**3. Studies of indoor radon emanation levels in South Africa and possible mitigation system**

Over the years, mining activities and mine dumps without proper regulation or disposal have led to the rise in background activity due to the presence of naturally occurring radioactive materials (NORM). Naturally occurring radioactive materials are in varying activities in soil, rocks, and underground water. In mining activities, when NORMs are processed, their activity becomes increased and is known as TENORM. NORMs contain radionuclides from the decay of uranium-238, thorium-232, and potassium-40, which result in the formation of radium and radon, posing a health hazard to exposed workers or nearby communities.

Many of the gold mines in South Africa process NORMs, and there is lot of mine waste, of which some is closer to communities in the Gauteng province [19]. There are abandoned mines of which some communities or instance Tudor-shaft houses build

*An Overview of Radon Emanation Measurement System for South African Communities DOI: http://dx.doi.org/10.5772/intechopen.109065*

on top of mine tailings. An intervention of government and regulatory body in terms of regulating mines especially waste and dust control is necessary for the lessening of health threat by radioactive materials from contaminated sites. Maximizing distance between the mine and communities and restricting access to abandoned mine dumps or tailing dams help in preventing NORMs from reaching dwellings.

#### **3.1 Radon emanation mitigation system**

Radon mitigation system is a set of steps designed with a goal to achieve the reduction of radon in buildings in order to minimize the risk of lung cancer as seen in **Figure 4**. USEPA [2] recommends that radon levels of 148 Bq/m3 (4 pc/l) or above in buildings must be reduced by radon mitigation system, also radon levels between 74 Bq/m3 (2 pc/l) and 148 Bq/m3 (4 pc/l) are to be considered for radon reduction, as no level of radon is safe.

For the application of radon mitigation systems on houses, how the house is constructed in terms of its foundation, as seen in **Figure 5**, determines the mitigation system. There are mainly three types of house foundation, namely:


**Figure 5.** *Foundation types [21].*

USEPA [2] recommends radon reduction methods that prevent radon from entering the house rather than a method that deals with radon when it has entered the house. A Radon Specialist runs diagnostic test to check possible pathways where radon emanates by shooting chemical smoke into cracks, holes, or drains and observing possible emission points. Then mitigation methods are followed.

### *3.1.1 Basement or a slab-on-grade foundation*

For house foundations that are basement or a slab-on-grade foundation type, a radon mitigation system applicable is commonly one of four types of soil suction: active or passive sub-slab suction, drain-tile suction, block-wall suction, or sumphole suction [2]. The sub-slab suction also known as sub-slab depressurization is a commonly used system whereby holes are drilled on the foundation of the house to beneath the foundation (to crushed rocks or soil), for insertion of suction pipes. Number of suction pipes installed depends on how radon air can be extracted from beneath the house concrete or slab with the use of the radon vent fan connected to the suction pipes to the air outside. Drain tiles or perforated pipes are commonly used in some homes for directing water away from the foundation. Therefore, suction on these pipes or tiles can effectively reduce radon levels.

Block wall suction is a radon mitigation system that is good for houses with basement where their walls are made of hollow blocks. The block wall suction system consists of a fan and ductwork, radon air is drawn from the hollow blocks of the basement and vented outside through exhaust fan. The block wall suction system is advantageous over other mitigation system as it prevents radon from reentering the building [22].

#### *3.1.2 Crawlspace*

Sub-membrane suction system is a mitigation system ideal for houses without basement. A high-density polyethylene plastic sheet is used as a radon reduction barrier by covering the exposed dirt or soil on the floor and also the walls as seen in **Figure 6**. Then, suction pipes are installed through the plastic sheet to depressurize the soil and draw the radon gas outside the house through installed radon fan and suction pipe [23].

*An Overview of Radon Emanation Measurement System for South African Communities DOI: http://dx.doi.org/10.5772/intechopen.109065*

**Figure 6.** *Example of sub-membrane suction system [23].*

Other types of radon mitigation systems applicable to any house foundations include sealing, natural ventilation, house or room pressurization [2].

The sealing of cracks and openings method to is the primary part of most radon mitigation systems. Identification of areas where there is radon entry is mostly not easily detectable as cracks happen overtime. Sealing of cracks or voids minimizes the flow of radon into the house.

House or room pressurization system keeps radon air trapped in the basement by the blowing of the air into the basement. The limitations of the technique affecting its effectiveness are the house construction, appliances in the house or house occupants' lifestyle.

Natural ventilation happens in all houses. Ventilation for radon reduction can be improved by opening doors, windows, and vents on lower floors. When windows and doors are closed, radon concentration returns to its previous value in about 12 hours [2].
