Eyes Underground: Lower Yakima Valley

Identification of wells with high nitrate helps to inform and protect community members that may be drinking contaminated water. Nitrate is a chemical which is present in groundwater in some areas of the Lower Yakima Valley. Nitrate has a drinking water standard of 10 mg N/L (milligrams of nitrate as nitrogen, per liter), and can cause health risks.  The following fact sheet describes these Health Effects:  Nitrate in Drinking Water  En Español -  Nitratos en el agua potable 

The Department of Health (DOH) conducted a health risk assessment to evaluate potential human health risks posed by nitrate contamination in the Lower Yakima Valley groundwater. This health assessment will be used to inform and recommend appropriate actions to protect the public health of the community.

This health risk assessment utilizes data collected from the Ambient Groundwater Monitoring Network. A link to this health assessment:  Evaluation of Risk from Exposure to Nitrate Contamination in the Groundwater of the Lower Yakima Valley, Washington 

Washington State Department of Health:  Environmental Public Health Science - Contacts and Programs   Important Information for Private Well Owners, 2019 

Yakima Health District:  Nitrate | Yakima County, WA 

Yakima County:  Groundwater Management | Yakima County, WA 

Nitrate is the most common groundwater contaminant because there are so many sources, and because nitrate is the most mobile form of nitrogen. It can easily move through soil with rain or irrigation water.

Nitrogen can come from:

• Human waste from septic systems and wastewater treatment plants
• Animal waste from livestock, dairies, hobby farms, and pets
• Fertilizer use for agriculture, parks and lawns
• Natural sources from the atmosphere, and plants

All these sources are present in the Lower Yakima Valley.  The widespread nature of the problem means that nitrate is coming from multiple sources.  Wells near contamination sources are at risk of becoming contaminated.

Water has a natural ability to dissolve and transport materials, including contaminants like nitrate, from the land surface to the aquifer. An aquifer is an underground layer of saturated, permeable rock that can store groundwater. The Washington State Department of Agriculture and Yakima County studied where nitrate comes from in the Lower Yakima Valley. The pie chart estimates the contribution of nitrogen (Bahr et al., 2018).   Estimated Nitrogen Available for Transport in the Lower Yakima Valley GWMA, 2018 . 

For more information about nitrogen, go to the chapter on  Nitrogen in the environment .

The Ambient Groundwater Monitoring Network sampled 170 wells including 34 monitoring wells and 136 drinking water wells located at people's homes throughout the Groundwater Management Area. Our samples were analyzed for nitrate+nitrite. We sampled all wells every three months for the first two years and now we will begin sampling annually starting in the Spring 2024.

The ambient groundwater monitoring network helps us 1) Assess long term nitrate trends in the aquifer 2) Assess nitrate trends in individual wells 3) Understand seasonal variability 4) Evaluate if strategies to reduce nitrate concentrations are working

To ensure our results are consistent and reliable, we use the same methods to sample the same locations at regular intervals. We also maintain diligent quality assurance and quality control measures. Our goal is to produce credible data that the community can trust, and to understand groundwater quality in the Lower Yakima Valley and how it changes over time. These measures support the goal of assessing the long-term health of groundwater in the Lower Yakima Valley.

Monitoring wells and drinking water wells need different methods to collect samples.

Groundwater monitoring wells are installed at the top of the aquifer, also called the water table, to establish a baseline nitrate concentration. If land use practices affect groundwater quality, these wells will detect those changes sooner than wells drilled deeper into the aquifer. The median monitoring well depth is 52 feet below land surface, with the deepest well at 275 feet.

Drinking water wells are designed to produce enough water to supply a home. These wells are typically drilled deeper into the aquifer and are screened (openings where water enters the well) over a greater depth below the water table. Samples from these wells tell us about the quality of water people are drinking, and additionally help to measure the aquifer's health over time.

In 2019, Yakima County installed 30 groundwater monitoring wells across the extent of the Groundwater Management Area (GWMA). Four additional wells were added to the network at the Port of Sunnyside and the City of Grandview. Monitoring wells include a vertical blue well marker, bolted flush mount well cover, and locked compression plug, all to ensure the wells are visible and secure. All monitoring wells in this study are screened (where water enters the well) across the water table (top of the aquifer) and are constructed to the Well Construction standards ( Chapter 173-160 WAC ).

