News

Guest Opinion: Groundwater in Palo Alto is a valuable resource, not construction waste

In August, while Palo Alto was urging residents to save water under California's mandated restrictions and to carry buckets of water from our showers to our gardens, we and other neighbors watched numerous construction projects pump 50-100 gallons per minute of groundwater, 24/7, directly into the storm drains. This pumping occurred unabated for months.

Finally we asked, "Why in the fourth year of a severe drought is this groundwater being wasted?" Upon investigation we learned this groundwater was being extracted for construction of residential basements. As concerned residents and neighbors, we joined to form Save Palo Alto's Groundwater. Our goal was to educate residents and City leaders of the value of this discarded groundwater. Now we are working to encourage City leaders to implement policies that protect, preserve and use our groundwater for the benefit of all residents.


Keith Bennett, co-founder of Save Palo Alto's Groundwater
In 2015, using a method known as "dewatering," between 100 to 160 million gallons (300-500 acre-feet) of Palo Alto's groundwater was pumped from our shallow aquifer to allow construction of 14 residential basements. This amount of water, if contained on an 8,000 square foot residential lot, would reach a height of almost 2,000 feet and be higher than the World Trade Center. It is also close to the total amount of groundwater Palo Alto's consultants estimated could be sustainably extracted annually for use as an emergency water supply or a significant percentage of the rainwater flowing into our aquifers. It is a lot of water!

The volume of groundwater extracted for residential basement construction has tripled in the last decade. More than 99 percent of the water originates from beneath the surrounding properties. Greater than 98 percent of the extracted groundwater is shunted directly into the Bay; only 1-2 percent is used for any beneficial purpose.

This groundwater extraction and discharge adversely affects our ecosystem. Groundwater provides support and stability for all structures and infrastructures, recharges our aquifers and maintains normal levels of soil moisture. We know groundwater is a valuable, limited resource, essential to all humanity and all ecosystems. We believe Palo Alto's leaders are not managing our groundwater prudently.

Over the years conflicting engineering reports have influenced Palo Alto's groundwater policies and management. The 2004 report by consultants EIP incorrectly states the effects of dewatering extend only "a few tens of feet" from the property, when in fact groundwater is likely significantly lowered up to 1,000 feet away. The report also states our shallow aquifers, from which groundwater is pumped for basement construction, and our deeper aquifers are "hydrologically separated." However, other engineering reports and two groundwater experts have confirmed the shallow aquifer water directly and indirectly replenishes the deeper aquifer's water. The pumped groundwater being dumping into the Bay could be part of our emergency water supply.

Unfortunately the amount of groundwater sustainably available for Palo Alto's use, and details of the flows between the shallow and deeper aquifers, are not precisely known. The 2003 Carollo Engineering Report estimated Palo Alto could safely pump 500 acre-feet yearly from the deep aquifer; additional sustained pumping could lead to repeat subsidence and/or saltwater intrusion. Recently neighboring cities have improved their existing wells or are planning new wells to enhance their water supply resources. How will these changes affect Palo Alto's emergency groundwater supply when so many are planning to extract water from the same aquifer system? Can Palo Alto afford to allow a few to use so much valuable groundwater in a time of drought, climate change and growing population demands? Remember that aquifers don't make water; they are replenished from precipitation and percolation.

Save Palo Alto's Groundwater is asking the City Council to impose an immediate moratorium on the issuing of new dewatering permits for residential basement construction until State and locally mandated drought restrictions are lifted and Palo Alto has developed a Groundwater Management Plan that clearly allocates and monitors this valuable resource for the benefit of all residents. The California Sustainable Groundwater Management Act empowers local agencies to adopt such Groundwater Management Plans. Palo Alto would be wise to formulate a Groundwater Management Plan; this will take time, research and hard work.

Some residents claim that dewatering is not a problem or that Palo Alto has bigger problems to solve. We disagree. Should Palo Alto wait until our water supply from Hetch Hetchy is disrupted or severely limited to discover our emergency water supply is inadequate? That may be too late. Is it not better to use best practices for basement construction that preserve our groundwater?

This need not be a divisive issue; we all want water security. Let us work together and promote methods of basement construction that protect our valuable groundwater for now and future generations. Let us leave a legacy of ample groundwater supplies and stellar management practices.

To quote Dr. Seuss in The Lorax, "Unless someone like you cares a whole awful lot, nothing is going to get better. It's not." We invite all of you to tell Palo Alto's leaders that you care about your groundwater, your emergency water supply and your future.

Make suggestions, write letters to the editor and the City Council and attend City Council meetings. The council's Policy & Services Committee will be addressing dewatering on 12/15; we invite you to become involved. More information is available at http://savepaloaltosgroundwater.org/.

Keith Bennett, Ph.D., is an applied physicist and concerned citizen who lives in Old Palo Alto and can be emailed at pagroundwater@luxcsci.net. Rita Vrhel is a resident of Community Center, a business owner and a RN concerned about population growth and diminishing resources.

Comments

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Posted by healthy?
a resident of Charleston Gardens
on Dec 11, 2015 at 10:07 am

How much of the water in Palo Alto is even potable though? I live near California Avenue and much of the land here is part of an EPA site. The water is polluted by silicon chip manufacturing and it is extremely dangerous to drink it. We can't even eat the fruit in our yard.


15 people like this
Posted by CMC
a resident of Duveneck/St. Francis
on Dec 11, 2015 at 10:26 am

Very well written, and thank you for your hard work Keith and Rita. Rita, it has been a pleasure getting to know you a bit and I admire the hard work that you've both put into this.


32 people like this
Posted by mutti
a resident of Adobe-Meadow
on Dec 11, 2015 at 11:38 am

We have lived in our home for 40+ years, and so this is our 3rd or 4th drought. The well that was dug when our home was built has worked just fine through all the prior droughts -- keeping our shrubs alive and our grass green. It is about 35 feet deep. But this summer, for the first time ever, our well failed. It would run fine for 5-10 min at 20 psi, and then start to dribble. Why? Not the drought. It was the house 500 feet down the street pumping gallons and gallons of water out of the ground. That water about 6 feet down not only feeds the root systems of the trees and large shrubs on our block, but also percolates down into the next layer of ground water that feeds our well.
True, that water is not 'potable' but we've had it tested and it would be perfectly safe to drink in an emergency, especially with a few drops of bleach added. So, when the earthquake hits and the water pipes burst, come to our house for a few gallons of water -- unless it's all been pumped out into the bay.

The other part I don't really understand is why a family of 4 needs a 4200 square foot house with a 2000 square foot basement. That lot had a beautiful home, about 3,000 square feet, built in the 1980's. I'm a believer in smaller homes make closer families.


