EVIDENCE OF A SEWER VAPOR TRANSPORT PATHWAY Findings from Work Performed at the Indianapolis USEPA Research Duplex Midwestern States Environmental Consultants Association Spring Seminar Rob Uppencamp May 3, 2018
Discussion USEPA Indianapolis Duplex Study https://www.sciencedirect.com/science/article/pii/s0048969717309737
EPA Test House 420/422 East 28 th Street
EPA Test House Indy Duplex Residential duplex built in about 1915. Two-story with brick foundation basement. Geology: shallow silty clay and fill underlain by sand and gravel. Hydrogeology: Near Fall Creek groundwater typically 10-15 feet. 10 dry cleaners historically located up gradient. Extensively studied since 2010 under USEPA NERL funding and direction. Geophysical Survey Subject of many USEPA publications and conference presentations over the past 7 years. Latest sewer evaluation effort brought by Tom McHugh (GSI) with funding from DOD through the ETSCP program.
Local Sewer Network
Abstract Sewer lines as preferential pathways for vapor intrusion is poorly understood. Importance of sewer lines for VOC transport has been documented at a small number of sites with vapor intrusion. Sewer lines not routinely sampled during most vapor intrusion investigations. Tracer study and VOC concentration measurements used to evaluate the role of the combined sanitary/storm sewer line in VOC transport. Tracer study demonstrated gas migration from the sewer main line into the duplex. Migration pathway appears to be complex and may include leakage from the sewer lateral at a location below the building foundation. Vapor samples collected from the sewer line demonstrated the presence of PCE and chloroform in the sewer main in front of the duplex and at multiple sample locations within the sewer line upstream of the duplex.
Abstract Test results combined with results from the prior multi-year study of the duplex indicate that the sewer line plays an important role in transport of VOCs from the subsurface source to the immediate vicinity of the duplex building envelope.
Sewers Background Buried utilities as preferential pathways should be considered as part of all VI evaluations (Conceptual Site Model). Historically, utility bedding/backfill material was main focus. More recent evidence of vapor transport within sewers. What is it about sewers? Construction, integrity, etc... Clay, concrete, PVC, brick... Minimal initial testing. Laterals not tested. Eventual leakage ground settles, backfill incorrect, misaligned joints, etc. I&I (Inflow and Infiltration)
Investigating Sewer Backfill For direct buried utility investigation, clusters of three soil gas points can be used to evaluate bedding material: A. directly above/next to the utility in backfill material, B. laterally separated from the utility corridor, and C. just above the groundwater interface. Used to distinguish bulk groundwater transport from a preferential pathway. Not a preferential pathway when surrounding geology has greater or equal permeability.
Sewer Vapor Transport
Conceptual Illustration of Sewer Preferential Pathways A. Sanitary or Combined Sewer B. Foundation or Land Drain A) Most residences (i.e., those without septic tanks), are connected to the sanitary (or combined storm and sanitary) sewer system. B) Some residences have foundation drain systems connected to land drain or storm sewer systems. Although prohibited by current building codes, some residences may have older or illegal foundation drains connected to the sanitary sewer system. Clean-outs and manholes are not shown.
Sewer Preferential Pathway Documented cases of sewer preferential pathways. Floor drain not frequently wetted resulted in a dried out vapor trap and a direct conduit to the municipal sewer system. Preferential pathway was shown to briefly exist in a residence under renovation, until installation of a plumbing trap was completed.
Evidence Prompting Study Battelle Panel (2016) Evidence against a local groundwater source for PCE. Evidence for a sewer preferential pathway. When vapors originate from groundwater, we generally see a clear vertical gradient in groundwater and soil gas. Max conc. In groundwater too low. No vertical gradient in groundwater. PCE concentrations in deep soil gas too high. No vertical gradient in soil gas. PCE concentrations in sub-slab similar to deep soil gas. PCE and chloroform results broadly similar. Floor Drain sample. Effects of sub-slab depressurization. Mass flux analysis.
Early Evidence from Duplex Floor Drain First Floor Drain Test Results: Chloroform = 300 ug/m 3 PCE = 300 ug/m 3 Note: Other drains tested at same time showed much lower VOC concentrations.