More details on monitoring well construction and locations:  Lower Yakima Valley GWMA Ambient Groundwater Monitoring Well Installation Report, 2019 

First, we measure the static water level with a water level meter.  Knowing where the top of the water table is located, allows us to precisely lower the bladder pump to collect a sample at the top of the aquifer.  The bladder pump uses compressed air that is forced down one tube causing groundwater to rise in another tube.  An anchor cable is also attached to the pump to safely and accurately lower the pump intake at the right interval.

Before collecting a sample, we slowly purge groundwater from the well. We use low flow sampling methods that minimally disturb the water in the well and targets groundwater within the screened interval. 

While purging, we use a multi-probe field meter and water level meter to collect measurements, which include: · Water level · Temperature · pH · Electrical conductivity · Dissolved oxygen · Oxidation reduction potential

These measurements tell us when fresh groundwater is entering the well, since our goal is to collect fresh groundwater rather than stagnant well water.  Once the field measurements have stabilized, we collect our sample. 

Groundwater samples are filtered through a 0.45 micron filter, collected in a laboratory supplied bottle containing sulfuric acid, then placed in a secured cooler with ice. The Manchester Environmental Laboratory analyzes our samples for nitrate+nitrite. Ammonia-nitrogen is also sampled and analyzed if dissolved oxygen is low (<1 mg/L) in the water. This provides an accurate account of all nitrogen that may be present in groundwater.

All tubing is dedicated to each monitoring well.  Any equipment that is used on multiple wells is cleaned between uses. An equipment blank is collected weekly to assure that there is no cross-contamination between wells.

More information on sampling protocol is contained in the Quality Assurance Project Plan (QAPP):  QAPP Lower Yakima Valley GWMA, Ambient Groundwater Monitoring Network, 2021 

We chose the 136 drinking water wells in our study based on:

• Available well log
• Proper well construction following to state well construction standards ( Chapter 173-160 WAC )
• Undamaged well casing and surface seal
• Ability to sample water before water treatment systems
• Well provides water that is representative of the aquifer
• Owner permission to access the well

Since drinking water wells are constructed differently and already have dedicated pumps installed, the sampling process is different than monitoring wells.

We sample drinking water wells from an outside faucet as close to the wellhead as possible. We don't open wellheads to avoid introducing bacteria or other contaminants into the well.

We attach a Y-splitter to the outdoor faucet, which regulates flow. Tubing on one side of the Y-splitter routes water to a multi-probe field meter, which we use to measure temperature, pH, electrical conductivity, dissolved oxygen, and oxidation reduction potential. On the other side of the Y-splitter, a garden hose allows us to purge more water. We collect our sample after the field parameters have stabilized so that we collect water from the aquifer rather than a storage tank.

The samples are filtered through a 0.45 micron filter, collected in a laboratory supplied bottle containing sulfuric acid, then placed in a secured cooler with ice.

We clean the tubing and Y-splitter after sampling each well. Like when we sample monitoring wells, we collect an equipment blank sample each week to ensure there is no cross-contamination between wells.

Quality management processes provide credible data, which is important since this information is shared with homeowners and the community. We also collect quality assurance samples which include:

• Replicate samples collected for at least 10% of wells sampled
• Travel blanks
• Equipment blanks or decontamination blanks

• The field meter is calibrated at the beginning of the week, with a post-calibration check conducted at the end of each day to make sure our measurements are accurate.
• Field notes are recorded and maintained.
• Chain of custody procedures are followed.
• Additionally, a quarterly field audit is conducted by a licensed hydrogeologist.

For more information about why you should trust our data, go to the chapter:  Credible data .

We collected over 2,000 samples from 170 wells during the last two years. These results indicate that there is seasonal variability, or natural changes that occur with nitrate concentrations, in most wells in the Lower Yakima Valley. We noticed differences in nitrate concentrations based on areas. We found that monitoring wells had higher nitrate concentrations than drinking water wells. And we noticed that there is a connection between well depth and nitrate concentrations, with higher nitrate concentrations in the shallower wells. Each of these findings are discussed in greater detail below.

We saw changes in nitrate concentrations every time we sampled. These changes are shown in the time-lapsed map of our groundwater results. These variations coincide with changes in rainfall, temperature, irrigation, the growing season, and groundwater use by the community.

Seasonal variability is common in groundwater quality. Understanding the natural changes of nitrate concentrations in groundwater allows us to know if the changes we will see in the future are natural seasonal variations or if they are true increases or decreases over time. 

We collected samples from each well every three months for two years in the Ambient Groundwater Monitoring Network, to understand and quantify this variability.  It is common for there to be changes in nitrate concentrations that occur seasonally.  Example 1 shows an increase of approximately 5 mg N/L of nitrate from summer to winter in this well, and then a similar decrease from winter to summer.

