WHO Lowers Particulate Pollution Level

The World Health Organization (WHO) recently revised its guideline for a safe level of exposure to fine particulate pollution to 5 µg/m³ from 10 µg/m³. According to this new lower standard 97.3 % of the global population has unsafe air. This includes 92.8% of the United States population exposed to particulate pollution above 5 µg/m³ .

Air pollution in the form of fine particles with diameters smaller than 2.5 microns, called PM 2.5, lodge in the lungs which can aggravate other conditions both immediately and long term –cutting months off of lives of those with comorbidities. The Air Quality Life Index (AQLI) group at the University at Chicago find that reducing the particulate air pollution to the WHO guideline would increase global average life expectancy by 2.2 years. AQLI says that this is comparable to the impact from quitting smoking. 

PM2.5 is is fine particle matter, and when inhaled can have immediate health impacts: itchy, watery eyes, increased respiratory symptoms such as irritation of the airways, coughing or difficulty breathing and aggravated asthma. Long term health effects can result from both short-term and long-term exposure to particulate pollution. Exposure to particles can cause premature death in people with pre-existing cardiac or respiratory disease. Researchers are still working to identify which types and sources of particles are most hazardous to human health, but they have been making progress in that area recently.

Particle are either directly emitted or formed in the atmosphere. Directly-emitted particles come from a variety of sources such as cars, trucks, buses, industrial facilities, power plants, construction sites, tilled fields, unpaved roads, stone crushing, and burning of wood. Other particles are formed indirectly when gases produced by fossil fuel combustion react with sunlight and water vapor. Many combustion sources, such as motor vehicles, power plants, refineries, and wildfires both emit particles directly and emit precursor pollutants that form secondary particulates. Surprisingly, during 2020, the first year of the Covid-19 pandemic, when widespread lockdowns slowed the world’s economy, the global annual average particulate pollution (PM2.5) was largely unchanged from 2019 levels.

The U.S. Environmental Protection Agency, EPA, requires states to monitor air pollution to assess air quality and ensure that they meet minimum air quality standards. The US EPA has established both annual and 24-hour PM2.5 air quality standards (as well as standards for other pollutants). The annual standard established in 2012 is 12 µg/m³ (an AQI of 39). The 24-hr standard remained at 35 µg/m³ (an AQI of 99) and will remain unchanged. States had until 2020 to meet this PM2.5 health standard, but not all areas are in compliance. If you want to take a look at real time particulate pollution levels you can see what the monitors nearest your home are reporting. Note that the levels are reported in AQI (0-50 AQI is good air quality and 51-99 is moderate air quality), but the detail on many sites includes the PM2.5 levels. Long Park in Haymarket Virginia was reporting an AQI level of 19 as I was finishing this article. Long Park is about 3 miles from my house down route 15. The other site below that is Washington Street in San Francisco where I lived for about 20 years.

 
The wild fires that annually burn across the West (and many parts of the world) carry smoke and particulate pollution great distances, even to the east coast. Wildfires are becoming more frequent and destructive in an environment more and more shaped by mankind’s choices in a changing climate. Fine particulate matter, PM2.5, in wildfire smoke adversely impacts human health. Recent toxicological studies suggest that wildfire particulate matter may be more toxic than equal doses of ambient PM2.5.
"In epidemiological studies, it has been shown that PM2.5 from wildfire smoke can exacerbate a range of health problems including respiratory and cardiovascular issues."

So, if you want to take a look at real time particulate pollution levels you can see what the monitors nearest your home or any where else in the world are reporting at this link.

Forever Chemicals- Now What

The U.S. Environmental Protection Agency (EPA) announced updated interim health advisory levels for four compounds in drinking water that are part of a group of compounds called PFAS (per- and polyfluoroalkyl substances) commonly referred to a "forever chemicals." Drinking water health advisories provide information on contaminants but are non-enforceable and non-regulatory.

