A pH of 11 is still very alkaline, and may wind up damaging the soil and any critters in it. There is, fortunately, a remedy: use a small canister of chlorine gas, the same as ones customarily used for chlorinating pools. A small quantity of chlorine gas, “bubbled through” the waste liquid, will strongly reduce the pH of the result. One has to be careful, therefore, to continuously measure the pH and stop the process when it approaches the neutral point, to prevent the opposite problem of acidification. Also, it is likely that the area needs to be well-ventilated, so as to prevent damage to one’s lungs from the chlorine gas.

The recycling of burial plots actually started in Paris in the early 19th century. When the city of Paris realized that just about every plot of land near to the city had a cemetery, a law was passed, putting an upper limit on how long a body may remain in its plot. AIUI, similar laws have since been adopted by large cities in both Europe and North America, and possibly elsewhere as well.