Inverting negative voltage back to positive with LM324
The LM324 datasheet says:


  Large Output Voltage Swing 0 V to V+ − 1.5 V.


With a 10 V supply you can expect the output to go as high as 8.5 V which matches what you are seeing.

If you're feeding this into an Arduino 5 V ACD  then you need a gain of only -0.5 to allow you to measure -10 V to 0 V. To achieve that you simply reduce R6 by a factor of two. The simple way to do this with reasonable accuracy is to put two 47k resistors in parallel.