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The longest total flow distance for mobilized pesticides between the closest cultivation plot edge and the POCIS sampling station was 187 m for diazinon (Station ID: 020d) and 42 m for carbofuran (Station ID:008d) (Table 4). The positive sampling stations with the longest flow distances between the cultivation plot and the sampling station also correspond with larger drainage areas than other detections with 0.43 km² (Station ID: 020d) and 2.03 km² (Station ID: 008d) for diazinon and carbofuran, respectively. All downstream diazinon-positive sampling stations occurred where upstream drainage areas fell within the lower quartile compared to all downstream sampling stations (Figure 3). The area draining to the downstream sampling station where carbofuran was detected was approximately equal to the median of all downstream sampling stations.

Table 4

POCIS summary for deployments and sampling stations where laboratory analysis confirmed soluble pesticides

Station ID	National forest	Overland flow distance (m)	In-stream flow distance (m)	Deployment duration (days)	Time since eradication (days)	Drainage area (km²)	Result
007d	Six Rivers	68.36	44.66	44	102	0.27	Diazinon
008d	Plumas	4.37	37.54	181	92	2.03	Carbofuran
020d	Shasta-Trinity	24.29	162.36	38	91	0.43	Diazinon
026d	Six Rivers	75.52	101.18	36	104	0.13	Diazinon
036u	Eldorado	n.a.	n.a.	56	496	0.28	Carbofuran

Station ID	National forest	Overland flow distance (m)	In-stream flow distance (m)	Deployment duration (days)	Time since eradication (days)	Drainage area (km²)	Result
007d	Six Rivers	68.36	44.66	44	102	0.27	Diazinon
008d	Plumas	4.37	37.54	181	92	2.03	Carbofuran
020d	Shasta-Trinity	24.29	162.36	38	91	0.43	Diazinon
026d	Six Rivers	75.52	101.18	36	104	0.13	Diazinon
036u	Eldorado	n.a.	n.a.	56	496	0.28	Carbofuran

Overland and in-stream flow distances represent the minimum downslope flow distance between the nearest cultivation plot edge and the sampling station. All positive detections were recorded during only one sampling deployment and tested negative during subsequent deployments.

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Figure 3

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Box plot of the area draining to all polar organic chemical integrative sampling stations deployed both up- and downstream of trespass cannabis cultivation complexes as part of the microscale study. Sampling stations where diazinon was detected are indicated by red triangles and carbofuran-positive sampling stations by black diamonds. Please refer to the online version of this paper to see this figure in colour: http://dx.doi.org/10.2166/wqrj.2022.101.

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