Arsenic is a toxic element that is both naturally occurring in the Earth’s crust and artificially produced from agricultural and industrial processes. Arsenic can enter groundwater sources from rock erosion, mining activity, volcanic eruptions, or forest fires. When contaminated groundwater is used to irrigate fields, arsenic can accumulate in soil and crops, entering surface water through runoff.
In 2001, the U.S. Environmental Protection Agency lowered the arsenic standard for drinking water from 50 parts per billion to 10 ppb. At the time, there were 3,000 water systems serving 11 million people that were in violation. A decade later, there were nearly 1,000 water systems serving 1.1 million people that were still not in compliance, and California was the state with the most violators. In 2010, California had 144 systems that were not in compliance, affecting nearly 450,000 people.
The California Department of Public Health has data on arsenic tests from around the state, in addition to data on many other toxic contaminants. For the Choke Point: Index package, Circle of Blue focused on arsenic tests in eight southern farming counties — Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare — that rely heavily on the San Joaquin Delta for water supplies.
Also called the Central Valley, this region is home to 3.7 million people, or about 10 percent of the state’s total population. It is well documented that water quality in this region is poor, and so are its citizens. While 21.5 percent of California households fell at or below the poverty threshold of about $US 25,000 in annual income in 2010, all of these eight counties fared worse — upwards of 30 percent of residents in Fresno County, for instance. Children in the eight counties were most at risk. Between 27 percent and 39 percent of children in the region lived below the poverty line, compared to just 22 percent at the state level.
In other measures of well-being, Central Valley residents fared worse than the average Californian. Central Valley residents were about 10 percent less likely to have graduated from high school, and they were 14 percent less likely to have graduated from a four-year college. The 2010 median household income in the eight Central Valley counties was $US 46,000, or $US 13,700 less than the statewide median income. On average, the unemployment rate was 1.5 percent worse here than in the rest of the state.
The relationship between the region’s poverty and its largely unsuccessful work in Sacramento, the state’s capital, and in county seats to improve the region’s drinking water have been documented for decades. Between 2006 and 2013, more than 30,000 tests for arsenic were performed at 11,000 sites in more than 4,600 unique water systems within the Central Valley, according to data from the California Department of Public Health. Some sites were tested multiple times per year, while others were tested sporadically. With Choke Point: Index, Circle of Blue clarified the links using large data sets, or what’s commonly called “big data.” Our team gathered data from a multitude of sources — federal, state, localized non-profit agencies — and built the visualizations below.
Click the image below to launch an interactive Google Fusion Tables map that shows data on arsenic in the Central Valley from 2006 to 2013. The eight Central Valley counties that rely on the San Joaquin Delta are bordered in light blue; their zip codes are shaded according to the average arsenic level for all tests on all systems between 2006 and 2013. Click a zip code to compare the breakdown of each individual water system within that zip code and its neighboring zip codes. Toggle on the water systems that were tested, and click on an individual marker to learn more about that site’s test results, where that site is located, and how many people the site serves. Click a county name at the top to see the likelihood that a water system within that county will fall within a given range for arsenic. (Data gathered from Census, U.S. Geological Survey, and California Department of Public Health.)
Infographic: Arsenic contamination in California’s Central Valley from 2006 to 2013. Map © Jordan B. Bates and Aubrey Ann Parker / Circle of Blue. Click image to enlarge.
This map was created by Jordan B. Bates and Aubrey Ann Parker, Circle of Blue’s web producer and chief data analyst, respectively. Contributors included Holly Jo Sparks and Brett Walton of Circle of Blue, with assistance from Sreeram Balakrishnan of Google Fusion Tables; Sheng Long and Alysha Chan, graduate students with the Columbia Water Center in New York City; and Andrew Girrell, a freelance data analyst who is based in Traverse City, Michigan. Columbia interns were overseen by Upmanu Lall and Margo Weiss. Reach Circle of Blue’s data team at info@99.198.125.162/~circl731.
Choke Point: Index is produced in collaboration with Google Research, Qlikview, and the Columbia Water Center, with financial support from the Rockefeller Foundation.
