Effects of Agriculture and Urbanization on Quality of Shallow Ground Water in the Arid to Semiarid Western United States, 1993

Scientific Investigations Report 2007–5179

Table 4. Median values for selected well, aquifer, and land-use characteristics for regional National Water-Quality Assessment Program study units in the arid to semiarid Western United States, 1993–2004.

[Number in parentheses indicates number of wells sampled. Abbreviations: CAZB, Central Arizona Basins; GRSL, Great Salt Lake Basins; NVBR, Nevada Basin and Range; RIOG, Rio Grande Valley; SACR, Sacramento River Basin; SANJ, San Joaquin-Tulare Basins; SOCA, Southern California Basins; All, agricultural and urban land uses; Ag, agricultural land use; Urb, urban land use; ft, foot; kg, kilogram; people/km², people per square kilometer; kg/km², kilogram per square kilometer; m, meter; nd, not determined]

Well, aquifer, or land-use characteristic	CAZB		GRSL		NVBR		RIOG		SACR		SANJ		SOCA
Ag (9)	Urb (30)	All (142)	Ag (61)	Urb (81)	All (89)	Ag (65)	Urb (24)	All (47)	Ag (28)	Urb (19)	Ag (110)	Urb (26)
Well depth (ft)	43		69		30	27	32		20	20	27		38	35	63	129	24
Deep, coarse-grained soils with high infiltration rates¹ (percent)	0.0		0.0		0.0	0.0	0.0		15	15	10		0.0	0.0	0.0	29	7.0
Moderately deep, moderately fine to moderately coarse soils, with moderate infiltration rates¹ (percent)	100		24		10	6.0	28		60	60	74		9.4	9.2	9.4	71	75
Soils with layers impeding downward movement of water or moderately fine to fine soils, with slow infiltration rates¹ (percent)	0.0		76		55	71.5	18		4.0	14	4.0		4.1	16	15	6.0	0.0
Clay soils, with high water table or shallow impervious layer, with very slow infiltration rates¹ (percent)	0.0		0.0		21	17.3	30		12	24	12		76	50	23	0.0	18
1990 Population density (people/km²)	18.5		1,810		88.1	11.0	1,230		4.5	2.6	679		12.0	4.8	1,860	33.2	2,940
2000 Population density (people/km²)	24.5		1,990		223	12.7	1,360		4.6	2.8	719		11.4	4.7	2,650	30.0	2,880
Households on public sewers (percent)	29.4		99.4		90.6	3.0	96.1		2.4	1.6	72.2		61.7	5.4	99.3	5.4	99.8
Households on septic systems (percent)	70.6		0.6		8.7	93.3	3.7		89.8	94.6	27.5		38.3	94.4	0.5	92.0	0.0
1992 Nitrogen fertilizer application on farm land (kg/km²)	9,896		156		nd	229	0.0		nd	8,117	0.0		nd	7,117	14	8,470	91
2000 Nitrogen fertilizer application on farm land (kg/km²)	10,217		146		nd	1,369	0.0		nd	10,811	0.0		nd	10,036	18	11,020	86
1992 Nitrogen fertilizer application on non-farm land (kg/km²)	0.0		1,469		nd	0.0	374		nd	0.0	855		nd	0.0	1,647	0.0	1,697
2000 Nitrogen fertilizer application on non-farm land (kg/km²)	0.0		1,990		nd	0.0	831		nd	0.0	889		nd	0.0	2,916	0.0	2,793
Small-grain crops¹ (percent)	27.5		0.0		0.0	0.0	0.0		0.0	0.0	0.0		87.0	99.7	0.0	0.2	0.0
Row crops¹ (percent)	56.3		0.0		0.0	0.0	0.0		32.4	38.8	0.0		0.0	0.0	0.0	3.2	0.0
Pasture/hay crops¹ (percent)	0.8		2.7		4.3	60.3	0.0		10.0	17.4	0.0		0.0	0.0	0.0	5.9	0.1
Orchard/vineyard/other crops¹ (percent)	0.0		0.0		0.0	0.0	0.0		0.0	0.0	0.0		0.0	0.0	0.0	78.4	0.0
Irrigated land¹ (percent)	70.8		1.4		4.4	59.4	0.0		59.9	71.5	0.0		79.5	81.2	0.0	84.0	0.0

Well, aquifer, or
land-use characteristic

CAZB

GRSL

NVBR

RIOG

SACR

SANJ

SOCA

Ag
(9)

Urb
(30)

All
(142)

Ag
(61)

Urb
(81)

All
(89)

Ag
(65)

Urb
(24)

All
(47)

Ag
(28)

Urb
(19)

Ag
(110)

Urb
(26)

Well depth (ft)

129

Deep, coarse-grained soils with high infiltration rates¹ (percent)

0.0

7.0

Moderately deep, moderately fine to moderately coarse soils, with moderate infiltration rates¹ (percent)

100

6.0

9.4

9.2

9.4

Soils with layers impeding downward movement of water or moderately fine to fine soils, with slow infiltration rates¹ (percent)

0.0

71.5

4.0

4.1

6.0

0.0

Clay soils, with high water table or shallow impervious layer, with very slow infiltration rates¹ (percent)

0.0

17.3

0.0

1990 Population density (people/km²)

18.5

1,810

88.1

11.0

1,230

4.5

2.6

679

12.0

4.8

1,860

33.2

2,940

2000 Population density (people/km²)

24.5

1,990

223

12.7

1,360

4.6

2.8

719

11.4

4.7

2,650

30.0

2,880

Households on public sewers (percent)

29.4

99.4

90.6

3.0

96.1

2.4

1.6

72.2

61.7

5.4

99.3

5.4

99.8

Households on septic systems (percent)

70.6

0.6

8.7

93.3

3.7

89.8

94.6

27.5

38.3

94.4

0.5

92.0

0.0

1992 Nitrogen fertilizer application on farm land (kg/km²)

9,896

156

229

0.0

8,117

0.0

7,117

8,470

2000 Nitrogen fertilizer application on farm land (kg/km²)

10,217

146

1,369

0.0

10,811

0.0

10,036

11,020

1992 Nitrogen fertilizer application on non-farm land (kg/km²)

0.0

1,469

0.0

374

0.0

855

0.0

1,647

0.0

1,697

2000 Nitrogen fertilizer application on non-farm land (kg/km²)

0.0

1,990

0.0

831

0.0

889

0.0

2,916

0.0

2,793

Small-grain crops¹ (percent)

27.5

0.0

87.0

99.7

0.0

0.2

0.0

Row crops¹ (percent)

56.3

0.0

32.4

38.8

0.0

3.2

0.0

Pasture/hay crops¹ (percent)

0.8

2.7

4.3

60.3

0.0

10.0

17.4

0.0

5.9

0.1

Orchard/vineyard/other crops¹ (percent)

0.0

78.4

0.0

Irrigated land¹ (percent)

70.8

1.4

4.4

59.4

0.0

59.9

71.5

0.0

79.5

81.2

0.0

84.0

0.0

¹Percentage of land area in designated class within 500-m buffer around the well.

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