Wednesday, August 20, 2014

Ask the expert: ‘Well’ we be OK?

From page A1 | February 14, 2013 |

* Editor’s note: This is the sixth in a series of “Ask the expert” columns appearing in advance of the Measure I election, regarding various technical aspects of the city’s water utility and the proposed Woodland-Davis surface water project.

The expert: Ed Schroeder, UC Davis professor emeritus of civil and environmental engineering. Schroeder specializes in biological process engineering and has authored more than 150 publications and three books on wastewater treatment, waste gas treatment and water quality.

The question: If the city elected to continue to supply its residents with only well water, what would it have to do to ensure that the supply meets all regulatory standards — including those effluent standards coming up in 2017? Or in other words, what upgrades would it have to make to the system? Can you estimate how long those upgrades would last? And how much it would cost the city to do?

The answer: A combination of wells from the intermediate and deep aquifers probably can provide water that meets both drinking water and treated wastewater discharge standards for some time. The length of time and cost are impossible to predict for several reasons.

New wells will be needed to replace aging ones and increase the draw from the deep aquifer. The intermediate aquifer quality is deteriorating, particularly with respect to nitrates, and wells already have been taken out of service that exceed the U.S. Environmental Protection Agency’s primary drinking water standard.

Increased reliance on the deep aquifer raises a number of questions because we cannot predict the rate of transmission of constituents from the intermediate aquifer due to increased pumping or the rate of replenishment of the deep aquifer.

At present, the quality of water delivered to our homes varies throughout Davis. In general terms, the water will be similar to the well closest to our home and we can see the very large differences by looking at the data provided by the city for individual wells. How this situation will change over time if deep aquifer pumping is increased is unknown.

Subsidence is a possibility if deep aquifer pumping exceeds the sustained yield and would cause damage to underground utilities, foundations, sidewalks and streets. Committing to a groundwater-only policy risks subsidence but the extent is unknowable without further information about the sustained yield of the deep aquifer. If subsidence were significant, the cost to repair the resulting damage would be very high, however.

Meeting the treated wastewater discharge standards will require greater use of the deep aquifer. Selenium is the current mineral of greatest concern but others, including the total dissolved solids (TDS or total salts), may become issues. We should note that drinking water standards for many minerals are much less stringent than environmental standards and selenium provides an example.

The primary drinking water limit for selenium is 50 micrograms per liter while the discharge limit for Davis is 5 micrograms per liter. Treatment to the 5 micrograms per liter is very problematic without going to reverse osmosis, which in turn raises problems with energy requirements, cost and brine disposal.



Tom Sakash

Tom Sakash covers the city beat for The Davis Enterprise. Reach him at, (530) 747-8057 or @TomSakash.


Report details the face of hunger in Yolo County

By Anne Ternus-Bellamy | From Page: A1 | Gallery

Summer jobs aren’t always in the bag

By Spencer Ault | From Page: A1 | Gallery

Davis Arts Center gets a new look, thanks to Brooks

By Enterprise staff | From Page: A1 | Gallery

Bob Dunning: Taking on a Specktacular challenge

By Bob Dunning | From Page: A2 | Gallery

For the record

By Enterprise staff | From Page: A2

The big moveout, on ‘Davisville’

By Enterprise staff | From Page: A3

Sunder campaign will be at Farmers Market

By Enterprise staff | From Page: A3

Classic car show slated in Woodland

By Enterprise staff | From Page: A3

Students can practice safe bike routes to junior highs

By Special to The Enterprise | From Page: A3

‘Monsters University’ to be screened in Central Park

By Enterprise staff | From Page: A3

California regulators approve PG&E rate hike

By The Associated Press | From Page: B3

America’s ‘it’ school? Look west, Harvard

By New York Times News Service | From Page: B3

School board preps for new academic year

By Jeff Hudson | From Page: A3

Public opinion sought about Nishi Gateway

By Lily Holmes | From Page: A4

Davis Art Garage honored; bench dedication set

By Special to The Enterprise | From Page: A8 | Gallery

Woodland historical award winners announced

By Enterprise staff | From Page: A8



Can’t understand this change

By Creators Syndicate | From Page: B5

Tom Meyer cartoon

By Debbie Davis | From Page: A6

Delta-friendly water bond is a win for all of California

By Special to The Enterprise | From Page: A6

Bravo! The road diet works

By Rich Rifkin | From Page: A6

Support water bond in November

By Letters to the Editor | From Page: A6

Relay for Life team says thanks

By Letters to the Editor | From Page: A6



Aggie QB is back to pass … Touchdown, Tina! Tina?

By Bruce Gallaudet | From Page: B1 | Gallery

Hard hoops schedule features defending national champs at UCD

By Bruce Gallaudet | From Page: B1 | Gallery

Crisp’s big hit helps A’s

By The Associated Press | From Page: B1 | Gallery

UCD roundup: Aggie gymnasts are awesome at academics

By Enterprise staff | From Page: B8 | Gallery

Sacramento scores early to snap skid

By Enterprise staff | From Page: B8

Unplayable? Cubs, rain hand Giants a loss

By The Associated Press | From Page: B8



Food that travels well for cooking out

By Julie Cross | From Page: A5 | Gallery



Crowd funding campaign offers support for Art Theater of Davis

By Special to The Enterprise | From Page: A7

Visit Crawfish and Catfish Festival in Woodland

By Enterprise staff | From Page: A7

Artists invited to paint at Yolo Bypass Wildlife Area

By Special to The Enterprise | From Page: A7 | Gallery

Goldberg, Milstein to play at Village Homes

By Enterprise staff | From Page: A7 | Gallery

The voice on the CD comes alive at Music Together concert

By Enterprise staff | From Page: A7





Railroad museum will host Aberbach memorial

By Enterprise staff | From Page: A4



Comics: Wednesday, August 20, 2014

By Creator | From Page: B6