SGM-SF_2017with 12/20 Revisions

3 SGM-SF SGM-SF Discussion CG SECTION 4: GENERAL PRACTICES 4.1 Assemble Building Information 4.2 Proposals 4.3 Notification and Hazards 4.4 Jurisdictional Authorities and Codes Existing measurements and building specifications are important to design of any soil gas mitigation system. Responsible proposals, notification to occupants and compliance with jurisdictional codes and statutes are components when providing professional service. CG SECTION 5: SYSTEMS DESIGN 5.1 Health and Safety 5.2 Long-Term Considerations 5.3 Appropriate Systems 5.4 Nondestructive Investigation 5.5 Diagnostic Investigation 5.6 Design Decisions Design features should facilitate long-term ease in maintaining, operating and monitoring effectiveness of the system. Nondestructive and diagnostic Investigations provide information to informmitigation strategy and design decisions. Discussion Pressure Field Extension (PFE) CG 5.5 ASD designs PFE evaluations help to characterize conditions under a slab or membrane. PFE evaluations include consideration that: 1. Conditions at one location under a slab or membrane can be very different at other locations across the floor; 2. You cannot tell for certain the degree of contributions to indoor soil gas concentrations that are coming from other foundation areas to the building; 3. PFE evaluations conducted in mild weather during the daytime will often have different results than those conducted under heating conditions across colder seasons. Other considerations include: 1. Restricted or blocked PFE due to tight soil or barriers such as footings; or 2) Diminished or lost PFE due to unclosed openings between soil gas and indoor or outdoor air. Note—On occasion, PFE is similarly lost at large void spaces under a slab due to fill settlement or, in certain regions, due to natural caves, cavities or highly permeable stone aggregates that extend deep into the earth. Understanding Permeability Range of Hydraulic Conductivity of Natural Soils USCS Soil Type Hydraulic Conductivity Range Permeability description class gallons per day/ft 2 GP Uniform gravel 4,000 to 20,000 High GW Well-graded gravel 1,000 to 6,000 Moderate to high SP Uniform sand 100 to 4,000 Moderate to high SW Well-graded sand 20 to 2,000 Low to moderate SM Silty sand 20 to 100 Low SC Clayey sand 20 to 20 Low to very low ML Silt 1 to 2 Very low CL Clay 0.02 to 0.2 Very low to impermeable This table helps illustrate the relative differences you can encounter that dictate the ease of extending a vacuum across distances. Those highlighted with gray present challenges in achieving PFE.