What happens to a Hillside East sale in January when the engineer's test shows the drainfield needs work and nobody can dig until the ground thaws? In Anchorage, the sale usually continues. The fix moves into an escrow account, and the closing goes ahead with money held back for spring construction.
That conditional path is the most important thing a Hillside seller or buyer can understand about the Certificate of On-Site Systems Approval, or COSA. In winter, a COSA depends on test results that expire on different schedules and, when repairs have to wait, on escrowed repair money. If you plan around both, a winter closing can stay on schedule.
The seller owns the certificate, and the engineer has to find every pipe
The Municipality of Anchorage says on its Wells & Septic page that a home served by a septic system or private well needs a COSA before ownership transfers, and that getting it is the seller's job. The city's Property Owner's FAQ says a registered professional engineer certifies that the systems meet code and are adequate for the home. Staff in the On-Site Water & Wastewater Section then review the engineer's submittal and issue the certificate. The FAQ also says the COSA confirms to both the buyer and the lender that the systems were inspected and tested, which is why it sits on the critical path to closing.
The city's COSA page lists the steps. The engineer pulls the municipal records to confirm that a documented, approved system exists, reviews an as-built survey, and locates the septic standpipes. Every pipe shown in the records has to be accounted for in the field, and the city adds a line any November seller will notice: "This also applies to pipes buried in the snow."
The rest of the list:
- Field measurements of separation distances between wells and septic systems, judged against the rules in effect when the system went in. Encroachments require waivers, which bring added engineering charges and MOA fees.
- Checks that the well casing extends far enough above grade: 18 inches for wells drilled after August 1998, 12 inches for older wells. The well wires must be in conduit, and the well needs a working, removable sanitary seal.
- Water samples tested for nitrates, arsenic and coliform bacteria.
- Confirmation that the septic tank was pumped, and any lift station or pump vault maintained, within the past 12 months.
- Adequacy tests on both the well and the septic system.
If the system isn't documented, it has to be documented before approval. On an older Hillside property, that step alone can take more time than anything else on the list.
When the drainfield needs work in January
The city's COSA Guidelines, revised April 2025, say the On-Site Section can issue a full approval, issue a conditional approval, or disapprove an application. They say conditional approvals are granted only in special circumstances, and the example they give is "winter conditions prohibiting excavation."
That path has conditions. Under the guidelines, there can be no imminent health hazard and no obvious code violation such as overflowing sewage or an unsealed well. The engineer has to certify that the conditional approval will cause no adverse effect. A compliance date must be set, and the conditional COSA fee must be paid. The institution holding the escrow funds must send On-Site a letter saying the money will stay in escrow until a final, unconditional COSA is issued. After the engineer reports that the work is done, the department issues the full approval.
How much money gets held back depends on which system needs the work. Septic falls under AMC 15.65.060. Wells fall under the rewritten water-well chapter, AO 2025-21(S), which the Anchorage Assembly passed on February 25, 2025.
| Conditional COSA requirement | Septic, AMC 15.65.060 | Well, AMC 15.55 per AO 2025-21(S) |
|---|---|---|
| Fee | Conditional COSA fee paid | Conditional COSA fee paid |
| Design and permit | Approved design and permit, if required | Approved design and issued permit, if required |
| Construction estimates | Three | At least two |
| Escrow amount | 1.5 times the highest estimate | 1.5 times the highest of three estimates, or 2 times the higher of two |
| Small-repair exception | Estimates and escrow waived under $2,000 | Estimates and escrow waived under $2,000 |
The multiplier matters for whoever negotiates the holdback. A drainfield repair with a top bid of $20,000 means $30,000 sits in escrow until summer. On the well side, two bids instead of three raise the multiplier to 2 times. Getting a third estimate can lower the amount held, but it also takes time when contractors are booked through winter.
