Central Valley Groundwater Pollution
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Central Valley Groundwater Pollution

In California, agriculture is a 47.1 billion dollar industry, making up 2% of the state's economy.[1] At the heart of this industry lies The Central Valley of California, a vital agricultural hub for the state and country. Consisting of both the San Joaquin Valley and Sacramento Valley, the Central Valley has an estimated two thirds of the state's cropland with 7 million acres.[2] California is also the leading dairy producer in the country, with 1.8 million mature cow in the Central Valley contributing to 80% of California's dairies.[3][4] By being a crucial region for large agricultural output in a state that often suffers from drought, water quantity and quality have been a leading concern for the Central Valley.Contaminated groundwater in the Central Valley of California is a growing problem in many of the agriculture-based communities based in the area.[5] Groundwater in the Central Valley is now a resource that is being threatened due to contamination overuse and is a public health concern for the industries and communities that depend on this as their leading water source.[5] Combined with the overdraft of the underground aquifers, groundwater contamination is becoming increasingly worrisome as the amount of clean groundwater dwindles down.[6] Near-term solutions to this growing problem are often costly and hard to implement in a timely manner while also clearing the water as safe to use. Currently nitrates are the most abundant of these pollutants in the Central Valley due to the copious amounts of agricultural runoff that comes from the numerous farms in the valley.[7] Concentration of naturally occurring arsenic is also an issue.[8]


The pumping of groundwater has been happening in the valley since 1850 when residents began to construct pumps to help make up for the lack of surface water in the area.[7] At the turn of the 20th century, California established itself as a leading agricultural state due to its technological advancements in land management, irrigation and machinery. The Central Valley had the ideal economic and climate conditions for a diverse range of crop growth and drew in wealthy landowners to grow their industry in the region. Throughout the early 1900's, technology for waste management did not advance at the same speed as the growth in agriculture.[9] This makes these aquifers extremely important because groundwater supplies much of the water needed for agricultural purposes and serves as the only source of water for several communities throughout the valley.[10]

However, there is not a reciprocal amount of water available to recharge the aquifers and recent years have seen an increase in wells drying up. This overdraft of groundwater is causing numerous problems for farmers throughout the valley and is only made worse with the effects of climate change.[7] Groundwater contaminated by nitrates comes from 50 years of unregulated management of livestock waste disposal, septic systems and commercial fertilizers.The Californian Sustainable Groundwater Management Act of 2014 was the first of its kind to specify how to manage groundwater in way that would not harm or endanger future generation's access to clean groundwater.[7]

Before this act, there were no regulations surrounding groundwater management other than the federal Safe Drinking Water Act and the Clean Water Act. Even these acts do not totally protect Central Valley residents. Consistent monitoring didn't begin until the 1950's, with only 13,000 tests completed in the 1980's. Today, the California Spatio Temporal Information on Nitrate in Groundwater (CASTING) database comes from over 133,329 tests in the Central Valley region.[11] With advancements in testing and research, the Central Valley is increasing in efforts to reduce the impact of nitrate water pollution that is expected to drastically increase in the next couple decades.[12]

Regulations and Standards

Set by the California Department of Public Health (CDPH), the Maximum Contaminant Level (MCL) of nitrates, in CCR §63341, are 45 milligrams per liter (mg/L) for nitrate as NO3 (equivalent to 10 mg/L for nitrate as nitrogen or "N"); 10 mg/L for nitrate plus nitrite as N; and 1 mg/L for nitrite as N. Public wells are required to annual water testing, where they submit their nitrate levels to the CDPH, however private wells are not subject to do this. Though 98% of the state has access to water with a suitable level of nitrates, there are disparities in  who does not have access to clean water.[13]

Despite modern data and methods for agricultural safety, 92 water systems in the Central Valley were attached to wells containing illegal levels of nitrates between 2005 and 2008, impacting the 1,335,000 residents in the area.[13]  Historically, programs to address the public health and economic impact nitrates have on communities and industries run at around $1 million each, making this a costly and slow process for change.[14]

The Californian Sustainable Groundwater Management Act of 2014 was the first of its kind to specify how to manage groundwater in a way that would not harm or endanger future generation's access to clean groundwater.[6] Signed by Gov. Jerry Brown in 2014, this three-bill legislative package created a framework for preserving and managing groundwater at the local and state level. This creates a regulatory process, mandating that Groundwater Sustainability Agencies (GSAs) to adopt Ground Water Sustainability Plans (GSPs) to manage supply. Before this act, regulations were only at the federal level with the Safe Drinking Water Act and the Clean Water Act, and failed to protect Central Valley residents. Based on these laws, farms and oil drilling sites could not put wastewater into the ground if it impacted clean drinking water; however, if water was not suitable to drink, these sources could dump lethal waste into the water, thus eliminating any access to the aquifer for residents.[11]

Sources of Nitrogen

Manure, fertilizer, septic and natural causes are the leading sources of nitrates in groundwater. Depending on the area in the Central Valley, manure and fertilizer are the largest sources of nitrates. Fertilizers have roughly 11.5 million tons of nitrogen added to them annually in the United States. The nitrogen in the fertilizer is then released into the atmosphere as ammonia gas or the rest is saturated into the soil and taken up by plants. The nitrogen in the soil is converted to nitrates, which is the main form nitrogen is found in for groundwater contamination.  In the U.S. 53% of nitrates originate from fertilizers, making this a priority for Californian officials. Manure produces around 6.5 million tons of nitrogen, that when not handled properly can contaminate soil and water sources. Natural causes, such as nitrates occurring in crops, is consistently a minimal source.[15]