EPA plans to propose a PFAS National Drinking Water Regulation in fall 2022. As EPA develops this proposed rule, the agency is also evaluating additional PFAS beyond PFOA and PFOS and considering actions to address groups of PFAS.

The health advisories addressed four PFAS chemicals: perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS), and the chemicals that have replaced them in the United States in recent years. In chemical and product manufacturing, GenX chemicals are considered a replacement for PFOA, and perfluorobutane sulfonate (PFBS) is considered a replacement for PFOS. The health advisory levels focus on these four chemical compounds: PFOA, PFOS, GenX, and PFBS.

• Interim updated Health Advisory for PFOA = 0.004 parts per trillion (ppt)
• Interim updated Health Advisory for PFOS = 0.02 ppt
• Final Health Advisory for GenX chemicals = 10 ppt
• Final Health Advisory for PFBS = 2,000 ppt

As Fairfax Water points out: “Water utilities are passive receivers of PFAS.  They do not produce or manufacture PFAS.  Instead, these chemicals are present in source waters that are treated to produce drinking water.”

In anticipation of future regulations, Fairfax Water hired an independent lab to test their water in spring 2021using current EPA-approved methods that can detect PFAS at much lower concentrations than previous methods. Fairfax Water also participated in the Virginia Department of Health (VDH) Occurrence Study that was completed in 2021. However, the practical quantitative limit was two to three orders of magnitude above the health advisory limit. (The PQL for PFOS and PFOA were both 3.5 ppt in their study.) An additional round of PFAS testing will be performed this month.

Below is a summary of all Fairfax Water PFAS Data, analyzed using EPA Method 533:

from Fairfax Water

As you can see, some of Fairfax Water’s results for PFOS and PFAS are above EPA’s 2022 health advisory levels. However, at this time, the lowest level that instruments can detect even at the special laboratory is 2 ppt, therefore results cannot be quantified down to the EPA’s Interim HA levels for PFOS and PFOA.

In 2016, the EPA health advisory was 70 parts per trillion (ppt) for PFOA and PFOS combined.  Since then, analytical methods have improved, and utilities are now able to test down to lower levels, but not yet low enough to screen for PFOA and PFOS at the new interim health advisory levels. 

Fairfax Water states:

“We are following the guidance of EPA and VDH Office of Drinking Water. Our next round of voluntary occurrence testing will occur in June of 2022. We will also be collecting PFAS samples in 2023 for the EPA’s Unregulated Contaminant Monitoring Rule (UCMR5). We await further guidance and will take action if necessary to meet future state and federal regulations when they are established.”

What do you do if you are concerned? Bottled water is not the answer, there is no standard for PFAS for bottled water, and bottled water is more lightly regulated than drinking water. If you are concerned about PFAS in your drinking water, you may consider purchasing a home treatment device. Though there are devices that have been certified as removing PFAS, the effectiveness of the removal has not been certified down to the level of the health advisory. According to the American Chemistry Council the level of new health advisory cannot be achieved with existing treatment technology and, are below levels that can be reliably detected using existing EPA methods.

Nonetheless, there is some home filter that have been independently certified to remove PFAS at a higher detection limit and it might help. NSF International, the Water Quality Association, Underwriters Laboratories and CSA International all certify home treatment products for removal of contaminants. NSF/ANSI Standards 53 and 58 are certified to remove PFAS at a higher level and are filters you can buy for your refrigerator ice maker and water tap. It is important to follow the manufacturer’s operation and maintenance instructions carefully to give the filter the best shot of removing contaminants.

See the entire VDH sampling report here. Loudoun Water participated in PFAS sampling both as an independent utility, and in collaboration with the Virginia Department of Health (VDH). Only one sample was found above the 2 ppt sample PQL - PFOA at 4.5 ppt. 

WSSC and the Washington Aqueduct have yet to respond to the EPA's new health advisory.

