Scientific Investigations Report 2006–5290

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5290

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Table 6. Summary of microbiological data, by type of principal-aquifer lithology, collected from wells in 22 study units of the National Water-Quality Assessment program, 1993–2004.

[Type of lithology: residuum, remains from chemical and physical weathering of parent aquifer materials or formation. Abbreviations: CFU/100mL, colony-forming units per 100 milliliters; <, less than; >, greater than; –, no data or not applicable]

Tests Type of lithology Number
of wells		 Number of wells
with detections
(percentage)		 Concentration
(CFU/100mL)
Median Range
Total coliform Carbonate rocks (limestone, dolomite) 202 121 (59.9) 2 <1 – 1,600
Sandstone, shale 118 45 (38.1) <1 <1 – 420
Crystalline rocks 74 38 (51.4) 1 <1 – >80
Semiconsolidated sand, residuum 112 30 (26.8) <1 <1 – >80
Volcanic 48 10 (20.8) <1 <1 – >18
Sand, gravel 301 61 (20.3) <1 <1 – >110
Alluvium 111 12 (10.8) <1 <1 – 60
Escherichia coli Carbonate rocks (limestone, dolomite) 253 65 (25.7) <1 <1 – 1,200
Volcanic 130 2 (1.5) <1 <1 – 90
Crystalline rocks 63 4 (6.3) <1 <1 – 38
Sand, gravel 280 13 (4.6) <1 <1 – 23
Semiconsolidated sand, residuum 112 13 (11.6) <1 <1 – 15
Sandstone, shale 89 7 (7.9) <1 <1 – 33
Alluvium 51 0 (0) <1 –
Coliphage Semiconsolidated sand, residuum 86 3 (3.5) – –
Volcanic 40 2 (5.0) – –
Carbonate rocks (limestone, dolomite) 78 6 (7.7) – –
Sand, gravel 192 2 (1.0) – –
Crystalline rocks 12 0 (0) – –
Sandstone, shale 0 – – – –
Alluvium 15 1 (6.7) – –

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