Indonesia Mining Water Management: The Drainage, Settling-Pond and Acid-Drainage Duties on an IUP Holder

Indonesia's mining permit is a right to mine and a set of water duties that run from the first exploration hole to the day the pit is flooded and handed back. At an Indonesian mine, water is not an engineering afterthought: it is a named obligation under the ministry's good-mining-practice rulebook, and a breach of it is a licence risk before it is an environmental one.

This explainer sets out what Indonesia mining water management requires of an IUP or IUPK holder — the studies that come first, the rainfall standard a settling pond must satisfy, how a water system has to be operated, and how acid drainage must be prevented before it is treated. Every rule below is taken from the two primary texts: Permen ESDM No. 26 of 2018 and Kepmen ESDM No. 1827 K/30/MEM/2018, both read in the official JDIH Kementerian ESDM copies.

Where the water rules sit

Article 20 of Permen 26/2018 defines the environmental-management duty as two things: carrying out management *and* monitoring in line with the Dokumen Lingkungan Hidup — the project's AMDAL or UKL-UPL — and controlling and restoring the environment where pollution or damage occurs. The water rules in the decree's Annex II and Annex V are how that duty is worked out on the ground.

What counts as "mine water"

The decree fixes its own vocabulary, and it matters for diligence:

• Mine water (*air tambang*) — water located at the mine and/or originating from mining activities, including run-off within the mining area.
• Surface run-off (*air larian permukaan*) — rainwater flowing over the surface.
• Acid mine drainage (*air asam tambang*) — water that has become acidic through the oxidation of sulphide minerals in mining activities.
• Process water (*air kerja*) — water used in processing and/or refining.

Before you build: the hydrology, hydrogeology and geochemistry studies

Annex II folds water into the technical feasibility study (*studi kelayakan*). The technical assessment must at least include a hydrology and hydrogeology study and an acid mine drainage study, and the hydrology and hydrogeology study must cover:

• hydrology — the type and location of water sources, discharge measurement, and the direction of surface flow; and
• hydrogeology — the type and number of aquifers, their hydraulic characteristics, groundwater-flow direction, water-table measurement, and the measurement of spring or seepage discharge;

together with a rainfall record of at least the mine life, or 10 years for a mine with a life shorter than 10 years, and the measured catchment area.

The acid-drainage work begins even earlier. The decree requires a geochemical rock study — separating potentially acid-forming (PAF) from non-acid-forming (NAF) material — to start at the exploration stage, with samples taken through exploration or geotechnical drilling.

Out of the hydrology study comes a technical recommendation that must at least fix four things: the dimensions of the mine-water storage and management facilities, the dimensions of the drainage channels, the pump capacity, and a mine water management map (*peta pengelolaan air tambang*).

The rainfall standard a pond must meet

The engineering rule is specific. Mine-water storage and settling facilities must have capacity of at least 1.25 times the volume of mine water in the highest rainfall over 84 hours.

The plan for the water system must be drawn as a map and a table showing the drainage channels and the direction of drainage; the location, dimensions and capacity of the storage and management facilities; the number and capacity of the pumps, sized against the mine-water discharge; and the rainfall and rainfall-duration data, measured continuously from the start of construction.

Operating the system

Once running, the water system has a fixed trigger and a stop rule:

• Management of the storage facility begins when it is filled to 80 per cent or more of capacity, and includes desilting, pumping out sediment, adding pump capacity, and/or adding storage capacity.
• Where run-off becomes uncontrolled, the affected mining activity stops — except the work of handling that run-off.
• A settling facility must sit at least 500 metres from the outer edge of the pit, or at a distance set by technical study.
• Mine-water management is itself defined to include the periodic inventory and evaluation of mine-water sources, the construction of a mine-water drainage system, and the maintenance of the water-handling facilities.

Dewatering (*pengurangan kadar air*) also appears as a listed processing operation.

The settling pond has to be able to shut itself off

Annex V adds a set of construction conditions for the settling pond (*kolam pengendap*). It must be built at a stable location, to a technical design suited to the activity, and at a safe distance from rivers, housing, public facilities and farmland or plantations. It is built by clearing vegetation, stripping and managing the topsoil, and compacting the pond base to design criteria — and it must be equipped, among other things, with:

• a device that stops the outflow to public waters if the environmental quality standard is exceeded at the outlet;
• a flow meter at the outlet; and
• a public information board showing the water-quality monitoring results.

It must be maintained periodically so that it keeps working.

Acid mine drainage: know first, prevent next, treat last

For the mine's operating phase, the decree sets a clear sequence for mine water and run-off:

1. Mine water must be routed through a working drainage system to a settling pond before it is released to public waters.
2. Before release, mine water must meet environmental quality standards under the prevailing rules.
3. Surface run-off heading toward the pit from undisturbed surrounding land must be diverted around it.