Prince William and Our Regional Climate Goals

 In November 2020 the Prince William Board of County Supervisors voted to adopt the Metropolitan Washington Council of Governments’ (COG) Region Forward Vision including a sustainability goal that calls for a decrease in greenhouse gas emissions of 50 % below 2005 levels by 2030 as the first step.

So, using the information available from COG and the U.S. Energy Information Agency (EIA) let’s take a look at where we are and what the data tells us so that we can move forward together in Prince William.

What you see above is the basic plan for how the region will meet the 2030 goal of reducing greenhouse gas emissions by 50%. Reductions in the carbon intensity of the grid were planned to account for half of the 2030 goal. This was to be achieved by switching to clean energy for a portion of the demand and switching from coal to natural gas for the rest under the Virginia Clean Economy Act which plans to achieve 30% renewable energy by 2030,  and creates the path to a carbon-free electric grid by 2045. 

The Virginia utilities have made great progress in building solar farms, switching fuel to the existing power plants and Dominion Energy is moving forward with the 2,640- megawatt Coastal Virginia Offshore Wind (CVOW) commercial project, the largest planned offshore wind farm in the United States. Over the past decade the carbon intensity of the electricity generated in Virginia has fallen by over 40%.

However, in 2020, electricity sales in Virginia were 115,585 GWh more than 30% greater than they were the decade before. This has led to the mass emissions levels of CO2 (e) remaining relatively constant. 

from EIA

In the Metropolitan Washington area as a whole, overall greenhouse gas emission have fallen 13% over the region since 2005 as you can see in the chart above. However, as is shown in the chart below, Prince William County greenhouse gas emissions have grown 19% since 2005.

 

 Let’s walk through the areas of greenhouse gas emission growth and reduction to understand how Prince William County ended up with a 19% increase in greenhouse gas emissions over a time when greenhouse gas emissions were shrinking in the region overall. Residential use stayed fairly constant, while commercial and transportation both grew. Take a look at the chart below.

 

We start with greenhouse gas emissions around 4,125,000 metric tons of CO2 equivalents per year in 2005. Between 2005 and 2018 the “increase commercial kWh/foot squared added around 1,075,000 metric tons of CO2 per year. What this is saying is that the average power usage per square foot of commercial space increased significantly over this period. Grocery stores, office buildings, restaurants and shops did not start using more power per square foot. What happened was that energy intensive uses grew in Prince William County. Data Centers use much more power than any other commercial use and they began to proliferate during this time.

The other large area of growth was population growth. while homes use power for heat, air conditioning, electricity that use stayed fairly constant. The growth was in transportation and mobility-all those new residents drive to work, the grocery etc. The big reduction in greenhouse gas emissions over the period came from the power companies change in electricity fuel mix (the change from coal fired turbines to natural gas fired turbines). The fuel change accounted for a reduction of about 1,000,000 metric tons of CO2 equivalents per year.

By building out data centers (which are increasing) we overwhelmed any benefit the change in electricity fuel mix would have given us. Had we not built the datacenters the CO2 equivalent emissions would have been reduced by about 7% instead of increasing. The choices our community makes about development, housing and transportation matter to the future of Prince William, Virginia and our planet.  

PFAS Health Advisory Announced

After years of delay, last week at the 3rd National PFAS Conference in Wilmington, North Carolina the U.S. Environmental Protection Agency (EPA) in the person of Assistant Administrator Water Radhika Fox announced updated interim health advisory levels for four compounds in drinking water that are part of a group of compounds called PFAS (per- and polyfluoroalkyl substances). In February 2021 the EPA had made the final determinations to regulate perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in drinking water. These regulations are now expected in fall 2022.

These substances have been used in industrial settings and production of consumer products like non-stick pans, waterproof clothing, and fire suppression foams since the 1940s. The concern is that PFAS generally break down very slowly, meaning that concentrations can accumulate in people, animals, and the environment over time.

