SGM-SF_2017with 12/20 Revisions

Vapor Intrusion (VI)—Informational Guidance 65 ANSI/AARST SGM-SF 2017 (with 1220 revisions) Soil Gas Mitigation Standards for Existing Homes A-3.3.3 Use of seasonal information Information gained by the initial seasonal monitoring events can be used to guide protective stewardship choices for subsequent monitoring events by identifying conditions that represent average or worst-case conditions. If radon testing was included in seasonal monitoring and indicated consistency with other soil gas entry, inexpensive radon testing, if deemed acceptable, can sometimes suffice for future monitoring events. A-3.3.4 Indoor Air Testing To reproducibly account for testing variables such as natural day-to-night variability in soil gas entry and dilution after entry, it is recommended to: a) Conduct short-term indoor air measurements under closed-building conditions for durations that should be no less than about 2 days; b) Conduct at least one measurement in the lowest occupiable location within the home for use as the most reproducible measurement when evaluating seasonal measurement differences; c) Follow appropriate guidance for sampling and laboratory analysis, such as EPA TO-15 and TO-17 15 ; d) Conduct measurements of ambient outside air sufficient to characterize the influence of ambient concentrations on indoor measurement results; and e) Use care to reduce influences on test results such as chemicals contained in household cleaning products. Note—See Companion Guidance for guidance examples that help to control test conditions. A-3.4 Ongoing stewardship A-3.4.1 Mechanical Systems It is recommended that inspection be conducted yearly for mechanical operations and system integrity, to include PFE and system pressure measurements and related mechanical systems and components. A-3.4.2 Indoor Air Measurements It is recommended that the monitoring events include measurements of indoor air at least every 2 years. A-3.4.3 Cessation of Biennial Indoor Air Measurements It is recommended that biennial retests for mitigated buildings be maintained for as many years as the system is operational unless replaced with 5-year test cycles for only those buildings where: a) systems have shown continued effectiveness to the satisfaction of jurisdictional authorities ; and b) the mitigation systems are operated under a written operation and maintenance (O&M) plan that includes regular monitoring of mechanical equipment and requires a professional's signature verifying that systems continue to function in the same manner as the last test. A-3.4.4 Additional Monitoring Events Informative advisory —It is recommended to conduct additional monitoring events: a) based on observed variability or evidence of plume movement; and b) if any of the following circumstances occur: ü a new addition is constructed or alterations for building reconfiguration or rehabilitation occur; ü heating or cooling systems are altered with changes to air distribution or pressure relationships; ü ventilation is altered by extensive weatherization, changes to mechanical systems or comparable procedures; ü sizable openings to soil occur due to: — groundwater or slab surface water control systems are added or altered (e.g., sumps, drain tiles, shower/tub retrofits, etc.); or — natural settlement causing major cracks to develop; ü earthquakes, construction blasting or formation of sink holes nearby; or ü an installed mitigation system is altered or repaired. 15 EPA/600/4-90/010 1990 Compendium of Methods for the Determination of Air Pollutants in Indoor Air, and EPA/625/R-96/01b 1999 Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air - Second Addition