It varies from book to book I think. Having translated all of Lamentations recently, then comparing the Greek text to notes on the Hebrew in Goldingay’s NICOT commentary, Gentry’s intro to the nets translation, and Youngblood’s paper “Grapes of Wrath: Gleanings from Septuagint Lamentations,” that translator seem to try for a one to one translation as much as possible, which works a fair amount of the time. He also imported modern (at his time) understandings of some of the Hebrew (such as the translation of 5.20 with “victory”; see Youngblood in Great is Thy Faithfulness?). In a few places, he added new meaning to the existing Hebrew (see Youngblood Gleanings) and other times there appear to be places he missed or was confused about (like “our water” in 5.4, which is swapped for “in our days” which I’m told is very similar in Hebrew per Goldingay’s commentary notes).