Groundwater Ambient Monitoring & Assessment (GAMA)
Domestic Groundwater Well Sampling Groundwater Ambient Monitoring & Assessment Program
Northern Sacramento Valley; view is eastward toward Lassen Peak.
In 2012, the Groundwater Ambient Monitoring & Assessment Priority Basin Project (GAMA-PBP) began water-quality assessments of shallow aquifers, the groundwater resources typically used for private domestic and small system drinking-water supplies. These groundwater resources typically are shallower than the groundwater resources used for public drinking-water supplies.
GAMA-PBP is designed to identify where and to what extent water quality inside groundwater aquifers meets benchmarks that have been established for drinking water. Results of GAMA-PBP sampling are used to determine how groundwater quality is changing and to help explain patterns in chemical concentrations at the basin scale.
What We Want to Learn
For these studies, the USGS is sampling domestic wells that we expect to draw water from the shallow part of the aquifer. As in the deep aquifer study, the new study is defining the percentage of the water source with water quality above drinking water benchmarks.
This is important for several reasons:
- It provides information about which communities may need groundwater treatment systems.
- Shallow and deep groundwater slowly mix, so knowing more about the shallow system can help interpret trends in the entire groundwater system.
- Regulatory programs are in place to protect groundwater quality; understanding the complete resource can help determine if management systems are working.
Northern Sacramento Valley Area Groundwater Quality
Sampling Underway Winter/Spring 2018/2019
The Northern Sacramento Valley domestic-supply aquifer study includes two study areas — the Redding area and the Red Bluff area. The areas are separated geologically by the Red Bluff arch, a buried geologic structure that creates a groundwater divide (California Department of Water Resources, 2014)[PDF, 43MB]. Water that recharges the aquifer north of the arch flows into the Redding area aquifers and recharge water south of the arch flows into the aquifers of the North Sacramento Valley area.
In 2007-2008, GAMA-PBP sampled the public-supply aquifer zone (about 200-400 feet deep) in the Northern Sacramento Valley. That part of the aquifer typically supplies water used for public drinking water.
Results of that study can be viewed here to get a sense of water quality in public-supply aquifers (note that the public-supply aquifer study area is different from the new domestic-supply aquifer study area). In general, <1% of the deep aquifer area contains concentrations of organic constituents above human health benchmarks. About 2% has concentrations of inorganic constituents above the benchmarks. Groundwater quality results presented by GAMA-PBP represent the raw (untreated) resource. Groundwater delivered for public-supply is treated; therefore, people are not drinking this water directly from the ground.
Overview of water-quality results presented in USGS Fact Sheet 2011-3004.
Groundwater Well Sampling Area
What to Expect as a Participating Well Owner
Volunteer well owners who participate in the study will receive a free chemical analysis of their well water.
Before releasing data or reports to the public, the State Water Resources Control Board (SWRCB) and USGS will provide results to individual well owners. Well owner information will be kept confidential.
If you choose to participate, your first step will be a conversation with a USGS scientist about the following details:
- Well construction: For example, well depth and depth to perforation. If you don't have a well completion report, we can look it up at the California Department of Water Resources archives.
- Sampling access: Is there a place to collect a raw groundwater sample from your well? Typically this is a spigot or threaded plug between the well and any treatment system. A USGS scientist can help determine this with you at your well.
- Pipe access: Can we measure the depth to water?
- Water flow: Can the pump be run continuously for about an hour?
If your well can be used in the study, we will make an appointment to visit your well with our field team and mobile laboratory to conduct sampling.
How and Why
There are several things we need:
- Well Construction Details
For example, well depth and depth to perforation. If you don't have a well completion report, we can look it up at the California Department of Water Resources archives.
- Sampling Access
A place we could sample water from, typically a spigot or threaded plug between the well and any treatment system.
- Pipe Access
Can we measure the depth to water?
- Water Flow
Can the pump be run continuously for about one hour?
What Well Owners are Saying
- "Thank you for the drillers log, I thought my well was more shallow. I must be thinking of the pump depth."
- "I am drinking bottled water now and I shared my results with my neighbors. I am so glad I ran into you that day. I would still be drinking that water unknowingly. I always felt the water was actually really good because it tastes so good."
- "Thank you! I will talk to our well guy to compare it to the pump depth."
The Sacramento Metropolitan Shallow Groundwater Study consists of three groundwater basins with a relatively high density of domestic wells. A total of 49 wells were sampled from August through November 2017 with well depths from about 60—250 feet deep. Sampling results were mailed to well owners in May 2018 and the public data release is currently in preparation.
In 2004 and 2005, GAMA-PBP sampled the deep aquifer zone (about 250—500 feet deep) in the southern Sacramento and northern San Joaquin valleys. That part of the aquifer supplies water to public drinking water districts. Results of that study can be viewed here and here.
The Mojave Shallow Groundwater Study focused on two areas — the floodplain aquifer and the regional aquifer surrounding it. Both areas are tapped by private domestic wells with depths from about 90—600 feet deep. A total of 59 wells were sampled (some of which were monitoring wells) from January through May 2018 with well depths from about 50—250 feet deep. Sampling results are currently being prepared for release.
In 2008, GAMA-PBP sampled the deep aquifer zone (about 200-1,000 feet deep) in the Mojave Desert. That part of the aquifer supplies water to public drinking water districts. Results of that study can be viewed here. Additional water quality results for selected water-quality constituents for sampling activities completed during 2000—12 as part of the Mojave Regional Groundwater Study conducted by the USGS can be found on the Mojave Regional Groundwater Studies Data Map.
In Cooperation With
To learn more about GAMA-PBP shallow aquifer sampling, please contact:
Water Quality Results Map
This short list is a small fraction of the public information available; the USGS does not endorse any commercial products or services.