Conclusions and Suggestions for Future Work


Groundwater simulations show that commingling wells are a significant and likely dominant cause of groundwater level declines in the study area. Further, the model allowed evaluation of vulnerability and possible management scenarios for restoration of aquifer water levels. The main conclusions are that the value of artificial recharge or aquifer storage and recovery will be greater if at least some commingling well repairs are accomplished first and that there are locations where repair of commingling wells is of higher value than in other areas. Highest vulnerability and highest value wells for repair are generally near the Oregon Water Resources Department administrative area with diminishing vulnerability and value upslope to the south.


Although the groundwater-flow simulation model was adequate for the analyses described in this report, the model has limitations that prevent its use for transient simulations, making it inadequate to predict the time necessary for the system to recover. The time for recovery likely will be different from the time it took for the system to decline because the rate of decline was controlled by how fast water leaks from the system, but if the system were completely repaired, the system recovery time will be controlled by the rate of recharge. In practice, the rate of recovery also will be limited by the rate of repair.


Potential groundwater-flow model improvements include better time-variable representation of commingling wells, the ability to represent the basalt aquifers as unconfined to allow dewatering of these aquifers to supply other aquifers through commingling wells, and representation of the apparent hydraulic conductivity contrast upslope of the Oregon Water Resources Department administrative area. Model calibration can be improved by establishing stream gages at the mouths of Mosier, Rock, and Rowena Creeks. 


If commingling well repairs are accomplished, groundwater levels and streamflow also should be monitored. Ideally, a specialized monitoring network would be developed. These monitoring wells should be open to only one aquifer, and there should be a minimum of one monitoring well per aquifer. A potential alternative would be to install recording submersible pressure transducers at select wells in aquifers during well decommissioning. Collection of this data can become valuable for evaluation of the repair and recovery process.


First posted March 1, 2012