So far, the focus on the archeological digs along Oahu’s planned rail route has centered on protecting iwi kupuna — the bones of Native Hawaiian ancestors.

But with the digging done and an Archaeological Inventory Survey report under review, the focus appears to be shifting. Local environmental groups and Native Hawaiians say they’re worried that not enough is being done to ensure rail won’t harm hidden, underground springs and coral caves deemed vital to cultural practices and the islands’ ecology.

"The fact is, iwi can be moved," said Mike Kumukauoha Lee, a Native Hawaiian cultural practitioner who said he uses the algae, seaweed and invertebrates that grow in these systems elsewhere to practice traditional medicine and ceremonies. "This underground network needs to be preserved."

Lee and others, including the Kailua-based Hawaii’s Thousand Friends, further contend the State Historic Preservation Division isn’t doing all it can to make sure such sites aren’t damaged if they lie under the rail line’s path.

The groups expressed their concerns in formal responses submitted to the rail project’s draft Archaeological Inventory Survey report, and provided copies to the Star-Advertiser. SHPD officials say they’ve opted not to release any of the public’s comments submitted on the report until the division has completed its review of them.

Honolulu Authority for Rapid Transportation, the semiautonomous government agency overseeing the rail project, says worries over such subterranean resources are unfounded, and that none of its geo-technical studies of the ground below the 21-mile route show any karst, or region of coral caverns or underground streams that eventually feed into the ocean.

"We’ve done geo-technical borings and the existence of karst caverns, which some have said exist, have not ever been proven to be in existence along the route that we’re traveling," HART CEO Dan Grabauskas said Thursday. There’s no need for the project to include a karst mitigation plan, he added.

In an April 12 letter to state Department of Land and Natural Resources Director William Aila, Grabauskas said most of the pillars used to support the elevated rail guideway will be built into soil and not in coral areas where karst caverns are found.

Only the rail line’s westernmost planned station, at East Kapolei, was found to be above coral and that HART’s studies "have not encountered any indication" of karst caverns there, Grabauskas further wrote.

But Hawaii’s Thousand Friends and Kanehili Hui, a nonprofit group formed last year to monitor the rail project, question whether sufficient studies have been done to confirm no such features lie in the rail line’s path.

"How far down did they dig?" Lee, a member of both groups, said Friday. Lee said his review of historical Land Commission Award records dating from the mid-1800s shows 13 potential sites along the rail path that could contain underground karst or springs. Many of the potential karst sites he’s identified may have been buried under generations of plantation farm soil, he said.

Lee said Kanehili Hui is prepared to sue if the state doesn’t "appropriately" answer how the project plans to avoid damaging those potential natural resources.

Hawaii’s Thousand Friends is part of a group that’s already suing in federal court to try to halt the $5.26 billion rail project. Donna Wong, the group’s executive director, said it’s still "very premature" to say whether it would join a lawsuit over the karst issue.

"The board definitely has to go back and review what, and if, there’s any action they want to take" based on state and rail officials’ response, Wong said.

A ruling by federal Judge A. Wallace Tashima last year in the lawsuit that Thousand Friends is party to required rail officials to further study cultural sites that could be affected by the rail project. That decision "gave us an opportunity to put forth the importance of the karst," Wong said Thursday.

Thousand Friends further blasted SHPD in its AIS comments for a "lack of leadership in preserving cultural properties." The division, Thousand Friends says, relied on a single report to agree with HART that rail would have no effect on potential traditional cultural properties in a large stretch of the line. SHPD should have done more analysis, the environmental group states.

An SHPD representative declined Friday to comment on Thousand Friends’ specific criticism, saying the division would wait until its full review of the comments is complete.

The division, which is part of the state Department of Land and Natural Resources, received about 12 comments on the AIS report, including some that are "quite voluminous," DLNR information specialist Deborah Ward said in an email.

SHPD’s lead reviewer for Oahu archaeology is on vacation, so the division expects it won’t finish reviewing the comments until close to July, Ward added.