16 people like this
Posted by Rita
a resident of Crescent Park
on Dec 11, 2015 at 11:44 am

The quality of the pumped groundwater varies according to location, as would be expected.

However on 12/1 the Public Works Staff indicated the quality of much of the pumped groundwater exceeds that of the groundwater Palo Alto buys and uses to replenish the aquifers. This seems like a huge waste of groundwater and tax papers money.

A 2nd Policy and Services Committee meeting to discuss dewatering is scheduled on 12/15 at 250 Hamilton Ave. Dewatering is scheduled for 7 pm. Please check the City of Palo Alto website to confirm time.

Despite the Policy and Services Committee 12/1 directions, current Staff response is tepid. Continued dewatering was recommended; with no limit of the permits being issued.

Our request for an immediate moratorium on the issuing of dewatering permits for residential basement construction until State mandated water restrictions were lifted and a Groundwater Management Plan for Palo Alto was created were ignored. We are disappointed, but not deterred.

If you believe dewatering for residential basement construction and the flushing of millions of gallons of our groundwater to the storm drains is acceptable as we continue on State mandated water restrictions or

If placing our emergency water supply in possible jeopardy as we enter another year of drought concerns you, please:

1. Send an email with your thoughts to all City Council members @ city.council@cityofpaloalto.org,

2. Attend the 12/15 Policy and Services Committee meeting, stand or speak to this issue,

3. go to Web Link; sign our petition, become informed and involved.

It is your groundwater and your future. The status quo is no longer acceptable.

Working together we can have water security and a sustainable future.

Thank you.


11 people like this
Posted by commonsense
a resident of Adobe-Meadow
on Dec 11, 2015 at 11:53 am

This is a non-issue as any geologist will tell you. The water that is being pumped for basements is simply taking a different route to the same destination, the bay. It has absolutely nothing to do with saving water for your lawns or showers. Let the council spend as much time on real issues, not this misinformation nonsense.


2 people like this
Posted by Plane Speaker
a resident of Crescent Park
on Dec 11, 2015 at 1:32 pm

QUESTION ... can anyone who has studied this and knows tell us where
Palo Alto's groundwater comes from and why it seems to be such an
inexhaustable resource?

It doesn't seem like it comes from the rain, and since it is replenished
so quickly it must be on the move underground.

It's not coming from rivers or the east bay.

What would happen to it if it just stays where it is ... is there an underground
river, aquifer that is allowing this water to flow ... and where does it flow ...
from and to?

So, where does it come from and where does it go to if it does not get
pumped out of someone's basement construction project?

Point being, if a gallon of water has a "lifespan" ... it starts somewhere
as RAIN, soaks into the GROUND, flows through an aquifer into Palo Alto
ends up WHERE?

Would is simply stay under the ground in Palo Alto if it was not pumped
out, and when it is pumped out, what is replacing it?

I think the people complaining about this need to grasp the whole picture,
I know I would like to hear it, or someone's opinion what it is.


4 people like this
Posted by commonsense
a resident of Adobe-Meadow
on Dec 11, 2015 at 1:36 pm

it flows into the bay


5 people like this
Posted by Plane Speaker
a resident of Crescent Park
on Dec 11, 2015 at 1:42 pm

mutti ...
> We have lived in our home for 40+ years, and so this is our 3rd or 4th drought. The
> well that was dug when our home was built has worked just fine through all the prior
> droughts -- keeping our shrubs alive and our grass green. It is about 35 feet deep.
> But this summer, for the first time ever, our well failed. It would run fine for 5-10 min
> at 20 psi, and then start to dribble.

That is a good and honest question ... but if your well is 35 feet deep, does it stand to
reason that there are few to no basements that are 35 feet deep, so that "dewatering"
might probably not be to blame for your well's problems? Maybe it is you and your
neighbors who have sucked up too much water at that level and the refreshing rate
of the aquifer is slowing down or insufficient?

Even if "dewatering" could suck up every bit of water that was above the level of
the lowest basement, there still should be plenty of water at 35 feet ... no?

It sure seems like a lot of people are jumping to conclusions about what is going
on and using very loose coincidence and very little evidence to assign blame in what
might not be correct and have nothing to do with "dewatering".

If this is such a valuable resource ... ie value = money ... I would think you would
want to find and hire someone who can tell you what is going on, or support a
real effort by the city to map this system out so you and others know for sure.


2 people like this
Posted by Plane Speaker
a resident of Crescent Park
on Dec 11, 2015 at 1:46 pm

commonsense ... it flows into the bay

That stands to reason, but prove it.
Also, if it flows into the bay like any other river, it is flowing and moving
whether there is "dewatering" going on or not?

What do we really lose by "dewatering" compared to what we lose
by it flowing under out town and NOT being pumped up and it flowing
into the bay?

Will Bay water backflow into our aquifers and change the salinity or
anything about this water.

We already know this is not drinkable water ... which many on the
alarmist side have claimed over and over when presuably that know
better or just disagree with.


16 people like this
Posted by Jane
a resident of College Terrace
on Dec 11, 2015 at 2:04 pm

Many of our mature trees have much deeper taproots than the 5' the city arborist claims. Yes, smaller trees tend to have roots nearer the surface. However, mature trees can have roots that extend much deeper, some with tap roots that grow 20' down. When the water table is slowly lowered during a drought roots are encouraged and do grow deeper and deeper to seek water.

Large trees are the ones that need the most protecting as when they are stressed they are also more vulnerable to disease. A replacement tree takes decades and decades to reach the same mature size. Some of these large trees also add considerably to a property's value.

The planning department employees and the arborist are strongly lobbied by architects and builders to interpret guidelines in their favor, especially the large developers who have repeated contact and develop ongoing relationships with the staff. When I hear the council agree to codes that allow the planners leeway to interpret them I cringe. This encourages more pressure on staff to find the most loopholes and most generous interpretation. Which sets a new standard. So why write these allowable interpretations in the code in the first place.

During the rewrite of the Comprehensive Plan I hear the director of panning and her staff as well as the city lawyer, testify that in many instances they are changing the wording to reflect what has become current practice, this is a backdoor in eroding the intent of the code. Especially problematic considering previous councils have conducted business with such a laissez faire attitude toward development.


11 people like this
Posted by commonsense
a resident of Adobe-Meadow
on Dec 11, 2015 at 2:37 pm

it does flow to the bay whether dewatered for a basement or left in the ground. I don't have time to prove it.

The argument that dewatering is killing trees is laughable.

This is not an issue any more than building over 50' tall is the Manhattanization of little old Palo Alto. Please!


11 people like this
Posted by Real Expert
a resident of Midtown
on Dec 11, 2015 at 2:44 pm

[Portion removed.]

Construction de-watering has zero meaningful effect on the shallow groundwater conditions.