Seasonal changes are not necessarily consistent for all wells.  Example 2 illustrates two wells that are located in the same area but have different highs and lows.  We do not fully understand the reasons why these wells are so different, but we think there could be a local cause that is affecting the nitrate groundwater quality.  Groundwater travels slowly (feet per year), so groundwater quality is often affected by what happens at the land surface near the well.

Our study is transitioning to annual sampling.  Since we now have seasonal data from all the wells in our study, we can gage the variability of nitrate in each well and understand when true changes are occurring.

We also evaluated the data from all of the wells combined to find the time of year when the variability was generally the lowest.  By identifying the low variability timeframe, it will allow us to identify true changes in water quality as we continue to monitor groundwater into the future.  We determined that Spring is the least variable season for the Lower Yakima Valley, so we will conduct our annual sampling every Spring.

We sorted our data by area and found elevated nitrate concentrations in Granger groundwater. Summary statistics for the drinking water wells identify that Granger has the highest: maximum, median and mean nitrate concentrations.

Please note that the following information is based only on data from private domestic drinking water wells and does not include municipal drinking water systems.

One of our goals with finding wells for our study, was to get good spatial coverage across the extent of the Lower Yakima Valley GWMA area.  This wasn't easy, since this is a big area covering over 175,000 acres.

We sorted our sample results by location and the closest city, and then we calculated summary statistics for each of the areas. This information may be useful as efforts are made to reduce nitrogen loading in the Lower Yakima Valley.

A couple of things to note; first, the median is the middle value in a set of numbers and is not affected by outlying values, so it is often a better representation of water quality than the mean (average), and second, the larger number of wells in the area, the more likely that the summary statistics will be representative of the area.

We have learned many things from spending time in the Lower Yakima Valley, sampling wells, talking to residents, and learning about what is important to the community.

• Clean and safe drinking water is important.
• People want to know that when they turn on their faucet, that the water will be safe to drink.
• The Lower Yakima Valley is home to people with different backgrounds, cultures and beliefs. People appreciate when we make the effort to communicate with them in a way that they can understand.
• People want clean groundwater, and they want to know about specific things they can do to make it better.
• Not everyone understands what nitrate is, or where it comes from. We know we have a lot of work to do.

Additionally, our data has helped us better understand nitrate in groundwater.

• Twenty-one percent of the nitrate samples we collected exceeded the drinking water standard of 10 mg N/L.
• The maximum nitrate value was 96 mg N/L.
• The median value, for each quarterly sampling event, ranged from 4.4 to 5 mg N/L.

• Seasonal variability with nitrate concentrations is present in many wells.
• Spring is the time when there is the least amount of variability, so we will conduct our annual sampling beginning in Spring 2024. This should allow us to identify true changes in groundwater quality over time.

• Analysis of the nitrate data in the Lower Yakima Valley by area or city, can assist us in identifying areas that may need more help.

• Monitoring wells (45%) have consistently higher exceedances of the drinking water standard, than drinking water wells (15%).

• There is a connection between nitrate concentrations and well depth.
• We found 90% of the wells which are less than 22 feet deep exceed the drinking water standard. We also found that 0% of wells greater than 250 feet deep exceed the drinking water standard.
  • All of the wells in our study that are less than 50 feet deep, are monitoring wells.
  • All of the wells in our study that are greater than 250 feet are completed in lower confined aquifers and have consistently lower nitrate concentrations.

The Lower Yakima Valley is a beautiful rural community in Central Washington. Over 2 billion dollars in agricultural commodities are grown and raised in this area, including dairy, hops, wine grapes, apples, pears, cherries, corn, triticale, alfalfa, pasture grass, wheat, mint, asparagus, and many others.

It is important to manage groundwater quality so that residents have safe drinking water, as well as having clean irrigation water that can be used to grow crops and water livestock.

Our hope is that by raising awareness and encouraging better land use management practices, that we will reduce nitrate concentrations in groundwater. This Ambient Groundwater Monitoring Network is the measuring stick that will gage how well we are doing into the future.

This StoryMap will be updated as we continue our annual sampling of the Lower Yakima Valley Ambient Groundwater Monitoring Network.

Our main webpage:  Lower Yakima Valley Groundwater Management Area 

Being able to trust our data is important, especially if residents are using our data to make decisions about how they invest in their futures and their community. Quality assurance and quality control measures ensure that the data collected are valid, credible and usable. 

