13
Permeable Reactive Barriers
regarding cost is made available to private users, it is extremely rare to see
detailed cost breakdowns that would allow the reviewer to judge the realism of the cost elements.
Thus, the costs of remediation summarized in Table 1.1 are approximate
only and are likely to vary with the contaminated site, including the local
hydrogeology of the region and the depth to groundwater.
The potential for aquifer restoration decreased with increasing complexity of the aquifer. In 1993, the US Environmental Protection Agency
issued technical impracticability (TI) waiver guidance (USEPA, 1993). This
guidance specified that the waivers were appropriate for sites where the
agency deems that restoration of groundwater to drinking water standards is technically impracticable. As of August 2012, the USEPA issued
91 TI waivers, 85 of which applied to groundwater (USEPA, 2012). The
majority (67%) of the TI waivers granted were related to VOC contamination. In Australia, regulatory authorities have approached groundwater
remediation using a risk-based strategy where Remediation to the Extent
Necessary (SA EPA) or CleanUp to the Extent Practicable (EPA Vic) is recognized as the most reliable and reasonable approach to in situ manage
contaminated groundwater. Where groundwater is remediated to the
extent necessary, natural attenuation of contaminants becomes the strategy driving remediation. There has nevertheless been significant concern
with regard to residual groundwater contamination postremediation and
strategies that need to be put in place to minimize the potential impact of
contaminants remaining in the environment, and in particular, the endpoints for remediation of sites contaminated with NAPL. This has led to
recognition of the need for new innovative solutions for the treatment of
contaminated groundwater.
1.4 PRBs: Emerging Technology for Groundwater Remediation
During the past decade and a half, PRBs have been emerging as an alternative passive in situ but effective remediation technology in the United States
and Europe. As a consequence, this technology has also found its way to
Australia. It is based on a relatively simple concept which includes underground construction of a vertical treatment wall using a reactive material
in the subsurface vadose zone at a location that intercepts the groundwater contaminant plume (Figure 1.1) (Baciocchi et al., 2003; Birke et al., 2003;
Meza, 2009; Thiruvenkatachari et al., 2008). Groundwater remediation technologies listed in Table 1.1 range from “least green” (pump-and-treat) to
“most green” (monitoring natural attenuation [MNA]). ITRC (2011) reported
PRBs lie next to MNA in terms of their green characteristics and are considered particularly sustainable when used for 10 years or more. PRBs are
Permeable Reactive Barriers
regarding cost is made available to private users, it is extremely rare to see
detailed cost breakdowns that would allow the reviewer to judge the realism of the cost elements.
Thus, the costs of remediation summarized in Table 1.1 are approximate
only and are likely to vary with the contaminated site, including the local
hydrogeology of the region and the depth to groundwater.
The potential for aquifer restoration decreased with increasing complexity of the aquifer. In 1993, the US Environmental Protection Agency
issued technical impracticability (TI) waiver guidance (USEPA, 1993). This
guidance specified that the waivers were appropriate for sites where the
agency deems that restoration of groundwater to drinking water standards is technically impracticable. As of August 2012, the USEPA issued
91 TI waivers, 85 of which applied to groundwater (USEPA, 2012). The
majority (67%) of the TI waivers granted were related to VOC contamination. In Australia, regulatory authorities have approached groundwater
remediation using a risk-based strategy where Remediation to the Extent
Necessary (SA EPA) or CleanUp to the Extent Practicable (EPA Vic) is recognized as the most reliable and reasonable approach to in situ manage
contaminated groundwater. Where groundwater is remediated to the
extent necessary, natural attenuation of contaminants becomes the strategy driving remediation. There has nevertheless been significant concern
with regard to residual groundwater contamination postremediation and
strategies that need to be put in place to minimize the potential impact of
contaminants remaining in the environment, and in particular, the endpoints for remediation of sites contaminated with NAPL. This has led to
recognition of the need for new innovative solutions for the treatment of
contaminated groundwater.
1.4 PRBs: Emerging Technology for Groundwater Remediation
During the past decade and a half, PRBs have been emerging as an alternative passive in situ but effective remediation technology in the United States
and Europe. As a consequence, this technology has also found its way to
Australia. It is based on a relatively simple concept which includes underground construction of a vertical treatment wall using a reactive material
in the subsurface vadose zone at a location that intercepts the groundwater contaminant plume (Figure 1.1) (Baciocchi et al., 2003; Birke et al., 2003;
Meza, 2009; Thiruvenkatachari et al., 2008). Groundwater remediation technologies listed in Table 1.1 range from “least green” (pump-and-treat) to
“most green” (monitoring natural attenuation [MNA]). ITRC (2011) reported
PRBs lie next to MNA in terms of their green characteristics and are considered particularly sustainable when used for 10 years or more. PRBs are