Contour plot -R

Hello I would like to create contour plot with this dataset data_Al. Now I would like to trace specific contours to represent when Al concentrations are above natural limits (threshold: 1.35 (min) and 4.35 (max)). Did you have any suggestions or can you help me please?
I have to do same for others metals and some of them have different threshold for example for Co I have at 50m 0.008 (min), 0.016 (max) and at 300m 0.004 (min), 0.008 (max).

Thank you

data_Al
Nom_Metal Depth Station C_F C_NF ratio Station_ID
1 Al 50 L1_2016_Dec 3.9277229728 3.9277229728 100.00000000 1
2 Al 100 L1_2016_Dec 2.9465089790 3.4510276081 85.38062611 1
3 Al 200 L1_2016_Dec 17.1638004712 28.7529068216 59.69414007 1
4 Al 250 L1_2016_Dec 39.9059132292 254.0168419658 15.70994778 1
5 Al 300 L1_2016_Dec 11.4667022202 16.4236208833 69.81835675 1
55 Al 50 L1_2017_Jan 2.6503154062 3.4093746151 77.73611602 2
56 Al 100 L1_2017_Jan 5.5689476237 5.5689476237 100.00000000 2
57 Al 200 L1_2017_Jan 7.4032966440 11.4916709718 64.42315188 2
58 Al 250 L1_2017_Jan 42.8354527847 369.3703725526 11.59688377 2
59 Al 300 L1_2017_Jan 7.4403208406 20.8675905377 35.65491103 2
110 Al 50 L1_2017_Jul 1.1111903681 1.7834559648 62.30545581 3
111 Al 100 L1_2017_Jul 1.3419567651 1.5426517839 86.99025788 3
112 Al 200 L1_2017_Jul 11.3210248729 12.4887450620 90.64981963 3
113 Al 250 L1_2017_Jul 3.8473443073 4.7850836226 80.40286463 3
114 Al 300 L1_2017_Jul 4.4178724766 6.1507786472 71.82623095 3
162 Al 50 L1_2017_Aug 0.7860731377 0.8011084887 98.12318166 4
163 Al 100 L1_2017_Aug 1.3318181823 1.3668913589 97.43409186 4
164 Al 200 L1_2017_Aug 3.1192583743 3.1643785304 98.57412267 4
165 Al 250 L1_2017_Aug 6.4888585122 9.7735235624 66.39221229 4
166 Al 300 L1_2017_Aug 8.5066131267 13.2933939847 63.99128121 4
217 Al 50 L1_2019_Oct 7.7728288387 8.8153500145 88.17379714 5
218 Al 100 L1_2019_Oct 4.4319612198 6.1552388981 72.00307402 5
219 Al 200 L1_2019_Oct 7.4287677643 13.1674427288 56.41769566 5
220 Al 250 L1_2019_Oct 15.6710710651 22.9226578537 68.36498265 5
221 Al 300 L1_2019_Oct 54.9703891336 52.2710775539 105.16406339 5
271 Al 50 L1_2020_Aug 4.1877658427 35.9106862704 11.66161463 6
272 Al 100 L1_2020_Aug 11.0921835239 15.2153555977 72.90124409 6
273 Al 200 L1_2020_Aug 43.9188685949 42.4740475844 103.40165605 6
274 Al 250 L1_2020_Aug 14.9489584248 14.9489584248 100.00000000 6
275 Al 300 L1_2020_Aug 65.7508287995 65.7508287995 100.00000000 6
326 Al 50 L1_2021_Oct 4.4275070942 7.7100852003 57.42487896 7
327 Al 100 L1_2021_Oct 6.7695177161 8.4021079390 80.56927815 7
328 Al 200 L1_2021_Oct 13.4941417362 16.3470708681 82.54776556 7
329 Al 250 L1_2021_Oct 24.7883206587 28.4534127334 87.11897195 7
330 Al 300 L1_2021_Oct 7.8482051031 40.7121765215 19.27729189 7

I wrote this code:

p ← plot_ly(data_Al, x = ~Station_ID, y = ~-Depth, z = ~C_F, type = “contour”,
color = ~C_F,
contours = list(coloring = “heatmap”, showlabels = TRUE)) %>%
layout(xaxis = list(title = “Station ID”),
yaxis = list(title = “Depth (m)”),
legend = list(title = " Al Concentration"))

p