PA Environment Digest Blog: DEP: MarkWest Liberty Midstream Pipeline Construction Results In 20,000 Gallon Spill Into Coal Mine Voids Under Washington County, For The 3rd Time

On October 28, 2025, the Department of Environmental Protection was notified by MarkWest Liberty Midstream & Resources LLC that horizontal drilling operations on the construction of the shale gas-related Chiarelli to Imperial pipeline on October 27 resulted in the loss of approximately 20,000 gallons of a water and bentonite mixture into coal mine voids under Robinson Township, Washington County.

MarkWest said there was no evidence of any “inadvertent returns” on the surface as a result of the incident.

MarkWest informed DEP “During our previous two HDDs [horizontal drilling construction] in this area, we encountered very similar situations where returns were lost to suspected mine voids and the bores were completed with no inadvertent returns to the surface.” Read more here.

MarkWest said mine voids were identified in the erosion and sedimentation permit package approved by DEP prior to construction.

The company planned to continue drilling along the proposed path with additional staff to “continually inspect the bore path” once drilling is resumed.

MarkWest said, “Our contractor has all materials and equipment on site to immediately implement our inadvertent return contingency plan should a return to the surface be observed.

“We discussed potentially moving the bore path, but pipeline integrity concerns were identified due to the additional pipelines within the ROW/bore path. We also cannot positively confirm that a change in path would avoid the mine void.” Read more here.

The exchanges between DEP and MarkWest happened in phone calls and emails, according to the three inspection reports posted by DEP as of this writing--

-- DEP Inspection 4082379

-- DEP Inspection 4082380

-- DEP Inspection 4082428

DEP issued one violation to MarkWest for this incident-- failing to notify the agency immediately of the loss of drilling fluid-- then immediately closed it and marked it “corrected/abated.” Read more here.

Report Violations

To report oil and gas violations or any environmental emergency or complaint, visit DEP’s Environmental Complaint webpage.

Text photos and the location of abandoned wells to 717-788-8990.

Check These Resources

Visit DEP’s Compliance Reporting Database and Inspection Reports Viewer webpages to search their compliance records by date and owner.

Sign up for DEP’s eNOTICE service which sends you information on oil and gas and other permits submitted to DEP for review in your community.

Use DEP’s Oil and Gas Mapping Tool to find if there are oil and gas wells near or on your property and to find wells using latitude and longitude on well inspection reports.

(Photos: Maps in DEP’s inspection reports provided by MarkWest of the incident area (left) and the underground coal mine void locations (right).)

[Note: If you believe your company was listed in error, contact DEP’s Oil and Gas Program.]

[Note: These may not be all the NOVs issued to oil and gas companies during this time period. Additional inspection reports may be added to DEP’s Oil and Gas Compliance Database.]

PA Oil & Gas Industry Public Notice Dashboards:

-- PA Oil & Gas Weekly Compliance Dashboard - Nov. 1 to 7 - Failed To Plug Shale Gas Well For 1,521 Days; 20,000 Gallon Spill Into Mine Void; 99% Of Conventional Well Owners Fail To Comply With Methane Rule [PaEN]

-- DEP: More Than 99% Of Conventional Oil & Gas Facility Owners Failed To Comply With VOC/Methane Reduction Regulations Covering 64,660 Wells; Had 193 Days To File [PaEN]

-- DEP: Spills, Releases Continue At Seneca Resources Taft Shale Gas Well Pad In Middlebury Twp., Tioga County For 373 Days And Counting [PaEN]

-- DEP: MarkWest Liberty Midstream Pipeline Construction Results In 20,000 Gallon Spill Into Coal Mine Voids Under Washington County, For The 3rd Time [PaEN]

-- DEP: EQM Gathering Has 6th ‘Inadvertent’ Release During Pipeline Construction In Nottingham Twp., Washington County [PaEN]

-- DEP: LPR Energy LLC Fails To Plug Abandoned Shale Gas Well For 1,521 Days And Counting In Fayette County [PaEN]

-- PA Oil & Gas Industrial Facilities: Permit Notices, Opportunities To Comment - November 8 [PaEN]

-- DEP Invites Comments On Chapter 105 Permit For MarkWest Liberty Midstream 20-Inch Natural Gas Gathering Pipeline In Mount Pleasant & Cecil Townships, Washington County [PaEN]

-- DEP Invites Comments On Air Quality Permit For 15 Natural Gas Generators To Power 15 Iron City A.I. Computing Centers In Karthaus Twp., Clearfield County [PaEN]

-- DEP Invites Comments On Renewal Of Title V Air Quality Permit For United Refinery In City Of Warren, Warren County [PaEN]

-- Susquehanna River Basin Commission Meets Dec. 4 On 2026 Fee Schedule, Water Withdrawal Requests, Including 3 Related To Shale Gas Development [PaEN]