdoor for their cooperation and John Girman S. M.; Moed, B. A.; Nero, A. V. "Exper and indoor air: a national VOCs data of the Califomia Depeutment of Heedth iments on pollutant transport from soil base," Environ. Sci. Technol. 22: 1381 into residential basements by pressure- (1988). Services (currently with the U.S. EPA) driven airflow," Environ. Sci. Technol. 18. Johnson, P. C; Ettinger, R. A. "Heuris for his eissistance and comments. 21:459(1987). tic model for predicting the intrusion 9. Prill, R. J.; Fisk, W. J.; Turk, B. H. rate of contaminant vapors into "Evaluation of radon mitigation sys buildings," Environ. Sci. Technol. 25: References tems in 14 houses over a two-year 1445(1991). period," J. Air Waste Manage. Assoc. 1. California Air Resources Board, "The 40: 740 (1990). Landfill Geis Testing Program: A Sec 10. Garbesi,K.G.;Sextro,R.G. "Modeling ond Report to the Cidifomia Legisla and field evidence of pressure-driven A. T. Hodgson, Dr. Sextro, and ture," Presented at a meeting of the entry of soil gas into a house through Dr. Daisey are staff scientists with Air Resources Botird, Sacramento, CA, permeable below-grade walls," Envi June 8-9,1989. ron. Sci. Technol. 23:1481 (1989). the Indoor Environment Program of 2. Wood, J. A; Porter, M. L. "Hazardous 11. Sherman, M.H.; Grimsrud, D.T. "Mea the Energy and Environment Divi pollutants in class II landfills," JAPCA surement of Infiltration using Fan De sion at Lawrence Berkeley Labora 37: 609 (1987). pressurization and Weather Date," in tory, Berkeley, CA 94720. Dr. Dai 3. Nazaroff, W. W.; Feustal, H.; Nero, Proceedings of the 1st Symposium of sey is the head of the Indoor A v.; Revzan, K. L.; Grimsrud, D. T.; the Air Infiltration Center on Instru Environment Program. K. Garbesi Essling, M. A.; Toohey, R. E. "Radon mentation and Measurement Tech is a doctoral candidate with th^ En treuisport into a detached one-story niques, Windsor, England, October 6-8, ergy and Resources Group, Univer house with a basement," Atmos. Envi 1980. sity of California, Berkeley, CA ron. 19: 31 (1985). 12. Day, P. R. "Particle Fractionation and 4. D'Ottavio, T. W.; Dietz, R. N.; Kunz, Particle-Size Analysis," in Methods of 94720. This manuscript was submit C; Kothari, B. "Radon Source Mea Soil Analysis, Pari I, Black, C. A.; ted for peer review in September surement using Multiple Perfiuoro- Evans, D. D.; White, J. L.; Ensminger, 1988. The revised manuscript was carbon Tracers," in Proceedings of the L. E.; Clarck, F. E.; Dinauer, R. C, received on October 11,1991. 4th International Conference on Indoor Eds., American Society of Agronomy, Air Quality, Berlin (West), August 17- Wisconsin, Chapter 43, 1965.
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