The test clock keeps running while the listing sits
Fall listings that carry into spring run into a second winter issue, because the tests behind a COSA don't all expire on the same schedule. According to the Property Owner's FAQ:
- Well flow and drainfield adequacy tests are valid for two years.
- Arsenic, nitrate and bacteria results are valid for one year.
- The septic tank must have been pumped within the past year.
- Lift station maintenance must have been done within the past two years.
The guidelines let a COSA be reissued to the same owner at no charge when those requirements are still met. A new seller can get one for a renewal fee. The FAQ adds that reissuing for the same owner requires new water sample results, taken by the engineer, and that the required maintenance may need to be done again.
In practice, the expensive tests on the well and drainfield last two years, while the water samples and septic pumping have to be current within the past year. A seller who did all the work last fall and is still listed this fall may only need new samples and a pumping. Knowing which items have lapsed tells you who to call first.
Two lines on the certificate that can surprise a buyer
The first is the bedroom count. The COSA page explains that AMC 15.65 sizes septic systems by number of bedrooms and assumes two occupants per bedroom. Each system is approved for a set number of bedrooms, and that number appears on the COSA. The city notes that it "may or may not match the number of bedrooms listed on the municipal tax records." On a Hillside home with a finished lower level or a den used as a bedroom, the listing, the tax record and the septic approval can each show a different number. That's useful to find before an appraisal or offer.
The second is well yield. Under the 2025 water-well code, a yield test is required for wells serving three or fewer homes. If sustained production and recovery come in below 150 gallons per day per bedroom, the department issues an advisory notice with the COSA identifying the well as low yield. The code calls for an advisory, not a denial. A low-yield well can still receive a COSA, and the buyer receives the flag as information.
Why these items carry weight on the Hillside
The geology explains why the yield and water-quality lines get attention here. A December 2011 municipal study of Hillside well water estimated more than 6,000 wells drawing from glacial and bedrock groundwater on the Hillside. It described the glacial aquifers as commonly thin, discontinuous layers of sand and gravel within glacial till. Across much of the upper Hillside, it said, bedrock sits at or near the surface and holds water in fractures.
The same study, using data from 1989 to 2010, found higher nitrate readings clustered around Furrow Creek near Huffman and Elmore, Potter Creek east of Goldenview, the Abbott and Birch area, and Hillside Drive between Abbott and DeArmoun. It also found large differences between neighboring lots. Its conclusion was that the nitrate trends it observed did not significantly reduce the long-term viability of on-site wells and wastewater systems. This is background from more than a decade ago, not a reading of any particular property today. Because neighboring lots can differ so much, the samples taken for the COSA are what tell you about a specific house.
Pull the lot's file before you write an offer
Any buyer can look at a property's well and septic history before making an offer. The municipality keeps historical on-site documents in a public WebLink database, organized by legal description. The FAQ uses a Hillside example: for RABBIT CREEK VIEW & HEIGHTS BLK 11H LT 10A, open the "R" folder, then the subdivision, then the block, then the lot. The file can show whether the system has documented municipal approval. The seller's engineer starts the COSA process from these same records.
Quick answers
Who pays for the COSA? The municipality assigns the job of obtaining it to the seller. How costs are split beyond that, including any escrow holdback, is set in the purchase agreement.
Does every transfer need one? The guidelines list exceptions for transfers between spouses or to a family trust. A typical sale to a new buyer needs one.
What if the tank itself is failing? The FAQ says a septic tank that is no longer watertight, or has compromised components, must be replaced. Upgrading a failing system requires a design by an Alaska-registered engineer and a municipal permit.
This post is general information about municipal requirements, not legal or financial advice. Confirm your own property's situation with a registered engineer, the On-Site Water & Wastewater Section, and your attorney or escrow officer.
If your Hillside home is on a well or septic and you're thinking about a winter listing, Calling Alaska Home can help you sort out which tests are still current, line up the engineer early, and price your home with any conditional COSA already planned for. Start with a free home valuation, and we'll go through the on-site file together.
