Site visit: USGS groundwater study at San Diego Chollas Park
Posted by George J Janczyn on June 7, 2011
Recently Wes Danskin, Project Chief for the U.S. Geological Survey (USGS) San Diego Hydrogeology Project, shared notes from his log (here and here) regarding installation of a monitoring well at Chollas Park that will be used as part of a study to learn about water quality, quantity, and flow characteristics in the San Diego Formation aquifer. Funding for the well comes from the City of San Diego.
Last Thursday I received an email from Danskin: “Stop by if you’d like, we’ll be on site for about another week completing the piezometer installation.” No need for a second invitation; the next morning I grabbed my camera and headed over to the project site.
The well is just west of Chollas Lake which itself is just west of the College Grove shopping center near the SR-94 freeway at College Avenue.
Several other visitors were already there, including a few members of the San Diego Association of Geologists (SDAG). 10News reporter Joe Little was there, preparing to interview Danskin for the evening news.
(all photos can be clicked for enlargement)
Wes animatedly talked about a new three-dimensional geologic map of the region that he’s been working on. No previous geologic studies in the San Diego/Tijuana area have produced such a map. According to the SDAG website (“Mapping the San Diego Underground”):
“A total of 91 wells, which showed stratigraphy older than Quaternary age, helped provide depth information to produce this 3D hydrogeologic framework model. This study relied on pre-existing GIS (geographic information systems) datasets including DEM (digital elevation model), surface geologic maps, drilling and e-logs, and literature references to wells or outcrops. Direct examination of USGS multi-depth wells provided the most reliable “ground truth” for geologic boundaries used in the model.”
Danskin explained there are three types of wells: 1) monitoring wells to identify water levels and quality and geology of the groundwater basin; 2) pilot production wells to determine the quantity of water flowing through the ground; 3) full scale production wells. For the San Diego study, the first two types are being used.
Continuing, Danskin said the San Diego Formation extends north-south from La Jolla to south of the border, and west-east from the ocean to the vicinity of the I-805 freeway. Groundwater has been extracted from the San Diego Formation for over 50 years. Sweetwater Authority has been distributing it to National City and Chula Vista.
“The important part about this well is that we’re actually able to get down into the hard rock,” said Danskin. “None of the other wells, with the exception of one near Qualcomm Stadium, were we able to identify this important part of the geologic story,” he said, noting that “the critical part of what we’re doing is defining how the geologic layers are arranged and that allows us to understand how the water moves through them.”
An interesting fact: using carbon dating they found that it could be up to 30,000 years since that groundwater was last in the atmosphere.
Little asked whether pumping and treating groundwater can be cost-effective. Danskin replied that Sweetwater Authority’s pumping of groundwater shows it is already cost-effective. It will gradually become even more competitive because the price of imported water continues to increase. It is becoming more attractive from a reliability point of view too, because we import up to 90% of our water from the Colorado River and the Sacramento-San Joaquin Delta, and both of those sources are climatologically, environmentally, and politically at risk.
Danskin said chances are that most of the water in the Formation will be salty and require reverse osmosis treatment…not as salty as the ocean but it may contain the same salt level as V-8 juice. Still he has an optimistic outlook about the project finding a reliable groundwater flow. “It’s taken about ten years,” he said, “but things are finally starting to make sense.”
Here’s video I shot while Danskin discussed the project:
See also Joe Little’s report on Channel 10 News: