I am wondering if the nature of the material you used--concrete--is going to influence the pH of the soil. Isn't concrete tending toward basic--higher than 7 pH, which is not what most vegetables like. Also any other contaminants in the product--is that a problem as it deteriorates over time? Just wondering--have heard these two issues brought up in relation to this kind of product. Once the soil is contaminated--well, you would have to remove it all in order to get it away from your crops, and start from scratch. Anyone know the answer?