The water removed from shallow conditions does not negatively impact trees as the overall water content of the soils that trees use to access water is imperceptibly modified by de-watering. Typical native trees have shallow root systems that will not tolerate submersion in water. These trees DO NOT send roots into the water. The giant redwoods and the large oak trees do not have tap roots. Period...they both grab moisture from the upper three or four feet of soil.

As far as effecting the shallow groundwater, the extraction is at the very top of the table. In most cases the water level is reduced 2 or three feet across the project. This is a microscopic volume of water when compared to the entire city geology.

The water is not lost from the bayshore ecology. The natural gradient for these waters is to flow from the hills to the bay. Where the groundwater meets a stream channel, it leaks in and contributes to the volume of water heading into the bay. Dewatering water is placed in the storm water system and diverted into the creek system much like mother nature does on its own. So the net net seen by the Bay is the SAME!

[Portion removed.]


6 people like this
Posted by Save Palo Alto's Groundwater
a resident of Old Palo Alto
on Dec 11, 2015 at 7:51 pm

It may surprise some to learn that 22% of the water in San Francisquito Creek flows into the aquifers and not into the Bay, per a detailed USGS study.

Web Link

We would welcome any data that supports the contention that all of the water in the surface aquifer flows to the Bay. It almost certainly does not; it is also used by some residents for irrigation. Some of the water in the surface aquifer does flow to the Bay in the winter / spring, but, like San Francisquito Creek, the flows in the summer and autumn are very slow at best, especially in dry years.

Neither the water in the Tuolumne River nor Crystal Springs Reservoir, that supply Palo Alto are "potable." They are treated to become potable. But, there are many uses for water, such as irrigation, that don't require potable water, and Palo Alto's surface groundwater can and is used for irrigation.

Groundwater provides many ecosystem services in the ground, in particular, it is well known that pumping groundwater causes subsidence, and in fact the report above quotes a study by Poland and Ireland (1988) that subsidence in Palo Alto was 2 to 4 feet. The same report also indicates that salt water intrusion was 5 miles - and the salt content of the Riconada Well that Palo Alto uses was higher in the early 60's when groundwater was heavily used for Palo Alto water. It has since declined, but we can't take that decline for granted.




11 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 11, 2015 at 8:47 pm

I have a shallow well on my property. Despite all the hoopla around basement dewatering, my well isn't down much at all from last year or the years before. Maybe 1' lower, which is probably from the drought.


I can't imagine this affects the trees, houses, ecosystem, or frankly, anything. The editorial draws some shocking analogies about the amounts of water(if we stack this up it is taller than the moon...) but the correct analogy is that the basement water extracted from Palo Alto, when spread out across Palo Alto is very little. 500acre feet of water across Palo Alto's flatlands is about an inch or water.

That's the magnitudes we are talking about...



5 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 11, 2015 at 8:56 pm

Someone asked where groundwater comes from - geo studies on the balance of water show sources as rain in the watershed of San Francisquito + irrigation + leaked in water pipes + leaks in sewer pipes.

Where does it go? - wells, and excess flows to the bay.

What are levels? In the 1960's before Hetch Hetchy groundwater was pumped down about 160' below surface. It was the primary source of water. Now it is about 20' below grade (on average across town). Shallower at lower elevations. Some places only 10' down. As long as the amount removed doesn't drawdowns below sea level, saltwater intrusion is avoided. We are nowhere near the levels of pumping in the past.


8 people like this
Posted by What Nonsense
a resident of Adobe-Meadow
on Dec 11, 2015 at 9:02 pm

Too much effort on a non issue

'commonsense'...thank you for your comment!


7 people like this
Posted by Plane Speaker
a resident of Crescent Park
on Dec 11, 2015 at 10:35 pm

So, we've heard from most people who know what they are talking about
and can explain this better than I.

So my final question is ... why doesn't this subject ever just drop? It's not
an issue yet I see this subject getting posted as if it is an urgent catastrophe
every month or so, or someone mentions it in another forum and it starts all
up again.

I wonder if the sociology department at Stanford is experimenting on us or
something to try to show how low or little people learn. Can we let this
subject drop please ... it will be too see if I ever hear the term "dewatering"
again! ;-)


16 people like this
Posted by Long Time Resident
a resident of Old Palo Alto
on Dec 11, 2015 at 11:29 pm

Impacts of pumping out large amounts of groundwater in expansive clay soils can be found in soil engineering text books (civil engineering).
You can read abstracts from the American Society of Civil Engineers on the Impacts of Dewatering on Surrounding Structures.

Web Link

The impacts of dewatering inducted settlement from dewatering is well know, but rarely dealt with in residential construction.

Pumping out large volumes of water dries out the soils, and can crack foundations and underground piping.
Soils need a certain amount of moisture for strength.

There is a "zone of influence" or "radius of influence" around each well. These wells vacuum out water from a large area around the building site.
During drought the damage is worse since people have cut back on watering their landscaping.

Dewatering also changes the natural structure of the soil (fines/grains) under existing structures.
On small properties, when the new concrete is in place, it creates a barrier to flow and channels the natural water paths elsewhere. When it rains on these smaller properties with basements in a high water table, there is no place for the water to flow, so it flows away from the property with the basement and onto and under other properties.

There are plenty of books and articles about the effects of dewatering and collateral damage.
Impacts to trees and vegetation are also mentioned in these books and articles.

Settlement around a basement built in high groundwater may not happen right away.
The water table may have to re-establish itself and the underlying soils saturate before settling is seen.

I wish to see our city restrict this large scale construction engineering.
I am not expecting a ban on basements, but a restriction on basement construction which requires large volume dewatering.


9 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 12, 2015 at 7:58 am

Subsidence is not an issue from the Carollo report. Any subsidence has already happened in the 1960's when water was pumped down to ~200 ft. That's baked in to today's elevations, as long as we don't pump the aquifer deeper than that:

"As discussed above, the loss of elevation associated with subsidence is the result of the reorientation of clay minerals within clay deposits. The compaction of these deposits is essentially irreversible in that when water levels subsequently rise, the clay minerals do not return to their original orientation. However, since these materials are now compacted, the lowering of water levels does not result in significant further compaction. If the City’s wells were used at the capacity limits considered herein, the result would be a transient lowering of water levels to levels less than 25 percent of the historical lows. As such, use of the wells should not result in renewed subsidence."

Pg16. Web Link


6 people like this
Posted by Resident
a resident of Another Palo Alto neighborhood
on Dec 12, 2015 at 8:49 am

My take on this.

The underground water table is there and when it is removed it will cause problems with things like subsidence. There have been sink holes appearing in other places due to this type of interference. As yet none have occurred in Palo Alto, but I won't be in the slightest surprised when one appears here.

