SGM-SF_2017with 12/20 Revisions

Vapor Intrusion (VI)—Informational Guidance ANSI/AARST SGM-SF 2017 (with 1220 revisions) Soil Gas Mitigation Standards for Existing Homes 63 Informative advisory —Monitoring event procedures described in Appendix C-3 should be used in lieu of a different regimen of monitoring events required by state or other authority. Table A-3 Recommended Post-mitigation Monitoring Events for Chemical Vapor Intrusion Rapid Response indicated if estimated exposure exceeds health protective concentration for short-term or acute exposure No prior assessment Class 3 Continuous or Chronic Risk Class 2 Subchronic Risk Class 1 Acute Risk If suspected concerns exist, Preemptive m itigation may be warranted. Concerns of harmful effects from average low-level exposure across many years (e.g., ≥ 26 years) or repeated exposure events to somewhat higher concentrations Concerns of harmful effects from average exposure across 10% of a life span or repeated exposure events to higher concentrations Concerns of harmful effects from immediate or short-term exposure (e.g., < 30 days) Initial Post- mitigation Monitoring Events For Preemptive mitigation : Initial PFE and system pressure measurements. Indoor air measurements recommended but not required Initial Frequency for a minimum of 1 year: Seasonally until a baseline is established that indicates successful effectiveness. (See Section 16.3) Initial Frequency for a minimum of 1 year: Seasonally (or more frequently) until a baseline is established that indicates successful effectiveness. (See Section 16.3) Initial Frequency for a minimum of 2 years: Seasonally (or more frequently) until a baseline is established that indicates successful effectiveness. (See Section 16.3) Each monitoring event includes measurements of indoor air (contracted by responsible party) and measurements of PFE , system pressure and review for fan and mechanical systems. Note : Longer durations or more frequent monitoring may be warranted dependent upon: a) the degree to which measured concentrations exceed the action level, or b) the degree of observed variability above the action level especially post- mitigation . Note : Radon testing is recommended pre-mitigation. Include in all initial monitoring events If concentrations found can aid evaluations of system effectiveness and confirm a health benefit. Monitoring Event s Thereafter Every year: Mechanical inspection ( PFE , system pressure and mechanical systems.) Every 2 years: Indoor air measurements Increase frequency of monitoring events based on observed variability or evidence of plume movement. In addition, concentrations should be retested if any of the following circumstances occur : • A new addition is constructed or significant renovation occurs; • Heating or cooling systems are significantly altered resulting in changes to air pressures or distribution; • Ventilation is significantly altered by extensive weatherization, changes to mechanical systems or comparable procedures; • Significant openings to soil occur due to: - changes in water control systems (e.g. sumps, drain tiles, shower/tub retrofits, etc.) or, - natural settlement causing major cracks to develop; • Earthquakes, construction blasting, or formation of sink holes nearby; or • An installed mitigation system is altered or repaired. Cessation of biennial indoor air measurements: Biennial Indoor air measurements can be replaced with 5-year test cycles only for 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.