5 research outputs found
Trends in Drinking Water Nitrate Violations Across the United States
Drinking
water maximum contaminant levels (MCL) are established
by the U.S. EPA to protect human health. Since 1975, U.S. public water
suppliers have reported MCL violations to the national Safe Drinking
Water Information System (SDWIS). This study assessed temporal and
geographic trends for violations of the 10 mg nitrate-N L<sup>–1</sup> MCL in the conterminous U.S. We found that the proportion of systems
in violation for nitrate significantly increased from 0.28% to 0.42%
of all systems between 1994 and 2009 and then decreased to 0.32% by
2016. The number of people served by systems in violation decreased
from 1.5 million in 1997 to 200 000 in 2014. Periodic spikes
in people served were often driven by just one large system in violation.
On average, Nebraska and Delaware had the greatest proportion of systems
in violation (2.7% and 2.4%, respectively), while Ohio and California
had the greatest average annual number of people served by systems
in violation (278 374 and 139 149 people, respectively).
Even though surface water systems that serve more people have been
improving over time, groundwater systems in violation and average
duration of violations are increasing, indicating persistent nitrate
problems in drinking water
Box and whisker plots of nitrate uptake velocity (Ê‹<sub>f</sub>) in the buried and open reaches in Cincinnati, Ohio and Baltimore, Maryland, as reported in Beaulieu et al. [20] and Pennino et al. [21].
<p>Literature data were derived from a recent survey of 72 streams spanning several biomes and land-use conditions [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132256#pone.0132256.ref016" target="_blank">16</a>]. Plots display 10<sup>th</sup>, 25<sup>th</sup>, 50<sup>th</sup>, 75<sup>th</sup>, and 90<sup>th</sup> percentiles and individual data points outside the 10<sup>th</sup> and 90<sup>th</sup> percentiles. Nitrate uptake velocity was 13 times greater in open than buried reaches (p<0.001, paired <i>t</i>-test).</p
Results of simulation scenarios involving an even distribution of burial across the watershed with incremental increases of 5%.
<p>The primary y-axis and solid line represent the average volumetric NO<sub>3</sub><sup>-</sup> uptake rate among in the open reaches. The secondary y-axis and dashed line represent total NO<sub>3</sub><sup>-</sup> uptake in the open reaches.</p
Percent change in nitrate export in response to stream burial simulation scenarios.
<p>The simulation scenarios involve an even distribution of burial across the watershed with incremental increases of 5% and include: 1) Allowing both uptake rate constants and water velocities to change in response to burial (Combined response); 2) Allowing water velocity to change following burial, but holding uptake rate constants at open reach values; and 3) Allowing uptake rate constants to change following burial, but holding water velocities at open reach values.</p
Stream burial is an extreme, but ubiquitous, consequence of urbanization in stream ecosystems.
<p>The buried stream channels in the cited studies were constructed from various materials including (a) a cement-lined corrugated metal pipe in Baltimore, Maryland (USA), (b) a concrete tunnel in Cincinnati, Ohio (USA), and (c) a corrugated metal pipe in Cincinnati.</p