Trees will grow their roots in whatever direction they can find water. These roots could end up causing big problems.

If the water is being pumped up and then drained, it makes sense that it should be used for watering landscaping rather than allowed to run down the drain. If nothing else, let the water be collected and then used.

If we are teaching our children on the one hand to conserve water at home or at school, and then they see water running down the street and into the drain, what lesson is it teaching them? They learn from adult practices of what they see. This is a bad lesson for them.

Likewise when the city flushes out the water main. That water should be collected, not just allowed to run off.


13 people like this
Posted by Rita
a resident of Crescent Park
on Dec 12, 2015 at 1:03 pm

Glad to see this topic continues to be discussed.

On 12/10 the City of Palo Alto posted it's latest update of State mandated water restrictions and water savings by residents. We were all urged to continued following State restrictions.

This goes to the issue of some residents "wasting" and most residents "conserving". Water is water; when it is "endangered" is not the time to start planning conservation and best practices.

Resources are limited. Our history is full of wasteful practices and then shortages: cod, sardines, farm lands,etc, all improperly managed and left in a depleted state. Reasonable use, education and planning for the needs of future generations would resulted in a different legacy.

We are requesting an immediate moratorium on the issuing of permits for dewatering for residential basement construction while the complexity of the aquifers and their interactions are studied in conjunction with our neighboring cities who use these same aquifers. This is a prudent and not unreasonable request. If not now; when?

We have over time developed recycling programs for our glass, cans and other wastes. We have second hand stores for no longer need clothes, bicycles, and other everyday items. We have Charitable organizations requesting our older cars; so many things are no longer discarded and wasted.

The above programs required a change in thinking and a realization that "wasting" was not sustainable or desired; the status quo was no longer acceptable. People complained and questioned the value of these programs; now few would.

We can't "manufacture" water without great cost and significant by products. Is it not better to start the investigation process and determine how the aquifers interact and their actual capacity? Who is using and how much water is withdrawn each year? Is this level of use sustainable? Do changes need to occur? Once it is in short supply, we are in trouble.

Predicted changes in our climate of extended drought and flooding will also upset resource status quo; probably faster than anticipated. Our actions are important; time is not on our side.

Dewatering wastes precious community groundwater; basements can be constructed without dewatering. Vital to life community resources are best used for community and not individual benefit. And everything is best not wasted.

Please attend the 12/15 Policy and Services Committee meeting.




6 people like this
Posted by Slow Down
a resident of Community Center
on Dec 12, 2015 at 1:07 pm

Slow Down is a registered user.

@Rita - "Water is water" Come on, you know that's not true, so why even say it? It discredits your whole POV. There is obviously a massive difference between the great drinkable water we get from Hetch Hetchy, sewer water, bay water, deep well water, and the shallow construction water.


3 people like this
Posted by Rita
a resident of Crescent Park
on Dec 12, 2015 at 1:23 pm

Sorry to disagree but water is water is water.

Some communities are using treated waste water as drinking water. This is being touted as the new normal as populations expand and water becomes scare. Treated waste water is commonly used in Palo Alto for irrigating; the purple covers at the Main Library indicate use of recycled waste water. My grey water systems use grey water for irrigation.

Most water can be treated and made potable or used for irrigation. I am unsure regarding water with heavy metal contaminants so will exclude that water.

When the "natural" water becomes limited other sources of water will be treated and used. Personally I would rather conserve and manage our "natural" sources of water than drink treated waste water. But I will drink it if it comes to that.

Desalinization is also an option but is expensive and produces mounds of salt as a by product. Maybe other techniques will be invented but I believe my statement is true

If you do not,we can just politely disagree.


21 people like this
Posted by Allen
a resident of Menlo Park
on Dec 12, 2015 at 4:21 pm


As a groundwater hydrologist who has worked in the field for over 50 years prior to retirement some years ago I should like to comment on the “non-issue” as written by “commonsense”. I quote: "This is a non-issue as any geologist will tell you. The water that is being pumped for basements is simply taking a different route to the same destination, the bay. It has absolutely nothing to do with saving water for your lawns or showers."

Pumping 9 million gallons of water over less than a 6 month period for construction of a single basement is enough water to cover an acre of land to a depth of 27 feet! This water is taken primarily from the shallow water-table aquifer but some will inevitably be extracted from the deep-seated aquifers because no geological materials are completely impermeable to the flow of water given time and sufficient pressure differential. As stated by others water in the deep aquifer under the City of Palo Alto should be left untouched for future emergencies. There are many reasons pointed out by others why basement construction in regions of high water table should not be permitted but In the time of draught, especially, it is unconscionable to pour usable groundwater directly into the bay. This has everything to do with saving water. All up and down the peninsula adjacent to the bay people are paying for potable water and using much of it to irrigate landscape and flush toilets.


6 people like this
Posted by Rita
a resident of Crescent Park
on Dec 12, 2015 at 5:32 pm

Thank you Allan.. please consider emailing your comments to Palo Alto's City Council: city.council@cityofpaloalto.org.

The members of savepaloaltosgroundwater.org are not experts in the field of Hydrology but have varied degrees. We have searched for Engineering and other scientific studies and visit USGS's site frequently. Our website has varied and interesting articles on this groundwater,aquifers,and list other web sites for additional information. Our concerns re based on our reading and common sense.

The Policy & Services Committee (meeting 12/15 @ 7 pm; dewatering is Item # 4) would appreciated your comments as an expert in the field. They are interested in making sound decisions and giving Staff appropriate directions to address the issue of dewatering.

Thank you for whatever you can do and for your comments.


8 people like this
Posted by Slow Down
a resident of Community Center
on Dec 12, 2015 at 5:46 pm

Slow Down is a registered user.

@Rita - If you insist that all water is water, then you never have to worry about scarcity because there is plenty in the ocean. But, as you point out yourself, water has varying degrees of usefulness, so all water can't be the same.


14 people like this
Posted by Gulio
a resident of Crescent Park
on Dec 12, 2015 at 9:12 pm

dewatering your local neighborhood so you can have a basement is an ******* move if there ever was. Selfish, ignorant of the negative impact to neighbor's, and a HUGE waste of water.


2 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 12, 2015 at 11:55 pm

@Allen - can you explain how dewatering wells which are 15' deep could possibly affect deep water aquifers?

My understanding is that these specific type of wells run until their surface is dry. The cannot suck water up from below, as the dewatering well pipe only goes a few feet below the basement.


1 person likes this
Posted by Save Palo Alto's Groundwater
a resident of Old Palo Alto
on Dec 13, 2015 at 8:21 am

@Allen: correct me if my understanding is not correct.
@Waterwater: Technically, you are correct. Pumping does not remove water from the deeper aquifer.