FLOOR DRAIN APRIL 2011 April 2011 Drain Test 300 ug/m 3 PCE in Floor Drain >> PCE in 1 st floor drain was higher than sub-slab sample points at that time. Note: On May 10, 2011, all open drain lines were sealed, some with both bentonite and cement plugs 15
USEPA Duplex Sewer Testing Program Field sampling program conducted from June 12 to June 16, 2016. Vapor samples collected from sewer manholes, existing soil gas and sub-slab monitoring points, the sewer lateral line connecting the duplex to the sewer main, and locations inside the duplex. Liquid samples were collected from three sewer manholes and two existing groundwater monitoring wells. The analytical testing program included: on-site analysis of vapor samples, off-site laboratory analysis for vapor and liquid samples, and a tracer study.
USEPA Duplex Sewer Testing Program Vapor Sample Collection Collected from sewer manholes through vent holes in manhole cover or by moving the cover enough to allow passage of sampling tube. Liquid levels were measured using a water level meter. Vapor samples collected at depth of approximately 0.3 m above liquid level or 0.3 m above base of the manhole in cases where liquid did not cover the base outside of the invert flow channel. Vapor samples collected using weighted nylon tubing lowered to the sample collection depth. Prior to sample collection, more than three volumes of air were purged from the tubing using a syringe. Samples were collected in 1-L Tedlar bags or in 1-L Summa canisters.
USEPA Duplex Sewer Testing Program Vapor Sample Collection Collection of vapor samples from the existing soil gas and sub-slab monitoring points involved similar procedures for line purging and sample collection. Sewer lateral line sampled by drilling a hole into the PVC sewer lateral pipe in the basement and installing a sampling port. Indoor air samples collected either by grab sampling with 1-L Summa canisters, or by using a HAPSITE Smart Plus Gas GC/ MS. 55 vapor/air samples were collected. Thirty-nine (39) were analyzed on-site using the HAPSITE GC/MS. Remaining 16 samples collected in Tedlar bags and Summa canisters were shipped to fixed lab for analysis by USEPA Method TO-15.
USEPA Duplex Sewer Testing Program Liquid Sampling and Analysis Groundwater samples were collected from two existing monitoring wells (MW1A and MW1C). Sewer liquid samples were collected from three sewer manholes. All samples were collected using low-flow purge methods. Samples were shipped on ice to a fixed lab for analysis using USEPA Method 8260B. Note: Two significant rain events during project.
USEPA Duplex Sewer Testing Program Tracer Study Evaluate the interaction between the sewer and duplex. Brookhaven National Laboratory Passive perfluorocarbon tracer (PFT) sources and passive capillary adsorption tube samplers (CATS). Multiple PFT sources, each emitting a different perfluorocarbon compound, were deployed in 6 different areas. In the manholes, the sources were attached to a weighted line and suspended approximately 0.5 m above the top of the sewer line. PFT deployed on the first day of the study and remained in place throughout the testing period. CATS were deployed after 4 hrs and retrieved 93 hrs after deployment, then shipped to lab for analysis by GC-Electron Capture Detector (ECD).
USEPA Duplex Sewer Testing Program Tracer Source and Sample Locations PDCB = perfluoro-1,2-dimethylcyclobutane PMCP = perfluoromethylcyclopentane PMCH = perfluoromethylcyclohexane PTCH = perfluorotrimethycyclohexane ocpdch = perfluoro-1,2-(c/s)-dimethyicyclohexane ippch = perfluoro-isopropylcyclohexane
Tracer Study Release and Sample Locations
Results Sampling consisted of 1) VOC concentration measurements of sewer vapor, soil gas, indoor air, groundwater, and sewer liquid; and 2) a tracer study at the sewer manholes and inside the duplex. Complicated by two thunderstorm events on the June 14 & 15, which resulted in 2.4 in. and 3.0 in. of precipitation, respectively. Sewer line connected is a combined storm and sanitary sewer - rain events resulted in very high water flows through the sewer during both events. PCE and chloroform in the immediate vicinity of the duplex Well documented over years of groundwater, soil gas, sub-slab, and indoor air sampling. Concentrations detected in soil gas and sewer during study were similar.
Results PCE & chloroform in the immediate vicinity of the duplex (cont d) Before two storm events, concentrations in sewer were slightly higher than soil gas. After storm events, concentrations in soil gas were slightly higher than in sewer. PCE and chloroform concentrations in sewer lateral in duplex basement were lower than in sewer but higher than indoor air. PCE and chloroform concentrations in groundwater and sewer liquids were measured only after the storm events. PCE concentrations were non-detect or <1 μg/l in all sewer liquid samples. Chloroform concentrations were slightly higher in the sewer liquids (4.4 μg/l) than in the groundwater (1.7 and 2.1 μg/l).
