200754900 - Toppenish Creek Well Modification Project

Sponsor: Yakama Nation

Short description: Modify wells by installing deeper grout seals to prevent the drainage of shallow groundwater to deeper aquifers and to restore shallow groundwater which formerly supported springs, streamsflow and raparian habitat. Wells should not interconnect aquifers.

Location: Columbia Plateau province, Yakima subbasin

Budgets: FY08: $337,821 | FY09: $13,602

Primary species:
Anadromous: Chinook: Mid-Columbia River Spring ESU
Anadromous: Chinook: Snake River Fall ESU (threatened)
Anadromous: Pacific Lamprey
Anadromous: Steelhead: Middle Columbia River ESU (threatened)
Resident: Rainbow Trout


ObjectiveDescriptionSubbasin planStrategies
Toppenish Creek well modifications The proposed project is designed to reestablish shallow groundwater flow systems along the middle reach of Toppenish Creek and in the vicinity of the spring line which formerly existed to the south of the community of White Swan. The project will result in increased groundwater discharge to Toppenish Creek, increasing instream flows and improving raparian habitats. It is presumed that increased groundwater discharge will improve stream habitat by moderating stream temperatures and providing nutrients. It is also presumed that the project will provide water necessary to reestablish a raparian habitat similar to that present prior to uncontrolled diversions of surface water from Toppenish Creek was begun. The Yakama Nation Water Resources Program staff has conducted an evaluation of greater then 500 drillers' well logs in the White Swan region. It is estimated that roughly 80% of these wells are of substandard construction due to the installation of too shallow a grout annular seal. This allows the interconnectiin of shallower and deeper aquifers. Both the Yakama Nation Water Code and the Department of Ecology well construction standards state that wellbores shall not interconnect aquifers. The White Swan region, including the middle reach of Toppenish Creek, is located in a groundwater recharge area. Vertical hydraulic gradients are therefore downward. The combination of a downward hydraulic gradient with shallow well seals can allow shallow groundwater to move to deeper aquifers. It is reported that in the past the White Swan region had numerous springs and small streams supplied by shallow groundwater flow systems. Lush raparian areas were also reported present. It is thought that the construction of wells having too shallow of well seals has resulted in the drainage of groundwater from shallow flow systems to deeper aquifers contributing to the disappearance of the springs, small streams and raparian areas formerly present. It is possible through the modification of existing wells having too shallow of well seals to install deeper well seals thereby preventing wellbores from serving as interconnections between shallow groundwater and deeper aquifers. The interconnection of aquifers could also be eliminated by abandoning wells which are no longer in use. Water Resources Program staff are actively seeking funding to modify selected wells in the White Swan region, and to monitor groundwater levels and instream flows to evaluate the effects of aquifer separation through the installation of deeper well seals. The proposed project will modify or abandon 12 domestic wells along the middle reach of Toppenish Creek and begin a groundwater level monitoring program. Streamflow monitoring is currently, and will in the future, being conducted by the Water Resources and Fisheries Programs as parts of other projects. The Water Resources Program proposes to modify or abandon existing domestic wells located along the middle reach of Toppenish Creek. The wells as currently constructed allow the vertical drainage of shallow groundwater to "thief zones" in deeper aquifers. It is thought that by the proper grouting of a well's annular space the interconnection of shallow groundwater with deeper aquifers can be prevented. This should result in restablishing shallow groundwater flow systems within the Toppenish Creek alluvium and underlying Ellensburg Formation. Groundwater within the shallow flow system will discharge to Toppenish Creek downstream of the project area thereby increasing instream flows and moderating stream temperatures, and improve riparian habitats. The project area supported a diverse riparian habitat prior to upstream channel modifications for surface water diversions. These diversions have recently been modified by Yakama Engineering to again allow mountain front groundwater recharge to enter the Toppenish Creek alluvial fan. This groundwater recharge appears to move downgradient along Toppenish Creek until it reaches an area having domestic wells with inadequate annular seals which allows shallow groundwater to flow to deeper "thief zones" within the aquifers of the underlying Ellensburg Formation and Columbia River Basalt. Evaluation of well driller's logs by Water Resources Program staff has identified domestic wells along the middle reach of Toppenish Creek which appear to interconnect shallow groundwater with deeper aquifers. The Water Resources Program proposes to modify 12 domestic wells through the installation of a 4-inch diameter well casing and screen unside the current 6-inch diameter casing, and place a well seal to adequate depth as the 6-inch casing is removed from the wellbore.This concept has been discussed with potential well drillers, and it has been determined that it can be successfully accomplised. Similar techniques have been used elsewhere to successfully separate individual aquifers within multiaquifer systems. Groundwater level monitoring tubes will be installed inside and outside the 4-inch diameter casing. Groundwater level monitoring will show different groundwater levels are present within the shallower aquifer and the deeper production aquifer which are now separated by a grout seal seal where an open annulus previously existed. A well will be abandoned if upon inspection or because of its depth or location it is not thought suitable for modification. Well abandonment will be accomplished by pereforating the 6-inch diameter casing in place and backfilling the well with a cement, bentonite or cement/bentonite grout by pressure grouting. The techniques proposed for use in modifing and abandoning a well are commonly used well construction methods and can be adapted to any area underlain by a layered multiaquifer system. Temporal groundwater level monitoring will be used to evaluate the propsed Toppenish Creek well modification project. Groundwater levels will only be measured in those wells having water level monitoring tubes to prevent water level probes from becoming entangled with the centralizers, spiders, used to keep the pump plumb within a well. Water level monitoring tubes will be installed into at least two aquifers penetrated by a well when it is modified. Currently, the groundwater level in wells selected for modification should reflect that present within the deepest aquifer penetrated by a well as the potentiometric surface, the elevation of the groundwater level within a well, decreases with increasing depth in a groundwater recharge area. The groundwater levels within the "deep" production aquifer should remain approximately the same following well modification. The groundwater level in shallower aquifers should raise to a higher elevation following installation of a deeper well seal as the shallower aquifers are now separated from the deeper aquifer, and the potentiometric surface in a groundwater recharge area is at a higher elevation in shallower aquifers. Groundwater level monitoring will be conducted monthly for the duration of the project. The Bureau of Reclamation constructed 20 wells along Toppenish Creek in 1999 to evaluate the effects that modification of the Olney diversion might have on groundwater leveks within the Toppenish Creek alluvial fan. The groundwater levels in these wells will also be monitored during the project. Toppenish Creek streamflows are currently being monitored as parts of other projects. It is not thought that instream flow data will provide the data necessary to evaluate poroject success due to the short duration of the project, and the effects of natural variation and uncertainty.



  • ISRP: Unranked
  • Council: Not fundable
  • BPA: Not fundable