However, the shallow aquifer is a major "inlet" to the deeper aquifer. According to the Todd Engineer study of groundwater resources in the San Francisquito Creek Sub-basin, approximately 85% of the inflow into the deeper aquifer is from shallow aquifer sources. I will post a link to the report later.

Removing water from the shallow aquifer affects the recharge rate of the deeper aquifer, just as removing water from an inlet into a lake reduces the rate at which the lake fills, the flow through the lake, and reduces the amount of water sustainably available from that lake.


If the deeper aquifer is not full, then water flows downhill - from the shallow aquifer into deeper aquifer. Of course, if the deeper aquifer is full, water in the shallow aquifer will either stay in the shallow aquifer, drain to the surface water and / or the Bay, or be pumped out from a well.

The deep aquifer is currently not full.

Incidentally, the pumps are about 25 - 30 feet deep to lower the water level to about 15 feet below ground surface.


2 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 13, 2015 at 8:49 am

@Save - where is the data that indicates the deep aquifer is not full? The studies I have read indicated the are pretty tightly coupled...


I would like to understand this in more detail.

Thanks in advance for any pointers.



2 people like this
Posted by Rita
a resident of Crescent Park
on Dec 13, 2015 at 10:40 am

I would encourage you to visit savepaloaltosgroundwater.org for additional information on aquifers, shallow and deep, rainfall, cones of depression (the geographic extend of groundwater removal during dewatering) and other related water articles.

These include Engineering reports which call into serious doubt the validity of the 2003 EIP report, on which Palo Alto's water policies are based, as well as links to USGS and their wonderfully informative website USGSWaterSciencesSchool. This site discussed the entire natural Water Cycle.

Over the past several months,Keith Bennett has made informative presentations to the City Council which can also be reviewed on savepaloaltosgroundwater.org.

I did some canvasing in the Community Center area yesterday and met some delightful people. Many expressed concerns regarding groundwater pumping.

Some did not support an immediate moratorium on dewatering but did support investigation into the current status of the aquifers and better use of the pumped / discarded groundwater.

One resident reported a collapse in part of his lawn and difficulty with his doors sticking. One reported significant changes in shower and sink water flows and one had visually sunken pavers in their front yard. Others nearer the dewatering sites reported no problems.

Hopefully residents will email their concerns to the Policy and Services Committee members as well as the remainder of the City Council and City Manager. Show up at the 12/15 Policy and Services Committee meeting, speak and be heard.

I feel confident meaningful changes in dewatering and water waste practices will occur; but will these changes occur before the issue become critical?


10 people like this
Posted by Be Quiet
a resident of Adobe-Meadow
on Dec 13, 2015 at 3:39 pm

My god, give this subject a rest already.

The endless rants on here are ridiculous.

Obviously these people who are ranting have too much time on their hands.


Like this comment
Posted by Todd
a resident of Another Palo Alto neighborhood
on Dec 13, 2015 at 3:56 pm

Im shocked, SHOCKED that putting arbitrary restrictions on square footage and other attempts at micromanaging people's lives could somehow backfire! But hey, its not like we haven't learned out lesson and gone and banned multi story homes with such an obvious loophole in place...


5 people like this
Posted by PAmoderate
a resident of Old Palo Alto
on Dec 13, 2015 at 4:41 pm

PAmoderate is a registered user.

"Obviously these people who are ranting have too much time on their hands."

Or just jealous of other people who are following the code building what they want on their own property.


2 people like this
Posted by Plane Speaker
a resident of Crescent Park
on Dec 13, 2015 at 4:48 pm

Pumping 9 million gallons of water over less than a 6 month period for construction of a single basement is enough water to cover an acre of land to a depth of 27 feet!

Yes, 9,000,000 gallons is 27.62 acre-feet.

Who measured 9 million gallons coming out of one basement? Not sure I buy that.


4 people like this
Posted by Long Time Resident
a resident of Old Palo Alto
on Dec 13, 2015 at 5:30 pm

The volume of water that I have seen coming from multiple construction sites has been closer to 75,000-100,000 gallons / day. I verified the flow with one contractor many years ago on a site in the Community Center area.
Over 6 months think can add up to over 15 million gallons.


3 people like this
Posted by NetCruiser
a resident of Community Center
on Dec 13, 2015 at 7:21 pm

"Or just jealous of other people who are following the code building what they want on their own property."

It's that old home theater envy again.

The property owner has a choice between wasting a community resource during a shortage and having that dream home theater. Guess what wins. State of the art audio-video components do not function well under water, nor is watching Star Wars VII in a fully flooded basement a particulay enjoyable experience.


4 people like this
Posted by rationalobjectivism
a resident of Another Palo Alto neighborhood
on Dec 13, 2015 at 7:59 pm

I'm concerned about emotions: trying to blame sticky doors, shower and sink water flows, or sunken pavers on de-watering projects down the street. I'm concerned about viewing neighboring construction as selfish.

I'm happy some are thinking rationally and objectively about this. Maybe we need to reexamine the amount of water extracted and the impact. Maybe it makes sense to look more into how to recycle or recharge the water extracted. Maybe every new house in the city should have separate potable and non potable plumbing. Maybe it makes sense to measure and tax the extracted water to create an incentive to extract only when necessary and quickly dig-pour-backfill the project.

All within reason. City government time and tax dollars are shared with other equally valid community concerns and the energy spent in one area inevitably steals from another.


4 people like this
Posted by WhereIsThisGoing?
a resident of Community Center
on Dec 14, 2015 at 9:55 am

So I cannot tell where this is going. The basic complaint seems to be changing, and every time someone debunks some complaint, a new complaint springs up.

Subsidence!
- no, not really.
Shallow Aquifer is depleted!
- no, not really.
Trees!
- no, the shallow aquifer is fine. Can't be a problem...
Water is rerouted from groundwater to bay!
- no, not really an issue.
My door sticks.
- ? what is this?
Water is water
- no, sea water is worth less than gray water...
It's the deep aquifer!
- no evidence at all that there is a problem



Come on guys. If you want to impose legal restrictions on homeowners, you had better have actual data with actual geo & hydro studies that show a REAL problem, and one serious enough to justify the loss of property values you are suggesting through new restrictions. Where is the proof of a problem? This whole thread (and dozens that preceeded it) just read like an emotional rejection of basements. Whenever a point is debunked, the argument moves to some new aspect, which is further debunked. It really just feels like an emotional argument, not one based on identifying a real problem with provable data supporting this issue.

[Portion removed.]


7 people like this
Posted by PAmoderate
a resident of Old Palo Alto
on Dec 14, 2015 at 10:11 am

PAmoderate is a registered user.

"The property owner has a choice between wasting a community resource during a shortage and having that dream home theater. Guess what wins"

Guess what happens when government imposes Floor-Area Ratio limits, and now having neighbors imposing a ban on two-story housing?