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) are two of the most widely used and studied chemicals in the PFAS group. PFOA and PFOS have been replaced in the United States with other PFAS in recent years. In chemical and product manufacturing, GenX chemicals are considered a replacement for PFOA, and perfluorobutane sulfonate (PFBS) is considered a replacement for PFOS. The revised health advisory levels focus on these four chemical compounds: PFOA, PFOS, GenX, and PFBS.

• Interim updated Health Advisory for PFOA = 0.004 parts per trillion (ppt)
• Interim updated Health Advisory for PFOS = 0.02 ppt
• Final Health Advisory for GenX chemicals = 10 ppt
• Final Health Advisory for PFBS = 2,000 ppt

The interim updated health advisories for PFOA and PFOS are based on human studies in populations exposed to these chemicals. Human studies have found associations between PFOA and/or PFOS exposure and effects on the immune system, the cardiovascular system, human development (e.g., decreased birth weight), and cancer.

The final health advisories for GenX chemicals and PFBS are based on animal studies following oral exposure to these chemicals. GenX chemicals have been linked to health effects on the liver, the kidney, the immune system, and developmental effects, as well as cancer. PFBS has been linked to health effects on the thyroid, reproductive system, development, and kidney.

Drinking water health advisories provide information on contaminants but are non-enforceable and non-regulatory and generally provide technical information to states agencies and other public health officials on health effects, analytical methods, and treatment technologies associated with drinking water contamination.

EPA plans to propose a PFAS National Drinking Water Regulation in fall 2022. As EPA develops this proposed rule, the agency is also evaluating additional PFAS beyond PFOA and PFOS and considering actions to address groups of PFAS.

As part of a government-wide effort to confront PFAS pollution, EPA is making available $1 billion in grant funding through President Biden’s Bipartisan Infrastructure Law to help disadvantaged communities and communities facing disproportionate impacts reduce PFAS in drinking water. EPA is making $1 billion available in FY2022 and a total of $5 billion for fiscal years 2022-2026.

According to the American Chemistry Council, an industry trade group, these new levels cannot be achieved with existing treatment technology and, in fact, are below levels that can be reliably detected using existing EPA methods. This could be a significant problem with the proposed regulation and protecting public health if the level of detection in the method of analysis does not meet the level of sensitivity necessary to implement the interim standard.

We may have a local problem that could be very expensive to fix. In 2021 the Environmental Working Group (EWG) tested tap water samples from throughout Northern Virginia looking for a group of PFAS. They took samples from the tap water in 19 locations and found PFOA present in all 19 locations above the interim guidelines and PFOS present at 18 of the 19 samples above the interim guidelines. Though there were some samples with QC/QA issues and the work should be confirmed, the preponderous of the limited evidence is that the water supplied by Fairfax Water has contamination above the interim updated health advisories for PFOA and PFOS. The full results from the EWG can be found here.

USGS Studies PFAS Impact on Amphibians

In a recent article cited below and published in the journal Environmental Toxicology and Chemistry, scientists from Purdue University and the U.S. Geological Survey (USGS) studied the effects of PFAS pollution in water on tadpoles of three amphibian species. These three species are found throughout a wide portion of the U.S. and represent the three major amphibian groups that exist in our country.

PFAS or Per- and Polyfluoroalkyl (PFAS) substances are known as “forever chemicals” because they build up in animal tissues including blood and vital organs, bioaccumulate, and do not break down in the environment. We are still learning about the impact of PFAS on the ecology and human health. In 2009 the EPA set the first health advisory level (HAL) for PFOA and PFOA at 400 ppt each. In 2016 EPA reduced the health advisory level to a combined 70 ppt for PFAS. They have not yet established a health based MCL.

In this study, the scientists at Perdue and the USGS found that northern leopard frogs and eastern tiger salamanders were generally more susceptible to PFAS than American toads. 

“Amphibians are vital to ecosystem health, but can be sensitive to environmental stressors like chemical contaminants,” said Wes Flynn, a USGS scientist and the lead author of the study. “Our study shows that the effects of PFAS in surface water on amphibians is highly dependent on the species being exposed.” 

