how can i turn off jetty debuging?

I have a java app that runs jetty:

public class ServerRunner {

    private final static org.apache.log4j.Logger logger = LoggingUtils.getLogger();

    public static void main(String[] args) throws Exception {
        PromptoConfig.s.initLog();


        final int port = 8082;

        final Server jettyServer = new Server(port);
        final HandlerCollection handlers = new HandlerCollection();

        // Creating the first web application context
        final WebAppContext webappContext = new WebAppContext();

        System.out.println("===== PromptoConfig.s.RESOURCES_BASE " + PromptoConfig.s.RESOURCES_BASE);
        webappContext.setResourceBase(PromptoConfig.s.RESOURCES_BASE);
        webappContext.setContextPath("/");

        System.out.println("===== PromptoConfig.s.WEB_XML_PATH " + PromptoConfig.s.WEB_XML_PATH);
        webappContext.setDefaultsDescriptor(PromptoConfig.s.WEB_XML_PATH);
//        webappContext.setTempDirectory(new File(temp));


        DBSQLConfig.s().DB = com.waze.prompto.config.DBSQLConfig.s.DB;


        webappContext.setExtractWAR(false);
        handlers.addHandler(webappContext);

        // Adding the handlers to the server.
        jettyServer.setHandler(handlers);

        try {
            jettyServer.start();
            jettyServer.join();
        } catch (Exception ex) {
            logger.error("failed to init jetty server", ex);
        } finally {
            jettyServer.destroy();
        }
    }
}

i see in the logs debug info in intellij console:

633016 [org.eclipse.jetty.server.session.HashSessionManager@22fcf7abTimer] DEBUG org.eclipse.jetty.server.session  - Scavenging sessions at 1496325042425

How can i turn this debug logs off?