(S (S (BASENP (DT A) (NN 2006) (NN survey)) (VP (VBD indicated) (SBAR (IN that) (S (NP (BASENP (QP (RB only) (NN 15)) (NN percent)) (PP (IN of) (NP (BASENP (NNS wells)) (PP (IN in) (BASENP (NNP Djibouti)))))) (VP (VBD were) (VP (VBN equipped) (PP (IN with) (NP (BASENP (DT a) (JJ protective) (NN concrete) (NN wall)) (SBAR (S (VP (TO to) (VP (VB prevent) (BASENP (NN contamination)))))))))))))) (PERIOD .))