Aqueous film-foam release in Manassas, VA

PFAS can enter waterways from industrial and consumer activities and products, including the foams used to suppress gasoline, jet fuel and oil fires. Aqueous film‐forming foams are essential to effectively suppress fires associated with hydrocarbon‐based fuels, including gasoline and jet fuel, and are widely used at airports, military bases, chemical plants, and other industrial fire training areas. These aqueous film-forming foams are used to protect human life and property, but unfortunately they are becoming ubiquitous at trace levels.  

For this study, researchers used various concentrations of four PFAS that are found in surface water impacted by aqueous film‐forming foams use. They found that the chemicals affected size, body condition and speed of development of the tadpoles. All PFAS concentrations tested affected frogs and salamanders, but the toads, which develop into adults more quickly, were only affected by the highest levels not likely to be found in the environment.

The effects of PFAS on larval development differed between species. Frog development was delayed in the 10‐μg/L (ppb) PFHAS, 100‐μg/LPFOS, and 1000‐μg/L PFOS treatments while toads, development was only impacted by1000‐μg/L PFOA unlikely to be found in the environment.   

"Our results show that some amphibians could suffer health effects at sites highly contaminated by these PFAS present in fire-suppressing foams,” Flynn said. "More work is needed to determine whether such exposures could contribute to population declines. Our results indicate that evaluating the toxicity of PFAS using a single species is not sufficient for protective amphibian risk assessment. Future studies are needed.”

As a side note, in early March 2021 the Environmental Working Group (EWG) released the results of an analysis, they commissioned of tap water samples taken from various location throughout the Northern Virginia region. The EWG reported that they detected total PFAS in 19 samples of tap water ranged from about 6 parts per trillion, or ppt, in a state park in Fairfax County, to about 62 ppt in a public park in Prince William County. In 2019 the EWG had reported that the results from the sampling conducted as part of the EPA’s Unregulated Contaminant Monitoring Rule 3 from 2013 to 2015.  All results in Fairfax were non-detect, meaning that all results were below the detection limit of the test used. The Prince William County Service Authority Eastern service area was found to have 12 ppt of PFAS in 2014. Remember, 1 ug/L = 1,000 ppt so the levels found in the water supply in northern Virginia at various points were much lower than the levels the amphibians were exposed to.  

Flynn, R.W., Hoover, G., Iacchetta, M., Guffey, S., de Perre, C., Huerta, B., Li, W., Hoverman, J.T., Lee, L. and Sepúlveda, M.S. (2022), Comparative Toxicity of Aquatic Per- and Polyfluoroalkyl Substance Exposure in Three Species of Amphibians. Environ Toxicol Chem, 41: 1407-1415. https://doi.org/10.1002/etc.5319

Chesapeake Bay Gets a C

Near the end of May the University of Maryland Center for Environmental Science released their 15th annual report card on the health of the Chesapeake Bay. Overall, Chesapeake Bay scored 50% in 2021 up from a 45% in 2020 and down from the all time high of 55% in 2020. As you can see below, overall Chesapeake Bay Health Scores have been variable in the past and bounced around a bit.

 

Blue line is overall and black is the Potomac River in all exhibits

From 2015-2017 the overall Chesapeake Bay Health Scores were in the high C range (53, 54, 54). At that time the consecutive scores contributed to an overall positive trajectory and it appeared that we were making progress towards the U.S. EPA mandated TMDL goals. More time only served to show that the Health Index is a very flat graph with occasional break outs to the positive and negative sides. The overall health appears to be range bound and now it is on another upward trajectory. The Potomac River health has fallen from last year's high. 

 

 As you can see in the graphs above from the University of Maryland Bay Health | EcoHealth Report Cards (ecoreportcard.org), water clarity has been trending downward for years while nitrogen, phosphorus and aquatic grasses score (below)  have shown a possible improving trend. 