As for "wasting a community resource" - that's debatable. I still haven't seen real science behind this statement other than anecdotal comments. This is what happens when you have a bunch of people who think they're smarter than they think they are, which seems to be endemic to well-educated communities.

A liberal arts or engineering college degree from a prestigious institution apparently makes people experts in groundwater. And, no, Internet research doesn't count.


4 people like this
Posted by Marc
a resident of Midtown
on Dec 14, 2015 at 11:41 am

@PAmoderate. I think you hit the problem right on the head. This thread, the ones on nextdoor and all the others are full of comments from people who quote textbooks, internet searches, etc. and then claim that that is the basis for their expert opinion.

/marc


6 people like this
Posted by Douglas Moran
a resident of Barron Park
on Dec 14, 2015 at 1:58 pm

Douglas Moran is a registered user.

RE: Marc: "...full of comments from people who quote textbooks, internet searches, etc. and then claim that that is the basis for their expert opinion."

This misrepresents many (not all) of the comments -- they are not claiming to be experts, but are pointing out that textbooks and other authoritative sources (government websites, professional groups,...) provide information contrary to what the "experts" saying that de-watering is not a problem: For example, their claim that most trees don't have roots reaching the shallow aquifer.

Or playing the game of ill-logic and non-sequiturs, for example, claiming that there can't be immediate local effects (a few acres) because the amount of water pumped wouldn't have long-term, wide area effects (tens of square miles).

Or playing the game of claiming nothing should be done until there is more evidence, when their argumentation style indicates that no amount of evidence would change their beliefs (see Climate Deniers, Tobacco companies).

One doesn't need to be an expert in the subject matter to spot major problems in argumentation. And when the self-proclaimed subject matter expert employ fallacious/disingenuous/... argumentation, it is reasonable for the reader to infer that the claim is not related to their expertise, but another agenda.


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Posted by WaterWater
a resident of Old Palo Alto
on Dec 14, 2015 at 2:44 pm

@Doug - okay, what is THE definitive problem?

Can we at least get that?


3 people like this
Posted by Crescent Park Dad
a resident of Crescent Park
on Dec 14, 2015 at 3:21 pm

That being said...

No one is right and no one is wrong...until a real/verified engineering report can be produced.

Wait...we have one, the 2004 EIP. Of course, the people (aka "armchair engineers") against dewatering are not buying its findings as it goes against their opinions.

Report quotes such as:

The volume of groundwater pumped out of an excavation site is a small fraction of the total volume of the aquifer and does not deplete or lower the aquifer, except, of course, in the immediate vicinity of the excavation. The USGS reports that due to natural (rain) and manmade (irrigation, leaking sewer pipes, and the SCVWD’s groundwater recharge program) methods, more water is recharged into the shallow aquifers than is pumped out of it by all pumping in the Santa Clara Valley. The EIP report also confirmed that the water table is only drawn down locally (within tens of feet of the excavation) and reestablishes itself quickly after dewatering ceases. Therefore, the cumulative effect of dewatering on the shallow aquifers is negligible.

And apparently the city arborist doesn't know what he is talking about when it comes to the depth of PA tree roots.

From the same report:

The Planning Division arborist reports that in most of the developed areas of Palo Alto the preponderance of absorbing tree roots are not found in lower soil horizon levels below seven feet. Therefore, the majority of temporary dewatering projects are not expected to impact trees. If a tree’s roots are however deep enough and have been determined, on the basis of a certified arborist report or other qualified assessment, to be dependent on the water table, then the mitigation would be for the contractor to provide separate irrigation for the tree(s) during the dewatering period.



So do another study...I'm fine with that. But to just flat-out deny the validity of the existing report is the same as denying climate change and the effects on the polar ice caps. It exists and qualified engineers stand by their research.


5 people like this
Posted by Douglas Moran
a resident of Barron Park
on Dec 14, 2015 at 4:27 pm

Douglas Moran is a registered user.

RE: Crescent Park Dad:
"...Report quotes such as:...the SCVWD's groundwater recharge program..."

That program is the slow release of water from *reservoirs* down the creeks and often involves the placement of temporary dams across the creeks to create ponds in segments favorable to recharging. Unless things have changed in the past few years, there is no such recharge program in the Palo Alto area. There is some *natural* recharge during natural flows in the creeks.

"...more water is recharged into the shallow aquifers than is pumped out of it by all pumping in the Santa Clara Valley."

An example of my earlier point. Somehow ground water recharge in the eastern part of the county (for example from Anderson reservoir) remediates ground-water deficiencies in this area? The use of generic boilerplate for the local situation is an excellent example of the disingenuousness I cited.

"the *preponderance* of absorbing tree roots"
So apparently the remaining tree roots are irrelevant. If someone chopped off a victims head, leaving the preponderance of the body intact, would it not still be murder?

"If a tree's roots are however deep enough and have been determined, on the basis of a certified arborist report or other qualified assessment, to be dependent on the water table,..."

So if they don't do an assessment, or make an improper assessment, then the tree won't die from not having water? Transparently biased assessments by City Hall have long been a problem. It is long past the point of knowing that the citizenry knows that we can't trust City Hall to enforce the ordinances, we have learned that they routinely assist the scofflaws in subverting the ordinances.


2 people like this
Posted by Commentator
a resident of Professorville
on Dec 14, 2015 at 4:39 pm

"This thread, the ones on nextdoor and all the others are full of comments from people who quote textbooks, internet searches, etc. and then claim that that is the basis for their expert opinion."

Only those posters who value at least some facts, and good for them. The rest merely post their opinions as incontestable holy writ. That is hardly unique to this thread, BTW.


4 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 14, 2015 at 5:08 pm

@Doug - it is clear to me that trees cannot be suffering from basement dewatering:

- I have a shallow well. I can actually measure the shallow groundwater. I pointed out earlier that the current water levels are down about 1' for this time of year.

- most of that is likely drought, not dewatering.

- it is not down significantly for tree roots

- it is not down the height of world tade center as the op-ed projects.

- by your own math in another posting, the basement dewatering effects are 1" or less (1 inch!)


- public well records on well depths are similar: Library well same as 2014. Rinconada well up slightly in 2015 there is just no significant evidence that groundwater is lower, or lowered by basements.

So here is real data. Here are your own projections on dewater impact, city arborist comments that trees aren't affected, and the shallow groundwater is not really that impacted this year.

Can you (or anyone associated with this movement) explain what is the issue?


Claims of bad argument are to be rejected. I put forth my data, where is yours?


2 people like this
Posted by Mike-Crescent Park
a resident of Crescent Park
on Dec 14, 2015 at 7:08 pm

Mike-Crescent Park is a registered user.

