{"id":277,"date":"2025-06-01T19:42:59","date_gmt":"2025-06-01T23:42:59","guid":{"rendered":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/?p=277"},"modified":"2025-07-02T12:28:42","modified_gmt":"2025-07-02T16:28:42","slug":"chicago-and-milwaukees-tunnels","status":"publish","type":"post","link":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/2025\/06\/01\/chicago-and-milwaukees-tunnels\/","title":{"rendered":"What we can learn from deep tunnel systems in Chicago and Milwaukee"},"content":{"rendered":"\n
\n

By Mia Jaworski
UConn Journalism<\/strong><\/p>\n<\/blockquote>\n\n\n\n

Heavy rain over\u00adwhelms old city sewer sys\u00adtems, spilling raw sewage into rivers and water\u00adways. It\u2019s a prob\u00adlem cities around the world have faced for decades, and one grow\u00ading more urgent as cli\u00admate change fuels more intense and fre\u00adquent storms.<\/p>\n\n\n\n

One solu\u00adtion that\u2019s gained trac\u00adtion: mas\u00adsive under\u00adground stor\u00adage tun\u00adnels built deep beneath city streets.<\/p>\n\n\n\n

In Chicago and Milwaukee, where com\u00adbined sewer over\u00adflows used to be a reg\u00adu\u00adlar threat, deep tun\u00adnel sys\u00adtems have dras\u00adti\u00adcal\u00adly reduced the num\u00adber and sever\u00adi\u00adty of over\u00adflows.<\/p>\n\n\n\n

Although these tun\u00adnels do not address the root cause of CSOs\u2014namely, out\u00addat\u00aded and inad\u00ade\u00adquate 19th-cen\u00adtu\u00adry infrastructure\u2014they serve as a crit\u00adi\u00adcal solu\u00adtion to pre\u00advent imme\u00addi\u00adate envi\u00adron\u00admen\u00adtal and pub\u00adlic health risks.<\/p>\n\n\n\n

Few projects rival the scale and impact of Chicago\u2019s Tunnel and Reservoir Plan (TARP), also known as \u201cthe Deep Tunnel.\u201d The sys\u00adtem spans more than 100 miles, with tun\u00adnels as large as 33 feet in diam\u00ade\u00adter and buried as deep as 350 feet.<\/p>\n\n\n\n

Chicago<\/h2>\n\n\n\n

Launched in the 1970s and par\u00adtial\u00adly acti\u00advat\u00aded in 1984, the sys\u00adtem con\u00adtin\u00adues to expand and is expect\u00aded to reach full capac\u00adi\u00adty by 2029. According to the Metropolitan Water Reclamation<\/p>\n\n\n\n

District of Greater Chicago, TARP will store about 20 bil\u00adlion gal\u00adlons once com\u00adplet\u00aded in 2029.<\/p>\n\n\n\n

TARP has held back over\u00adflows that would have oth\u00ader\u00adwise sent untreat\u00aded waste into the Chicago River, Calumet River, and Lake Michigan.<\/p>\n\n\n\n

The sys\u00adtem includes four tun\u00adnel sys\u00adtems and reser\u00advoirs like the Majewski, Thornton, and McCook Reservoirs. The Thornton Reservoir has entire\u00adly elim\u00adi\u00adnat\u00aded CSOs with\u00adin its ser\u00advice area since 2020.<\/p>\n\n\n\n

The Metropolitan Water Reclamation District of Greater Chicago claims that TARP has sig\u00adnif\u00adi\u00adcant\u00adly reduced CSOs from an aver\u00adage of 100 days per year to 50. The envi\u00adron\u00admen\u00adtal ben\u00ade\u00adfits have been clear, with the num\u00adber of fish species in local rivers near\u00adly dou\u00adbling and water qual\u00adi\u00adty improv\u00ading dra\u00admat\u00adi\u00adcal\u00adly.<\/p>\n\n\n\n

