Table 3

Table 3. Summary of pesticides detected in surface water and Groundwater in the Potomac River Basin [MDL: Method Detection Limit; MRL: Minimum Reporting Limit; (E): concentration estimated; ug/L: micrograms per liter; <:less than]

		Surface Water					Groundwater
Chemical Name	MDL or MRL (µg/L)	Number of Samples Collected	Number of Sites Where Pesticide	Percent of Samples Having Detectable Concentration	90th Percentile Concentration (µg/L)	Maximum Reported Concentration (µg/L)	Number of Sites Sampled	Number of Sites Where Pesticide Detected	90th Percentile Concentration (µg/L)	Maximum Reported Concentration (µg/L)
Samples analyzed by gas chromatography with detection by mass spectrometry (Zaugg and others, 1995) (112 surface-water sites sampled for this analysis method)
Alachlor	0.002	279	14	24.4^a	0.029	3.100	105	1^a	<0.002	0.005
Atrazine	.001	279	92	88.2^a	.730	25.0 (E)	105	36	.250	1.20
Azinphos-methyl	.001	275	4	3.6^a	<.001	.130 (E)	104	0	< .001	< .001
Benfluralin	.002	277	1	0.7	<.002	.030	104	0	< .002	< .002
Butylate	.002	277	2	0.7	<.002	.018	104	0	< .002	< .002
Carbaryl	.003	279	23	28.3^a	.064	2.00 (E)	105	0	< .003	< .003
Carbofuran	.003	279	7	5.7^a	<.003	.460 (E)	105	0	< .003	< .003
Chlorpyrifos	.004	277^b	12	17.0^a	.008	.041	104	0	< .004	< .004
Cyanazine	.004	279^b	17	23.3^a	.078	3.00	105	0	< .004	< .004
DCPA	.002	277^c	9	12.6^a	.002	.045	104^c	1^a	< .002	.001 (E)
DCPA	.002	277^c	9	12.6^a	.002	.045	104^c	1^a	< .002	.001 (E)
p,p'-DDE	.006	277^c	6	2.2^a	<.006	.023	104^c	10^a	< .006	.001 (E)
Desethylatrazine	.002	279^b	80	79.6^a	.150	.690 (E)	105^b	38^a	.140	1.40 (E)
Diazinon	.002	277	21	30.0^a	.071	1.40	104	0	<.002	<.002
Dieldrin	.001	277	2	0.7	<.001	.018	104	0	<.001	<.001
2,6-Diethylanaline	.003	277^b	1	0.4^a	<.003	.014 (E)	104	0	<.003	<.003
EPTC	.002	277	5	3.6^a	<.002	.012	104	3^a	<.002	.013
Ethoprop	.003	279	1	0.4	<.003	.027	105	0	<.003	<.003
Fonofos	.003	277	3	2.2^a	<.003	.084	104	0	<.003	<.003
gamma-HCH	.004	277	2	1.1	<.004	.025	104	0	<.004	<.004
Linuron	.002	277	5	10.5	.009	1.40	104	0	<.002	<.002
Malathion	.005	277	5	5.1^a	<.005	.410	104	0	<.005	<.005
Methylparathion	.006	277	4	3.6^a	<.006	.080	104	0	<.006	<.006
Metolachlor	.002	279^b	83	84.9^a	.990	23.0 (E)	105	20^a	.009	.460
Metribuzin	.004	277	9	11.6^a	.008	.160	104	2^a	<.004	.012
Napropamide	.003	279	2	0.7	<.003	.024	105	0	<.003	<.003
Pebulate	.004	277	0	0.0	<.004	<.004	104	1^a	<.004	.004 (E)
Pendimethalin	.004	277	5	13.4^a	.022	.320	104	0	<.004	<.004
Prometon	.018	279^c	68	71.7^a	.077	1.70 (E)	105 ^c	16 ^a	.018	.900 (E)
Propachlor	.007	279^b	1	1.4^a	<.007	.046	105	0	<.007	<.007
Simazine	.005	279^b	83	84.9^a	.510	4.40	105	23^a	.065	.210
Tebuthiuron	.010	279^c	22	21.5^a	.010	.220	105	2^a	<.010	.086
Terbucil	.007	274^b	7	6.9^a	<.007	.130 (E)	104^c	1^a	<.007	.260 (E)
Trifluralin	.002	277	9	4.7	<.002	.027	104	0	<.002	<.002
Samples analyzed by high-performance liquid chromatography with detection by ultraviolet spectroscopy (Werner and others, 1996) (8 surface-water sites sampled for this analysis method)
Chlorothalonil	.035	126	1	0.8^a	<.035	.100	82	0	<.035	<.035
2,4-D	.035	127	4	19.7^a	.340	2.80	82	0	<.035	<.035
Dicamba	.035	127	0	0.0	<.035	<.100	82	1	<.035	.070
Dichlobenil	.020	128	0	0.0	<.020	<.100	82	1^a	<.020	.100 (E)
Dichlorprop	.032	127	1	0.8	<.032	.150	82	0	<.032	<.032
Diuron	.020	128^b	2	14.8^a	.090	.690 (E)	82	0	<.020	<.040
MCPA	.050	127	1	1.6	<.050	1.30	82	0	<.050	<.050
Oryzalin	.019	128	1	6.3^a	<.019	1.90	82	0	<.090	<.038
Propoxur	.035	118	0	0.0	<.035	<.035	77	1	<.035	.060
Triclopyr	.050	127	2	3.9^a	<.050	.830	82	0	<.050	<.050

^aSome detections of estimated values were reported for this pesticide. ^bLess than 50 percent of detectable concentrations were estimated below the MDL or MRL. ^c50 percent or more of detectable concentrations were estimated below the MDL or MRL.