Scholarly article on topic 'Peer review report 2 On “Groundwater methane in a potential coal seam gas extraction region”'

Peer review report 2 On “Groundwater methane in a potential coal seam gas extraction region” Academic research paper on "Earth and related environmental sciences"

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Academic research paper on topic "Peer review report 2 On “Groundwater methane in a potential coal seam gas extraction region”"

Journal of Hydrology: Regional Studies 3S (2015) 120-122

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Contents lists available at ScienceDirect

Journal of Hydrology: Regional Studies

journal homepage: www.elsevier.com/locate/ejrh

Peer Review Report

Peer review report 2 On "Groundwater methane in a potential coal seam gas extraction region"

1. Original Submission

1.1. Recommendation Minor Revision

2. Comments to Author:

Edit suggestions

The approach takes on an environmental bias, OK but need to be sure it reflects solid baseline science. Be sure the intro includes the need for baseline data, rather than a lot of background info on CH4 origins. The general assumption seems to be that future development will be CSG in the WCM, OK, but this does not take into account known conventional gas resources in the KCSS (also potential conventional and unconventional resources below the WCM).

#90: "Since CSG groundwater is enriched in CH4, salts and heavy metals, these constituents may travel via groundwater pathways into adjacent waterways" revise. CSG groundwater can be on the low end of brackish (see Owen et al., 2015). It is also possible that CSG aquifers are receiving waters from adjacent aquifers, rather than the CSG to other aquifer pathway. In fact, after water extraction for CSG, it is more likely that groundwater flow path will flow into CSG aquifer, not out of.

# 95 - 97. Brackish WCM water can be of agricultural value, as is the case in the Surat. i.e. it's not just about the low salinity water.

#118: Australian aquifer system......no meaning.. .should it be something like......"a catchment based study with

alluvial and sedimentary bedrock aquifers in an Australian setting".

#120: which aquifer? Bedrock, between formations, bedrock to alluvium.. ..be more specific.

#127: the intro is very global which is OK. But it would be useful to have a section 2 that is "Previous work in the area" this gets lost in the text. Several theses (Drury; Brodie on basalts), govt reports etc. #131 + the study is really focused in the northern part of the RRC? #144: RRC actually overlies the CMB.. .which is a large sedimentary basin etc. #154: this is the wider RRC.. .and includes Bungawalbin subcatchment. #208: from the unconsolidated sediments including those of the drainage system.?? #421: .. ..WCM.. .and which outcrop towards the edges of the catchment... #485:.......denitrification, manganese....

#540: however, there are some hydrogeological differences in Australian settings... Minor points.

The word "since" is often poorly used here, and could be better replaced by "because" or "as" for a more clear meaning. Fig. 2 A problem here is that the samples are from various aquifer types, or mixed waters. Maybe add "Fig 2c shows water type indicating aquifer type".

Fig. 3. caption could contain a note."two general groupings are evident......."

Refs used look to be appropriate in type and scope to cover this topic.

DOI of the original article:http://dx.doi.org/10.1016/j.ejrh.2015.06.022.

2214-5818/$ - see front matter http://dx.doi.org/10.1016Zj.ejrh.2015.12.043

Could add this: Moya, C.E., Raiber, M., Taulis, M. and Cox, M.E. 2015. Hydrochemical evolution and groundwater flow processes in the Galilee and Eromanga basins, Great Artesian Basin, Australia: A multivariate statistical approach. Science of the Total Environment, 508, 411-426.

Comments/suggested revisions

#1 Overall is well edited and clearly written. It is a relatively brief paper, and to a degree is descriptive. However, some useful information on monitoring parameters has been established.

#2 The study provides a good overview of background methane data prior to any CSG extraction. Baseline information is very important and the baseline information presented here is valuable. The paper, however, doesn't stress this enough and the reader is distracted from the baseline information with some speculative discussion on processes. There are also quite a few unsupported statements on hydrology and CSG, plus a non-scientific bias in the presentation.

#3 The overall idea of determining baseline conditions is a good .. .but if baseline conditions, need to also sample from the WCM and directly determine what the possible contaminants might be. Therefore determine whether there is some influence on the upper aquifers (KCSS, Piora and alluvium) from the WCM. This could account for variability within the WCM and give some basis as to whether future changes were related to CSG or other.

#4 The study is described as the Richmond River Catchment, but there are only three bores? sampled from the southern (Bungawalbin) subcatchment. Conditions in this area may be quite different from the rest of the catchment proper.

#5 Analysing methane samples for 2H as well as 13 C would help to give a clearer indication of the origin of methane and enable direct comparison with existing methane isotope data from exploration bores.