\u201cThanks to the tun\u00adnels and many other improve\u00adments,\u201d the MMSD says, \u201cwe have cap\u00adtured and cleaned 98.6 per\u00adcent of all the stormwa\u00adter and waste\u00adwater that\u2019s entered the region\u00adal sewer sys\u00adtem.\u201d<\/p>\n\n\n\n

Milwaukee<\/h2>\n\n\n\n

<\/p>\n\n\n\n

Operational since 1993, Milwaukee\u2019s sys\u00adtem has pre\u00advent\u00aded more than 160.2 bil\u00adlion gal\u00adlons of pol\u00adlu\u00adtion from enter\u00ading Lake Michigan, accord\u00ading to the Milwaukee Metropolitan Sewerage District (MMSD), which attrib\u00adut\u00ades that suc\u00adcess to the tun\u00adnel.<\/p>\n\n\n\n

For com\u00adpar\u00adi\u00adson, the nation\u00adal goal for cities with sim\u00adi\u00adlar sys\u00adtems is 85 per\u00adcent.<\/p>\n\n\n\n

The system\u2019s begin\u00adnings date to 1972, when the State of Illinois filed a law\u00adsuit against the city and its sew\u00ader\u00adage com\u00admis\u00adsion for pol\u00adlu\u00adtion. The case even\u00adtu\u00adal\u00adly reached the<\/p>\n\n\n\n

U.S. Supreme Court. Five years later, a for\u00admal agree\u00adment between the Milwaukee Metropolitan Sewerage District and the Wisconsin Department of Natural Resources (DNR) com\u00admit\u00adted the region to reduc\u00ading sewer over\u00adflows.<\/p>\n\n\n\n

These piv\u00adotal moments spurred the cre\u00adation of the Water Pollution Abatement Program (WPAP), which MMSD cred\u00adits with deliv\u00ader\u00ading \u201cmajor improve\u00adments to the region\u00adal waste\u00adwater treat\u00adment sys\u00adtem.<\/p>\n\n\n\n

Accompanying this envi\u00adron\u00admen\u00adtal shift was a major struc\u00adtur\u00adal and finan\u00adcial com\u00admit\u00adment. In 1982, the MMSD was estab\u00adlished. Between the 1980s and early 2000s, the region invest\u00aded $3 bil\u00adlion into water pol\u00adlu\u00adtion abate\u00adment, $1 bil\u00adlion of which fund\u00aded the deep tun\u00adnel sys\u00adtem.<\/p>\n\n\n\n

According to the dis\u00adtrict, those efforts reduced pol\u00adlu\u00adtion from an aver\u00adage of \u201c8 bil\u00adlion to 9 bil\u00adlion gal\u00adlons per year.\u201d By 2010, an addi\u00adtion\u00adal $1 bil\u00adlion was allo\u00adcat\u00aded through the Overflow Reduction Plan, expand\u00ading the system\u2019s capac\u00adi\u00adty and improv\u00ading its long-term per\u00adfor\u00admance.<\/p>\n\n\n\n

Here\u2019s how the colos\u00adsal tun\u00adnel was con\u00adstruct\u00aded:<\/p>\n\n\n\n

In 1993, 19.4 miles of tun\u00adnels were dug 275 to 340 feet under\u00adground, with diam\u00ade\u00adters rang\u00ading from 17 to 32 feet. The tun\u00adnels cap\u00adtured 405 mil\u00adlion gal\u00adlons of stormwa\u00adter and sewage, pro\u00advid\u00ading an imme\u00addi\u00adate boost in flood con\u00adtrol and pol\u00adlu\u00adtion reduc\u00adtion. While this marked a sig\u00adnif\u00adi\u00adcant mile\u00adstone, it was just the begin\u00adning of the jour\u00adney.<\/p>\n\n\n\n

