Figure 2.4.16: Ground water quality trends in the United States 50° 120° lusag
110° lusurb lusag lusag lusag 40° lusag
lusurb lusag
sus lusag sus
lusag lusag
lusag sus
sus sus 30° lusag sus lusurb sus 0 0 EXPLANATION Principal aquifer rock type Non-glacial sand and gravel aquifers
Glacial sand and gravel aquifers—Aquifers are discontinuous within area shown
Coastal Plain aquifers in semi-consolidated sand Sandstone aquifers
Sandstone and carbonate-rock aquifers Carbonate-rock aquifers
Igneous and metamorphic-rock aquifers Increase Decrease
Statistically significant change in nitrate concentrations at the network level shown as arrows, with the size of the arrow representing the median of the difference in concentration for the network in milligrams per liter as N. Yellow highlighting denotes location where median nitrate concentration for the network is greater than 10 milligrams per liter in the second full-network sampling event
Less than 0.1 0.1–0.5
Greater than 0.5 No significant change *
lusag lusurb sus
Source: Adapted from USGS-NAWQA 2015 87
Statistically significant change in network where more than half of the data are pairs of nondetects
Network type
Agricultural land-use study Urban land-use study Major aquifer study
250 250 500 MILES 500 KILOMETERS lusag lusurb lusurb lusag sus lusurb lusag lusurb lusag lusag sus lusag lusurb sus* lusag lusag sus sus* lusurb lusag lusurb sus lusag
