Pre-Purchase Surveys in Andover

The Legal and Technical Landscape of Property Drainage

Modern drainage compliance is governed primarily by the General Binding Rules, a set of statutory guidelines that dictate how small sewage discharges to ground or surface water must be managed. These rules are designed to minimise environmental harm and maintain groundwater quality, especially in locations like Andover where high water tables and sensitive aquifers may exist.

Purchasing a property without verifying whether its existing drainage installations meet the General Binding Rules is a common yet avoidable mistake. Non-compliant systems may require immediate upgrades, relocation, or even replacement. Equally, a failed percolation test can render a site unsuitable for discharge to ground, requiring a shift in system design or the acquisition of an Environmental Agency Discharge Permit. In such cases, early identification is not just helpful—it is essential.

What Pre-Purchase Drain Surveys Typically Uncover

Pre-purchase surveys are detailed inspections of a property’s drainage infrastructure and are especially critical when private systems (e.g., septic tanks or small treatment plants) are in use. Unlike a standard homebuyer’s report, a drainage survey examines not only structural integrity but also environmental and legal compliance.

Key insights from a well-conducted pre-purchase survey can include:

• The type and location of the existing system.
• Evidence of current or historic blockages, leaks, or surcharge.
• Proximity of discharge points to sensitive watercourses or boreholes.
• System design limitations (e.g., undersized drainage fields or unsealed chambers).
• Potential need for a percolation test or permit under the General Binding Rules.

Red Flags: Indicators That Further Investigation is Needed

Many system deficiencies are not immediately visible but can have far-reaching consequences. A robust survey can highlight these issues early, giving buyers the opportunity to renegotiate the sale price or request remediation before completion.

Common survey findings requiring further attention:

• Tanks discharging directly to watercourses—this often violates the General Binding Rules.
• Poor infiltration performance in the drainage field, suggesting a failed or missing percolation test.
• Inaccessible or undocumented systems.
• Signs of regular backing up, odour, or surface pooling—indicating poor system health.
• Unrecorded or outdated Environmental Agency Discharge Permits.

When detected before exchange of contracts, these issues can be factored into the purchase decision or rectified in advance, thereby avoiding breach of compliance later.

When a Percolation Test Becomes Essential

If a drainage system relies on discharge to ground, and its current function appears compromised, a percolation test may be recommended during a pre-purchase survey. This test measures the rate at which effluent is absorbed by the soil—a critical indicator of whether the land is suitable for a drainage field.

The percolation test process includes:

• Excavating trial holes to assess soil structure and saturation.
• Measuring infiltration rates following a controlled water fill.
• Comparing results against BS 6297 standards.
• Recommending alterations or alternatives if absorption fails.

A failed percolation test not only rules out ground discharge under the General Binding Rules, but it may also necessitate the purchase of a bespoke treatment system or require the application for an Environmental Agency Discharge Permit.