There are two sides represented in these comments:
A. Pumping groundwater for basement construction must have an effect on the water supply AND/OR it affects ground elevations, nearby structures, etc.
:
B. Pumping groundwater for basement construction has no effect whatsoever on the water supply nor does it affect ground elevations, nearby structures or anything else

No matter which is true I do believe this-if the water IS pumped it is no longer making its way anywhere else but it is physically above ground and therefor available for some use such as irrigation. Once pumped dumping it into the bay rather than utilize it during asteroids drought makes no sense unless it is toxic. Since many Palo Altans currently pay a firm like RainDance to truck in recycled water for use on lawns it is demonstrably economically viable. So how can it be pumped up and flushed away?


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Posted by Mike-Crescent Park
a resident of Crescent Park
on Dec 14, 2015 at 7:14 pm

Mike-Crescent Park is a registered user.

Extreme drought-not asteroid drought.

The spell checker always wins.


2 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 14, 2015 at 7:47 pm

It is free for the taking. Help yourself. Get a truck and load up.


10 people like this
Posted by Roger
a resident of College Terrace
on Dec 14, 2015 at 9:28 pm

The science is clear and incontrovertible: pumping groundwater in predominantly clayey soils of the type we have below us, and thereby lowering the water pressure in those clays, will result in a collapse of the soil structure and cause settlement. The amount of settlement depends on the amount of the pressure drop, its duration, and prior settlement caused by previous dewatering. And based on my study of the shallow water levels in Palo Alto, there has not been much, if any, water level change in the shallow groundwater, 0 to 50 feet below ground surface, over the last 50 years. Also, based on comparisons I performed of the shallow and deep groundwater levels, they appear to be isolated from each other in areas East of Middlefield, although they do interact in areas closer to the hills where recharge occurs. Thus, the lowering of water levels in deep drinking water wells prior to 1972 likely did not affect shallow groundwater levels significantly. Therefore, there appears to be a significant potential for land settlement due to prolonged basement dewatering since the shallow clay soils have not been dewatered historically. The fact that this settlement has not been seen may be because no one has done a before and after study at a dewatering site.

The EIP report makes some seriously flawed assumptions about the geology in the high groundwater areas of Palo Alto. The first is that the basement pumping is being conducted from aquifers open to the surface. Even a cursory review of well borehole logs in Palo Alto reveals that there is mainly clay with small layers of porous material from near the ground surface to well below the pumping zones of the basements, which are generally around 30 feet below ground surface (bgs). The shallow aquifer the EIP report describes actually only exists in the Palo Alto area of concern from 0 to at most 5 feet bgs. The second flaw is that water in this shallow area flows to the Bay, which I refute below. The third flaw is the stated opinion, without supporting evidence, that “the water table is only drawn down locally (within tens of feet of the excavation)” is not supported by science. My work using basic groundwater equations like Darcy’s law and with groundwater models shows that the zone if influence will be much greater than 20 feet and can be hundreds of feet from the wells.

Regarding groundwater flowing to the bay, the fact is that very little groundwater flows into the Bay via the aquifers, as these aquifers, even the shallow ones are overlain by bay mud clays that dip below the Bay bottom, not dump into the Bay. These clays (aquitards) restrict vertical flow and thus don’t provide an outlet of the groundwater to the bay; the main groundwater flow path to the Bay is seepage to creeks and seepage into storm drains, both well above the 30 foot depth of pumping. Therefore, the basement pumping is actually pumping water to the Bay that would otherwise remain in the soil and help maintain the soil pressusre and groundwater levels.

My credentials for making these statements are that I have been studying groundwater flow and subsidence in Santa Clara County for over 20 years.

@waterwater, do you live near an active dewatering site? If not then what does your 1 foot drop in water level have to do with the 25 foot drop produced at a basement dewatering site???

Regarding trees not having roots down 7 feet: The clay soil below us causes a phenomenon called capillarity, which is the rising of water higher than it would other rise in an open well. So standing water in a well at 7 feet will actually rise many feet higher and reach the roots of trees and bushes (I am surprised the City Arborist does not understand this). But when the water level drops to 30 feet bgs capillary action cannot make up for that and the trees are out of water.

The Library well is over 100 feet deep and the Rinconada well is about 500 feet deep so as I said previously their water levels don’t relate to the shallow water at 0 to 30 feet.

My credentials for making these statements are that I have a Master’s degree in Civil Engineering and Hydrogeology and I have been studying groundwater flow and subsidence in Santa Clara County for over 20 years.

I am not against basements, but the irresponsible way some are constructed allows the basement builders to externalize some of the costs, like investigation and mitigation, to their neighbors. Because there is a real risk to neighbors of differential settlement of their houses and the loss of trees, the basement builders should be required to do a geologic study of the potential for settlement of neighboring houses and also do a land survey of the neighboring properties to detect settlement. They should also be required to conduct frequent tree monitoring during construction. These seem to me like the minimum requirements and relative to the cost of building a house these measures will add only a few percent to the total house cost.




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Posted by Save Palo Alto's Groundwater
a resident of Old Palo Alto
on Dec 14, 2015 at 11:01 pm

@WaterWater

I would be happy to meet with you and show you quite a bit of data and analyses. If you're interested, send me an e-mail at pagroundwater@luxsci.net with contact info.

We agree!
The shallow aquifer is reasonably closely connected to the deeper aquifer, in much the same manner as a chain of ponds connected by streams are connected to a lake downstream. If water is removed from the ponds, it doesn't flow into the lake, or if the ponds are stagnant, for example late in the season, then they need to be refilled by water from the future rains before water will flow into the lake. Either way, removing water from the "inlet" ponds reduces the flows into the lake over a longer period of time.
Flows between aquifers are more complicated and there are multiple pathways for the water, however here, >80% of the deep aquifer recharge is through the shallow aquifer, so removing water from the shallow aquifer will reduce the recharge rate.

Water level history for 4 of Palo Alto's emergency water supply wells, which access the deep aquifer is in the chart below.

Web Link

For reference, the study performed by Carollo Engineers felt that it would be "safe" to lower the groundwater 8 feet, with a one year in 3 lowering of 25 feet, followed by no pumping until the water levels recovered. We are already below the "safe" sustainable limit, and although Palo Alto has not used it wells to supply emergency water.

A presentation with summary and more details of the inflows and outflows to our aquifers is available at:
Web Link

Tables with the original data from Todd Engineers for East Palo Alto's Groundwater Management Plan is included.


