We have no research that shows that pool water with chlorine has damaged plants.  Chlorine in pools will evaporate. That's why it must be added regularly to pool water.  Pool owners would not be likely to add chlorine and then immediately drain the pool, because that would waste the chlorine, which is not inexpensive. 

It is possible that the pine tree has been drowned by repeated drenching from water and the soil has remained soggy for too long. 

ECN

I beg to differ.  This is what I researched which refutes your comments that chlorine shows no damage to plants.

"Toxicity Symptoms

Chlorine is a trace element essential to tree nutrition, but too much chlorine is poisonous. The leaves of trees are the first structures to show effects of chlorine toxicity. They will show a burned or scorched appearance with brown, dead tissue on the tips and edges, as well as between the leaf veins. Affected leaves may also be stunted, turn yellow and drop off early."  and further the article gives the following information....

Poisoning Process

Chlorine dissolved in water reacts with soil elements to form chloride compounds taken up by tree roots. Excess chlorides lead to the symptoms of chlorine poisoning. Chlorine enters soil from swimming pool water runoff, water from heavily salted roads and driveways, chlorine from air pollution that dissolves in rainwater, and naturally occurring chloride salts in the soil that dissolve in irrigation water or rainwater. Chlorine levels in municipal drinking water generally are too low to harm trees, but as a general rule, if you can smell chlorine in the water, don’t use it to water your trees. The human nose can smell chlorine in concentrations as low as 1 part per million.

Susceptible Trees

Certain tree species are particularly sensitive to chlorine poisoning. Among them are most varieties of maple tree and box elder trees. Also chlorine-sensitive are ash, crabapple, dogwood, horse chestnut, mulberry, pin oak, sweet gum and yellowwood.

Tree Treatments

Treat trees damaged by waterborne chlorine by irrigating with plenty of clean, chlorine-free water. This clean water will dilute and carry away chlorides from the soil and plant tissues. If your only water source is heavily chlorinated, remove the chlorine by putting your water in a container in a sunny spot for a week before using it on trees. If your soil is heavily laden with chlorides, apply gypsum to extract the chlorine. Spread the gypsum at the rate of 58 pounds per 1,000 square feet and work it into the top soil. Water thoroughly to leach the toxic levels of chlorine from the soil.

by:

Chlorinated Water & Tree Damage

google_ad_section_end by Herb Kirchhoff, Demand Media

We didn't mean to imply it was not possible for chlorine to damage plants, but rather that typical pool run off does not have enough chlorine to cause problems.  It looks like the information you already found has some options that may help. 

I wish that the pool run off could be dismissed as the culprit.  My 30 foot tall pine tree was fine last year but this year the needles have dropped off severely leaving branches barren of needles for about three feet.... and I can't think of what else would have caused such damage.   I have been 'hosing' with water to dilute the salt.... I have a salt water pool ... and I suspect it is the salt water (which converts salt into chlorine) that has done the damage.  If there is anything you think I can do to save the tree, please let me know.  I read that gypsum can be of some help but I have a blanket of thick ivy growing at the foot of the tree which makes incorporating the gypsum into the soil a very difficult task.  Is there anything else you can suggest that I could do to add to the soil to extricate the salt....or dilute the salt?  Thank you.  Josey Gadzala, August 1, 2016

Please send a photo and tell us the species of pine.  We may be able to be more helpful with that information in case there is another problem going on. 

ECN

Hello,

I don't know if these photos are visible.  I can send more tomorrow, if you wish.  Please let me know ifyou wish me to send more.  Thanks, Josey.

Sending along a few more photos of the pine tree.  Josey

Sending along a few more photos of the pine tree.  Josey

Thank you for the photos.  However, we are unable to identify the exact species of your pine tree.  This factor may not be important since there are probably some other factors involved.  For example, we are aware that white pines are more susceptible to chlorine and salt than other pine trees, but your tree is not a white pine and it is situated in a location that is not totally conducive to a healthy tree.  There is an abundance of shade over the lower limbs which will inhibit foliar health.  The tree is adjacent to a probable birch tree and surrounded by English ivy which results in heavy competition for soil moisture and nutrients.  Additionally, there is a rather large concrete device near the base of the tree.  This, too, has an impact on the tree's root system.   Given, that the root system is environmentally compromised, any damage inflicted by chemical contamination could result in diminished root mass, especially the shallow roots that are responsible for taking in water and nutrients.  The infusion of large amounts of water, while recommended for chlorine or salt contamination, could further damage the small hair roots near the surface.  
If the upper foliage is still healthy, you could prune out the lower 'dead' limbs in order to prevent an invasion of bark beetles.  
Continue to provide supplemental irrigation during hot, dry periods.  Keep in mind that any evergreen plant would prefer to receive an inch of rainwater per week until the ground is frozen in late autumn.
LS