. 2017 Apr 19;12(4):e0175344. doi: 10.1371/journal.pone.0175344

Table 1. Number of chemicals used and their summed masses per event for oil and gas development (does not include water)^a.

		Chemicals per event				Mass per event (kg)
Pooled Activities	Events^a	Mean	Median	Min	Max	Mean	Median	Min	Max
Acidizing	256	25	20	1	41	4,132	3,459	10	24,043
Gravel packing	169	6	3	1	65	24,655	6,297	61	710,722
Hydraulic fracturing	13	25	23	15	37	129,910	142,245	4,526	243,219
Maintenance acidizing	390	30	35	2	52	2,779	2,028	155	15,548
Maintenance acidizing and gravel packing	3	27	27	27	27	7,712	6,632	6,518	9,985
Matrix acidizing	7	21	20	20	23	4,210	3,055	1,970	10,791
Well completion and rework—type not specified	43	20	21	1	71	16,287	8,028	215	100,566
Well drilling	186	46	54	3	72	1,828,619	97,669	96	309,284,305
Well drilling with gravel packing	136	57	58	26	66	239,305	181,098	21,552	1,233,365

^aThere are 1,207 events in the data set but four events have only water listed so they are not included in this table (N = 1,203).

Table 1. Number of chemicals used and their summed masses per event for oil and gas development (does not include water)a.