Drilling at Rocky Hill Power and Water block (NT Portion 4704) was undertaken to investigate the viability, or otherwise, of this site for future production bores for the Alice Springs town supply. Nested discrete interval piezometers were also installed at various depths for ongoing hydrogeological appraisal. On commencement of this program it became apparent, due to the monotonous nature of the sandstones and lack of any readily distinguishable marker beds within the sedimentary succession, that identification of stratigraphic horizons intersected by drilling would be difficult. Targeting of particular stratigraphic formations has been crucial for the success of production bores at the current Alice Springs public water supply borefield at Roe Creek. As Rocky Hill lies along geological strike from Roe Creek both new and previous drilling results were assessed for correlation with Roe Creek hydrogeology. This was achieved by careful description of drilling chip samples and collection of down hole gamma logs from the new investigation holes and from many previously drilled holes for which previous gamma log data was of variable quality. While still a difficult task, the new gamma log data allowed correlation between bores and usually identification of the top of the Mereenie Sandstone Unit B formation. On the basis of this correlation effort and a review of relevant Amadeus Basin geological literature, Rocky Hill lithology is considered analogous to the well-studied Roe Creek area. This is a somewhat simpler explanation of geology than presented in some previous studies. This explanation also links and reconciles previous studies at Roe Creek to help understand the hydrogeology of Rocky Hill. However, while both areas have a similar thickness of Mereenie Sandstones Unit C and B, the Mereenie Sandstone Unit A, present at Roe Creek, is absent at Rocky Hill. Furthermore, the portion of fractured high yielding Mereenie Sandstone Unit C used for production bores at Roe Creek, is yet to be encountered at Rocky Hill. Drilling data, however, indicates that the Mereenie Sandstone Unit B is a significant aquifer at Rocky Hill, although sanding problems and aquifer damage from mud drilling are technical difficulties encountered when drilling in the upper part of this unit. The lower part of this unit seems stable if drilling with mud is necessary to place screens for a water supply. Short of discovering a zone of high yielding fractured Mereenie Sandstone Unit C, the best chance for successful production bores at Rocky Hill is to employ the approach used at Roe Creek in the 1970s and 1980s of setting a casing string above and then drilling on with air an open hole section that straddles the contact between Mereenie Sandstone Units C and B. The Mereenie Sandstone Unit C is, however, a prospective aquifer in its own right at Rocky Hill as there are some significant yields recorded for a few bores when drilling this unit. Drilling with air through the prospective Mereenie Sandstone definitely provides higher yielding bores at both Roe Creek and Rocky Hill. The results of drilling an investigation hole 3 km to the east of the Power and Water block indicates Rocky Hill viticulture activities lie along strike of the known high yielding Mereenie aquifer zone earmarked for future Alice Springs drinking water supplies. This result should be considered when assessing contamination risk as it indicates the connection between viticulture and drinking water reserves might allow relatively rapid movement of salts.,
Notes
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Table of contents
1. Introduction, 2. Previous Work, 3. The case for Ooraminna, 4. Roe Creek to Rocky Hill Correlation, 5. Investigation 2017 - 2019, 6. Drilling Appraisal of Mereenie at Rocky Hill PWC block, 7. Conclusions, 8. Recommendations and Acknowledgements, 9. References, 10. Appendices,,
Language
English,
Subject
Rocky Hill,
Alice Springs,
aquifer,
drinking supplies,