Territory Stories

Alpurrurulam Community : bore completion report RN 16925 to RN 16927

Details:

Title

Alpurrurulam Community : bore completion report RN 16925 to RN 16927

Other title

Alpurrurulam Community, bore completion report RN 16925 to 16927.

Creator

Burton, S.; Dames & Moore

Issued by

Northern Territory. Power and Water Corporation

Collection

E-Publications; E-Books; PublicationNT; Report No: 39/1996

Date

1996-06-01

Location

Lake Nash

Language

English

Subject

Drilling and boring -- Northern Territory; Groundwater -- Northern Territory; Water-supply -- Northern Territory; Bores -- Northern Territory

Publisher name

Northern Territory Government

Place of publication

Alice Springs

Series

Report No: 39/1996

Format

1 v. : illustration, map ; 30 cm.

File type

application/pdf

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government

License

https://creativecommons.org/licenses/by/4.0/

Parent handle

https://hdl.handle.net/10070/229156

Citation address

https://hdl.handle.net/10070/673304

Page content

The limestone penetrated in the upper portion of RN 16927 is assigned to the Austral Downs Limestone. Dolomite, limestone, siltstone and sandstone intersected in the lower portion of RN 16927 and in RN 16925 and RN 16926 are assigned to the Meeta Beds. The Camooweal Dolomite has probably not been intersected at Alpurrurulam given the great thickness (330 m) of the Meeta Beds indicated by Randal (1966). 6.2 Hydrogeology The standing water level in the bores drilled at Alpurrurulam ranges between 35.8 mBGL and 37.5 mBGL and groundwater salinities range between 770 mg/L TDS and 990 mg/L TDS. Groundwater recharge is unknown, but likely elevated in regions of jointed rock exposure. Regional groundwater recharge is probably most significant at the Georgina River. The groundwater gradient is also unknown, but is probably locally controlled by mounding near extensive rock exposures after rainfall and the regional gradient is probably to the southsouth-west, away from the Georgina River and down the regional dip of the Georgina Basin strata. Jointed units within the Meeta Beds form the production aquifer. Primary porosity is probably negligible in the dolomite units, but likely contributes to aquifer permeability and storage in the sandstone. Some infilling of voids with calcite is evident in rocks exposed at the surface. The aquifer, hosted by the Meeta Beds, is regionally continuous. Local inhomogeneities, indicated by groundwater salinity and fluoride concentrations, indicate that either the aquifer is comprised of local, overlapping, permeable zones, or that groundwater recharge is heterogeneous on a small scale, or both. Geological logging does not indicate discrete permeable zones and confining beds, but does indicate somewhat variable jointing or fracturing which appears to be largely independent of lithology. Groundwater near the north-eastern boundary of Alpurrurulam, at the borefield, contains lower fluoride concentrations than that elsewhere in the community. This area corresponds with strongly jointed exposure of dolomite and limestone and may allow preferential recharge to the production aquifer. Groundwater salinity data is inconclusive in indicating preferential recharge in this area. Groundwater discharge is probably limited to leakage into underlying rocks and to abstraction from bores. Waterholes in the Georgina River are understood to represent ponded surface water and hence do not represent groundwater discharge features. The aquifer is probably not at risk of dewatering, however, under excessive abstraction, natural equilibria which suppress fluoride concentrations near the borefield may be unbalanced and high-fluoride groundwater may be drawn into the production bores. Local water levels may temporarily fall under heavy abstraction. 12


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