The project took anoth\u00ader step in 2006. The sys\u00adtem grew by 7.1 miles, with tun\u00adnels dug 120 to 165 feet under\u00adground and a 20-foot diam\u00ade\u00adter. This expan\u00adsion added anoth\u00ader 89 mil\u00adlion gal\u00adlons of stor\u00adage, increas\u00ading the system\u2019s abil\u00adi\u00adty to man\u00adage over\u00adflow.<\/p>\n\n\n\n

By 2010, the final stretch of tun\u00adnels was com\u00adplet\u00aded, adding 2 more miles, 300 to 325 feet under\u00adground, with a 21-foot diam\u00ade\u00adter. This sec\u00adtion added 27 mil\u00adlion gal\u00adlons of stor\u00adage, bring\u00ading the total capac\u00adi\u00adty to 521 mil\u00adlion gal\u00adlons across all stages. With this last com\u00adpo\u00adnent in place, the sys\u00adtem became fully oper\u00ada\u00adtional.<\/p>\n\n\n\n

<\/a>It\u2019s not just a Midwest solu\u00adtion. Cities like Boston, Washington D.C., Atlanta, and even London have embraced tun\u00adnel sys\u00adtems to tack\u00adle sewer over\u00adflows and mod\u00adern\u00adize aging infra\u00adstruc\u00adture.<\/p>\n\n\n\n

While each has taken a slight\u00adly dif\u00adfer\u00adent approach, their shared goal remains the same: to store excess stormwa\u00adter under\u00adground and keep pol\u00adlu\u00adtion out of rivers, lakes, and coastal waters.<\/p>\n\n\n\n

Hartford\u2019s tun\u00adnel isn\u2019t a car\u00adbon copy of Chicago\u2019s or Milwaukee\u2019s\u2014but it doesn\u2019t have to be. It will ben\u00ade\u00adfit from the insights of cities that have already dug deep\u2014literally\u2014to address sim\u00adi\u00adlar waste\u00adwater chal\u00adlenges. If it works as planned, it could be a major step in solv\u00ading Hartford\u2019s CSO prob\u00adlem.<\/p>\n\n\n\n

<\/div>

Mia Jaworski<\/p>

<\/p>

<\/div><\/div><\/div><\/div>\n\n\n\n
\n\n\n\n

TOP IMAGE: Chicago dug this reser\u00advoir, McCook Reservoir, to hold untreat\u00aded waste from its deep tun\u00adnel sys\u00adtem. This is how the reser\u00advoir looked on May 16, 2025. Photo from mwrd.org<\/a>, Chicago\u2019s Metropolitan Water Reclamation District.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

By Mia JaworskiUConn Journalism Heavy rain over\u00adwhelms old city sewer sys\u00adtems, spilling raw sewage into rivers and water\u00adways. It\u2019s a prob\u00adlem cities around the world have faced for decades, and one grow\u00ading more urgent as cli\u00admate change fuels more intense and fre\u00adquent storms. One solu\u00adtion that\u2019s gained trac\u00adtion: mas\u00adsive under\u00adground stor\u00adage tun\u00adnels built deep beneath\u2026<\/p>\n","protected":false},"author":991,"featured_media":278,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"wp_typography_post_enhancements_disabled":false,"ngg_post_thumbnail":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[8],"tags":[17],"class_list":["post-277","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-the-tunnel","tag-the-tunnel"],"jetpack_featured_media_url":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/files\/2025\/05\/Screenshot-2025-05-16-at-7.40.54\u202fPM.png","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/posts\/277","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/users\/991"}],"replies":[{"embeddable":true,"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/comments?post=277"}],"version-history":[{"count":5,"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/posts\/277\/revisions"}],"predecessor-version":[{"id":1034,"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/posts\/277\/revisions\/1034"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/media\/278"}],"wp:attachment":[{"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/media?parent=277"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/categories?post=277"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/digitaljournalism.uconn.edu\/hartford-north-end-chronic-flooding-sewage\/wp-json\/wp\/v2\/tags?post=277"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}