#6 There is a lot of focus on the 13C-CH4 isotope, but no data on 2H-CH4 or the relative concentrations of CH4 to other hydrocarbons. The latter are needed to make definitive conclusions about biogenic/thermogenic origins. The 13C-CH4 may be indicative of different pathways/origins, but it is important not to reach conclusions without the other data. Suggest revise all conclusions pertaining to 13C-CH4 and present options/possibilities of the 13C-CH4 signature. The value of this paper is in the baseline data for each geological unit. There is too much discussion on thermogenic/biogenic signatures and processes appears as speculation without other data and more WCM data.

#7 There is no WCM data presented in the entire study which is a major limitation. The study focuses on CH4 distribution in different geological features and shows it to vary. So it is possible that the WCM CH4 and CH4 isotopes also vary? This is the case for the Surat (see Hamilton 2014 and Golding 2013). While previous work suggests Clarence-Moreton (C-M) WCM CH4 in the local area is thermogenic, the paper doesn't identify where (location) this information refers to, relative to the other geological units in the study area. If no WCM is available, in order to address this issue, restrict data comparisons with the limited WCM data to a smaller section at the end, and also reduce discussions of thermogenic vs biogenic.

# 8 A suggestion is include the published WCM data in the plots, particularly the Piper plots and methane plots, so some preliminary comparisons can be made.

# 9 To move the paper a bit more towards a baseline reference "tool".... could include some reference tables or figures that allow readers to use it as a baseline data information source. For example, a basic 13C-CH4 conceptual figure, with lines showing the distribution/range of 13C-CH4 in each geological unit would be useful. A table summarising the data for each geological unit would also be useful.

#10- 120 -123 This hypothesis is not really needed here.. .and is not tested. Remove or reword. In any case, moving methane is unlikely to affect groundwater if rapid (ebullition) transport is occurring. Is the meaning actually.. ..that by describing baseline hydrochemistry and CH4 characteristics, it can be used as a baseline tool to assess any potential impacts?

#11- 153-157 This is a leading statement, need to confirm and present some the facts. Note: (a) agriculture probably takes more water from the basin than CSG will. In the Surat, twice as much water is taken for agriculture than CSG. (b) will the WCM water is used for any other purposes; (c) from Figure 1 it is clear that the WCM underlies all other aquifers assessed in this study. The authors are linking potential CSG impacts with potential groundwater resource problems for the local community. (d) it is not clear where the CSG exploration wells are located, and at what depth the CSG extraction might take place.

#12- 204+ Section 2.3 Experimental strategy. A table with the number of bores and samples from each geological feature would be useful. Also need to make it clear most bores used are in alluvium.

#13- 274 - 276. a highly speculative statement and is not backed up or even supported by studies in other areas. In the Surat the WCM hydrochemistry varies, and in many areas the CH4 concentration is very low if not non-existent. Suggest reword and highlight that WCM groundwater may or may not have any methane, or omit this sentence.

#14- 279 - 280. Check Owen et al., 2015 .. .this shows that some CSG groundwater have low HCO3, with Cl being the dominant anion. Also this paper discusses small increases in Ca and Mg and relationships with pH. Van Voast presented important seminal work on CSG hydrochemistry. Kinnon et al., 2010 only fleetingly mentions CSG hydrochemistry, and Hamawand doesn't really go into much detail. Maybe remove Kinnon et al., 2010 as a reference..it refers to the Bowen Basin with little on hydrochemistry.

#15- 385 - 386. The CH4 may have migrated from the WCM, but this is purely speculative without any other supporting

info. The next sentence then highlights that coal and plant fragments could be the source of CH4...........merge these two

sentences, presenting the two possible sources as options.

#16- 452 - 455.............present oxidation as a possible option only, and then discuss other options also.

#17- 521 Section 3.5 Implications. Need to be very careful with this. OK to address potential CSG use impacts, but the paper doesn't address the issues discussed in this section, so it appears speculative. Parts of this section could be easily integrated into the introduction and conclusions where appropriate and relevant to the data presented in this study.

#18- 567-569. This sentence is somewhat speculative given that no WCM data is provided in this study, that CH4 isotope signatures may vary in the C-M WCM, as they do in the Surat. Using the CWM CH4 signatures as a tracer is only appropriate when the isotopic spatial distribution of WCM in the C-M is better understood.. ..and is not the main focus of the paper.

Malcolm Edward Cox (PhD)1

Queensland University of Technology, School of Earth, Environmental & Biological Sciences, 2 George St, 4000,

GPO Box 2434, 4001, Brisbane, QLD, 4000, AUSTRALIA 1 +61 7 3138 1649, Mobile: 0421974628; fax: +61 3138 1535.

Available online 20 December 2015