ASR – Iindirect Surface Water Intakes For Water Supply Systems
Many regional and municipal water supply systems are considering incorporating an aquifer storage and recovery (ASR) component into their supply system. ASR is the subsurface storage of very large volumes of excess water when it is seasonally available and the later recovery of that water when it is needed. ASR has many benefits including making more efficient use of seasonally available sources of supply and thus reducing the need for or extending the timeframe for infrastucture (i.e. water treatment plant) expansions to meet peak demands. Many of these potential supply systems are evaluating the use of untreated or partially treated surface waters as the source water for an ASR system. Horizontal wells can provide a superior supply option to either direct surface water intakes or the use of numerous vertical wells situated along a river or canal for this purpose.
Horizontal wells provide a means of filtration if used in conjunction with surface water diversions. Such natural filtration is lacking in direct surface water intake systems. Also, a single horizontal well can typically produce as much as 20 vertical wells completed in the surficial aquifer.
In addition to the filtration provided by horizontal wells, reduction of many undesirable chemical compounds is obtained in the subsurface that would not otherwise occur using direct surface water intakes. Surface water systems typically have greatly fluctuating water quality. In addition to removal or reduction of some undesirable chemical compounds, use of horizontal wells can remove undesirable biological agents such as coliform bacteria and Cryptosporidia and Giardia. The added filtration and chemical/biological attenuation can substantially expedite the permitting process and reduce the need for construction of costly pretreatment systems while providing a more stable, dependable supply of quality water .
Hydrotech can provide a single 8″ horizontal well system 500 feet long, which can typically produce at a sustainable rate of up to 1,000,000 gallons per day. Larger yields can be obtained with larger diameter HDPE pipe and/or longer horizontal well runs.
Thus, the advantages of horizontal wells over both direct surface water intakes and shallow vertical wells are substantial.