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Posted by Save Palo Alto's Groundwater
a resident of Old Palo Alto
on Dec 14, 2015 at 11:13 pm

@Roger
Your comments are completely consistent with the experience of settling in at least one neighborhood which is a few blocks west of Middlefield, where differential settling of ~1" has occurred in several houses 200 - 400 feet from a dewatering site, and also consistent with the Theis equation for water drawdown using typical soil parameters, where approximately 3 - 4 foot lowering of the water table 300 feet from the dewatering site would be expected.

We believe that simple process improvements to shorten the pumping period (and therefore the construction time) combined with local re-injection of the water (as is required in some communities on Long Island for example) could significantly mitigate the problem and would not be expensive.
Also, the Romans set concrete under the sea, and builders in Palo Alto probably could do so as well.


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Posted by Plane Speaker
a resident of Crescent Park
on Dec 14, 2015 at 11:39 pm

GREAT! ... now that the comment list is about a mile long we are getting some good information. ;-)


3 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 14, 2015 at 11:46 pm

@Roger asks:

"@waterwater, do you live near an active dewatering site? If not then what does your 1 foot drop in water level have to do with the 25 foot drop produced at a basement dewatering site???"

I believe my point was taken out of context - I was responding to the sweeping claims made that our shallow groundwater is broadly affected and that 'trees' are suffering. Without clarifying statements, I could only assume this is wrong. 'Trees' in a general sense cannot be affected, as measurements show the shallow water aquifer is NOT broadly affected.

I have to say I appreciate your post - you have clearly stated that you believe the problem is localized to 100' of a dewatering site.

I really feel this movement would gain some credibility by abandoning hyperbole, broad claims of groundwater shortage/catastrophe and other easily disproved falsehoods.

We are discussing property rights fundamentally, and taking them away requires the petitioners to have solid data on clear problems. So far, despite my request to know the issues, only two very narrow issues seem clear:

1) Localized dewatering may affect local trees (<100')

2) Localized dewatering may affect local soils if they have not already subsided from historic dewatering. Again, very localized (<100') from site.



Now the real question: has either effect been shown with real data from a site in town? I doubt it, but would love to see data.

(One last comment - I believe both issues are mitigated by watering trees near construction with the water pulled from the well. If this simple mitigation were used, would that solve the problems?)


2 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 14, 2015 at 11:54 pm

@Save - you claim 1"subsidence occurring 400' from a dewatering site and speculate the water is lowered by 3'.

Do you have any evidence? Did you measure the water level? The reason I ask is because this claim seems dubious - we have 3' drops in water levels seasonally every year.

When rains come the shallow aquifer rises, during dry season it falls.

About 3'.

So how could a seasonal change not cause subsidence while you believe an unmeasured dewatering impact does subside?


Like this comment
Posted by Be Done
a resident of Adobe-Meadow
on Dec 15, 2015 at 6:37 am

[Post removed.]


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Posted by Save Palo Alto's Groundwater
a resident of Old Palo Alto
on Dec 15, 2015 at 9:45 am

@Waterwater,
Again, I'm happy to meet with you.

I would be very interested to see measurements or models that show the drawdown and recovery of the water table that maintain the drawdown to a small amount further than say 30' from the pumping location, as well as how rapidly and completely the water table recovers.

Alternatively measure the water during the construction process and show the spatio-temporal profile of the water drawdown. It is already required to measure the water table as part of the soils study prior to construction, so it should not be expensive to monitor the water levels at a number of points on and offsite before, during and after construction.

We have provided basic simulations for local soil conditions that indicate the drawdown is significant 100's of feet away, as also stated by Dr. Leah Rogers (in a letter to Council) and @Roger, who are not the same persons.

To answer your question, the clays that are dewwatered are likely virgin clays, i.e. they have been wet the entire time since homes were built. Without dewatering the "low" water level is relatively independent of whether the year was wet or dry. Dewatering can lower the water level below this "low" level, below the level where the clays have always been wet, hence the settling. Please see @Roger's comments.

Why can't Palo Alto simply adopt best practices that value groundwater? Is doing so prohibitively expensive for a home that sells for $3 - $5 million more than the lot on which it is built?




4 people like this
Posted by WaterWater
a resident of Old Palo Alto
on Dec 15, 2015 at 11:48 am

@Save - you recommend a great experiment. I would encourage you to move forward with this to gain convincing data!

As for clay subsidence, you may be viewing this wrong:
"clays that are dewwatered are likely virgin clays, i.e. they have been wet the entire time since homes were built. "

We live on an adobe clay plain with seasonal wet-dry climate. Your house foundation will experience soil expansion and contraction regardless of dewatering in town. More so in a drought. My yard has large cracks in it. That's just the reality of clay. And there is no dewatering nearby, and as I mentioned my measurements of shallow groundwater show no significant drop of groundwater. The drought and irrigation changes to the topsoil affect my clay more than the small change in water 15' down.

That is also why modern construction does soil reports, engineered fill and stronger reinforced foundations. To account for what is inevitable when building on clay.

Finally, you mention:
"Why can't Palo Alto simply adopt best practices that value groundwater? Is doing so prohibitively expensive for a home that sells for $3 - $5 million more than the lot on which it is built?"

Okay - this is a more interesting topic: what do you recommend?

The original op-ed called for an immediate halt to basement dewatering . Follow-on postings went further and called for a halt to all basements! That is a serious demand.

If you are simply asking for a better method to achieve the same goal, that's more interesting...


1 person likes this
Posted by PAmoderate
a resident of Old Palo Alto
on Dec 15, 2015 at 4:03 pm

PAmoderate is a registered user.

"The original op-ed called for an immediate halt to basement dewatering . Follow-on postings went further and called for a halt to all basements! That is a serious demand."

It's because it's not about dewatering - it's about stopping basements. It's not enough that people can't built second-stories - now they don't want you to build basements.

It's about ossifying Palo Alto into Disneyland, regardless of the science (or lack thereof).


Like this comment
Posted by Save Palo Alto's Groundwater
a resident of Old Palo Alto
on Dec 15, 2015 at 4:49 pm

@waterwater
Why don't we meet? You can e-mail me at pagroundwater@luxsci.net.
Yes, we are calling for adoption of best practices that very significantly reduce the amount of water removed and dumped into the storm drains for basement construction.

Could not a combination of optimized pumping protocols (to minimize the time) plus local re-charge and irrigation could both shorten the construction time and reduce the water used for basement construction by a very large amount? In Holland, basements are constructed under water without dewatering, as it is simply impossible to dewater as the flows are too high, and Phil Bobel (Public Works) stated at the 12/1 PSC meeting "we don't need to go to Holland," so there are clearly methods used in the US as well.


2 people like this
Posted by Slow Down
a resident of Community Center
on Dec 15, 2015 at 5:03 pm

Slow Down is a registered user.

[Post removed.]


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Posted by Shut Up
a resident of Barron Park
on Dec 15, 2015 at 7:19 pm

[Post removed.]


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