A bit of Javascript to pass the UTM to a WPForm since Pantheon strips the UTMs

PANTHEON_STRIPPED_WPFORMS_FIXER.js

// Get the UTMs with Javascript and pass them to the WPForm on the page
function getQueryParams(qs) {
    qs = qs.split('+').join(' ');
    var params = {},
        tokens, re = /[?&]?([^=]+)=([^&]*)/g;
    while (tokens = re.exec(qs)) {
        params[decodeURIComponent(tokens[1])] = decodeURIComponent(tokens[2]);
    }
    return params;
}

window.onload = function returnUTMs() {
  // Replace formID value with the ID number from the WPForm.
  var formID = 82;
    var query_params = getQueryParams(document.location.search);
    // console.log(query_params);
    utm_source = query_params['utm_source'];
    utm_medium = query_params['utm_medium'];
    utm_campaign = query_params['utm_campaign'];
    utm_content = query_params['utm_content'];
    document.getElementById('wpforms-'+formID+'-field_2').value = utm_source;
    document.getElementById('wpforms-'+formID+'-field_3').value = utm_medium;
    document.getElementById('wpforms-'+formID+'-field_4').value = utm_campaign;
    document.getElementById('wpforms-'+formID+'-field_5').value = utm_content;

    document.getElementById('wpforms-82-field_1').value = utm_source + " - " + utm_medium + " - " + utm_campaign + " - " + utm_content;
};