Results (Vapor) Samples collected before two storm events. PCE/Chloroform V = vapor sample (μg/m3) NS = Not sampled.
Results (Vapor) Samples collected after two storm events. PCE/Chloroform V = vapor sample (μg/m3) L = Liquid sample (μg/l). NS = Not sampled.
Results PCE in sewer manholes away from the duplex Analyzed vapor and liquid samples from sewer manholes further upstream of duplex along Central Avenue and other adjacent streets. At least two former dry cleaner sites with documented PCE plumes in groundwater are located on Central Avenue north (upstream) of the duplex. PCE was detected in upstream manholes at concentrations ranging from 0.6 to 353 μg/m 3. The highest PCE concentration (353 μg/m 3 ) was measured in a manhole adjacent to one of the dry cleaner sites. In addition, PCE concentrations above 100 μg/m 3 were detected in several manholes upstream of the two known dry cleaner sites.
PCE and Chloroform Vapor Concentrations Before first rain event. Between first and second rain event. After second rain event.
Results PCE in sewer manholes away from the duplex At duplex and adjacent to former dry cleaners, manhole depths were shallower than groundwater, suggesting PCE at these locations was not attributable to the local infiltration of groundwater into the sewer. Groundwater depths were not available for manholes further upstream. Therefore, it s not clear whether PCE detected in manholes is attributable to local infiltration of soil gas, upstream sources such as infiltration of contaminated groundwater, or wastewater discharge containing PCE. PCE concentrations in the upstream manholes were higher before the two storm events than after. Elevated chloroform concentrations were widely distributed across manholes tested, consistent with discharges of chlorinated water and bleach into the sewer system.
Results Tracer Study Six PFT compounds were used to evaluate air movement within the duplex and between the duplex and the sewer line. Sources and CATS deployed in the two manholes were covered by storm water flow during the two storm events. Uptake for one of the CATS likely affected. CAT not considered for the interpretation of the tracer study results. Evaluated the effect of water inundation on tracer release from sources and uptake by the CATS. No clear difference between sources in sewer mains that were inundated by storm events and sources in house that were not. Suggests that inundation events had only a minor effect on the rate of tracer release from sources in sewer mains.
Results Tracer Study Tracer study demonstrated air exchange between the sewer line and duplex based on detection of tracer released in both upstream and downstream sewer manholes inside the duplex. Sewer to indoor air attenuation factors ranged from <0.001 to 0.006 for the upstream manhole (500x dilution) and 0.010 to 0.021 for the downstream manhole (50x dilution).
Results Tracer Study Sewer to indoor air attenuation factors were similar in the basement and main floor. Storm events resulted in periods of high storm water flows that filled the sewer line. Although tracer study documents gas exchange between sewer line and duplex, attenuation factors measured may not be representative of more typical weather conditions when flows through the sewer are lower. Tracer compounds released into sewer manholes were detected in sewer lateral samples higher than those detected inside the duplex demonstrating migration through the sewer lateral. Tracer detected in the sewer lateral samples indicated similar magnitude of transport into the sewer lateral from the upstream manhole and the downstream manhole.
Results Tracer Study Higher amounts of tracer from the downstream manhole were detected inside the duplex (?). Tracer compound released into sewer lateral inside the basement was not detected in indoor air at any of the four sampling locations. Indicates limited leakage from the sewer lateral lines running through the basement. Instead, suggests that the sewer lateral leaks below the duplex foundation and that sewer vapors then enter the duplex through the foundation.
Conclusions Results from the tracer study demonstrated gas migration from the sewer main line into the duplex. The migration pathway appears to be complex and may include leakage from the sewer lateral at a location below the building foundation. Vapor samples collected from the sewer line demonstrated the presence of PCE and chloroform in the sewer main in front of the duplex and at multiple sample locations within the sewer line upstream of the duplex. These test results combined with results from the prior multi-year study of the duplex indicate that the sewer line plays an important role in transport of VOCs from the subsurface source to the immediate vicinity of the duplex building envelope. Mitigation system still effective.
Thank you! ROB UPPENCAMP Senior Scientist / Risk Assessor o 317 236 2807 c 317 752 3664 e robert.uppencamp@arcadis.com
Questions/Discussion