Acid drainage then follows a duty to know, a duty to prevent, and only then a duty to treat:

• The holder must run a geochemical rock study to establish whether a potential for acid formation exists.
• If it does, prevention comes first: managing where waste rock is placed, encapsulation (*dry cover*), submergence (*wet cover*), blending acid-forming material with non-acid or alkaline material, or other methods.
• Only if drainage still forms after prevention must it be treated to meet environmental quality standards before release — by active means (neutralising chemicals such as lime or caustic soda) and/or passive means (a constructed wetland, an open limestone channel, or other methods).

Monitoring is a listed obligation

Annex V requires environmental monitoring, carried out by competent technical personnel, covering among other things: surface-water quality; groundwater quality and quantity; seawater quality; wastewater quality; soil quality; air quality; biodiversity; land subsidence; and erosion and sedimentation.

Why it matters for a foreign investor

1. Water is a licence item, not a construction item. The Article 20 duty to manage and monitor the environment according to the project's own environmental document is enforceable, and the decree's Annexes tell an inspector what to look for.
2. The design brief is quantitative. The 1.25-times-volume-over-84-hours storage standard, the 500-metre settling-facility setback and the pump-sizing requirement are capital costs that belong in the feasibility study, not in a post-construction fix.
3. Acid drainage is a study-stage risk. The geochemical study starts at exploration. A project that has not characterised PAF and NAF material is carrying an unpriced treatment and closure liability.
4. The environmental document is the standard to diligence against. As with tailings, the decree does not hand down a single national numeric discharge figure for a diligence file to check against; the holder is measured against its own AMDAL or UKL-UPL and the quality standards those documents point to.

Catatan Teramine

*This section is Teramine's editorial assessment, not a statement from any government body and not a recommendation.*

Read together, the water rules describe a duty-of-conduct framework with a small number of hard numbers bolted on. The decree tells a holder to study, to design, to operate to a rainfall standard, and to know whether its rock will make acid — and it leaves the discharge figure to the prevailing environmental quality standards and the project's own environmental document. That places the weight on two things a diligence team can actually test: whether the feasibility study contains a real hydrology, hydrogeology and geochemistry study, and whether the designed ponds, channels and pumps match the 1.25-times/84-hour standard and the 500-metre setback. The second observation is currency. The operative guideline is from 2018 and the mining-law framework it sits under has been amended since, so a project should confirm the current text before it files rather than assume the 2018 wording is the last word.

What we could not verify

• A single national numeric discharge limit. The texts route mine-water discharge to "environmental quality standards under the prevailing rules"; we did not read a specific numeric effluent standard in the documents opened for this article.
• Any enforcement statistics. We read the design, operating and monitoring provisions; we did not find or read data on how often they have been enforced.
• The later amendments to the mining-law framework, article by article. This article describes the good-mining-practice texts; it does not restate the subsequent amendments to the framework those texts sit under.
• Any company, project, reserve or production figure. This article describes rules; it names no operating company and reports no deal.

Sources

Every rule and date below comes from an official text read in the relevant part, downloaded from the legal information database of Indonesia's Ministry of Energy and Mineral Resources (JDIH ESDM).

• Keputusan Menteri ESDM No. 1827 K/30/MEM/2018 on Guidelines for the Implementation of Good Mining Practice, dated 7 May 2018 — read for Annex II (the technical mining-management guideline: the hydrology and hydrogeology study and its four-item technical recommendation, the rainfall record and catchment-area requirements, the acid mine drainage study in the feasibility study, the 1.25-times-volume-over-84-hours storage and settling capacity, the 80 per cent management trigger, the 500-metre settling-facility setback, dewatering, and the mine water management map and table) and Annex V (the environmental-management guideline: the definitions of mine water, surface run-off, acid mine drainage and process water; the construction conditions for the settling pond including the outlet shut-off device, flow meter and public information board; the operating rules for mine water, run-off diversion and acid mine drainage prevention and treatment; and the environmental-monitoring list).
• Peraturan Menteri ESDM No. 26 of 2018 on the Implementation of Good Mining Practice and Supervision of Mineral and Coal Mining, 2018 (State Gazette 2018 No. 596) — read for Article 20 (the environmental-management duty anchored to the project's environmental document).

For the permit, document and compliance work behind this framework — the RKAB package, the environmental-document filings and the reporting — see our [permit services](/en/layanan-izin) page. Mining assets currently listed are on the [mining marketplace](/en/marketplace).

Read this alongside its sibling on the residue side, [Indonesia mine tailings management](/en/news/indonesia-mine-tailings-management); the end-of-mine obligations, [mine closure in Indonesia](/en/news/mine-closure-in-indonesia); the document that carries the water and environmental budget, [what the RKAB is](/en/news/what-is-rkab-indonesia); and the licence framework it sits under, [IUP vs IUPK](/en/news/iup-vs-iupk).