Before sampling, we developed a Quality Assurance Project Plan (QAPP).  The QAPP describes the steps to ensure we collect consistent samples that will meet the project goals and objectives. We design the study and describe the field and laboratory procedures.  Our QAPP also describes the criteria for including wells in the study, the process for sample collection, sample preservation, chain-of-custody procedures, and proper equipment cleaning between sampling locations.  We document our sampling procedures and field measurements, and field audits are performed to ensure proper and consistent sampling technique.

Our staff work closely with the Manchester Environmental Laboratory staff for further quality management.

Our quality objectives help our data meet the goals of the study by controlling for precision, bias, sensitivity, comparability, representativeness and completeness. 

In the field, our quality control processes include: following Ecology standard operating procedures (SOPs), calibrating field meters, collecting field duplicates, travel blanks and equipment blanks.  Quality control processes in the laboratory include conducting laboratory blanks, duplicates, matrix spikes and check standards. 

Our plan outlines corrective action processes to follow if these quality control criteria are not maintained.

Another important part of quality assurance is data management, which describes how information is transferred and managed.

The laboratory uses data verification methods to evaluate completeness, correctness, and conformance and compliance of the data set against the method, procedural and contractual requirements outlined in this study.

Our quality assurance project plan includes a data quality usability assessment, which evaluates all the components of the sampling and analytical process to determine if the data is suitable for use. It describes how data will be analyzed and presented to make decisions towards the goals and objectives of the study.

The figure below illustrates the continuous process of quality assurance within a study, including; monitoring, identifying, verifying and implementing actions to produce credible data.

Redding, M., 2021. Quality Assurance Project Plan: Lower Yakima Valley Groundwater Management Area (GWMA) Ambient Groundwater Monitoring Network. Washington State Department of Ecology, Environmental Assessment Program, Publication number 21-03-106, 53 pgs.

   QAPP Lower Yakima Valley GWMA, Ambient Groundwater Monitoring Network, 2021 

Click here to return back to  Study Design. 

   Drinking Water Testing Facilities | Yakima County, WA 

All our data is publicly accessible through Ecology’s EIM (Environmental Information Management) database.  This includes all analytical results, field measurements, well location (latitude and longitude), and well construction information.  Data are entered into EIM once the quality assessment on each data set is complete, and homeowners are notified of their results. Results can be accessed via   Lower Yakima Valley Ambient Groundwater Monitoring Network Data  (MRED0005). The study ID is MRED0005.

• Ammonium - the nitrogen cation NH4 and is a usable form for plants
• Aquifer - underground layer of saturated, permeable rock that can store and transmit groundwater.
• Attenuation - when a contaminant is immobilized in the soils. For example, ammonium is a positively charged ion which binds with negatively charged soil particles. This attraction immobilizes ammonium.
• Dissolved Oxygen - the measure of how much oxygen is dissolved in water. It can tell us if the water is aerobic or anerobic.
• Electrical Conductivity - The conductivity of water is a measure of the capability of water to pass an electrical current. This indicates the relative ion concentration, or salts, in the water.
• Equipment blank - This quality assurance sample measures how well we clean our equipment after sampling a well. We pour laboratory grade distilled water through the cleaned equipment and send the sample to the laboratory for analysis.
• GWMA - Groundwater Management Area
• Groundwater - is the water present below the land surface that flows between the pore space of soil and rocks.
• Leaching - is the process where nitrate moves through the soil, below the root zone, and into groundwater.
• Nitrate + Nitrite - Analytical method which we used in this study. In this report we discuss our findings as Nitrate. Nitrite is an unstable form of nitrogen in the environment and typically is not detected when sampled by itself.
• ORP (oxidation reduction potential) - measure of how likely a solution is to give or receive electrons. Molecules that receive electrons are reduced, and molecules that give electrons are oxidized.
• pH - measure of the acidity or alkalinity of water.
• Replicate - two or more samples collected at the same site. Replicate samples provide quality assurance information on precision, or the measure of variability between results that is due to random error.
• Screened interval - the portion of the well that has tiny openings which allow water to enter the borehole, but prevent sediments from getting in. This allows the driller to target the underground zone where they want water from the well.
• Temperature - a physical measurement of hotness or coldness.
• Travel blank - a quality assurance sample which is filled at the laboratory in a sealed bottle and travels in the field in the cooler during sampling and is returned to the laboratory for analysis.
• Water table - top of the surficial aquifer