Abstract:
An ASR metric and site rating index applied to over 120 municipal and
agricultural locations across Oregon, combined with comparison to case study data from
existing ASR sites, indicate that more than 50% of selected sites are hydrogeologically
suitable for ASR. The ASR metric is a ratio of aquifer storage to the rate at which surface
water is available for injection, with a result greater than one indicating sufficient aquifer
storage. The site rating index evaluates aquifer hydraulic parameters as well as economic
and engineering factors, and produces a percentage of ideal conditions. While economic
and engineering factors can determine ASR feasibility, transmissivity, depth to static
groundwater level and the desired injection rate are the controlling hydraulic parameters
for hydrogeologic ASR suitability. However, these factors have a flexible relationship;
for example, high transmissivity can compensate for small depth to groundwater and vice
versa.
In Oregon, most existing ASR sites target Columbia River Basalt interflow zones,
where transmissivity is high and native groundwater quality is generally suitable for
drinking water. These units are also prone to groundwater decline due to over-pumping,
which essentially creates storage for ASR. Results show that suitable potential sites
correspond predominantly with Columbia River Basalt, Quaternary and late Tertiary
sediments. Potential aquifer storage identified by this study is approximately equal to Oregon's annual public water supply in the year 2000, or 5 x 10⁸ m³ (160 billion gallons
or 502,809 ac-ft). This suggests that ASR expansion in Oregon can significantly increase
public supply and provide flexibility in the timing of water availability.
