Test Pumping: Comparing the Farmer Test, Constant Head Test and SANS 10299-4:2003 methodologies with regards to estimating groundwater abstraction. Data, analyses and recommendations.

Estimating pumping rates for the purpose of equipping boreholes with suitable pumps that will not over abstract either the boreholes or the aquifer(s) that are intersected is often assessed through test pumping of the boreholes prior to pump selection. While the South African National Standard has guidelines on the methodologies and durations of these tests (SANS 10299-4:2003), many production boreholes in the agricultural and industrial sectors are still equipped based upon so called Farmer Tests or Pump Inlet Tests (PIT), often of a short (6-24 hour) duration. These tests are also frequently and incorrectly confused with a Constant Head Test (CHT), both of which are different in methodology to SANS 10299-4:2003 testing, which relies to a high degree on data collected during a Constant Discharge/Rate Test (CDT or CRT) and recovery thereafter. The study will assess differences in test pumping methodology, data collection, analysis methodology and final recommendations made between Farmer Tests and SANS 10299-4:2003 methodology tests for 20 boreholes in which both tests were performed. The selected sites cover a variety of geological and hydrogeological settings in the Western Cape. Test comparisons include boreholes drilled into the Malmesbury Group, Table Mountain Group and Quaternary alluvial deposits, with tested yields ranging from 0.5 – 25 L/s.