Population Impact

There have been several studies done researching the impact of nitrogen on human health. The main finding that is consistent through all of the studies is the exposure period. In order for an actual risk of cancer to be significantly higher, the exposure period must be at least 5 and in some cases 10 years. This seems extensive, however when receiving pushback from the government, 10 years does not seem like such a lengthy period. Women who consume water with nitrate over 5 mg/L are at a higher risk of thyroid caner.[16] The important thing to realize here is that this 5 mg/L is 5 mg below the federally accepted limit. When consumed, the nitrate will compete with the iodine in the body, in which one is taken up by the thyroid. When the thyroid takes up nitrogen over iodine, the thyroid begins to lose function. This exposure is only 5 years before the risk of thyroid cancer increases significantly. Individuals are at a higher risk for colon and rectal cancer when they consume water with high (above 5 mg/L) nitrate levels. Exposure for 10+ years is associated with increased colon cancer risk among susceptible populations. (,[17][18]). These populations are usually communities that lack access to fresh fruits and vegetables, as a lack of vitamins C is a major risk factor. Drinking water and dietary sources of nitrate and nitrite cause increased cancer risks due to the nitrate compounds reacting with amines and amides to form carcinogens. There is also an increased risk of Non-Hodgkin's Lymphoma. A particular study indicated that long term exposure to elevated nitrate levels in the drinking water can contribute to the risk of NHL. The exact process of how this happens is still being researched.[19]


  1. ^ California laws relating to animal industry, 1919. Prepared by the California State Library for the State Department of Agriculture, Division of Animal Industry. Sacramento,: California State Printing Office,. 1919.CS1 maint: extra punctuation (link)
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  6. ^ a b T, Harter (2015-07-01). "California's agricultural regions gear up to actively manage groundwater use and protection". California Agriculture. 69 (3). ISSN 0008-0845.
  7. ^ a b c d "Groundwater Nitrate Sources and Contamination in the Central Valley". California WaterBlog. 2017-09-18. Retrieved .
  8. ^ Alexander, Kurtis (5 June 2018). "Overpumping of Central Valley groundwater has side effect: too much arsenic". Hearst Newspapers. San Francisco Chronicle. Retrieved 2019.
  9. ^ Olmstead, Alan; Rhode, Paul W. (2018-07-16), "Agriculture in American Economic History", The Oxford Handbook of American Economic History, vol. 1, Oxford University Press, pp. 158-182, ISBN 9780190882617, retrieved
  10. ^ "Groundwater in California - Public Policy Institute of California". Public Policy Institute of California. Retrieved .
  11. ^ a b Nelson, Timothy; Chou, Heidi; Zikalala, Prudentia; Lund, Jay; Hui, Rui; Medellín-Azuara, Josué (2016-03-23). "Economic and Water Supply Effects of Ending Groundwater Overdraft in California's Central Valley". San Francisco Estuary and Watershed Science. 14 (1). doi:10.15447/sfews.2016v14iss1art7. ISSN 1546-2366.
  12. ^ Aichele, Stephen S. (2004). "Arsenic, nitrate, and chloride in groundwater, Oakland County, Michigan". Fact Sheet. doi:10.3133/fs20043120. ISSN 2327-6932.
  13. ^ a b Balazs, Carolina; Morello-Frosch, Rachel; Hubbard, Alan; Ray, Isha (September 2011). "Social Disparities in Nitrate-Contaminated Drinking Water in California's San Joaquin Valley". Environmental Health Perspectives. 119 (9): 1272-1278. doi:10.1289/ehp.1002878. ISSN 0091-6765.
  14. ^ Sheehy, Robert D. (2006). "Stale-Dated Check Fraud: How Much Has Your City Lost?". PsycEXTRA Dataset. Retrieved .
  15. ^ "Nonpoint and Point Sources of Nitrogen in Major Watersheds of the United States". 1994. Cite journal requires |journal= (help)
  16. ^ Ward, Mary H.; Kilfoy, Briseis A.; Weyer, Peter J.; Anderson, Kristin E.; Folsom, Aaron R.; Cerhan, James R. (May 2010). "Nitrate Intake and the Risk of Thyroid Cancer and Thyroid Disease:". Epidemiology. 21 (3): 389-395. doi:10.1097/EDE.0b013e3181d6201d. ISSN 1044-3983.
  17. ^ De Roos, Anneclaire J.; Ward, Mary H.; Lynch, Charles F.; Cantor, Kenneth P. (November 2003). "Nitrate in Public Water Supplies and the Risk of Colon and Rectum Cancers:". Epidemiology. 14 (6): 640-649. doi:10.1097/01.ede.0000091605.01334.d3. ISSN 1044-3983.
  18. ^ De Roos, Anneclaire J.; Ward, Mary H.; Lynch, Charles F.; Cantor, Kenneth P. (November 2003). "Nitrate in Public Water Supplies and the Risk of Colon and Rectum Cancers". Epidemiology. 14 (6): 640-649. doi:10.1097/01.ede.0000091605.01334.d3. ISSN 1044-3983.
  19. ^ Ward, M. H.; Mark, S. D.; Cantor, K. P.; Weisenburger, D. D.; Correa-Villaseñor, A.; Zahm, S. H. (September 1996). "Drinking water nitrate and the risk of non-Hodgkin's lymphoma". Epidemiology (Cambridge, Mass.). 7 (5): 465-471. ISSN 1044-3983. PMID 8862975.

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