The Bay states continue with the Watershed Implementation Plans to meet the goals of the Chesapeake Clean Water Blueprint. However, I am not seeing any results from the money spent and effort.  Billions of dollars have been spent in Virginia trying to meet the pollution reductions mandated by the U.S. EPA in the Chesapeake Bay by 2025 that was supposed to lead to the "fishable, swimmable" waters. As it has for years, the Lower Bay in Virginia had the best health relative to the rest of the estuary. I attribute this to the money spent upgrading Virginia’s waste water treatment plants and proximity to tidal influence. The question has to be asked if the actions and investments are merely managing the Chesapeake Bay model rather than improving the health of the Bay. 

CA Hydropower and Drought

 

The following is excerpted from the U.S. Energy InformationAgency Report on Western Power Markets:

The extended drought in California could cut the state’s summer electricity generation from hydropower nearly in half compared with normal precipitation conditions, according to a modeling and analysis by the U.S. Energy Information Administration (EIA). EIA projects that hydropower will produce 8% of California’s electricity generation in a drought year, compared with 15% under normal precipitation conditions.

EIA projects that the decrease in hydropower generation will lead to an 8% increase in California’s electricity generation from natural gas, a 6% increase in energy-related carbon dioxide (CO2) emissions in the state, and an average 5% increase in wholesale electricity prices throughout the West given the current system's configuration.

“California has a diverse electricity fuel mix and is highly interconnected with the regional electric grid, but our study shows that a significant decrease in hydropower generation this summer could lead to higher electricity prices, among other effects,” said EIA Administrator Joe DeCarolis.

Hydropower is typically the third-largest source of electricity in California, but electricity generation from hydropower is highly reliant on snowpack that forms in the winter season. California’s snowpack was above normal as of December 2021, but it was 40% below normal levels by April 1 of this year. By May 11, 2022 update the snowpack was at 22% of normal. 

Over the last decade, California has experienced more frequent and intense drought conditions, and is currently in its third year of drought. Droughts limit water use in general and reduces hydropower in particular. Current drought conditions in the state can have a significant impact on power markets throughout the West, different than in past years. California has been aggressively accelerating growth in solar and wind energy which are intermittent in generating capacity and have been relying more heavily on power purchased and imported from other states. That imported power now accounts for nearly one-third of California’s power supply. Thus, the drought in California will require the import of more power- increasing the wholesale price.

As California has shifted toward more solar and wind energy resources for electric power generation and away from natural gas power plants the mix of power generation and its characteristics has changed. Since 2015, 58% of steam turbine natural gas units have been retired, or 6,500 megawatts (MW). Solar capacity, on the other hand, has increased by 8,800 MW (157%) since 2015. The increase in intermittent renewable generating capacity and the decrease in dispatchable resources -whose generation can ramp up or down to meet changes in system needs- means that fewer conventional power plants within the state are available to meet the system's. Over the same period power use has grown making the entire system more brittle. To help mitigate this situation, California has added significant battery storage capacity, growing from 11 MW in 2015 to 2,300 MW at the beginning of 2022. Batteries can provide system support to meet rapid changes in load and generation when renewables generate more or less than expected, but still only for brief periods. Even with California’s battery capacity additions, however, the total share of dispatchable resources is lower in 2022 than it was in 2015.

Water In Eastern Prince William County

There was a Town Hall meeting held at Jenkins Elementary School on Thursday, June 2nd  2022 about the changes planned in land us in the Comprehensive Plan Update and Amendments and what the impact will be on Prince William County. Below is my talk:

If you live in the eastern portion of Prince William County you should care very much about the fate of the Rural Crescent because the Rural Crescent is about water, your water. The public water supply in eastern Prince William (blue) comes from the Occoquan Reservoir. PWSA purchases 15 million gallons of water a day from Fairfax Water for you- it is all drawn from the Occoquan Reservoir. 

The Rural Crescent allows rain water to flow gently over vegetation, feed the aquifers that provide water to the private wells and the Evergreen water system, but also feeds the tributaries to Bull Run and the Occoquan River assuring the base flow to the rivers and streams that feed the Reservoir.

Development will impair the recharge of the groundwater aquifer, but also increase sediment and salt flow into the Occoquan Reservoir, reduce stream flow and deteriorate water quality while increasing demand for water to feed more homes, businesses and data centers.

Development increases impervious cover from roads, pavement and buildings does two things. It reduces the open area for rain and snow to seep into the ground and percolate into the groundwater and the impervious surfaces cause stormwater velocity to increase preventing water from having enough time to percolate into the earth, increasing storm flooding and preventing recharge of groundwater from occurring. According to the EPA groundwater recharge is reduced from 50% to about 15% and runoff increases from around 10% to 55%.

When generally open rural area is developed stormwater runoff increases in quantity and velocity washing away stream banks, flooding roads and buildings, carrying fertilizers, oil, grease, and road salt to the Occoquan Reservoir. The salt level in the Occoquan Reservoir is rising almost to the critical point, Fairfax Water says it will cost $1-$2 billion to build desalination treatment their plants.

Our future and our children’s future is our water. We can’t allow it to be destroyed by paving roads and building data centers, warehouses and housing developments that will produce windfall profits for the landowners while leaving us with the bill of one to two  billion dollars to remove the increasing salt level from the Occoquan Waters.

Parts of California are Sinking a Foot a Year

Since the 1920s, excessive pumping of groundwater at thousands of wells in California’s San Joaquin Valley has caused land in sections of the valley to subside, or sink, by almost 30 feet. This subsidence is exacerbated during droughts, when farmers rely heavily on groundwater to sustain one of the most productive agricultural regions in the nation. Once the land subsides it's capacity to hold groundwater cannot be restored.

from Vasco et al

Subsidence induced by groundwater depletion is a grave problem in California’s Tulare Basin, and while certainly not surprise, scientists at NASA have been alarmed by how much faster the areas of the San Joaquin Valley are sinking during this extended drought period. NASA found that sections of the Tulare Basin are sinking at a rate of about a foot a year.

Subsidence can also cause structural damage to the infrastructure we build on top of the earth- like roads, bridges, and pipes.  Often, permanently losing storage space for water as the earth compacts. A group of scientists supported by their various organizations combined the data from two orbiting satellite-based systems to monitor the variations within the Tulare basin at various timescales.

Using the Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) observations, which provide estimates of the displacements of the Earth’s surface, and terrestrial water storage changes measured from NASA’s Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-on (FO) missions the scientists were able to model the groundwater changes.

 However,  changes in the gravity field sensed by GRACE and GRACE-FO can be traced to a variety of sources such as ground movement, soil moisture, water table variations, and snow cover. Thus, it was  diffcult, if not impossible, for the scientists to distinguish between water mass changes in the shallow unconfined aquifer and in the underlying confined aquifer using gravitational observations alone.

Corcoran clay separates the shallower unconfined aquifer from the confined aquifer below. Recharge occurs in the unconfined aquifer from snow, runoff, and precipitation. Groundwater storage in both the unconfined and confined aquifers is detected by the GRACE satellites. Compaction, believed to occur predominantly in the confined aquifer, causes the displacement of the Earth’s surface measured by Sentinel-1 Synthetic Aperture Radar (SAR) satellites.

Though much more work needs to be done, results suggest that available Sentinel and GRACE satellite data can indeed monitor hydrological variations over time. With future improvements in observations, and additional satellites planned for 2023, there should be even better monitoring of the changes in the Tulare basin in the future.

Read the article here if you are interested.

Vasco, Donald W., Kim, Kyra H., Farr, Tom G., Reager, J. T., Bekaert, David, Sangha, Simran S., Rutqvist, Jonny Beaudoing, Hiroko K., 2022/03/09: “Using Sentinel-1 and GRACE satellite data to monitor the hydrological variations within the Tulare Basin, California,” Scientific Reports, 3867 vol 12 issue 1.